To compensate for the shortcomings of quasi-static law in anti-fatigue analysis of foundry crane metal structures,the fatigue life evaluation method of foundry crane metal structure considering load dynamic response a...To compensate for the shortcomings of quasi-static law in anti-fatigue analysis of foundry crane metal structures,the fatigue life evaluation method of foundry crane metal structure considering load dynamic response and crack closure effect is proposed.In line with the theory of mechanical vibration,a dynamic model of crane structure during the working cycle is constructed,and dynamic coefficients under diverse actions are analysed.Calculation models of the internal force dynamic change process of dangerous cross-sections and a simulation model of first principal stress-time history are established by using the steel structure design criteria,which is utilised to extract the change of first principal stress of danger points over time.Then,the double-parameter stress spectrum is obtained by the rain flow counting method.The fatigue life calculation formula is corrected by introducing a crack closure parameter that can be calculated by the stress ratio and the effective stress ratio.Under the finite element model imported into Msc.Patran,crack propagation analysis is performed by the growth method in the fatigue integration module Msc.Fatigue.Taking the metal structure of a 100/40t-28.5m foundry crane with track offset as an example,the accuracy of calculation results and the feasibility and applicability of the proposed method are verified by theoretical calculation and finite element simulation,which provide a theoretical basis for improvement of the fatigue resistance design of foundry cranes.展开更多
The state-of the-art of fatigue crack closure effect, involving the mechanisms, measurements,models, evaluation methods, innuencing factors and existing problems is briefly reviewed. Attention is concentrated on a new...The state-of the-art of fatigue crack closure effect, involving the mechanisms, measurements,models, evaluation methods, innuencing factors and existing problems is briefly reviewed. Attention is concentrated on a new consideration of closure effect and a re-definition of the effective d riving force for the propagation of a fatigue crack. A theoretical basis fOr measuring the closure effect is established. The proposed closure concept takes into account the role of the lower portion of loading cycle below the opening load. The conventionaI closure concept is proven to be correct only for some extreme cases which are practically non-existent fOr engineering materials. A miniature strain gauge tech nique is developed to measure the crack closure. Stressratio-change tests at threshold level clearly indicate the shortcomings of the conventional closure concept, and the validity of the newly-proposed closure concept. The application of the proposed concept can give rise to a new method for the determination of the effective fatigue threshold of materials. If the fatigue threshold is measured at a sufficiently negative stress ratio (R<Rcr) the tensile portion of the cyclic loading Just reflects the effective fatigue threshold of the material.展开更多
In this work, electrochemical plating treatments were applied to ASTM A36 steel specimens to study the efficiency and limitations of this method for arresting fatigue crack propagation. Electroplated iron was deposite...In this work, electrochemical plating treatments were applied to ASTM A36 steel specimens to study the efficiency and limitations of this method for arresting fatigue crack propagation. Electroplated iron was deposited onto the crack surfaces using a circuit in which Swedish Iron served as the anode in a solution of Ammonium Iron(II) Sulfate Hexahydrate. The iron ions were driven into fatigue cracks that were formed within ASTM E399 compact tension specimens. This work showed that an iron-plating treatment operated at 20°C can arrest fatigue crack propagation for a significant period of cycles. The propagation re-initiation lives that resulted ranged from 11,000 to 230,000 cycles. As observed in prior work, the propagation re-initiation life correlated strongly to the magnitude of the stress intensity factor range that was applied during cycling. As this stress intensity increased, the propagation re-initiation life decreased. Repeated treatments on the same crack provided extended service lives by as much as 370,000 cycles or 60% of the entire fatigue life of the component. Future work may show that re-application of the treatment, when conducted prior to crack re-initiation, could further extend the service life indefinitely. The Correia crack closure model was modified to provide an empirical expression for predicting the crack re-initiation life of the treated component. Interestingly, highly effective arrest behavior was still observed for cracks that were loaded to stress intensity factors of only 3 - 6 <img src="Edit_f69af9cd-e908-4aef-8ccb-3b1f36e16d08.png" alt="" />during the treatment but then subjected to 20 <img src="Edit_5ddb9cae-23ad-442d-8e6c-63b5e1d99a0f.png" alt="" /> during cyclic loading. Galvanic corrosion of the plated material exposed to simulated seawater was estimated to be 3 mpy. Future work will examine the use of less active plating alloys and the possibility of applying effective treatments into cracks that are in an unloaded state.展开更多
Advances in machine learning(ML)methods are important in industrial engineering and attract great attention in recent years.However,a comprehensive comparative study of the most advanced ML algorithms is lacking.Six i...Advances in machine learning(ML)methods are important in industrial engineering and attract great attention in recent years.However,a comprehensive comparative study of the most advanced ML algorithms is lacking.Six integrated ML approaches for the crack repairing capacity of the bacteria-based self-healing concrete are proposed and compared.Six ML algorithms,including the Support Vector Regression(SVR),Decision Tree Regression(DTR),Gradient Boosting Regression(GBR),Artificial Neural Network(ANN),Bayesian Ridge Regression(BRR)and Kernel Ridge Regression(KRR),are adopted for the relationship modeling to predict crack closure percentage(CCP).Particle Swarm Optimization(PSO)is used for the hyper-parameters tuning.The importance of parameters is analyzed.It is demonstrated that integrated ML approaches have great potential to predict the CCP,and PSO is efficient in the hyperparameter tuning.This research provides useful information for the design of the bacteria-based self-healing concrete and can contribute to the design in the rest of industrial engineering.展开更多
Welding residual stress in the engineering structure has a non-negligible influence on crack propagation,and crack closure is a significant factor affecting the crack propagation.Based on the elastoplastic finite elem...Welding residual stress in the engineering structure has a non-negligible influence on crack propagation,and crack closure is a significant factor affecting the crack propagation.Based on the elastoplastic finite element method and crack closure theory,we studied crack closure and residual compressive stress field of butt-welded plates under constant amplitude loading and overloading regarding the stress ratio,maximum load,overload ratio,and number of overloads.The results show that the welding residual tensile stress can decrease the crack closure because of a decrease in the residual compressive stress in the wake zone,but the effect is gradually reduced with increased stress ratio or maximum load.And the combined effect of welding residual tensile stress and overload can produce a stronger retardation effect on crack propagation.展开更多
A 3D displacement discontinuity method is applied to solve the fracture mechanics problems of the mixed mode crack under compression.Friction between the surface of the closed crack is considered by establishing a sim...A 3D displacement discontinuity method is applied to solve the fracture mechanics problems of the mixed mode crack under compression.Friction between the surface of the closed crack is considered by establishing a simple and efficient iterative algorithm based on method of contact resistance mitigation.On the surfaces of the closed crack,the Mohr-coulomb rule is satisfied by iteration when the crack is in condition of sliding.The stress intensity factors are obtained using displacement fitting method.It is shown that the numerical results agree with the experimental results well and that friction plays an important role in resisting crack propagation.展开更多
Large numbers of aircraft composite structures were researched,and the distribution of delamination sizes and though thickness positions in the composite laminates were investigated.An experiment was conducted to prob...Large numbers of aircraft composite structures were researched,and the distribution of delamination sizes and though thickness positions in the composite laminates were investigated.An experiment was conducted to probe into the effect of delamination sizes and through thickness positions on the compressive strengths of laminates with single embedded circular delamination with the most dangerous delamination sizes and positions defined from the distribution.A shell model was established for compressive strength prediction,and the virtual crack closure technique(VCCT) was employed for the strain energy release rate calculation.The finite element(FE) prediction was in good agreement with the experimental measurements,for the predicted compressive strengths stood within 10%error of experimental results.It was observed that the compressive strength was highly effected by the delamination size,while the though thickness position of delamination did not have significant effect on the compressive strength.展开更多
基金the National Science-technology Support Projects for the 13th Five-year Plan(2017YFC0805703-4).
文摘To compensate for the shortcomings of quasi-static law in anti-fatigue analysis of foundry crane metal structures,the fatigue life evaluation method of foundry crane metal structure considering load dynamic response and crack closure effect is proposed.In line with the theory of mechanical vibration,a dynamic model of crane structure during the working cycle is constructed,and dynamic coefficients under diverse actions are analysed.Calculation models of the internal force dynamic change process of dangerous cross-sections and a simulation model of first principal stress-time history are established by using the steel structure design criteria,which is utilised to extract the change of first principal stress of danger points over time.Then,the double-parameter stress spectrum is obtained by the rain flow counting method.The fatigue life calculation formula is corrected by introducing a crack closure parameter that can be calculated by the stress ratio and the effective stress ratio.Under the finite element model imported into Msc.Patran,crack propagation analysis is performed by the growth method in the fatigue integration module Msc.Fatigue.Taking the metal structure of a 100/40t-28.5m foundry crane with track offset as an example,the accuracy of calculation results and the feasibility and applicability of the proposed method are verified by theoretical calculation and finite element simulation,which provide a theoretical basis for improvement of the fatigue resistance design of foundry cranes.
文摘The state-of the-art of fatigue crack closure effect, involving the mechanisms, measurements,models, evaluation methods, innuencing factors and existing problems is briefly reviewed. Attention is concentrated on a new consideration of closure effect and a re-definition of the effective d riving force for the propagation of a fatigue crack. A theoretical basis fOr measuring the closure effect is established. The proposed closure concept takes into account the role of the lower portion of loading cycle below the opening load. The conventionaI closure concept is proven to be correct only for some extreme cases which are practically non-existent fOr engineering materials. A miniature strain gauge tech nique is developed to measure the crack closure. Stressratio-change tests at threshold level clearly indicate the shortcomings of the conventional closure concept, and the validity of the newly-proposed closure concept. The application of the proposed concept can give rise to a new method for the determination of the effective fatigue threshold of materials. If the fatigue threshold is measured at a sufficiently negative stress ratio (R<Rcr) the tensile portion of the cyclic loading Just reflects the effective fatigue threshold of the material.
文摘In this work, electrochemical plating treatments were applied to ASTM A36 steel specimens to study the efficiency and limitations of this method for arresting fatigue crack propagation. Electroplated iron was deposited onto the crack surfaces using a circuit in which Swedish Iron served as the anode in a solution of Ammonium Iron(II) Sulfate Hexahydrate. The iron ions were driven into fatigue cracks that were formed within ASTM E399 compact tension specimens. This work showed that an iron-plating treatment operated at 20°C can arrest fatigue crack propagation for a significant period of cycles. The propagation re-initiation lives that resulted ranged from 11,000 to 230,000 cycles. As observed in prior work, the propagation re-initiation life correlated strongly to the magnitude of the stress intensity factor range that was applied during cycling. As this stress intensity increased, the propagation re-initiation life decreased. Repeated treatments on the same crack provided extended service lives by as much as 370,000 cycles or 60% of the entire fatigue life of the component. Future work may show that re-application of the treatment, when conducted prior to crack re-initiation, could further extend the service life indefinitely. The Correia crack closure model was modified to provide an empirical expression for predicting the crack re-initiation life of the treated component. Interestingly, highly effective arrest behavior was still observed for cracks that were loaded to stress intensity factors of only 3 - 6 <img src="Edit_f69af9cd-e908-4aef-8ccb-3b1f36e16d08.png" alt="" />during the treatment but then subjected to 20 <img src="Edit_5ddb9cae-23ad-442d-8e6c-63b5e1d99a0f.png" alt="" /> during cyclic loading. Galvanic corrosion of the plated material exposed to simulated seawater was estimated to be 3 mpy. Future work will examine the use of less active plating alloys and the possibility of applying effective treatments into cracks that are in an unloaded state.
文摘Advances in machine learning(ML)methods are important in industrial engineering and attract great attention in recent years.However,a comprehensive comparative study of the most advanced ML algorithms is lacking.Six integrated ML approaches for the crack repairing capacity of the bacteria-based self-healing concrete are proposed and compared.Six ML algorithms,including the Support Vector Regression(SVR),Decision Tree Regression(DTR),Gradient Boosting Regression(GBR),Artificial Neural Network(ANN),Bayesian Ridge Regression(BRR)and Kernel Ridge Regression(KRR),are adopted for the relationship modeling to predict crack closure percentage(CCP).Particle Swarm Optimization(PSO)is used for the hyper-parameters tuning.The importance of parameters is analyzed.It is demonstrated that integrated ML approaches have great potential to predict the CCP,and PSO is efficient in the hyperparameter tuning.This research provides useful information for the design of the bacteria-based self-healing concrete and can contribute to the design in the rest of industrial engineering.
基金supported by the National Natural Science Foundation of China (Grant No. 51779198)
文摘Welding residual stress in the engineering structure has a non-negligible influence on crack propagation,and crack closure is a significant factor affecting the crack propagation.Based on the elastoplastic finite element method and crack closure theory,we studied crack closure and residual compressive stress field of butt-welded plates under constant amplitude loading and overloading regarding the stress ratio,maximum load,overload ratio,and number of overloads.The results show that the welding residual tensile stress can decrease the crack closure because of a decrease in the residual compressive stress in the wake zone,but the effect is gradually reduced with increased stress ratio or maximum load.And the combined effect of welding residual tensile stress and overload can produce a stronger retardation effect on crack propagation.
文摘A 3D displacement discontinuity method is applied to solve the fracture mechanics problems of the mixed mode crack under compression.Friction between the surface of the closed crack is considered by establishing a simple and efficient iterative algorithm based on method of contact resistance mitigation.On the surfaces of the closed crack,the Mohr-coulomb rule is satisfied by iteration when the crack is in condition of sliding.The stress intensity factors are obtained using displacement fitting method.It is shown that the numerical results agree with the experimental results well and that friction plays an important role in resisting crack propagation.
基金the financial support by the National Natural Science Foundation of China(NSFC,51931010,92163202)the Key Research Program of Frontier Science and International partnership program(GJHZ2029)。
基金National Basic Research Program of China(2012CB720000)
文摘Large numbers of aircraft composite structures were researched,and the distribution of delamination sizes and though thickness positions in the composite laminates were investigated.An experiment was conducted to probe into the effect of delamination sizes and through thickness positions on the compressive strengths of laminates with single embedded circular delamination with the most dangerous delamination sizes and positions defined from the distribution.A shell model was established for compressive strength prediction,and the virtual crack closure technique(VCCT) was employed for the strain energy release rate calculation.The finite element(FE) prediction was in good agreement with the experimental measurements,for the predicted compressive strengths stood within 10%error of experimental results.It was observed that the compressive strength was highly effected by the delamination size,while the though thickness position of delamination did not have significant effect on the compressive strength.
