Despite the success of guided wave ultrasonic inspection for internal defect detection in steel pipes,its application on polyethylene(PE)pipe remains relatively unexplored.The growth of internal cracks in PE pipe seve...Despite the success of guided wave ultrasonic inspection for internal defect detection in steel pipes,its application on polyethylene(PE)pipe remains relatively unexplored.The growth of internal cracks in PE pipe severely affects its pressure-holding capacity,hence the early detection of internal cracks is crucial for effective pipeline maintenance strategies.This study extends the scope of guided wave-based ultrasonic testing to detect the growth of internal cracks in a natural gas distribution PE pipe.Laboratory experiments and a finite element model were planned to study the wave-crack interaction at different stages of axially oriented internal crack growth with a piezoceramic transducer-based setup arranged in a pitch-catch configuration.Mode dispersion analysis supplemented with preliminary experiments was performed to isolate the optimal inspection frequency,leading to the selection of the T(0,1)mode at 50-kHz for the investigation.A transmission index based on the energy of the T(0,1)mode was developed to trace the extent of simulated crack growth.The findings revealed an inverse linear correlation between the transmission index and the crack depth for crack growth beyond 20%crack depth.展开更多
Ultrasonic testing(UT)is increasingly combined with machine learning(ML)techniques for intelligently identifying damage.Extracting signifcant features from UT data is essential for efcient defect characterization.More...Ultrasonic testing(UT)is increasingly combined with machine learning(ML)techniques for intelligently identifying damage.Extracting signifcant features from UT data is essential for efcient defect characterization.Moreover,the hidden physics behind ML is unexplained,reducing the generalization capability and versatility of ML methods in UT.In this paper,a generally applicable ML framework based on the model interpretation strategy is proposed to improve the detection accuracy and computational efciency of UT.Firstly,multi-domain features are extracted from the UT signals with signal processing techniques to construct an initial feature space.Subsequently,a feature selection method based on model interpretable strategy(FS-MIS)is innovatively developed by integrating Shapley additive explanation(SHAP),flter method,embedded method and wrapper method.The most efective ML model and the optimal feature subset with better correlation to the target defects are determined self-adaptively.The proposed framework is validated by identifying and locating side-drilled holes(SDHs)with 0.5λcentral distance and different depths.An ultrasonic array probe is adopted to acquire FMC datasets from several aluminum alloy specimens containing two SDHs by experiments.The optimal feature subset selected by FS-MIS is set as the input of the chosen ML model to train and predict the times of arrival(ToAs)of the scattered waves emitted by adjacent SDHs.The experimental results demonstrate that the relative errors of the predicted ToAs are all below 3.67%with an average error of 0.25%,signifcantly improving the time resolution of UT signals.On this basis,the predicted ToAs are assigned to the corresponding original signals for decoupling overlapped pulse-echoes and reconstructing high-resolution FMC datasets.The imaging resolution is enhanced to 0.5λby implementing the total focusing method(TFM).The relative errors of hole depths and central distance are no more than 0.51%and 3.57%,respectively.Finally,the superior performance of the proposed FS-MIS is validated by comparing it with initial feature space and conventional dimensionality reduction techniques.展开更多
The laser powder bed fusion(L-PBF)method of additive manufacturing(AM)is increasingly used in various industrial manufacturing fields due to its high material utilization and design freedom of parts.However,the parts ...The laser powder bed fusion(L-PBF)method of additive manufacturing(AM)is increasingly used in various industrial manufacturing fields due to its high material utilization and design freedom of parts.However,the parts produced by L-PBF usually contain such defects as crack and porosity because of the technological characteristics of L-PBF,which affect the quality of the product.Laser ultrasonic testing(LUT)is a potential technology for on-line testing of the L-PBF process.It is a non-contact and non-destructive approach based on signals from abundant waveforms with a wide frequency-band.In this study,a method of LUT for on-line inspection of L-PBF process was proposed,and a system of LUT was established approaching the actual environment of on-line detection to evaluate the method applicability for defects detection of L-PBF parts.The detection results of near-surface defects in L-PBF 316L stainless steel parts show that the crack-type defects with a sub-millimeter level within 0.5 mm depth can be identified,and accordingly,the positions and dimensions information can be acquired.The results were verified by X-ray computed tomography,which indicates that the present method exhibits great potential for on-line inspection of AM processes.展开更多
Common problems in engineering projects that involve artificial ground freezing of soil or rock include inadequate thickness,strength and continuity of artificial frozen walls.It is difficult to evaluate the freezing ...Common problems in engineering projects that involve artificial ground freezing of soil or rock include inadequate thickness,strength and continuity of artificial frozen walls.It is difficult to evaluate the freezing state using only a few thermometer holes at fixed positions or with other existing approaches.Here we report a novel experimental design that investigates changes in ultrasonic properties(received waveform,wave velocity V_(p),wave amplitude,frequency spectrum,centroid frequency f_(c),kurtosis of the frequency spectrum KFS,and quality factor Q)measured during upward freezing,compared with those during uniform freezing,in order to determine the freezing state in 150 mm cubic blocks of Ardingly sandstone.Water content,porosity and density were estimated during upward freezing to ascertain water migration and changes of porosity and density at different stages.The period of receiving the wave increased substantially and coda waves changed from loose to compact during both upward and uniform freezing.The trend of increasing V_(p) can be divided into three stages during uniform freezing.During upward freezing,V_(p) increased more or less uniformly.The frequency spectrum could be used as a convenient and rapid method to identify different freezing states of sandstone(unfrozen,upward frozen,and uniformly frozen).The continuous changes in reflection coefficient r_(φ),refraction coefficient t_(φ) and acoustic impedance field are the major reason for larger reflection and refraction during upward freezing compared with uniform freezing.Wave velocity V_(p),wave amplitude A_(h),centroid frequency f_(c) and quality factor Q were adopted as ultrasonic parameters to evaluate quantitatively the temperature T of uniformly frozen sandstone,and their application within a radar chart is recommended.Determination of V_(p) provides a convenient method to evaluate the freezing state and calculate the cryofront height and frozen section thickness of upward frozen sandstone,with accuracies of 73.37%-99.23%.展开更多
A high-precision evaluation of ultrasonic detection sensitivity for a micro-crack can be restricted by a corroded rough surface when the surface microtopography is of the same order of magnitude as the crack depth.In ...A high-precision evaluation of ultrasonic detection sensitivity for a micro-crack can be restricted by a corroded rough surface when the surface microtopography is of the same order of magnitude as the crack depth.In this study,a back-surface micro-crack is considered as a research target.A roughness-modified ultrasonic testing model for micro-cracks is established based on a multi-Gaussian beam model and the principle of phase-screen approximation.The echo signals of micro-cracks and noises corresponding to different rough front surfaces and rough back surfaces are obtained based on a reference reflector signal acquired from a two-dimensional simulation model.Further compari-son between the analytical and numerical models shows that the responses of micro-cracks under the effects of dif-ferent corroded rough surfaces can be accurately predicted.The numerical and analytical results show that the echo signal amplitude of the micro-crack decreases significantly with an increase in roughness,whereas the noise ampli-tude slightly increases.Moreover,the effect of the rough front surface on the echo signal of the micro-crack is greater than that of the rough back surface.When the root-mean-square(RMS)height of the surface microtopography is less than 15μm,the two rough surfaces have less influence on the echo signals detected by a focused transducer with a frequency of 5 MHz and diameter of 6 mm.A method for predicting and evaluating the detection accuracy of micro-cracks under different rough surfaces is proposed by combining the theoretical model and a finite element simulation.Then,a series of rough surface samples containing different micro-cracks are fabricated to experimentally validate the evaluation method.展开更多
Arctic sea ice area and thickness have declined dramatically during the recent decades.Sea ice physical and mechanical properties become increasingly important.Traditional methods of studying ice mechanical parameters...Arctic sea ice area and thickness have declined dramatically during the recent decades.Sea ice physical and mechanical properties become increasingly important.Traditional methods of studying ice mechanical parameters such as ice-coring cannot realize field test and long-term observation.A new principle of measuring mechanical properties of ice using ultrasonic was studied and an ultrasonic system was proposed to achieve automatic observation of ice mechanical parameters(Young’s modulus,shear modulus and bulk modulus).The ultrasonic system can measure the ultrasonic velocity through ice at different temperature,salinity and density of ice.When ambient temperature decreased from 0°C to-30°C,ultrasonic velocity and mechanical properties of ice increased,and vice versa.The shear modulus of the freshwater ice and sea ice varied from 2.098 GPa to 2.48 GPa and 2.927 GPa to 4.374 GPa,respectively.The bulk modulus of freshwater ice remained between 3.074 GPa and4.566 GPa and the sea ice bulk modulus varied from 1.211 GPa to 3.089 GPa.The freshwater ice Young’s modulus kept between 5.156 GPa and 6.264 GPa and sea ice Young’s modulus varied from 3.793 GPa to 7.492 GPa.The results of ultrasonic measurement are consistent with previous studies and there is a consistent trend of mechanical modulus of ice between the process of ice temperature rising and falling.Finally,this ultrasonic method and the ultrasonic system will help to achieve the long-term observation of ice mechanical properties of ice and improve accuracy of sea ice models.展开更多
Aimed at inner quality controlling for complex surface parts, an ultrasonic testing system for complex surface parts has been developed using ultrasonic NDT(Non-destructive Testing)which has features of strong penetra...Aimed at inner quality controlling for complex surface parts, an ultrasonic testing system for complex surface parts has been developed using ultrasonic NDT(Non-destructive Testing)which has features of strong penetration, well direction, high sensitivity, low cost, and harmless to people and material. The technologies of the computer, NC (Numerical control), precision mechanism, signal analysis and processing were integrated in the testing system. The system includes a PC, system software, ultrasonic data acquisition card, stepper motor drive card and five-axis precision mechanical device, etc. The software was developed using WIN98-based VC++. According to CAD data of the parts and interpolation methods, the scanning programs can be programmed. The five-axis scanning system is driven by the CNC(computer numerical control) system to control the attitude of ultrasonic probes. The system’s automatic scanning for complex surface parts, real-time acquiring ultrasonic data and automatic identifying flaw signal have been realized. This system can be used not only for testing complex surface parts, but for testing random curve parts. With fast testing speed, high sensitivity, high testing precision and high reliability, the system has a wide adaptability.展开更多
Marble is a metamorphic rock, which is one of the 3 basic rock types (magmatic, sedimentary, metamorphic) forming the earth’s crust. The major characteristic sought after in a rock mass in the field for it to be expo...Marble is a metamorphic rock, which is one of the 3 basic rock types (magmatic, sedimentary, metamorphic) forming the earth’s crust. The major characteristic sought after in a rock mass in the field for it to be exportable and usable as marble is its suitability to be cut in blocks. In the process of producing marble slabs from marble blocks, the blocks are expected not to contain potentially problematic hard or weak zones and their geomechanical and chemical properties should conform to the relevant standards. Ignoring of the geological properties of the rock in the process of deciding for marble production at a marble site and determination of production location, direction and method is the most important parameter that would increase production loss. In order to reduce losses by determination of geological properties of marble, many academic studies have been conducted on the effects of water saturation, temperature, freezing and thawing on its mechanical and fracture properties. There are further studies on crack propagation in marble under stress. However, even those marble blocks that are obtained based on geological parameters may suffer serious cracks or fractures due to stresses caused by their weight and geometry. Therefore, cutting direction is of critical importance in order to minimize marble waste in the process of cutting a marble block which is brought to the inventory or processing site with cracks, cavities or fractures. Certain studies exist within such context, where the geometry of the discontinuity within a block is determined using non-destructive methods, such as ultrasonic testing, in order to determine the appropriate cutting direction. Such studies made use of ultrasonic waves to determine the physical and chemical structures of magmatic and sedimentary rocks by measuring the progress velocity of sonic waves in the rock. Said studies, however, mostly worked on sedimentary and magmatic rock specimens, focusing less on metamorphic rocks such as marble due to their anisotropic properties. Understanding the academic literature studies on marble would provide significant contribution to the reduction of production losses during the processing marble blocks in processing plants and the achievement of production efficiency levels that are within economic limits. Within such scope, this study has reviewed the past academic studies on marble, classified them under 6 categories, and comprehensively analyzed each category based on materials, testing setups, test specimens, test parameters and research techniques.展开更多
In order to improve the work efficiency of non-destructive testing(NDT)and the reliability of NDT results,an automatic method to detect defects in the ultrasonic image was researched.According to the characterization ...In order to improve the work efficiency of non-destructive testing(NDT)and the reliability of NDT results,an automatic method to detect defects in the ultrasonic image was researched.According to the characterization of ultrasonic D-scan image,clutter wave suppression and de-noising were presented firstly.Then,the image is processed by binaryzation using KSW 2 D entropy based on image segmentation method.The results showed that,the global threshold based segmentation method was somewhat ineffective for D-scan image because of under-segmentation.Especially,when the image is big in size,small targets which are composed by a small amount of pixels are often undetected.Whereas,local threshold based image segmentation method is effective in recognizing small defects because it takes local image character into account.展开更多
The important status of guide ring in large power plants and its manufacturing methods were introduced. The advantages of manufacturing methods including welding and electrolysis were discussed.In order to ensure the ...The important status of guide ring in large power plants and its manufacturing methods were introduced. The advantages of manufacturing methods including welding and electrolysis were discussed.In order to ensure the brazing quality of the guide ring,ultrasonic nondestructive testing(UNDT) method was used in this study.According to the features of the defects that may show up during brazing,the feasibility and reliability of UNDT were proved in theory.Based on the theory,an ultrasonic C-scan imaging test method was developed using a water immersion focusing probe.According to the features of the inspected images,the defects were segmented using a morphology image processing based method.The defects can be localized and sized by employing the algorithm of area reconstruction.At last,the combination ratio of brazing interface can be calculated and the brazing quality of the guide ring can be evaluated.展开更多
Excavation Damaged Zone(EDZ)scope is important for optimizing excavation and support schemes in deep underground caverns.However,accurately predicting the full EDZ scope within the surrounding rock masses of deep unde...Excavation Damaged Zone(EDZ)scope is important for optimizing excavation and support schemes in deep underground caverns.However,accurately predicting the full EDZ scope within the surrounding rock masses of deep underground caverns during excavation remains a pressing problem.This study presents a comprehensive EDZ scope prediction approach(CESPA)for the brittle surrounding rock masses of deep underground caverns by coupling numerical simulation with quantitative analysis of borehole wall images and ultrasonic test results.First,the changes in both P-velocity(V_(p))and joint distribution of the surrounding rock masses before and after excavation damage are captured using ultrasonic tests and borehole digital cameras.Second,the quality Q-parameters of the surrounding rock mass before and after excavation damage are preliminarily rated with the rock mass descriptions provided by borehole wall images,and the rock mass V_(p)-parameter values are determined according to the V_(p)-borehole depth curves.Third,the Q-parameter ratings are further finely adjusted by updating the related Q-values to be similar with the Q-values estimated by V_(p)-parameter values.Fourth,the initial and residual mechanical parameters for the rock mass deterioration model(RDM)are estimated by the adjusted Q-parameter ratings based on the modified Q-based relations,and the elastic modulus deterioration index(EDI)threshold to describe the EDZ boundary is determined with the V_(p)-parameter values.Finally,EDZ scope is predicted using the elastoplastic numerical simulation with RDM and EDI based on the mechanical parameter estimates and EDI threshold.Analyses of applications in Sub-lab D1 in Jinping II project show that CESPA can provide a reliable and operable solution for predicting full EDZ scopes within the brittle surrounding rock masses of deep underground caverns.展开更多
HoekeBrown failure criterion is one of the widely used rock strength criteria in rock mechanics and mining engineering.Based on the theoretical expression of HoekeBrown parameter m of an intact rock,the parameter m ha...HoekeBrown failure criterion is one of the widely used rock strength criteria in rock mechanics and mining engineering.Based on the theoretical expression of HoekeBrown parameter m of an intact rock,the parameter m has been modified by crack parameters for fractured rocks.In this paper,the theoretical value range and theoretical expression form of the parameter m in HoekeBrown failure criterion were discussed.A critical crack parameter B was defined to describe the influence of the critical crack when the stress was at the peak,while a parameter b was introduced to represent the distribution of the average initial fractures.The parameter m of a fractured rock contained the influences of critical crack(B),confining pressure(s3)and initial fractures(b).Then the triaxial test on naturally fractured limestones was conducted to verify the modification of the parameter m.From the ultrasonic test and loading test results of limestones,the parameter m can be obtained,which indicated that the confining pressure at a high level reduced the differences of m among all the specimens.The confining pressure s3 had an exponential impact on m,while the critical crack parameter B had a negative correlation with m.Then the expression of m for a naturally fractured limestone was also proposed.展开更多
In the point of application to ultrasonic nondestructive testing of surface stress and defect in polymer component, the oblique suxface wave transducer is investigated on its acoustic property and especially the mecha...In the point of application to ultrasonic nondestructive testing of surface stress and defect in polymer component, the oblique suxface wave transducer is investigated on its acoustic property and especially the mechanism of acoustic attenuation of acoustic entrant material inside the transducer. A new kind of room temperature vulcanized silicone elastomer as wedge material, in which ultrasound can propagate in very low speed with weak attenuation, is developed through a great deal of trials. The corresponding ultrasonic transducer is also designed for further researches and application to detect surface stress and surface crack in aerospace transparent component.展开更多
Composite materials are increasingly used in the aerospace industry.To fully realise the weight saving potential along with superior mechanical properties that composites offer in safety critical applications,reliable...Composite materials are increasingly used in the aerospace industry.To fully realise the weight saving potential along with superior mechanical properties that composites offer in safety critical applications,reliable Non-Destructive Testing(NDT)methods are required to prevent catastrophic failures.This paper will review the state of the art in the field and point to highlight the success and challenges that different NDT methods are faced to evaluate the integrity of critical aerospace composites.The focus will be on advanced certificated NDT methods for damage detection and characterization in composite laminates for use in the aircraft primary and secondary structures.展开更多
Recent development trends in wind power generation have increased the importance of the safe operation of wind-turbine blades(WTBs). To realize this objective, it is essential to inspect WTBs for any defects before th...Recent development trends in wind power generation have increased the importance of the safe operation of wind-turbine blades(WTBs). To realize this objective, it is essential to inspect WTBs for any defects before they are placed into operation. However, conventional methods of fault inspection in WTBs can be rather difficult to implement, since complex curvatures that characterize the WTB structures must ensure accurate and reliable inspection. Moreover, it is considered useful if inspection results can be objectively and consistently classified and analyzed by an automated system and not by the subjective judgment of an inspector. To address this concern,the construction of a pressure-and shape-adaptive phased-array ultrasonic testing platform, which is controlled by a nanoengine operation system to inspect WTBs for internal defects, has been presented in this paper. An automatic classifier has been designed to detect discontinuities in WTBs by using an A-scanimaging-based convolutional neural network(CNN). The proposed CNN classifier design demonstrates a classification accuracy of nearly 99%. Results of the study demonstrate that the proposed CNN classifier is capable of automatically classifying the discontinuities of WTB with high accuracy, all of which could be considered as defect candidates.展开更多
Reduction pretreatment(RP)process,which is implemented after the billet is completely solidified,is an alternative process to further improve billet quality.Finite element method and experiment were used to investigat...Reduction pretreatment(RP)process,which is implemented after the billet is completely solidified,is an alternative process to further improve billet quality.Finite element method and experiment were used to investigate the effect of the RP process on the internal quality of 42CrMo billet.An ultrasonic testing technology was used to study the influence of the RP process on the micro-porosities.Through a three-dimensional finite element model,the mechanism of the RP process on the porosity closure was studied.The experimental results show that the RP process eliminates the macro-porosities of the billet center.The number of micro-porosities in the billets is effectively reduced,and the increase in deformation contributes to the reduction in micro-porosities.Compared with isothermal rolling,the RP process leads to a larger equivalent strain and hydrostatic integration in the billet center because of the temperature gradient,and the effect of the temperature gradient is greater with the increase in deformation.The closure effect of micro-porosity is related not only to the stress state,but also to the distribution of micro-porosity.The increase in three-dimensional compressive stress is beneficial to the porosity closure.If the micro-porosities distributed densely,excessive stress could induce micro-porosity coalescence,which has the risk of inducing cracks.展开更多
Objective:The study aimed to explore the relationship between the carotid intima-media thickness (IMT),lipids,high-sensitivity C-reactive protein(hs-CRP),homocysteine(Hcy) and other indices of laboratory and the tradi...Objective:The study aimed to explore the relationship between the carotid intima-media thickness (IMT),lipids,high-sensitivity C-reactive protein(hs-CRP),homocysteine(Hcy) and other indices of laboratory and the traditional Chinese medicine(TCM) syndrome of dyslipidemia.Methods:A total of 152 dyslipidemia patients and 8 healthy people(taken as the control group) were recruited.According to the theory of the TCM syndrome,152 dyslipidemia patients were assigned to 4 groups:the stagnation of phlegm(SP) grou...展开更多
Shot-peened,case-hardened gears can fail in the tooth root due to crack initiation below the surface of the steel matrix.Here,the crack is initiated at a non-metallic inclusion in the center of a so-called fisheye.Thi...Shot-peened,case-hardened gears can fail in the tooth root due to crack initiation below the surface of the steel matrix.Here,the crack is initiated at a non-metallic inclusion in the center of a so-called fisheye.This failure type can lead to a reduced endurance fatigue limit of the gears.It is for this reason that,over the last decade,much effort has been invested by steel manufacturers to reduce the non-metallic inclusion content of gear steels so as to mitigate or even completely prevent such crack initiation.These ultra-clean gear steels were achieved by various measures in the steel production process.However,as a result,the remaining non-metallic inclusions are inhomogeneously distributed in the steel volume in terms of both size and location.However,due to the inhomogeneity of ultra-clean steels,the question arose if the values derived according to the standards are still representative of ultra-clean steel batches.The results show that the standards can still be applied,but more effort must be applied.To determine the degree of cleanliness,six microsections are currently evaluated according to steel test specification(SEP)1571,method K.It is shown that an examination of 24 microsections starting from size class 0 seems beneficial to get more reliable and comparable results of the degree of cleanliness of these ultra-clean gear steels.In addition,it is shown that a high degree of cleanliness has been achieved for all steel batches investigated with the measures taken in the steel production process.展开更多
The failure to achieve minimum design overlap between secant piles compromises the ability of a structure to perform as designed,resulting in water leakage or even ground collapse.To establish a more realistic simulat...The failure to achieve minimum design overlap between secant piles compromises the ability of a structure to perform as designed,resulting in water leakage or even ground collapse.To establish a more realistic simulation and provide guidelines for designing a safe and cost-effective secant-pile wall,a three-dimensional model of a secant pile,considering the geometric imperfections of the diameter and direction of the borehole,is introduced.An ultrasonic cross-hole test was performed during the construction of secant piles in a launching shaft in Beijing,China.Based on the test results,the statistical characteristics of the pile diameters and orientation parameters were obtained.By taking the pile diameter D,inclination angleβ,and azimuth angleαas random variables,Monte Carlo simulations were performed to discuss the influence of different design parameters on the probability density functions of the overlap of secant piles.The obtained results show that the randomness of the inclination angle and pile diameter can be well described by a normal distribution,whereas the azimuth angle is more consistent with a uniform distribution.The integrity of the secant-pile wall can be overestimated without considering the uncertainty of geometric imperfections.The failure of the secant-pile wall increases substantially with increasing spatial variability in drilling inclination and diameter.A design flowchart for pile spacing under the target safety level is proposed to help engineers design a safe and economical pile wall.展开更多
基金the financial support provided by USDOT Pipeline and Hazardous Materials Safety Administration (PHMSA)through the Competitive Academic Agreement Program (CAAP)。
文摘Despite the success of guided wave ultrasonic inspection for internal defect detection in steel pipes,its application on polyethylene(PE)pipe remains relatively unexplored.The growth of internal cracks in PE pipe severely affects its pressure-holding capacity,hence the early detection of internal cracks is crucial for effective pipeline maintenance strategies.This study extends the scope of guided wave-based ultrasonic testing to detect the growth of internal cracks in a natural gas distribution PE pipe.Laboratory experiments and a finite element model were planned to study the wave-crack interaction at different stages of axially oriented internal crack growth with a piezoceramic transducer-based setup arranged in a pitch-catch configuration.Mode dispersion analysis supplemented with preliminary experiments was performed to isolate the optimal inspection frequency,leading to the selection of the T(0,1)mode at 50-kHz for the investigation.A transmission index based on the energy of the T(0,1)mode was developed to trace the extent of simulated crack growth.The findings revealed an inverse linear correlation between the transmission index and the crack depth for crack growth beyond 20%crack depth.
基金Supported by National Natural Science Foundation of China(Grant Nos.U22B2068,52275520,52075078)National Key Research and Development Program of China(Grant No.2019YFA0709003).
文摘Ultrasonic testing(UT)is increasingly combined with machine learning(ML)techniques for intelligently identifying damage.Extracting signifcant features from UT data is essential for efcient defect characterization.Moreover,the hidden physics behind ML is unexplained,reducing the generalization capability and versatility of ML methods in UT.In this paper,a generally applicable ML framework based on the model interpretation strategy is proposed to improve the detection accuracy and computational efciency of UT.Firstly,multi-domain features are extracted from the UT signals with signal processing techniques to construct an initial feature space.Subsequently,a feature selection method based on model interpretable strategy(FS-MIS)is innovatively developed by integrating Shapley additive explanation(SHAP),flter method,embedded method and wrapper method.The most efective ML model and the optimal feature subset with better correlation to the target defects are determined self-adaptively.The proposed framework is validated by identifying and locating side-drilled holes(SDHs)with 0.5λcentral distance and different depths.An ultrasonic array probe is adopted to acquire FMC datasets from several aluminum alloy specimens containing two SDHs by experiments.The optimal feature subset selected by FS-MIS is set as the input of the chosen ML model to train and predict the times of arrival(ToAs)of the scattered waves emitted by adjacent SDHs.The experimental results demonstrate that the relative errors of the predicted ToAs are all below 3.67%with an average error of 0.25%,signifcantly improving the time resolution of UT signals.On this basis,the predicted ToAs are assigned to the corresponding original signals for decoupling overlapped pulse-echoes and reconstructing high-resolution FMC datasets.The imaging resolution is enhanced to 0.5λby implementing the total focusing method(TFM).The relative errors of hole depths and central distance are no more than 0.51%and 3.57%,respectively.Finally,the superior performance of the proposed FS-MIS is validated by comparing it with initial feature space and conventional dimensionality reduction techniques.
基金the National Key R&D Program of China(Grant No.2018YFB1106100)。
文摘The laser powder bed fusion(L-PBF)method of additive manufacturing(AM)is increasingly used in various industrial manufacturing fields due to its high material utilization and design freedom of parts.However,the parts produced by L-PBF usually contain such defects as crack and porosity because of the technological characteristics of L-PBF,which affect the quality of the product.Laser ultrasonic testing(LUT)is a potential technology for on-line testing of the L-PBF process.It is a non-contact and non-destructive approach based on signals from abundant waveforms with a wide frequency-band.In this study,a method of LUT for on-line inspection of L-PBF process was proposed,and a system of LUT was established approaching the actual environment of on-line detection to evaluate the method applicability for defects detection of L-PBF parts.The detection results of near-surface defects in L-PBF 316L stainless steel parts show that the crack-type defects with a sub-millimeter level within 0.5 mm depth can be identified,and accordingly,the positions and dimensions information can be acquired.The results were verified by X-ray computed tomography,which indicates that the present method exhibits great potential for on-line inspection of AM processes.
基金supported by the National Natural Science Foundation of China(Grant Nos.51804157,51774183,and 11702094)the University of Sussex,UK.Both are gratefully acknowledged.
文摘Common problems in engineering projects that involve artificial ground freezing of soil or rock include inadequate thickness,strength and continuity of artificial frozen walls.It is difficult to evaluate the freezing state using only a few thermometer holes at fixed positions or with other existing approaches.Here we report a novel experimental design that investigates changes in ultrasonic properties(received waveform,wave velocity V_(p),wave amplitude,frequency spectrum,centroid frequency f_(c),kurtosis of the frequency spectrum KFS,and quality factor Q)measured during upward freezing,compared with those during uniform freezing,in order to determine the freezing state in 150 mm cubic blocks of Ardingly sandstone.Water content,porosity and density were estimated during upward freezing to ascertain water migration and changes of porosity and density at different stages.The period of receiving the wave increased substantially and coda waves changed from loose to compact during both upward and uniform freezing.The trend of increasing V_(p) can be divided into three stages during uniform freezing.During upward freezing,V_(p) increased more or less uniformly.The frequency spectrum could be used as a convenient and rapid method to identify different freezing states of sandstone(unfrozen,upward frozen,and uniformly frozen).The continuous changes in reflection coefficient r_(φ),refraction coefficient t_(φ) and acoustic impedance field are the major reason for larger reflection and refraction during upward freezing compared with uniform freezing.Wave velocity V_(p),wave amplitude A_(h),centroid frequency f_(c) and quality factor Q were adopted as ultrasonic parameters to evaluate quantitatively the temperature T of uniformly frozen sandstone,and their application within a radar chart is recommended.Determination of V_(p) provides a convenient method to evaluate the freezing state and calculate the cryofront height and frozen section thickness of upward frozen sandstone,with accuracies of 73.37%-99.23%.
基金Supported by the Key Research and Development Plan of Anhui Province(Grant No.202004a05020003)Anhui Provincial Natural Science Foundation(Grant Nos.2008085QE233,2008085J24)+1 种基金the Science and Technology Major Project of Anhui Province(Grant No.201903a05020010)the Doctoral Science and Technology Foundation of Hefei General Machinery Research Institute(Grant No.2019010383).
文摘A high-precision evaluation of ultrasonic detection sensitivity for a micro-crack can be restricted by a corroded rough surface when the surface microtopography is of the same order of magnitude as the crack depth.In this study,a back-surface micro-crack is considered as a research target.A roughness-modified ultrasonic testing model for micro-cracks is established based on a multi-Gaussian beam model and the principle of phase-screen approximation.The echo signals of micro-cracks and noises corresponding to different rough front surfaces and rough back surfaces are obtained based on a reference reflector signal acquired from a two-dimensional simulation model.Further compari-son between the analytical and numerical models shows that the responses of micro-cracks under the effects of dif-ferent corroded rough surfaces can be accurately predicted.The numerical and analytical results show that the echo signal amplitude of the micro-crack decreases significantly with an increase in roughness,whereas the noise ampli-tude slightly increases.Moreover,the effect of the rough front surface on the echo signal of the micro-crack is greater than that of the rough back surface.When the root-mean-square(RMS)height of the surface microtopography is less than 15μm,the two rough surfaces have less influence on the echo signals detected by a focused transducer with a frequency of 5 MHz and diameter of 6 mm.A method for predicting and evaluating the detection accuracy of micro-cracks under different rough surfaces is proposed by combining the theoretical model and a finite element simulation.Then,a series of rough surface samples containing different micro-cracks are fabricated to experimentally validate the evaluation method.
基金The National Natural Science Foundation of China under contract Nos 41606220 and 41776199the National Key Research and Development Program of China under contract No.2016YFC1402702。
文摘Arctic sea ice area and thickness have declined dramatically during the recent decades.Sea ice physical and mechanical properties become increasingly important.Traditional methods of studying ice mechanical parameters such as ice-coring cannot realize field test and long-term observation.A new principle of measuring mechanical properties of ice using ultrasonic was studied and an ultrasonic system was proposed to achieve automatic observation of ice mechanical parameters(Young’s modulus,shear modulus and bulk modulus).The ultrasonic system can measure the ultrasonic velocity through ice at different temperature,salinity and density of ice.When ambient temperature decreased from 0°C to-30°C,ultrasonic velocity and mechanical properties of ice increased,and vice versa.The shear modulus of the freshwater ice and sea ice varied from 2.098 GPa to 2.48 GPa and 2.927 GPa to 4.374 GPa,respectively.The bulk modulus of freshwater ice remained between 3.074 GPa and4.566 GPa and the sea ice bulk modulus varied from 1.211 GPa to 3.089 GPa.The freshwater ice Young’s modulus kept between 5.156 GPa and 6.264 GPa and sea ice Young’s modulus varied from 3.793 GPa to 7.492 GPa.The results of ultrasonic measurement are consistent with previous studies and there is a consistent trend of mechanical modulus of ice between the process of ice temperature rising and falling.Finally,this ultrasonic method and the ultrasonic system will help to achieve the long-term observation of ice mechanical properties of ice and improve accuracy of sea ice models.
文摘Aimed at inner quality controlling for complex surface parts, an ultrasonic testing system for complex surface parts has been developed using ultrasonic NDT(Non-destructive Testing)which has features of strong penetration, well direction, high sensitivity, low cost, and harmless to people and material. The technologies of the computer, NC (Numerical control), precision mechanism, signal analysis and processing were integrated in the testing system. The system includes a PC, system software, ultrasonic data acquisition card, stepper motor drive card and five-axis precision mechanical device, etc. The software was developed using WIN98-based VC++. According to CAD data of the parts and interpolation methods, the scanning programs can be programmed. The five-axis scanning system is driven by the CNC(computer numerical control) system to control the attitude of ultrasonic probes. The system’s automatic scanning for complex surface parts, real-time acquiring ultrasonic data and automatic identifying flaw signal have been realized. This system can be used not only for testing complex surface parts, but for testing random curve parts. With fast testing speed, high sensitivity, high testing precision and high reliability, the system has a wide adaptability.
文摘Marble is a metamorphic rock, which is one of the 3 basic rock types (magmatic, sedimentary, metamorphic) forming the earth’s crust. The major characteristic sought after in a rock mass in the field for it to be exportable and usable as marble is its suitability to be cut in blocks. In the process of producing marble slabs from marble blocks, the blocks are expected not to contain potentially problematic hard or weak zones and their geomechanical and chemical properties should conform to the relevant standards. Ignoring of the geological properties of the rock in the process of deciding for marble production at a marble site and determination of production location, direction and method is the most important parameter that would increase production loss. In order to reduce losses by determination of geological properties of marble, many academic studies have been conducted on the effects of water saturation, temperature, freezing and thawing on its mechanical and fracture properties. There are further studies on crack propagation in marble under stress. However, even those marble blocks that are obtained based on geological parameters may suffer serious cracks or fractures due to stresses caused by their weight and geometry. Therefore, cutting direction is of critical importance in order to minimize marble waste in the process of cutting a marble block which is brought to the inventory or processing site with cracks, cavities or fractures. Certain studies exist within such context, where the geometry of the discontinuity within a block is determined using non-destructive methods, such as ultrasonic testing, in order to determine the appropriate cutting direction. Such studies made use of ultrasonic waves to determine the physical and chemical structures of magmatic and sedimentary rocks by measuring the progress velocity of sonic waves in the rock. Said studies, however, mostly worked on sedimentary and magmatic rock specimens, focusing less on metamorphic rocks such as marble due to their anisotropic properties. Understanding the academic literature studies on marble would provide significant contribution to the reduction of production losses during the processing marble blocks in processing plants and the achievement of production efficiency levels that are within economic limits. Within such scope, this study has reviewed the past academic studies on marble, classified them under 6 categories, and comprehensively analyzed each category based on materials, testing setups, test specimens, test parameters and research techniques.
基金supported by the National Nature Science Foundation of China(51375002,51005056)。
文摘In order to improve the work efficiency of non-destructive testing(NDT)and the reliability of NDT results,an automatic method to detect defects in the ultrasonic image was researched.According to the characterization of ultrasonic D-scan image,clutter wave suppression and de-noising were presented firstly.Then,the image is processed by binaryzation using KSW 2 D entropy based on image segmentation method.The results showed that,the global threshold based segmentation method was somewhat ineffective for D-scan image because of under-segmentation.Especially,when the image is big in size,small targets which are composed by a small amount of pixels are often undetected.Whereas,local threshold based image segmentation method is effective in recognizing small defects because it takes local image character into account.
基金the Fund of the State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology(No.welding 10-013)
文摘The important status of guide ring in large power plants and its manufacturing methods were introduced. The advantages of manufacturing methods including welding and electrolysis were discussed.In order to ensure the brazing quality of the guide ring,ultrasonic nondestructive testing(UNDT) method was used in this study.According to the features of the defects that may show up during brazing,the feasibility and reliability of UNDT were proved in theory.Based on the theory,an ultrasonic C-scan imaging test method was developed using a water immersion focusing probe.According to the features of the inspected images,the defects were segmented using a morphology image processing based method.The defects can be localized and sized by employing the algorithm of area reconstruction.At last,the combination ratio of brazing interface can be calculated and the brazing quality of the guide ring can be evaluated.
基金funded by the National Natural Science Foundation of China under Grant Nos.51979268,U1765206,41877256。
文摘Excavation Damaged Zone(EDZ)scope is important for optimizing excavation and support schemes in deep underground caverns.However,accurately predicting the full EDZ scope within the surrounding rock masses of deep underground caverns during excavation remains a pressing problem.This study presents a comprehensive EDZ scope prediction approach(CESPA)for the brittle surrounding rock masses of deep underground caverns by coupling numerical simulation with quantitative analysis of borehole wall images and ultrasonic test results.First,the changes in both P-velocity(V_(p))and joint distribution of the surrounding rock masses before and after excavation damage are captured using ultrasonic tests and borehole digital cameras.Second,the quality Q-parameters of the surrounding rock mass before and after excavation damage are preliminarily rated with the rock mass descriptions provided by borehole wall images,and the rock mass V_(p)-parameter values are determined according to the V_(p)-borehole depth curves.Third,the Q-parameter ratings are further finely adjusted by updating the related Q-values to be similar with the Q-values estimated by V_(p)-parameter values.Fourth,the initial and residual mechanical parameters for the rock mass deterioration model(RDM)are estimated by the adjusted Q-parameter ratings based on the modified Q-based relations,and the elastic modulus deterioration index(EDI)threshold to describe the EDZ boundary is determined with the V_(p)-parameter values.Finally,EDZ scope is predicted using the elastoplastic numerical simulation with RDM and EDI based on the mechanical parameter estimates and EDI threshold.Analyses of applications in Sub-lab D1 in Jinping II project show that CESPA can provide a reliable and operable solution for predicting full EDZ scopes within the brittle surrounding rock masses of deep underground caverns.
基金financial support from Beijing Outstanding Young Scientist Program,China(Grant No.BJJWZYJH01201911413037)the National Natural Science Foundation of China(Grant No.41877257)Shaanxi Coal Group Key Project,China(Grant No.2018SMHKJ-A-J-03)。
文摘HoekeBrown failure criterion is one of the widely used rock strength criteria in rock mechanics and mining engineering.Based on the theoretical expression of HoekeBrown parameter m of an intact rock,the parameter m has been modified by crack parameters for fractured rocks.In this paper,the theoretical value range and theoretical expression form of the parameter m in HoekeBrown failure criterion were discussed.A critical crack parameter B was defined to describe the influence of the critical crack when the stress was at the peak,while a parameter b was introduced to represent the distribution of the average initial fractures.The parameter m of a fractured rock contained the influences of critical crack(B),confining pressure(s3)and initial fractures(b).Then the triaxial test on naturally fractured limestones was conducted to verify the modification of the parameter m.From the ultrasonic test and loading test results of limestones,the parameter m can be obtained,which indicated that the confining pressure at a high level reduced the differences of m among all the specimens.The confining pressure s3 had an exponential impact on m,while the critical crack parameter B had a negative correlation with m.Then the expression of m for a naturally fractured limestone was also proposed.
文摘In the point of application to ultrasonic nondestructive testing of surface stress and defect in polymer component, the oblique suxface wave transducer is investigated on its acoustic property and especially the mechanism of acoustic attenuation of acoustic entrant material inside the transducer. A new kind of room temperature vulcanized silicone elastomer as wedge material, in which ultrasound can propagate in very low speed with weak attenuation, is developed through a great deal of trials. The corresponding ultrasonic transducer is also designed for further researches and application to detect surface stress and surface crack in aerospace transparent component.
基金the support of NVIDIA Corporation with the donation of the Titan Xp GPU used for this researchsupported by EPSRC grant EP/R002495/1the European Metrology Research Programme through grant 17IND08。
文摘Composite materials are increasingly used in the aerospace industry.To fully realise the weight saving potential along with superior mechanical properties that composites offer in safety critical applications,reliable Non-Destructive Testing(NDT)methods are required to prevent catastrophic failures.This paper will review the state of the art in the field and point to highlight the success and challenges that different NDT methods are faced to evaluate the integrity of critical aerospace composites.The focus will be on advanced certificated NDT methods for damage detection and characterization in composite laminates for use in the aircraft primary and secondary structures.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) “Development of System for Damage Detection on the Outer of Fibrous Composite Blade for Wind Power Plants In-process and In-service Inspection”(No. 20153030024070)funded by the Ministry of Trade,Industry,and Energy (MOTIE),Korea。
文摘Recent development trends in wind power generation have increased the importance of the safe operation of wind-turbine blades(WTBs). To realize this objective, it is essential to inspect WTBs for any defects before they are placed into operation. However, conventional methods of fault inspection in WTBs can be rather difficult to implement, since complex curvatures that characterize the WTB structures must ensure accurate and reliable inspection. Moreover, it is considered useful if inspection results can be objectively and consistently classified and analyzed by an automated system and not by the subjective judgment of an inspector. To address this concern,the construction of a pressure-and shape-adaptive phased-array ultrasonic testing platform, which is controlled by a nanoengine operation system to inspect WTBs for internal defects, has been presented in this paper. An automatic classifier has been designed to detect discontinuities in WTBs by using an A-scanimaging-based convolutional neural network(CNN). The proposed CNN classifier design demonstrates a classification accuracy of nearly 99%. Results of the study demonstrate that the proposed CNN classifier is capable of automatically classifying the discontinuities of WTB with high accuracy, all of which could be considered as defect candidates.
文摘Reduction pretreatment(RP)process,which is implemented after the billet is completely solidified,is an alternative process to further improve billet quality.Finite element method and experiment were used to investigate the effect of the RP process on the internal quality of 42CrMo billet.An ultrasonic testing technology was used to study the influence of the RP process on the micro-porosities.Through a three-dimensional finite element model,the mechanism of the RP process on the porosity closure was studied.The experimental results show that the RP process eliminates the macro-porosities of the billet center.The number of micro-porosities in the billets is effectively reduced,and the increase in deformation contributes to the reduction in micro-porosities.Compared with isothermal rolling,the RP process leads to a larger equivalent strain and hydrostatic integration in the billet center because of the temperature gradient,and the effect of the temperature gradient is greater with the increase in deformation.The closure effect of micro-porosity is related not only to the stress state,but also to the distribution of micro-porosity.The increase in three-dimensional compressive stress is beneficial to the porosity closure.If the micro-porosities distributed densely,excessive stress could induce micro-porosity coalescence,which has the risk of inducing cracks.
基金Supported by the National Natural Science Foundation of China(No.90209001)
文摘Objective:The study aimed to explore the relationship between the carotid intima-media thickness (IMT),lipids,high-sensitivity C-reactive protein(hs-CRP),homocysteine(Hcy) and other indices of laboratory and the traditional Chinese medicine(TCM) syndrome of dyslipidemia.Methods:A total of 152 dyslipidemia patients and 8 healthy people(taken as the control group) were recruited.According to the theory of the TCM syndrome,152 dyslipidemia patients were assigned to 4 groups:the stagnation of phlegm(SP) grou...
基金The underlying research work was funded in equal proportions by the“Arbeitsgemeinschaft industrieller Forschungsvereinigungen e.V.(AiF)”,the German Federal Ministry of Economics and Technology(BMWi,IGF no.16662 N)and the FVA.The results presented in this paper were taken from the FVA research project 293 III“Späte Zahnfußbrüche/Reinheitsgrad”.More detailed information on the influence of non-metallic inclusions is given in the final report.
文摘Shot-peened,case-hardened gears can fail in the tooth root due to crack initiation below the surface of the steel matrix.Here,the crack is initiated at a non-metallic inclusion in the center of a so-called fisheye.This failure type can lead to a reduced endurance fatigue limit of the gears.It is for this reason that,over the last decade,much effort has been invested by steel manufacturers to reduce the non-metallic inclusion content of gear steels so as to mitigate or even completely prevent such crack initiation.These ultra-clean gear steels were achieved by various measures in the steel production process.However,as a result,the remaining non-metallic inclusions are inhomogeneously distributed in the steel volume in terms of both size and location.However,due to the inhomogeneity of ultra-clean steels,the question arose if the values derived according to the standards are still representative of ultra-clean steel batches.The results show that the standards can still be applied,but more effort must be applied.To determine the degree of cleanliness,six microsections are currently evaluated according to steel test specification(SEP)1571,method K.It is shown that an examination of 24 microsections starting from size class 0 seems beneficial to get more reliable and comparable results of the degree of cleanliness of these ultra-clean gear steels.In addition,it is shown that a high degree of cleanliness has been achieved for all steel batches investigated with the measures taken in the steel production process.
基金the National Natural Science Foundation of China(Grant Nos.51978040 and 51378054)the National Basic Research Program of China(973 program,No.2015CB057800)for supporting this research.
文摘The failure to achieve minimum design overlap between secant piles compromises the ability of a structure to perform as designed,resulting in water leakage or even ground collapse.To establish a more realistic simulation and provide guidelines for designing a safe and cost-effective secant-pile wall,a three-dimensional model of a secant pile,considering the geometric imperfections of the diameter and direction of the borehole,is introduced.An ultrasonic cross-hole test was performed during the construction of secant piles in a launching shaft in Beijing,China.Based on the test results,the statistical characteristics of the pile diameters and orientation parameters were obtained.By taking the pile diameter D,inclination angleβ,and azimuth angleαas random variables,Monte Carlo simulations were performed to discuss the influence of different design parameters on the probability density functions of the overlap of secant piles.The obtained results show that the randomness of the inclination angle and pile diameter can be well described by a normal distribution,whereas the azimuth angle is more consistent with a uniform distribution.The integrity of the secant-pile wall can be overestimated without considering the uncertainty of geometric imperfections.The failure of the secant-pile wall increases substantially with increasing spatial variability in drilling inclination and diameter.A design flowchart for pile spacing under the target safety level is proposed to help engineers design a safe and economical pile wall.
