This paper concentrates on simulating fracture in thin walled single-lap joints connected by resistance spot-welding(RSW)process which were subjected to tensile loading.For this purpose,three sets of lap-joints with d...This paper concentrates on simulating fracture in thin walled single-lap joints connected by resistance spot-welding(RSW)process which were subjected to tensile loading.For this purpose,three sets of lap-joints with different spot configurations were tested to achieve the joints’tensile behavior.To simulate the joints tensile behavior,firstly a 2D axisymmetric finite element(FE)model was used to calculate residual stresses induced during the welding process.Then the results were transferred to 3D models as pre-stress.In this step,cohesive zone model(CZM)technique was used to simulate fracture in the models under tensile load.Cohesive zone parameters were extracted using coach-peel and shear lap specimens.The results were employed to simulate deformation and failure in single lap spot weld samples.It has been shown that considering the residual stresses in simulating deformation and fracture load enables quite accurate predictions.展开更多
The three-point bending experiments were applied to investigating effects of loading rates on fracture toughness of Huanglong limestone. The fracture toughness of Huanglong limestone was measured over a wide range of ...The three-point bending experiments were applied to investigating effects of loading rates on fracture toughness of Huanglong limestone. The fracture toughness of Huanglong limestone was measured over a wide range of loading rates from 9 × 10-4 to 1.537 MPa.m1/2/s. According to the approximate relationship between static and dynamic fracture toughness of Huanglong limestone, relationship between the growth velocity of crack and dynamic fracture toughness was obtained. The main conclusions are summarized as follows. （1） When the loading rate is higher than 0.027 MPa-ml/2/s, the fracture toughness of Huanglong limestone increases markedly with increasing loading rate. However, when loading rate is lower than 0.027 MPa-ml/2/s, fracture toughness slightly increases with an increase in loading rate. （2） It is found from experimental results that fracture toughness is linearly proportional to the logarithmic expression of loading rate. （3） For Huanglong limestone, when the growth velocity of crack is lower than 100 m/s, the energy release rate slightly decreases with increasing the growth velocity of crack. However, when the growth velocity of crack is higher than 1 000 m/s, the energy release rate dramatically decreases with an increase in the crack growth velocity.展开更多
DNA double-strand break （DSB） is the most deleterious form of DNA damage and poses great threat to genome stability. Eu- karyotes have evolved complex mechanisms to repair DSBs through coordinated actions of protein...DNA double-strand break （DSB） is the most deleterious form of DNA damage and poses great threat to genome stability. Eu- karyotes have evolved complex mechanisms to repair DSBs through coordinated actions of protein sensors, transducers, and effectors. DSB-induced small RNAs （diRNAs） or Dicer/Drosha-dependent RNAs （DDRNAs） have been recently discovered in plants and vertebrates, adding an unsuspected RNA component into the DSB repair pathway. DiRNAs/DDRNAs control DNA damage response （DDR） activation by affecting DDR loci formation and cell cycle checkpoint enforcement and are required for efficient DSB repair. Here, we summarize the findings of diRNAs/DDRNAs and discuss the possible mechanisms through which they act to facilitate DSB repair.展开更多
文摘This paper concentrates on simulating fracture in thin walled single-lap joints connected by resistance spot-welding(RSW)process which were subjected to tensile loading.For this purpose,three sets of lap-joints with different spot configurations were tested to achieve the joints’tensile behavior.To simulate the joints tensile behavior,firstly a 2D axisymmetric finite element(FE)model was used to calculate residual stresses induced during the welding process.Then the results were transferred to 3D models as pre-stress.In this step,cohesive zone model(CZM)technique was used to simulate fracture in the models under tensile load.Cohesive zone parameters were extracted using coach-peel and shear lap specimens.The results were employed to simulate deformation and failure in single lap spot weld samples.It has been shown that considering the residual stresses in simulating deformation and fracture load enables quite accurate predictions.
基金Projects(50490275, 50621403, 50778184) supported by the National Natural Science Foundation of ChinaProject(NCET-07-0911) supported by Program of New Century Talents of Ministry of EducationProject(CSTC, 2009BA4046) supported by the Natural Science Foundation of CQ CSTC
文摘The three-point bending experiments were applied to investigating effects of loading rates on fracture toughness of Huanglong limestone. The fracture toughness of Huanglong limestone was measured over a wide range of loading rates from 9 × 10-4 to 1.537 MPa.m1/2/s. According to the approximate relationship between static and dynamic fracture toughness of Huanglong limestone, relationship between the growth velocity of crack and dynamic fracture toughness was obtained. The main conclusions are summarized as follows. （1） When the loading rate is higher than 0.027 MPa-ml/2/s, the fracture toughness of Huanglong limestone increases markedly with increasing loading rate. However, when loading rate is lower than 0.027 MPa-ml/2/s, fracture toughness slightly increases with an increase in loading rate. （2） It is found from experimental results that fracture toughness is linearly proportional to the logarithmic expression of loading rate. （3） For Huanglong limestone, when the growth velocity of crack is lower than 100 m/s, the energy release rate slightly decreases with increasing the growth velocity of crack. However, when the growth velocity of crack is higher than 1 000 m/s, the energy release rate dramatically decreases with an increase in the crack growth velocity.
基金supported in part by China National Funds for Distinguished Young Scientists(31225015)National Key Scientific Research Program of China(2012CB910900)to Qi YiJun
文摘DNA double-strand break （DSB） is the most deleterious form of DNA damage and poses great threat to genome stability. Eu- karyotes have evolved complex mechanisms to repair DSBs through coordinated actions of protein sensors, transducers, and effectors. DSB-induced small RNAs （diRNAs） or Dicer/Drosha-dependent RNAs （DDRNAs） have been recently discovered in plants and vertebrates, adding an unsuspected RNA component into the DSB repair pathway. DiRNAs/DDRNAs control DNA damage response （DDR） activation by affecting DDR loci formation and cell cycle checkpoint enforcement and are required for efficient DSB repair. Here, we summarize the findings of diRNAs/DDRNAs and discuss the possible mechanisms through which they act to facilitate DSB repair.
