A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by hig...A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.展开更多
The infrared radiation temperature(IRT)variation concerning stress and crack evolution of rocks is a critical focus in rock mechanics domain and engineering disaster warning.In this paper,a methodology to extract the ...The infrared radiation temperature(IRT)variation concerning stress and crack evolution of rocks is a critical focus in rock mechanics domain and engineering disaster warning.In this paper,a methodology to extract the key IRT features related to stress and crack evolution of loaded rocks is proposed.Specifically,the wavelet denoising and reconstruction in thermal image sequence(WDRTIS)method is employed to eliminate temporal noise in thermal image sequences.Subsequently,the adaptive partition temperature drift correction(APTDC)method is introduced to alleviate temperature drift.On this basis,the spatial noise correction method based on threshold segmentation and adaptive median filtering(OTSU-AMF)is proposed to extract the key IRT features associated with microcracks of loaded rocks.Following temperature drift correction,IRT provides an estimation of the thermoelastic factor in rocks,typically around 5.29×10^(-5) MPa^(-1) for sandstones.Results reveal that the high-temperature concentrated region in cumulative thermal images of crack evolution(TICE)can elucidate the spatiotemporal evolution of localized damage.Additionally,heat dissipation of crack evolution(HDCE)acquired from TICE quantifies the progressive failure process of rocks.The proposed methodology enhances the reliability of IRT monitoring results and provides an innovative approach for conducting research in rock mechanics and monitoring engineering disasters.展开更多
Heat-ray absorbing film is used to be bonded on the existing sheet glasses of the windows.It is effective for air-conditioning energy saving against the global warming,because it absorbs heat-ray in the thin film and ...Heat-ray absorbing film is used to be bonded on the existing sheet glasses of the windows.It is effective for air-conditioning energy saving against the global warming,because it absorbs heat-ray in the thin film and decreases the incoming heat-ray into the room.On the other hand,the sheet glasses increase the temperature at the surface which the sheet is bonded and sometimes yield heat cracks by thermal stresses.It is important to know the state of thermal stresses accurately in order to develop the heat-ray absorbing film with higher performance and without heat cracks.In this paper,the analysis model is treated as the two-layer plate of the conventional soda sheet glass and the heat-ray absorbing film with different absorptivities.The unsteady temperature and thermal stresses are analyzed and calculated numerically.The influence of the patch side,which the heat-ray absorbing film is bonded at the exterior side or the interior side,on the heat-ray absorbing performance and the thermal stresses is discussed.It is found that the alternative patch side has no effect on the heat-ray absorbing performance and that the patch side is recommended to be interior side from a view point of decreasing thermal stresses against the heat crack of glasses.展开更多
Heat-ray absorbing sheet glass can decrease electric energy used for air-conditioning by controling the incoming heat-ray through windows into the rooms.On the other hand,the glasses increase the temperature and somet...Heat-ray absorbing sheet glass can decrease electric energy used for air-conditioning by controling the incoming heat-ray through windows into the rooms.On the other hand,the glasses increase the temperature and sometimes yield heat cracks by thermal stresses.It is important to know the state of thermal stress accurately in order to develop heat-ray absorbing sheet glasses with higher performance and without heat cracks.A conventional design manual at field site treats the steady state and the thermal boundary condition that all heat-rays are absorbed at glass surface.In this paper,it is assumed that the heat-ray is absorbed over all the plate thickness.The idea of the local absorptibity per unit length is introduced.The modeling of internal heat absorbing process is proposed.It can explain well that the total absorptivity depends on the plate thickness.The temperature and the thermal stresses are calculated and discussed.Sudden weather changes such as rain and/or wind after the glass is heated to be steady state are also discussed.Those weather changes are treated with the change of amount of absorbed heat-ray and/or the change of heat transfer coefficient between the glass surface and the outside atmosphere.展开更多
The early age performance of spread footing, especially the growth of cracks, is deeply influenced by the heat of hydration of cement. In this paper, 3D finite element method(FEM)models are set up to analyze the tempe...The early age performance of spread footing, especially the growth of cracks, is deeply influenced by the heat of hydration of cement. In this paper, 3D finite element method(FEM)models are set up to analyze the temperature distribution and thermal stresses of the spread footing during the first seven days after concrete placement. The mechanical properties of early age concrete are calculated, which are further used in the FEM models. The possibilities of crack growth are estimated by the method of crack index. The crack indexes of quite a number of points are very close to the allowable limit of 1.0 during the last three days. It is also indicated that the influence of foundation ring on the thermal stresses of concrete can be neglected.展开更多
The Al-Si coating of ultra-high strength steel has been applied to hot stamping more and more widely, owing to solving the problem of oxidation and decarburization. However, the evolution of Al-Si coating during the h...The Al-Si coating of ultra-high strength steel has been applied to hot stamping more and more widely, owing to solving the problem of oxidation and decarburization. However, the evolution of Al-Si coating during the heating process was rarely studied in the previous study. The tests about the influence of heating parameters, such as heating temperature, heating rates and dwell time, on properties of the Al-Si coating were carried out on the Gleeble-3500 thermal simulator. The properties of the Al-Si coating, for instance, volume fraction of FeAl intermetallics, α-Fe layer as well as porosity and 3D surface topography, were explored in the study. Results showed that more and more Kirkendall voids and cracks appeared in the Al-Si coating when the heating temperature exceeded 600°C. The heating rates almost had no influence on properties of the Al-Si coating when the temperature was equal to or lower than 500°C. The volume fraction of FeAl intermetallics in the coating with dwell time from 3 s to 8 min at 930°C was0, 6.19%, 17.03% and 20.65%, separately. The volume fraction of the α-Fe layer in the coating changed from zero to 31.52%with the prolonged dwell time. The porosity of the coating ranged from 0.51% to 4.98% with the extension of dwell time. The unsmooth degree of the surface of the coating rose gradually with the increasing of heating rates and the extension of dwell time.The 3D surface topography of the coating was determined by the comprehensive effect of atoms diffusion, new formed phases,surface tension and the degree of oxidation of the coating surface. Experiments indicated that rapid heating was not suitable for the coating when the temperature exceeded 500°C. Experiments also demonstrated that enough dwell time was essential to obtain the superior properties of the coating.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 10574073)
文摘A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.
基金supported by the National Natural Science Foundation of China(No.51874280)the Fundamental Research Funds for the Central Universities(No.2021ZDPY0211)+2 种基金the Graduate Innovation Program of China University of Mining and Technology(No.2023WLKXJ046)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX23_2811)the Project of Liaoning Provincial Department of Education(No.JYTMS20231458).
文摘The infrared radiation temperature(IRT)variation concerning stress and crack evolution of rocks is a critical focus in rock mechanics domain and engineering disaster warning.In this paper,a methodology to extract the key IRT features related to stress and crack evolution of loaded rocks is proposed.Specifically,the wavelet denoising and reconstruction in thermal image sequence(WDRTIS)method is employed to eliminate temporal noise in thermal image sequences.Subsequently,the adaptive partition temperature drift correction(APTDC)method is introduced to alleviate temperature drift.On this basis,the spatial noise correction method based on threshold segmentation and adaptive median filtering(OTSU-AMF)is proposed to extract the key IRT features associated with microcracks of loaded rocks.Following temperature drift correction,IRT provides an estimation of the thermoelastic factor in rocks,typically around 5.29×10^(-5) MPa^(-1) for sandstones.Results reveal that the high-temperature concentrated region in cumulative thermal images of crack evolution(TICE)can elucidate the spatiotemporal evolution of localized damage.Additionally,heat dissipation of crack evolution(HDCE)acquired from TICE quantifies the progressive failure process of rocks.The proposed methodology enhances the reliability of IRT monitoring results and provides an innovative approach for conducting research in rock mechanics and monitoring engineering disasters.
文摘Heat-ray absorbing film is used to be bonded on the existing sheet glasses of the windows.It is effective for air-conditioning energy saving against the global warming,because it absorbs heat-ray in the thin film and decreases the incoming heat-ray into the room.On the other hand,the sheet glasses increase the temperature at the surface which the sheet is bonded and sometimes yield heat cracks by thermal stresses.It is important to know the state of thermal stresses accurately in order to develop the heat-ray absorbing film with higher performance and without heat cracks.In this paper,the analysis model is treated as the two-layer plate of the conventional soda sheet glass and the heat-ray absorbing film with different absorptivities.The unsteady temperature and thermal stresses are analyzed and calculated numerically.The influence of the patch side,which the heat-ray absorbing film is bonded at the exterior side or the interior side,on the heat-ray absorbing performance and the thermal stresses is discussed.It is found that the alternative patch side has no effect on the heat-ray absorbing performance and that the patch side is recommended to be interior side from a view point of decreasing thermal stresses against the heat crack of glasses.
文摘Heat-ray absorbing sheet glass can decrease electric energy used for air-conditioning by controling the incoming heat-ray through windows into the rooms.On the other hand,the glasses increase the temperature and sometimes yield heat cracks by thermal stresses.It is important to know the state of thermal stress accurately in order to develop heat-ray absorbing sheet glasses with higher performance and without heat cracks.A conventional design manual at field site treats the steady state and the thermal boundary condition that all heat-rays are absorbed at glass surface.In this paper,it is assumed that the heat-ray is absorbed over all the plate thickness.The idea of the local absorptibity per unit length is introduced.The modeling of internal heat absorbing process is proposed.It can explain well that the total absorptivity depends on the plate thickness.The temperature and the thermal stresses are calculated and discussed.Sudden weather changes such as rain and/or wind after the glass is heated to be steady state are also discussed.Those weather changes are treated with the change of amount of absorbed heat-ray and/or the change of heat transfer coefficient between the glass surface and the outside atmosphere.
基金Supported by the National Natural Science Foundation of China(No.51379142)International Science and Technology Cooperation Program of China(No.2012DFA70490)Tianjin Municipal Natural Science Foundation(No.13JCQNJC06900)
文摘The early age performance of spread footing, especially the growth of cracks, is deeply influenced by the heat of hydration of cement. In this paper, 3D finite element method(FEM)models are set up to analyze the temperature distribution and thermal stresses of the spread footing during the first seven days after concrete placement. The mechanical properties of early age concrete are calculated, which are further used in the FEM models. The possibilities of crack growth are estimated by the method of crack index. The crack indexes of quite a number of points are very close to the allowable limit of 1.0 during the last three days. It is also indicated that the influence of foundation ring on the thermal stresses of concrete can be neglected.
基金supported by the National Natural Science Foundation of China(Grant Nos.51275185,51405171,U1564203)
文摘The Al-Si coating of ultra-high strength steel has been applied to hot stamping more and more widely, owing to solving the problem of oxidation and decarburization. However, the evolution of Al-Si coating during the heating process was rarely studied in the previous study. The tests about the influence of heating parameters, such as heating temperature, heating rates and dwell time, on properties of the Al-Si coating were carried out on the Gleeble-3500 thermal simulator. The properties of the Al-Si coating, for instance, volume fraction of FeAl intermetallics, α-Fe layer as well as porosity and 3D surface topography, were explored in the study. Results showed that more and more Kirkendall voids and cracks appeared in the Al-Si coating when the heating temperature exceeded 600°C. The heating rates almost had no influence on properties of the Al-Si coating when the temperature was equal to or lower than 500°C. The volume fraction of FeAl intermetallics in the coating with dwell time from 3 s to 8 min at 930°C was0, 6.19%, 17.03% and 20.65%, separately. The volume fraction of the α-Fe layer in the coating changed from zero to 31.52%with the prolonged dwell time. The porosity of the coating ranged from 0.51% to 4.98% with the extension of dwell time. The unsmooth degree of the surface of the coating rose gradually with the increasing of heating rates and the extension of dwell time.The 3D surface topography of the coating was determined by the comprehensive effect of atoms diffusion, new formed phases,surface tension and the degree of oxidation of the coating surface. Experiments indicated that rapid heating was not suitable for the coating when the temperature exceeded 500°C. Experiments also demonstrated that enough dwell time was essential to obtain the superior properties of the coating.
