The changes in mechanical properties and fracture toughness by dynamic loading were investigated with experiments. The parameter R, which can reflect the effect of the loading rate and the temperature rising during th...The changes in mechanical properties and fracture toughness by dynamic loading were investigated with experiments. The parameter R, which can reflect the effect of the loading rate and the temperature rising during the high loading rate, could be employed to describe the constituent relation for the typical structure steel and its weld metal. The dynamic loading effect on the stress/strain fields and the temperature variation in the vicinity of the crack tip was analyzed by the finite element method, the dynamic fracture behavior was evaluated based on the local approach. It has been found that the Weibull stress is an effective fracture parameter, independent of the temperature and the loading rate.展开更多
The former studies indicate that loading rates significantly affect dynamic behavior of brittle materials,for instance,the dynamic compressive and tensile strength increase with loading rates.However,there still are m...The former studies indicate that loading rates significantly affect dynamic behavior of brittle materials,for instance,the dynamic compressive and tensile strength increase with loading rates.However,there still are many unknown or partially unknown aspects.For example,whether loading rates have effect on crack dynamic propagating behavior(propagation toughness,velocity and arrest,etc).To further explore the effect of loading rates on crack dynamic responses,a large-size single-cleavage trapezoidal open(SCTO)specimen was proposed,and impacting tests using the SCTO specimen under drop plate impact were conducted.Crack propagation gauges(CPGs)were employed in measuring impact loads,crack propagation time and velocities.In order to verify the testing result,the corresponding numerical model was established using explicit dynamic software AUTODYN,and the simulation result is basically consistent with the experimental results.The ABAQUS software was used to calculate the dynamic SIFs.The universal function was calculated by fractal method.The experimental-numerical method was employed in determining initiation toughness and propagation toughness.The results indicate that crack propagating velocities,dynamic fracture toughness and energy release rates increase with loading rates;crack delayed initiation time decreases with loading rates.展开更多
To investigate the effect of dynamic loading on fracture behavior of weldedjoints of structural steel Q235B and 16Mn in common use and compare the earthquake resistances ofthe two kinds of materials, dynamic tension a...To investigate the effect of dynamic loading on fracture behavior of weldedjoints of structural steel Q235B and 16Mn in common use and compare the earthquake resistances ofthe two kinds of materials, dynamic tension and fracture toughness tests are carried out at roomtemperature. On the basis of the tests, the stress-strain fields near the crack tip of the compactspecimens are analyzed by three-dimensional finite element model. The test results and finiteelement analysis results show that, the fracture toughness of welds and base metal of 16Mn steelincreases with the increment of loading rate. Compared with 16Mn steel, Q235B steel is moresensitive to dynamic loading. The fracture toughness of welds of Q235B is comparatively low understatic loading and dynamic loading at room temperature. Compared with the static loading, thefracture toughness of Q235B parent metal under dynamic loading decreases by about four times.Therefore, it can be concluded that compared with 16Mn steel, the earthquake resistances of weld andparent metal of Q235B are rather poor.展开更多
A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method...A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.展开更多
基金supported by the National Natural Science Foundation of China,No.50275107 Fok Ying Tung Education Foundation No.81405.
文摘The changes in mechanical properties and fracture toughness by dynamic loading were investigated with experiments. The parameter R, which can reflect the effect of the loading rate and the temperature rising during the high loading rate, could be employed to describe the constituent relation for the typical structure steel and its weld metal. The dynamic loading effect on the stress/strain fields and the temperature variation in the vicinity of the crack tip was analyzed by the finite element method, the dynamic fracture behavior was evaluated based on the local approach. It has been found that the Weibull stress is an effective fracture parameter, independent of the temperature and the loading rate.
基金Projects(11672194,U19A2098)supported by the National Natural Science Foundation of ChinaProject(2018SCU12047)supported by Fundamental Research Funds for the Central Universities,ChinaProject(2018JZ0036)supported by the Project of Science and Technology of Sichuan Province,China。
文摘The former studies indicate that loading rates significantly affect dynamic behavior of brittle materials,for instance,the dynamic compressive and tensile strength increase with loading rates.However,there still are many unknown or partially unknown aspects.For example,whether loading rates have effect on crack dynamic propagating behavior(propagation toughness,velocity and arrest,etc).To further explore the effect of loading rates on crack dynamic responses,a large-size single-cleavage trapezoidal open(SCTO)specimen was proposed,and impacting tests using the SCTO specimen under drop plate impact were conducted.Crack propagation gauges(CPGs)were employed in measuring impact loads,crack propagation time and velocities.In order to verify the testing result,the corresponding numerical model was established using explicit dynamic software AUTODYN,and the simulation result is basically consistent with the experimental results.The ABAQUS software was used to calculate the dynamic SIFs.The universal function was calculated by fractal method.The experimental-numerical method was employed in determining initiation toughness and propagation toughness.The results indicate that crack propagating velocities,dynamic fracture toughness and energy release rates increase with loading rates;crack delayed initiation time decreases with loading rates.
基金This project is supported by National Natural Science Foundation of China (No.59975066).
文摘To investigate the effect of dynamic loading on fracture behavior of weldedjoints of structural steel Q235B and 16Mn in common use and compare the earthquake resistances ofthe two kinds of materials, dynamic tension and fracture toughness tests are carried out at roomtemperature. On the basis of the tests, the stress-strain fields near the crack tip of the compactspecimens are analyzed by three-dimensional finite element model. The test results and finiteelement analysis results show that, the fracture toughness of welds and base metal of 16Mn steelincreases with the increment of loading rate. Compared with 16Mn steel, Q235B steel is moresensitive to dynamic loading. The fracture toughness of welds of Q235B is comparatively low understatic loading and dynamic loading at room temperature. Compared with the static loading, thefracture toughness of Q235B parent metal under dynamic loading decreases by about four times.Therefore, it can be concluded that compared with 16Mn steel, the earthquake resistances of weld andparent metal of Q235B are rather poor.
基金supported by the 111 Project (B07050)the National Natural Science Foundation of China (10932008)
文摘A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.
