多晶体金属疲劳寿命随晶粒尺寸变化的理论研究

在疲劳断裂非平衡统计理论框架的基础上，根据界面能模型，推导出了多晶体金属的疲劳寿 命随晶粒尺寸、应变振幅的变化公式.还与有关实验结果进行了比较，发现理论与实验较为 相符. 关键词： 疲劳寿命 晶粒尺寸 非平衡统计理论 界面能模型     

金属穿晶脆性断裂统计理论

讨论了金属穿晶脆性断裂统计理论.根据穿晶裂纹和晶界作用的界面能模型及断裂非平衡统计理论框架,推导出了裂纹扩展速率、断裂强度、断裂韧性、脆性—韧性转变温度及其统计分布函数随晶粒尺度和界面能变化的公式. 关键词：     

非平衡定态相图新概念及其应用——激活低压金刚石气相生长热力学

在激活的低压条件下，金刚石气相稳定生长的同时石墨会被腐蚀．这是近二三十年来国际上的一个热力学难题，甚至被认为是“热力学的悖论”．用非平衡热力学耦合理论可以给予很好的解释，并推导出非平衡定态相图的全新概念．在新型相图中金刚石在低压下是稳定相，而石墨被激活成为亚稳相．理论计算与文献报道的大量实验数据定量化地相符     

锰氧化物相竞争的理论研究

势函数是在平衡态统计物理中应用得十分成功的理论,将势函数理论推广到非平衡系统是非平衡态统计物理的一项十分重要的任务。本文综述了非平衡态势函数理论的一个重要方面,即利用对随机过程的研究来建立系统的势函数,本文阐述了非平衡系统势函数的定义和概念;论证势函数在系统演化过程中的单调性质;详细介绍了各种计算非平衡势函数的方法;同时介绍了利用势函数解析地研究在噪声作用下的非线性系统的非定态演化行为。整个研究包含了一维和多维系统的广泛系统。     

非平衡定态相图新概念及其应用

在激活的低压条件下，金刚石气相稳定生长的同时石墨会被腐蚀、这是近二三十年来国际上的一个热力学难题，甚至被认为是“热力学的悖论”，用非平衡热力学耦合理论可以给予很好的解释，并推导出非平衡定态相图的全新概念，在新型相图中金刚石在低压下是稳定相，而石墨被激活成为亚稳相，理论计算与文献报道的大量实验数据定量化地相符。     

非平衡系统的势函数理论

势函数是在平衡态统计物理中应用得十分成功的理论，将势函数理论推广到非平衡系统是非平衡态统计物理的一项十分重要的任务。本文综述了非平衡态势函数理论的一个重要方面，即利用对随机过程的研究来建立系统的势函数，本文阐述了非平衡系统势函数的定义和概念；论证势函数在系统演化过程中的单调性质；详细介绍了各种计算非平衡势函数的方法；同时介绍了利用势函数解析地研究在噪声作用下的非线性系统的非定态演化行为。整个研究包     

瞬态激光作用下的弛豫过程

概述了国内外在非平衡统计方面有关的理论和方法。着重介绍了中国科学院金属研究所在固体非平衡性质方面研究工作的一些新近进展，其中包括激光脉冲激发下的非平衡声子动态过程，一维链中非线性声子交互作用形成的孤子状激发，无序固体低温下声子输运的量子理论，瞬态激光作用下温度和长度变化的不同步效应。最后讨论了这方面今后应进行的理论和实验工作。     

非保守耦合系统的统计能量分析原理

传统的统计能量分析(SEA)理论不能解决非保守耦合系统的能量分析问题。本文在非保守耦合振子的能量分布与功率流特征的研究基础上,推导了互不相关随机激励条件下非保守耦合系统的功率平衡方程式及各有关功率项的计算式,建立了非保守耦合系统的统计能量分析理论。研究结果表明,保守耦合仅是非保守耦合的一个特例,耦合阻尼对非保守耦合系统的能量分布和功率流的特征有着显著的影响,只有在耦合阻尼远小于系统内阻尼时这种影响才可近似忽略。作为理论的一个应用实例,本文对非保守耦合板的能量问题进行了理论和实验研究。     

分子整流器整流特性的键桥调控效应

利用密度泛函理论和非平衡格林函数方法,研究了基于同一分子在不同空间构型下形成的三个不同分子器件的电子输运特性及整流效果. 研究表明:旋转中间苯环(键桥——π桥),能明显改变整流效果,这是因为改变了分子轨道的离域性,这一发现说明通过改变键桥的空间取向能有效地调控分子整流器的整流性质,这对于设计新型分子整流器有重要意义. 关键词： 分子整流器 键桥 密度泛函理论 非平衡格林函数     

时间反演对称和非平衡统计定常态(Ⅰ)

本文是作者从微观量子统计理论出发应用微观可逆性原理讨论非平衡统计定常态普遍性质的第一部份。文中给出了非平衡量子统计格林函数(闭路格林函数)在定常态上关于时间反演对称的表达方式。把生成泛函技术和时间反演对称结合起来,得到了具有时间反演对称性的非平衡统计定常态上统计格林函数和顶点函数所满足的时间反演对称关系。 关键词：     

Fatigue life of metal treated by magnetic field

This paper investigates theoretically the influence of magnetization on fatigue life by using non-equilibrium statistical theory of fatigue fracture for metals. The fatigue microcrack growth rate is obtained from the dynamic equation of microcrack growth, where the influence of magnetization is described by an additional term in the potential energy of microcrack. The statistical value of fatigue life of metal under magnetic field is derived, which is expressed in terms of magnetic field and macrophysical as well as microphysical quantities. The fatigue life of AISI 4140 steel in static magnetic field from this theory is basically consistent with the experimental data.     

Non-equilibrium statistical theory about microscopic fatigue cracks of metal in magnetic field

This paper develops the non-equilibrium statistical fatigue damage theory to study the statistical behaviour of micro-crack for metals in magnetic field. The one-dimensional homogeneous crack system is chosen for study. To investigate the effect caused by magnetic field on the statistical distribution of micro-crack in the system, the theoretical analysis on microcrack evolution equation, the average length of micro-crack, density distribution function of micro-crack and fatigue fracture probability have been performed. The derived results relate the changes of some quantities, such as average length, density distribution function and fatigue fracture probability, to the applied magnetic field, the magnetic and mechanical properties of metals. It gives a theoretical explanation on the change of fatigue damage due to magnetic fields observed by experiments, and presents an analytic approach on studying the fatigue damage of metal in magnetic field.     

Vocal Fatigue: Current Knowledge and Future Directions

Vocal fatigue is a complex multifaceted clinical phenomenon. Several hypotheses exist concerning its underlying mechanism, and a range of empirical studies have examined its manifestation. This article reviews the literature pertaining to the nature, underlying processes, and salient features of vocal fatigue. First, vocal fatigue is defined, its major symptoms are discussed, and hypotheses concerning its primary physiological and biomechanical mechanisms are considered. Second, studies of experimentally induced vocal fatigue in humans are evaluated. Third, research investigating the clinical and occupational manifestations of vocal fatigue is discussed. Fourth, directions for ongoing research in this area are offered.     

Critical Plane Orientation Influence on Multiaxial High-Cycle Fatigue Assessment

In the present paper, the multiaxial fatigue lifetime of structural components failing in the high-cycle fatigue regime is evaluated by employing the modified Carpinteri-Spagnoli (C-S) multiaxial fatigue criterion based on the critical plane approach. In the above criterion, the critical plane position is linked to averaged principal stress directions through an off-angle 8. Then, the fatigue damage parameter used is determined by a nonlinear combination of an equivalent normal stress amplitude and the shear stress amplitude acting on the critical plane. In the present paper, some modifications of the original expression for the off-angle 8 are implemented in the modified Carpinteri-Spagnoli criterion. In particular, modified expressions recently proposed by Lagoda et al. are in accordance with the assumption originally developed by Carpinteri and co-workers, that is, the off-angle is a function of the ratio between the fatigue limit under fully reversed shear stress and that under fully reversed normal stress. Such expressions can be employed for metals ranging from mild to very hard fatigue behaviour. Some experimental data available in the literature are compared with the theoretical estimations and, only for materials with hard and very hard fatigue behaviour, the modified 8 relationships are shown to yield fatigue lifetime results slightly better than those determined through the original 8 expression.     

Experimental and theoretical study of multiscale damage-failure transition in very high cycle fatigue

Multiscale mechanisms of failure of metals (Armco iron, titanium, aluminum) are studied for high cycle and very high cycle fatigue. By correlating with the results of structural studies, a theoretical approach is developed to describe fatigue crack kinetics in damaged material under high cycle and very high cycle fatigue loading conditions. Stages of crack nucleation and propagation are analyzed using the profilometry data from the fracture surface. The scale invariance of fracture surface roughness is established, which allows an explanation of the self-similar nature of fatigue crack kinetics under high cycle and very high cycle fatigue. Variation of elastic-plastic properties of Armco iron under very high cycle fatigue is studied using an acoustic resonance method. It is found that the material density decreases during fatigue damage accumulation, with the minimum of the material density in the bulk of the specimen.     

On the sonic fatigue life estimation of skin structures at room and elevated temperatures

Fighter/trainer empennages and STOL (Short Take-Off and Landing) aircraft flap systems are subjected to severe acoustic pressure levels as high as 150–170 dB. As a result, acoustic fatigue has become one of the major factors in design. Empennages and flap systems are also subject to high temperatures and thus the influence of thermal buckling on fatigue life must be taken into consideration. To estimate the sonic fatigue life of skin structures, combined use is made of the Monte Carlo method of non-linear panel response analysis and local stress-strain simulations with rheological models. Calculations were conducted and comparison of the results with experimental data shows that the method estimates the sonic fatigue life accurately when adequate values of fatigue notch factors are chosen. Example calculations with thermal as well as static pressure effects were also carried out and the effect of thermal buckling on sonic fatigue life is clarified.     

Spectral analysis of surface EMG based on empirical mode decomposition

Muscle fatigue is a common experience in daily life. Some researchers have defined it as the incapacity to maintain the required or expected force. Obviously, force, power and torque recordings as direct measurements of muscle fatigue are difficult to be obtained in one experiment. The main issue when using conventional sEMG variables to quantify fatigue is their poor association with direct measures of fatigue. Therefore, there is a need to develop muscle fatigue approaches that relate changes in sEMG variables with muscle fatigue. The empirical mode decomposition which is a recent tool for the analysis of nonlinear and nonstationary time-series is presented.     

Reliability analysis of stochastic structural system considering static strength, stiffness and fatigue

Multi-failures are possible to appear in the process of using the structural system, such as dead load failure, fatigue failure and stiffness failure. The expression of residual resistance is given based on the impact of random crack propagation in- duced by the fatigue load on the critical limit stress and section modulus in this paper. The failure modes of every element of the structural system are analyzed under dead and fatigue loads, and the influence of the correlation of failure modes on reliability of the element is considered. Failure mechanism and the correlation of failure modes under dead and fatigue loads are discussed, and the method of reli- ability analysis considering static strength, fatigue and stiffness is given. A nu- merical example is analyzed, which indicates that the failure probability is different for different use life and the influence of dead and fatigue loads on reliability of the structural system is different as well. This method of reliability analysis, in the pa- per, is better than the method only considering a single factor (or static strength, or fatigue, or stiffness, etc.) in the case of practical engineering.     

Fatigue damage detection using a speckle-contrast technique

An optical setup based on speckle-contrast measurement is proposed as an alternative to analyze fatigue damage on surfaces of metal samples. Based on the dispersion of the light, generated by a laser beam reflected by the surface, roughness and fatigue damage are analyzed after a specially designed fatigue test of metallic samples. The experimental results are obtained from an aluminum alloy type A319 modified with strontium with nodular silicon precipitates that was subjected to a fatigue procedure based in the norm ASTM E647.