提出了疲劳寿命预腐蚀影响系数曲线(C- T 曲线)通用性分析的 C值直接对比法和C -T 曲线参数统计对比法,并进行相关试验研究,得到了 C -T 曲线和载荷谱、应力水平以及裂纹尺寸基本无关的结论。C- T曲线是进行腐蚀条件下飞机结构疲劳寿命...提出了疲劳寿命预腐蚀影响系数曲线(C- T 曲线)通用性分析的 C值直接对比法和C -T 曲线参数统计对比法,并进行相关试验研究,得到了 C -T 曲线和载荷谱、应力水平以及裂纹尺寸基本无关的结论。C- T曲线是进行腐蚀条件下飞机结构疲劳寿命评定和分析的基础,为验证分析 C- T 曲线和载荷谱、应力水平以及裂纹尺寸的相关性,从C的定义和分布规律出发,提出了 C值直接对比法和C -T 曲线参数统计对比法,近似谱、不同恒幅应力水平以及不同指定裂纹尺寸下的预腐蚀疲劳寿命数据均表明了 C- T 曲线基本具有通用性;并进行了某型飞机结构主梁模拟试件在随机谱及恒幅谱下的预腐蚀疲劳试验,试验结果同样验证了上述结论,从而说明了C- T 曲线的通用性。展开更多
Tensile failure(spalling or slabbing)often occurs on the sidewall of deep tunnel,which is closely related to the coupled stress state of deep rock mass under high pre-static load and dynamic disturbance.To reveal the ...Tensile failure(spalling or slabbing)often occurs on the sidewall of deep tunnel,which is closely related to the coupled stress state of deep rock mass under high pre-static load and dynamic disturbance.To reveal the mechanism of rock tensile failure caused by this coupled stress mode,the Brazilian disc tests were carried on red sandstone under high pre-static load induced by dynamic disturbance.Based on the pure static tensile fracture load of red sandstone specimen,two static load levels(80%and 90%of the pure static tensile fracture load)were selected as the initial high pre-static loading state,and then the dynamic disturbance load was applied until the rock specimen was destroyed.The dynamic disturbance loading mode adopted a sinusoidal wave(sine-wave)load,and the loading wave amplitude was 20%and 10%of the pure static tensile fracture load,respectively.The dynamic disturbance frequencies were set to 1,10,20,30,40,and 50 Hz.The results show that the tensile failure strength and peak displacement of red sandstone specimens under coupled load actions are lower than those under pure static tensile load,and both parameters decrease significantly with the increase of dynamic disturbance frequency.With the increase of dynamic disturbance frequency,the decrease range of tensile strength of red sandstone increased from 3.3%to 9.4%when the pre-static load level is 80%.While when the pre-static load level is 90%,the decrease range will increase from 7.4%to 11.6%.This weakening effect of tensile strength shows that the deep surrounding rock is more likely to fail under the coupled load actions of pre-static load and dynamic disturbance.In this tensile failure mechanism of the deep surrounding rock,the stress environment of deep sidewall rock determines that the failure mode of rock is a tensile failure,the pre-static load level dominates the tensile failure strength of surrounding rock,and dynamic disturbance promotes the strength-weakening effect and affects the weakening range.展开更多
1 Introduction Early detection and diagnosis of stable coronary artery disease （SCAD） is essential for proactive secondary prevention of myocardial infarction （MI）, control of disease progress, and reduction of mo...1 Introduction Early detection and diagnosis of stable coronary artery disease （SCAD） is essential for proactive secondary prevention of myocardial infarction （MI）, control of disease progress, and reduction of mortality. Clinical decision-making in modem medicine is increasingly dependent on cardiovascular imaging techniques. 2012 ACCF/AHA/ACP/AATS/ PCNA/SCAI/STS guideline for the diagnosis and management of patients with stable ischemic heart disease has been issued by American Heart Association （AHA）. European Society of Cardiology （ESC） has issued 2013 ESC guidelines on the management of stable coronary artery disease.展开更多
Pre-stressed bolt anchorage is the key technology for jointed rock masses in rock tunnelling,slope treatment and mining engineering.To investigate the mechanical properties and reinforcement effect of jointed rock mas...Pre-stressed bolt anchorage is the key technology for jointed rock masses in rock tunnelling,slope treatment and mining engineering.To investigate the mechanical properties and reinforcement effect of jointed rock masses with pre-stressed bolts,in this study,uniaxial compression tests were conducted on specimens with different anchoring types and flaw inclination angles.ABAQUS software was used to verify and supplement the laboratory tests.The laws of the uniaxial compressive strength(UCS)obtained from the numerical simulations and laboratory tests were consistent.The results showed that under the same flaw angle,both the UCS and elastic modulus of the bolted specimens were improved compared with those of the specimens without bolts and the improvements increased with an increase in the bolt pre-stress.Under the same anchoring type,the UCS and elastic modulus of the jointed specimens increased with an increase in the flaw angle.The pre-stressed bolt could not only restrain the slip of the specimens along the flaw surface but also change the propagation mode of the secondary cracks and limit the initiation of cracks.In addition,the plot contours of the maximum principal strain and the Tresca stress of the numerical models were influenced by the anchoring type,flaw angle,anchoring angle and bolt position.展开更多
文摘提出了疲劳寿命预腐蚀影响系数曲线(C- T 曲线)通用性分析的 C值直接对比法和C -T 曲线参数统计对比法,并进行相关试验研究,得到了 C -T 曲线和载荷谱、应力水平以及裂纹尺寸基本无关的结论。C- T曲线是进行腐蚀条件下飞机结构疲劳寿命评定和分析的基础,为验证分析 C- T 曲线和载荷谱、应力水平以及裂纹尺寸的相关性,从C的定义和分布规律出发,提出了 C值直接对比法和C -T 曲线参数统计对比法,近似谱、不同恒幅应力水平以及不同指定裂纹尺寸下的预腐蚀疲劳寿命数据均表明了 C- T 曲线基本具有通用性;并进行了某型飞机结构主梁模拟试件在随机谱及恒幅谱下的预腐蚀疲劳试验,试验结果同样验证了上述结论,从而说明了C- T 曲线的通用性。
基金Projects(42077244,41877272,41472269)supported by the National Natural Science Foundation of ChinaProject(2242020R10023)supported by the Fundamental Research Funds for the Central Universities of Southeast University,China。
文摘Tensile failure(spalling or slabbing)often occurs on the sidewall of deep tunnel,which is closely related to the coupled stress state of deep rock mass under high pre-static load and dynamic disturbance.To reveal the mechanism of rock tensile failure caused by this coupled stress mode,the Brazilian disc tests were carried on red sandstone under high pre-static load induced by dynamic disturbance.Based on the pure static tensile fracture load of red sandstone specimen,two static load levels(80%and 90%of the pure static tensile fracture load)were selected as the initial high pre-static loading state,and then the dynamic disturbance load was applied until the rock specimen was destroyed.The dynamic disturbance loading mode adopted a sinusoidal wave(sine-wave)load,and the loading wave amplitude was 20%and 10%of the pure static tensile fracture load,respectively.The dynamic disturbance frequencies were set to 1,10,20,30,40,and 50 Hz.The results show that the tensile failure strength and peak displacement of red sandstone specimens under coupled load actions are lower than those under pure static tensile load,and both parameters decrease significantly with the increase of dynamic disturbance frequency.With the increase of dynamic disturbance frequency,the decrease range of tensile strength of red sandstone increased from 3.3%to 9.4%when the pre-static load level is 80%.While when the pre-static load level is 90%,the decrease range will increase from 7.4%to 11.6%.This weakening effect of tensile strength shows that the deep surrounding rock is more likely to fail under the coupled load actions of pre-static load and dynamic disturbance.In this tensile failure mechanism of the deep surrounding rock,the stress environment of deep sidewall rock determines that the failure mode of rock is a tensile failure,the pre-static load level dominates the tensile failure strength of surrounding rock,and dynamic disturbance promotes the strength-weakening effect and affects the weakening range.
文摘1 Introduction Early detection and diagnosis of stable coronary artery disease （SCAD） is essential for proactive secondary prevention of myocardial infarction （MI）, control of disease progress, and reduction of mortality. Clinical decision-making in modem medicine is increasingly dependent on cardiovascular imaging techniques. 2012 ACCF/AHA/ACP/AATS/ PCNA/SCAI/STS guideline for the diagnosis and management of patients with stable ischemic heart disease has been issued by American Heart Association （AHA）. European Society of Cardiology （ESC） has issued 2013 ESC guidelines on the management of stable coronary artery disease.
基金Project(51979281)supported by the National Natural Science Foundation of ChinaProject(ZR2018MEE050)supported by the Natural Science Foundation of Shandong Province,ChinaProject(18CX02079A)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Pre-stressed bolt anchorage is the key technology for jointed rock masses in rock tunnelling,slope treatment and mining engineering.To investigate the mechanical properties and reinforcement effect of jointed rock masses with pre-stressed bolts,in this study,uniaxial compression tests were conducted on specimens with different anchoring types and flaw inclination angles.ABAQUS software was used to verify and supplement the laboratory tests.The laws of the uniaxial compressive strength(UCS)obtained from the numerical simulations and laboratory tests were consistent.The results showed that under the same flaw angle,both the UCS and elastic modulus of the bolted specimens were improved compared with those of the specimens without bolts and the improvements increased with an increase in the bolt pre-stress.Under the same anchoring type,the UCS and elastic modulus of the jointed specimens increased with an increase in the flaw angle.The pre-stressed bolt could not only restrain the slip of the specimens along the flaw surface but also change the propagation mode of the secondary cracks and limit the initiation of cracks.In addition,the plot contours of the maximum principal strain and the Tresca stress of the numerical models were influenced by the anchoring type,flaw angle,anchoring angle and bolt position.
