Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerica...Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerically. In this research, the cracks coalescence paths in Brazilian disc and rectangular specimens made from rock-like material containing multi-holes are investigated. These concrete specimens are specially prepared from an appropriate mixture of Portland Pozzolana Cement （PPC）, fine sands, and water. The pre-holed Brazilian discs and rectangular specimens are experimentally tested under compression. The breakage load in the ring type disc specimens containing an axial hole with varying diameters is measured and the distribution of the induced lateral stress is obtained. The mechanism of cracks propagation in the wall of the ring type specimens is also stud- ied. In the case of multi-hole Brazilian disc and rectangular specimens, the cracks propagation and cracks coalescence are also investigated. These experiments are numerically modeled by a modified higher order displacement discontinuity method. It has been shown that the corresponding experimental and numerical results are in good agreement with each other. The results presented in this research vali date the accuracy and applicability of these crack analyses procedures.展开更多
The deformation and damage evolution of sandstone after heat treatment greatly influence the efficient and safe development of deep geothermal energy extraction.To investigate this issue,laboratory confined compressio...The deformation and damage evolution of sandstone after heat treatment greatly influence the efficient and safe development of deep geothermal energy extraction.To investigate this issue,laboratory confined compression tests and numerical simulations were conducted on pre-holed sandstone specimens after heat treatment.The laboratory test results show that the failure modes are closely related to the heat treatment temperature,with increasing treatment temperature,the failure modes change from mixed and shear modes to a splitting mode.The cracks always initiate from the sidewalls of the hole and then propagate.The failure process inside the hole proceeds as follows:calm period,particle ejection period,rock fragment exfoliation period and rock failure period.The specimens have different final failure features for the entire rock after heat treatment,but have the same failure features inside the hole.These phenomena can be explained by numerical simulations.The numerical simulations reveal that the failure modes in the numerical results agree very well with those observed in the experimental results.The damage zone always occurs at sidewalls of the hole and then propagates to the entire rock affected by shear or tensile damage.From 20℃to 200℃,thermal effect may promote shear damage and restrain tensile damage,while from 200℃to 800℃,thermal effect promotes tensile damage and restrains shear damage.Notably,the damage zone near the sidewalls of the hole has the same distribution range and pattern.Finally,the differences in the mechanisms due to increasing heat temperature are evaluated using scanning electron microscope(SEM)observations.展开更多
The forming mechanism of hole flanging on a thick-wall heavy cylinder forging is simulated by DEFORM3D. The cylinder is 4 390 mm in diameter and 390 mm in thickness. The results show that the compound deformation with...The forming mechanism of hole flanging on a thick-wall heavy cylinder forging is simulated by DEFORM3D. The cylinder is 4 390 mm in diameter and 390 mm in thickness. The results show that the compound deformation with bending and expanding happens in the process of hole flanging. The diameter of pre-hole of the workpiece is one of the key parameters in the process of hole flanging. The optimal diameter is obtained for reverse-conical hole of average diameter 40 mm by simulation of hole flanging process on 5 pre-holes with different diameters and 3 pre-holes with different shapes. The results can provide the scientific base for engineering application of the process.展开更多
基金sponsored by Iran’s National Elites Foundation (INEF)
文摘Crack propagation processes in specially prepared concrete discs and rectangular specimens containing a single cylindrical hole or multiple holes of varying diameters have been studied both experimentally and numerically. In this research, the cracks coalescence paths in Brazilian disc and rectangular specimens made from rock-like material containing multi-holes are investigated. These concrete specimens are specially prepared from an appropriate mixture of Portland Pozzolana Cement （PPC）, fine sands, and water. The pre-holed Brazilian discs and rectangular specimens are experimentally tested under compression. The breakage load in the ring type disc specimens containing an axial hole with varying diameters is measured and the distribution of the induced lateral stress is obtained. The mechanism of cracks propagation in the wall of the ring type specimens is also stud- ied. In the case of multi-hole Brazilian disc and rectangular specimens, the cracks propagation and cracks coalescence are also investigated. These experiments are numerically modeled by a modified higher order displacement discontinuity method. It has been shown that the corresponding experimental and numerical results are in good agreement with each other. The results presented in this research vali date the accuracy and applicability of these crack analyses procedures.
基金the National Basic Research Program of China(973 Program)Grant No.2014CB046905the National Natural Science Foundation of China(No.51174197).
文摘The deformation and damage evolution of sandstone after heat treatment greatly influence the efficient and safe development of deep geothermal energy extraction.To investigate this issue,laboratory confined compression tests and numerical simulations were conducted on pre-holed sandstone specimens after heat treatment.The laboratory test results show that the failure modes are closely related to the heat treatment temperature,with increasing treatment temperature,the failure modes change from mixed and shear modes to a splitting mode.The cracks always initiate from the sidewalls of the hole and then propagate.The failure process inside the hole proceeds as follows:calm period,particle ejection period,rock fragment exfoliation period and rock failure period.The specimens have different final failure features for the entire rock after heat treatment,but have the same failure features inside the hole.These phenomena can be explained by numerical simulations.The numerical simulations reveal that the failure modes in the numerical results agree very well with those observed in the experimental results.The damage zone always occurs at sidewalls of the hole and then propagates to the entire rock affected by shear or tensile damage.From 20℃to 200℃,thermal effect may promote shear damage and restrain tensile damage,while from 200℃to 800℃,thermal effect promotes tensile damage and restrains shear damage.Notably,the damage zone near the sidewalls of the hole has the same distribution range and pattern.Finally,the differences in the mechanisms due to increasing heat temperature are evaluated using scanning electron microscope(SEM)observations.
文摘The forming mechanism of hole flanging on a thick-wall heavy cylinder forging is simulated by DEFORM3D. The cylinder is 4 390 mm in diameter and 390 mm in thickness. The results show that the compound deformation with bending and expanding happens in the process of hole flanging. The diameter of pre-hole of the workpiece is one of the key parameters in the process of hole flanging. The optimal diameter is obtained for reverse-conical hole of average diameter 40 mm by simulation of hole flanging process on 5 pre-holes with different diameters and 3 pre-holes with different shapes. The results can provide the scientific base for engineering application of the process.
