In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into...In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into shakedown after tens （or hundreds） of thousand cycles. After the ratcheting strain is saturated under the condition that stress amplitude is half of peak stress, it will bring about subsequent fatigue failure, and relationship between fatigue life and one of peak stress and saturated ratcheting （SR） strain meets power law. As the alloy is under stress jiggling with stress amplitude that is 1%-2.5% of peak stress, the ratcheting strain still become remarkable and goes into shakedown after several hundreds of thousand cycles but there exists little accessional strain caused by creep effect. It is notable that, when the peak stress is 85%-100% of yield stress, the long-cyclic stressing will lead SR strain to be from 1.4% to 2.5% even if the initial ratio of ratcheting strain is zero. Based on ratcheting threshold property of peak stress and monotonicity of relationship between the peak stress and SR strain, a saturated ratcheting model （SRM） is developed to predict SR strain and to estimate saturated creep strain also. In addition, the classes of ratcheting evolutions of metals are discussed.展开更多
The investigation based on experiments and crystal plasticity simulation is carried out to undertake research on mesodeformation inhomogeneity of metals under cyclic loading at grain level.Symmetrical tension-compress...The investigation based on experiments and crystal plasticity simulation is carried out to undertake research on mesodeformation inhomogeneity of metals under cyclic loading at grain level.Symmetrical tension-compression cycle tests are performed on pure copper specimens to observe the inhomogeneous distribution of slip deformation and its evolution with cycle number.Cyclic hardening process and stable hysteretic behavior of pure copper under cyclic loading are simulated by applying a crystal plasticity constitutive model including nonlinear kinematic hardening associated with the polycrystalline representative volume element(RVE)constructed by Voronoi tessellation.Inhomogeneous deformation processes of materials under six different strain amplitudes are simulated by 1600 cycles,respectively.We discuss the variation law of the inhomogeneous meso-deformation distribution of material with the increase in cycle number,and research the rationality of characterizing the inhomogeneous deformation distribution and variation with the statistical standard deviation of the micro-longitudinal strain or the statistical average of the first principal strain based on the statistical analysis of the inhomogeneous deformation of the polycrystalline RVE model during the cycling process.It is found that these two parameters are related to and approximately inversely proportional to the length of measuring gauge.展开更多
Using the methods of the Gutenberg magnitude energy empirical formula and the Benioff seismic strain energy release curve,we make a systematic study on seismic strain energy release of historical earthquakes in the so...Using the methods of the Gutenberg magnitude energy empirical formula and the Benioff seismic strain energy release curve,we make a systematic study on seismic strain energy release of historical earthquakes in the southeastern margin of the Qinghai-Tibetan Plateau since 1500.This paper provides a periodic table of the earthquake strain energy release in the fault zones and the fault block areas.The study shows that seismic strain energy release is strong in the east and south,and weak in the west and north.The overall seismic strain energy release of the Yushu-Xianshuihe-Xiaojiang fault system is consistent with the quasi-periodic pattern.The seismic cycle of some fault zones and fault block areas shows synchronization to a certain extent.The risk cannot be ignored in the current large release period of seismic strain energy in the southeastern margin of the Qinghai-Tibetan plateau.Local seismic risk analysis shows that seismic risk is very high on the Anninghe-Zemuhe and Xiaojiang fault zones.These dangerous zones need follow-up research.In future,it is necessary to combine different research methods to improve the reliability of seismic risk assessment.展开更多
Fluctuating stress on the implanted coronary stents within cardiac cycle is an important mechanism of fatigue fracture,which is associated with in-stent restenosis and stent thrombosis.We developed a novel computation...Fluctuating stress on the implanted coronary stents within cardiac cycle is an important mechanism of fatigue fracture,which is associated with in-stent restenosis and stent thrombosis.We developed a novel computational modelling to calculate the dynamic stress of stents based on the time sequence angiography immediately after treatment.Two groups of patient-specific cases(one same stent design treated in 4 different coronary arteries and one same artery actually/virtually implanted one stent with 3 different designs)were performed the dynamic stress analysis by this computational modelling and subsequently assessed the fatigue fracture risk by Goodman method.The motion of target arteries significantly impacts on distribution of the stress and the risk of stent fracture,particularly in the site of hinge motion.Both the location of stent stress concentration in the obtuse marginal artery and the“unsafe”region in the inverse fatigue safety factor contour co-registered with the position of complete transverse fracture 13 months later after implantation.Three stents with different designs had the same location of highest stress concentration at the hinge motion site of the actually/virtually treated artery.Higher strength stent materials are significantly lower the risk of stent fracture rather than stent designs.This new computational modelling might be a useful tool in assessment of fracture risk of the implanted stent and in optimizing new design of dedicated stent treated specific coronary arteries and mechanical properties in vivo of bioresorbable scaffold during degradation process.展开更多
The crystal orientation significantly affects the low-cycle fatigue (LCF) propertiesof single crystal (SC) superalloys. However, the orientation-dependent LCF life model withprecise mechanisms and strong applicability...The crystal orientation significantly affects the low-cycle fatigue (LCF) propertiesof single crystal (SC) superalloys. However, the orientation-dependent LCF life model withprecise mechanisms and strong applicability is still lacking. This investigation aims at establishing an energy-based LCF life evaluation method that could consider the orientation effect. First,the influencing factors of anisotropy were identified through the literature review. Secondly, themultiaxial formula of the Ramberg-Osgood (ReO) equation was established to describe theanisotropic cyclic deformation characteristics. Furthermore, the strain energy density of SC superalloys was determined based on this equation, and the effective strain energy density wasintroduced to account for the effect of orientation. Finally, the energy-based method was validated by its application to several SC superalloys. Results showed that the crystallographicorientation with a lower Young’s modulus usually exhibits better LCF resistance. This phenomenon could be attributed to the different values of strain energy density dissipated in one cycle.The multiaxial ReO relationship could capture the anisotropic cyclic deformation response ofDD6. Compared with the classical methods, the energy-based model is favored by its precisemechanism and strong applicability. And it also exhibited better prediction accuracy. Most datapoints of different crystallographic orientations lay within the 3 error band.展开更多
文摘In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into shakedown after tens （or hundreds） of thousand cycles. After the ratcheting strain is saturated under the condition that stress amplitude is half of peak stress, it will bring about subsequent fatigue failure, and relationship between fatigue life and one of peak stress and saturated ratcheting （SR） strain meets power law. As the alloy is under stress jiggling with stress amplitude that is 1%-2.5% of peak stress, the ratcheting strain still become remarkable and goes into shakedown after several hundreds of thousand cycles but there exists little accessional strain caused by creep effect. It is notable that, when the peak stress is 85%-100% of yield stress, the long-cyclic stressing will lead SR strain to be from 1.4% to 2.5% even if the initial ratio of ratcheting strain is zero. Based on ratcheting threshold property of peak stress and monotonicity of relationship between the peak stress and SR strain, a saturated ratcheting model （SRM） is developed to predict SR strain and to estimate saturated creep strain also. In addition, the classes of ratcheting evolutions of metals are discussed.
基金the National Natural Science Foundation of China(Nos.11632007 and 11472085)the Project of Promoting the Basic Ability of Scientific Research of Young and Middle-aged Teachers in Universities of Guangxi(No.2019KY1365),which are gratefully acknowledged.
文摘The investigation based on experiments and crystal plasticity simulation is carried out to undertake research on mesodeformation inhomogeneity of metals under cyclic loading at grain level.Symmetrical tension-compression cycle tests are performed on pure copper specimens to observe the inhomogeneous distribution of slip deformation and its evolution with cycle number.Cyclic hardening process and stable hysteretic behavior of pure copper under cyclic loading are simulated by applying a crystal plasticity constitutive model including nonlinear kinematic hardening associated with the polycrystalline representative volume element(RVE)constructed by Voronoi tessellation.Inhomogeneous deformation processes of materials under six different strain amplitudes are simulated by 1600 cycles,respectively.We discuss the variation law of the inhomogeneous meso-deformation distribution of material with the increase in cycle number,and research the rationality of characterizing the inhomogeneous deformation distribution and variation with the statistical standard deviation of the micro-longitudinal strain or the statistical average of the first principal strain based on the statistical analysis of the inhomogeneous deformation of the polycrystalline RVE model during the cycling process.It is found that these two parameters are related to and approximately inversely proportional to the length of measuring gauge.
基金funded jointly by the China Geological Survey (Project Grant No. 1212011120163, 12120114002101)the National Natural Science Foundation of China (Project Grant No: 41171009)the basal research fund of Institute of Geomechanics,Chinese Academy of Geological Sciences (DXLXJK201410)
文摘Using the methods of the Gutenberg magnitude energy empirical formula and the Benioff seismic strain energy release curve,we make a systematic study on seismic strain energy release of historical earthquakes in the southeastern margin of the Qinghai-Tibetan Plateau since 1500.This paper provides a periodic table of the earthquake strain energy release in the fault zones and the fault block areas.The study shows that seismic strain energy release is strong in the east and south,and weak in the west and north.The overall seismic strain energy release of the Yushu-Xianshuihe-Xiaojiang fault system is consistent with the quasi-periodic pattern.The seismic cycle of some fault zones and fault block areas shows synchronization to a certain extent.The risk cannot be ignored in the current large release period of seismic strain energy in the southeastern margin of the Qinghai-Tibetan plateau.Local seismic risk analysis shows that seismic risk is very high on the Anninghe-Zemuhe and Xiaojiang fault zones.These dangerous zones need follow-up research.In future,it is necessary to combine different research methods to improve the reliability of seismic risk assessment.
文摘Fluctuating stress on the implanted coronary stents within cardiac cycle is an important mechanism of fatigue fracture,which is associated with in-stent restenosis and stent thrombosis.We developed a novel computational modelling to calculate the dynamic stress of stents based on the time sequence angiography immediately after treatment.Two groups of patient-specific cases(one same stent design treated in 4 different coronary arteries and one same artery actually/virtually implanted one stent with 3 different designs)were performed the dynamic stress analysis by this computational modelling and subsequently assessed the fatigue fracture risk by Goodman method.The motion of target arteries significantly impacts on distribution of the stress and the risk of stent fracture,particularly in the site of hinge motion.Both the location of stent stress concentration in the obtuse marginal artery and the“unsafe”region in the inverse fatigue safety factor contour co-registered with the position of complete transverse fracture 13 months later after implantation.Three stents with different designs had the same location of highest stress concentration at the hinge motion site of the actually/virtually treated artery.Higher strength stent materials are significantly lower the risk of stent fracture rather than stent designs.This new computational modelling might be a useful tool in assessment of fracture risk of the implanted stent and in optimizing new design of dedicated stent treated specific coronary arteries and mechanical properties in vivo of bioresorbable scaffold during degradation process.
基金This work is supported by the National Natural Science Foundation of China(52105137)the National Science and Technology Major Project(2017-IV-0012-0049).
文摘The crystal orientation significantly affects the low-cycle fatigue (LCF) propertiesof single crystal (SC) superalloys. However, the orientation-dependent LCF life model withprecise mechanisms and strong applicability is still lacking. This investigation aims at establishing an energy-based LCF life evaluation method that could consider the orientation effect. First,the influencing factors of anisotropy were identified through the literature review. Secondly, themultiaxial formula of the Ramberg-Osgood (ReO) equation was established to describe theanisotropic cyclic deformation characteristics. Furthermore, the strain energy density of SC superalloys was determined based on this equation, and the effective strain energy density wasintroduced to account for the effect of orientation. Finally, the energy-based method was validated by its application to several SC superalloys. Results showed that the crystallographicorientation with a lower Young’s modulus usually exhibits better LCF resistance. This phenomenon could be attributed to the different values of strain energy density dissipated in one cycle.The multiaxial ReO relationship could capture the anisotropic cyclic deformation response ofDD6. Compared with the classical methods, the energy-based model is favored by its precisemechanism and strong applicability. And it also exhibited better prediction accuracy. Most datapoints of different crystallographic orientations lay within the 3 error band.
