he evolution and nucleation of microcracks in typical tectonics are investigated in the experiment of fracture of marble specimen. The change of state during nucleation of microcracks is observed. The controlling effe...he evolution and nucleation of microcracks in typical tectonics are investigated in the experiment of fracture of marble specimen. The change of state during nucleation of microcracks is observed. The controlling effect of tectonics on evolution of microcracks is analyzed by using thc damage mechanics theory. These characteristics can be analogized to kilometer meters as the first effect of earthquake precursors. These studies may be helpful to interpret-the foreshock or general foreshock in the moderate or short stage before strong earthquakes. The other physical precursors are second or third effect. The local density of microcracks increasing abruptly may be helpful to interpret the phenomenon that part precursor records appear catastrophic jump. The part out of nucleation where some microcracks heal and the density change reversibly may be helpful to interpret the phenomenon that some precursors records appear reverse change. The area difference of microcracks accumulation and evolution in different part of typital tectonics is studied. This difference may be helpful to interpret the characteristics (including the area) of earthquake preparation of diffcrent tectonics, and further to interpret the difference of the precursors beween plate edge and intraplate. These differences may be introduced by the scholars with different points of view as to discuss about the existence of precursors before earthquakes. However, when the precursor records are studied, one must notice the geology background in different areas.展开更多
Based on approximate theoretical analyses on a typical spherical cellcontaining a spherical rnicrovoid, the influences of matrix materials' microscopic scale on themacroscopic constitutive potential theory of poro...Based on approximate theoretical analyses on a typical spherical cellcontaining a spherical rnicrovoid, the influences of matrix materials' microscopic scale on themacroscopic constitutive potential theory of porous material and microvoid growth have beeninvestigated in detail. By assuming that the plastic: deformation behavior of matrix materialsfollows the strain gradient (SG) plastic theory involving the stretch and rotation gradients , theratio (λ = l/a) of the matrix materials' intrinsic characteristic length l to the micro-void radiusa is introduced into the plastic constitutive potential and the void growth law. The presentresults indicate that, when the radius a of microvoids is comparable with the intrinsiccharacteristic length l of the matrix materials, the influence of microscopic size effect on neitherthe constitutive potential nor the micro-void evolution predicted can be ignored. And when the voidradius a is much lager than the intrinsic characteristic length l of the matrix materials, thepresent model can retrogress automatically to the improved Gur-son model that takes into account thestrain hardening effect of matrix materials.展开更多
Based on the phenomena that the deformation gap was observed before the great Tangshang earthquake, this paper discusses the strain gap according to test and theory. The (strain) patterns were recorded photographicall...Based on the phenomena that the deformation gap was observed before the great Tangshang earthquake, this paper discusses the strain gap according to test and theory. The (strain) patterns were recorded photographically by real-time holographic interferometry and shadow optical method of caustics, as soon as the loading process started. In the meantime, the AE (acoustic emission) signals were recorded by a micro crack information storage-analysis sys-tem. According to damage theory and location of micro fracture, we have studied the stain gap and gained: a) It is necessary that strain gap appears under the condition of linear elasticity theory, and its situation is relatively stable, corresponding to stress concentration. b) Micro fractures, which appear initially at area of high stress, occur rarely at the strain gap, and their locations are finally in the zone between the stress concentration area and the strain gap, which indicate the clusters or groups. However, the major macro fracture (final rupture) started from the shadow areas, and then grew quickly towards the strain gaps, which resulted in failure of sample.展开更多
In this paper,stress states under corresponding condition of an aero-engine fan blade using finite element stress-strain analysis for three work cycles in the 900 h load spectrum are obtained.Through the nominal stres...In this paper,stress states under corresponding condition of an aero-engine fan blade using finite element stress-strain analysis for three work cycles in the 900 h load spectrum are obtained.Through the nominal stress method,we calculated the fatigue notch factor and combined the material characteristics of TC6 to correct the material curve to the fan blades curve. Finally,the fatigue life of a fan blade was estimated using the linear cumulative damage rule and nonlinear cumulative damage theory.展开更多
For this study, the Binzhou perpetual pavement test sections constructed in Shandong Province, China, were simulated for long-term fatigue performance using the layered viscoelastic pavement analysis for critical dist...For this study, the Binzhou perpetual pavement test sections constructed in Shandong Province, China, were simulated for long-term fatigue performance using the layered viscoelastic pavement analysis for critical distresses (LVECD) finite element software package. In this framework, asphalt concrete was treated in the context of linear visco- elastic continuum damage theory. A recently developed unified fatigue failure criterion that defined the boundaries of the applicable region of the theory was also incorporated. The mechanistic modeling of the fatigue mechanisms was able to accommodate the complex temperature variations and loading conditions of the field pavements in a rigorous manner. All of the material models were conveniently characterized by dynamic modulus tests and direct tension cyclic fatigue tests in the laboratory using cylindrical specimens. By comparing the obtained damage characteristic curves and failure criteria, it is found that mixtures with small aggregate particle sizes, a dense gradation, and modified asphalt binder tended to exhibit the best fatigue resistance at the material level. The 15 year finite element structural simulation results for all the test sections indicate that fa- tigue performance has a strong dependence on the thickness of the asphalt pavements. Based on the predicted location and severity of the fatigue damage, it is recommended that Sections 1 and 3 of the Binzhou test sections be emoloved for perpetual pavement design.展开更多
By taking the frozen soil as a particle-reinforced composite material which consists of clay soil (i.e., the matrix) and ice particles, a micromechanical constitutive model is established to describe the dynamic com...By taking the frozen soil as a particle-reinforced composite material which consists of clay soil (i.e., the matrix) and ice particles, a micromechanical constitutive model is established to describe the dynamic compressive deformation of frozen soil. The proposed model is constructed by referring to the debonding damage theory of composite materials, and addresses the effects of strain rate and temperature on the dynamic compressive deformation of frozen soil. The proposed model is verified through comparison of the predictions with the corresponding dynamic experimental data of frozen soil obtained from the split Hopkinson pressure bar (SHPB) tests at different high strain rates and temperatures. It is shown that the predictions agree well with the experimental results.展开更多
Purpose It is a challenge for the primary hospitals to manage multiple trauma patients.In this article,we explored the advantage of establishing a surgical intensive care unit(SICU)predominant by cardiothoracic surgeo...Purpose It is a challenge for the primary hospitals to manage multiple trauma patients.In this article,we explored the advantage of establishing a surgical intensive care unit(SICU)predominant by cardiothoracic surgeons in the early management of multiple trauma.Methods This was a retrospective study and patients with multiple trauma in our hospital were collected and divided into two groups,based on time period and treat modes:group A(retrospective observation group)where patients were treated with the traditional treatment mode from January 2017 to December 2017 and group B(study group)where patients were treated in the SICU predominant by cardiothoracic surgeons from January 2018 to December 2018.Clinical data including demographics,injury severity score(ISS),causes of injury,time intervals from reception to entering SICU or operating room and mortality three days after injuries were collected.Data were analyzed by SPSS 20.0 software.Categorical variables were presented as number and/or frequency and continuous variables as mean±SD.Results Altogether 406 patients were included in this study,including 217 patients in group A and 189 patients in group B.General data between the two groups revealed no significant difference:mean age(years)(35.51±12.97 vs.33.62±13.61,p=0.631),gender distribution(mean/female,130/87 vs.116/73,p=0.589)and ISS(15.92±7.95 vs.16.16±6.89,p=0.698).Fall from height were the dominant mechanism of injury,with 135 cases in group A(71.4%)and 121 cases in group B(55.8%),followed by traffic accidents.Injury mechanism showed no significant differences between two groups(p=1.256).Introduction of the SICU significantly improved the care of trauma patients,regarding speed and mortality.Time intervals between reception and entering SICU or operating room was(108.23±6.72)min and(45.67±7.96)min in group A and B,respectively(p=0.001).Mortality three days after injuries was 13.89%and 5.53%in group A and B,respectively(p=0.005).Conclusion Establishing a SICU predominant by cardiothoracic surgeons can reduce the early mortality rates in multiple trauma patients.展开更多
文摘he evolution and nucleation of microcracks in typical tectonics are investigated in the experiment of fracture of marble specimen. The change of state during nucleation of microcracks is observed. The controlling effect of tectonics on evolution of microcracks is analyzed by using thc damage mechanics theory. These characteristics can be analogized to kilometer meters as the first effect of earthquake precursors. These studies may be helpful to interpret-the foreshock or general foreshock in the moderate or short stage before strong earthquakes. The other physical precursors are second or third effect. The local density of microcracks increasing abruptly may be helpful to interpret the phenomenon that part precursor records appear catastrophic jump. The part out of nucleation where some microcracks heal and the density change reversibly may be helpful to interpret the phenomenon that some precursors records appear reverse change. The area difference of microcracks accumulation and evolution in different part of typital tectonics is studied. This difference may be helpful to interpret the characteristics (including the area) of earthquake preparation of diffcrent tectonics, and further to interpret the difference of the precursors beween plate edge and intraplate. These differences may be introduced by the scholars with different points of view as to discuss about the existence of precursors before earthquakes. However, when the precursor records are studied, one must notice the geology background in different areas.
基金the National Natural Science Foundation of China (No.A10102006)
文摘Based on approximate theoretical analyses on a typical spherical cellcontaining a spherical rnicrovoid, the influences of matrix materials' microscopic scale on themacroscopic constitutive potential theory of porous material and microvoid growth have beeninvestigated in detail. By assuming that the plastic: deformation behavior of matrix materialsfollows the strain gradient (SG) plastic theory involving the stretch and rotation gradients , theratio (λ = l/a) of the matrix materials' intrinsic characteristic length l to the micro-void radiusa is introduced into the plastic constitutive potential and the void growth law. The presentresults indicate that, when the radius a of microvoids is comparable with the intrinsiccharacteristic length l of the matrix materials, the influence of microscopic size effect on neitherthe constitutive potential nor the micro-void evolution predicted can be ignored. And when the voidradius a is much lager than the intrinsic characteristic length l of the matrix materials, thepresent model can retrogress automatically to the improved Gur-son model that takes into account thestrain hardening effect of matrix materials.
基金The Dual Project of China Seismological Bureau (9691309020301) the Specialized Funds for National Key Basic Study (G1998040704) the project for the MOST under contract (2001BA601B02) and Youth Funds for applied basic study of the Science and Technolo
文摘Based on the phenomena that the deformation gap was observed before the great Tangshang earthquake, this paper discusses the strain gap according to test and theory. The (strain) patterns were recorded photographically by real-time holographic interferometry and shadow optical method of caustics, as soon as the loading process started. In the meantime, the AE (acoustic emission) signals were recorded by a micro crack information storage-analysis sys-tem. According to damage theory and location of micro fracture, we have studied the stain gap and gained: a) It is necessary that strain gap appears under the condition of linear elasticity theory, and its situation is relatively stable, corresponding to stress concentration. b) Micro fractures, which appear initially at area of high stress, occur rarely at the strain gap, and their locations are finally in the zone between the stress concentration area and the strain gap, which indicate the clusters or groups. However, the major macro fracture (final rupture) started from the shadow areas, and then grew quickly towards the strain gaps, which resulted in failure of sample.
文摘In this paper,stress states under corresponding condition of an aero-engine fan blade using finite element stress-strain analysis for three work cycles in the 900 h load spectrum are obtained.Through the nominal stress method,we calculated the fatigue notch factor and combined the material characteristics of TC6 to correct the material curve to the fan blades curve. Finally,the fatigue life of a fan blade was estimated using the linear cumulative damage rule and nonlinear cumulative damage theory.
基金financial support from the Federal Highway Administration DTFH61-08-H00005 Project,hot mix asphalt performance-related specification based on viscoelasticity continuum damage(VEPCD)models
文摘For this study, the Binzhou perpetual pavement test sections constructed in Shandong Province, China, were simulated for long-term fatigue performance using the layered viscoelastic pavement analysis for critical distresses (LVECD) finite element software package. In this framework, asphalt concrete was treated in the context of linear visco- elastic continuum damage theory. A recently developed unified fatigue failure criterion that defined the boundaries of the applicable region of the theory was also incorporated. The mechanistic modeling of the fatigue mechanisms was able to accommodate the complex temperature variations and loading conditions of the field pavements in a rigorous manner. All of the material models were conveniently characterized by dynamic modulus tests and direct tension cyclic fatigue tests in the laboratory using cylindrical specimens. By comparing the obtained damage characteristic curves and failure criteria, it is found that mixtures with small aggregate particle sizes, a dense gradation, and modified asphalt binder tended to exhibit the best fatigue resistance at the material level. The 15 year finite element structural simulation results for all the test sections indicate that fa- tigue performance has a strong dependence on the thickness of the asphalt pavements. Based on the predicted location and severity of the fatigue damage, it is recommended that Sections 1 and 3 of the Binzhou test sections be emoloved for perpetual pavement design.
基金Project supported by the National Natural Science Foundation of China(No.11172251)the Open Fund of State Key Laboratory of Frozen Soil Engineering(No.SKLFSE201001)+1 种基金the Opening Project of State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology,No.KFJJ13-10M)the Project of Sichuan Provincial Youth Science and Technology Innovation Team,China(No.2013TD0004)
文摘By taking the frozen soil as a particle-reinforced composite material which consists of clay soil (i.e., the matrix) and ice particles, a micromechanical constitutive model is established to describe the dynamic compressive deformation of frozen soil. The proposed model is constructed by referring to the debonding damage theory of composite materials, and addresses the effects of strain rate and temperature on the dynamic compressive deformation of frozen soil. The proposed model is verified through comparison of the predictions with the corresponding dynamic experimental data of frozen soil obtained from the split Hopkinson pressure bar (SHPB) tests at different high strain rates and temperatures. It is shown that the predictions agree well with the experimental results.
基金The present study was supported by the Foundation of the Key scientific and technological projects in Henan Province,China(202102310133).
文摘Purpose It is a challenge for the primary hospitals to manage multiple trauma patients.In this article,we explored the advantage of establishing a surgical intensive care unit(SICU)predominant by cardiothoracic surgeons in the early management of multiple trauma.Methods This was a retrospective study and patients with multiple trauma in our hospital were collected and divided into two groups,based on time period and treat modes:group A(retrospective observation group)where patients were treated with the traditional treatment mode from January 2017 to December 2017 and group B(study group)where patients were treated in the SICU predominant by cardiothoracic surgeons from January 2018 to December 2018.Clinical data including demographics,injury severity score(ISS),causes of injury,time intervals from reception to entering SICU or operating room and mortality three days after injuries were collected.Data were analyzed by SPSS 20.0 software.Categorical variables were presented as number and/or frequency and continuous variables as mean±SD.Results Altogether 406 patients were included in this study,including 217 patients in group A and 189 patients in group B.General data between the two groups revealed no significant difference:mean age(years)(35.51±12.97 vs.33.62±13.61,p=0.631),gender distribution(mean/female,130/87 vs.116/73,p=0.589)and ISS(15.92±7.95 vs.16.16±6.89,p=0.698).Fall from height were the dominant mechanism of injury,with 135 cases in group A(71.4%)and 121 cases in group B(55.8%),followed by traffic accidents.Injury mechanism showed no significant differences between two groups(p=1.256).Introduction of the SICU significantly improved the care of trauma patients,regarding speed and mortality.Time intervals between reception and entering SICU or operating room was(108.23±6.72)min and(45.67±7.96)min in group A and B,respectively(p=0.001).Mortality three days after injuries was 13.89%and 5.53%in group A and B,respectively(p=0.005).Conclusion Establishing a SICU predominant by cardiothoracic surgeons can reduce the early mortality rates in multiple trauma patients.