纯弯曲梁的应变损伤失效分析和预测

提出了纯弯曲梁的应变损伤失效分析方法,与Kachanov的材料受载横截面减少定义拉伸损伤变量类似,以梁的弯曲惯性矩阵减少定义弯曲损伤变量。推导了梁的弯曲应变损伤基本方程,其中的材料常数可由Kachanov拉伸损伤模型的材料常数确定。并且提出了便于工程应用的应变失效预测方程。     

梁的蠕变开裂各向同性弯曲损伤分析

在梁的纯弯曲损伤基本假设条件下，导出了弯曲损伤的基本方程，与Ｋａｃｈａｎｏｖ的材料刚度劣化（受载横截面积减小）定义拉伸损伤变虽类似，以梁的弯曲刚度劣化（惯性矩减小）定义弯曲损伤变量，从而建立了与Ｋａｃｈａｎｏｖ拉伸损伤模型相类似的梁的各向同性弯曲损伤模型。最后，以受蠕变纯弯曲梁为实例进行了损伤分析，所得计算结果与Ｋａｃｈａｎｏｖ拉伸损伤模型所得结果比较吻合，表明该弯曲损伤模型是合理适用的。     

考虑轴力作用时梁的弯曲损伤失效分析

对考虑轴力作用时梁的弯曲损伤进行了分析,推导了其损伤分析的基本方程,分析表明,中性轴随损伤的发展而偏移,有向上、向下和保持不动三种情况,其偏移的方向和范围完全由比例加载系数决定,并且在特定的比例加载系数时,中性轴能保持不动,最后获得了梁在弯曲损伤时的中性轴起始偏移点、极限偏移点和极限载荷的计算公式,以及它们的简化计算公式;讨论了损伤极限状态时轴力和弯矩的交互作用曲线;轴力对弯曲损伤的影响较为显著,有轴力作用时应尽可能考虑其影响。     

梁的蠕变开裂各向同性弯曲损伤分析

在梁的纯弯曲损伤基本假设条件下，导出了弯曲损伤的基本方程，与Ｋａｃｈａｎｏｖ的材料刚度劣化（受载横截面积减小）定义拉伸损伤变虽类似，以梁的弯曲刚度劣化（惯性矩减小）定义弯曲损伤变量，从而建立了与Ｋａｃｈａｎｏｖ拉伸损伤模型相类似的梁的各向同性弯曲损伤模型。最后，以受蠕变纯弯曲梁为实例进行了损伤分析，所得计算结果与Ｋａｃｈａｎｏｖ拉伸损伤模型所得结果比较吻合，表明该弯曲损伤模型是合理适用的。     

轴力对矩形梁弯曲损伤的影响

就轴力对矩形截面梁弯曲损伤的影响进行了分析,并对中性轴的偏移、损伤极限曲线等进行了计算、讨论;计算表明其影响是非线性的。     

考虑损伤的粘弹性梁的纯弯曲

根据粘弹性损伤理论,分析了带损伤粘弹性矩形梁在受纯弯曲时损伤对应力的影响,得到了在Laplace变换域内损伤场和应力场的分布.利用Laplace数值逆变换,分别得到了损伤弹性梁和损伤粘弹性梁的最大应力和最大损伤值,分析了材料的粘性对梁内应力和损伤的影响.     

考虑轴力二阶效应的损伤梁弯曲摄动解

将损伤梁等效为阶梯型变刚度Euler-Bernoulli梁,利用Heaviside广义函数,给出了阶梯型变刚度梁抗弯刚度的统一表达式．在此基础上,考虑轴向压力二阶效应,并以损伤为摄动参数,得到了均布横向载荷作用下,简支损伤梁弯曲挠度的一阶和二阶摄动解析解,并数值分析了摄动解析解的精度和损伤梁的弯曲变形特性,结果表明：随着轴向压力和刚度损伤参数的增加,挠度一阶和二阶摄动解析解误差增加,挠度二阶摄动解析解误差通常小于其一阶摄动解析解误差,且二阶摄动解的误差很小,满足工程应用的精度．同时,损伤梁的挠度和转角分布与完整梁的挠度和转角分布差异较大,在刚度变化位置处损伤梁转角斜率存在突变．这些结果可为轴力作用下Euler-Bernoulli梁损伤识别提供理论支撑．     

功能梯度材料纯弯曲梁的弹塑性分析

假设功能梯度材料为一理想弹塑性材料,其弹性模量和屈服强度沿梁高度方向按照幂函数变化,在小变形及平截面假设下研究功能梯度材料纯弯曲梁的弹塑性性能.根据Mises屈服准则导出了纯弯曲梁的弹性极限弯矩的解析表达式,建立了梁在弹塑性状态时截面弯矩与截面弹、塑性区分布之间的关系式,给出了梁进入塑性极限状态时中性轴的位置以及塑性极限弯矩的解析计算公式.数值算例的结果表明,功能梯度材料梁的弹塑性性能与均匀材料梁不同,其屈服不一定首先产生于截面最大应力点,而可能有多种不同的屈服模态及相应的塑性扩展.弹性模量及屈服强度的梯度变化对功能梯度材料纯弯曲梁的中性轴位置、截面弹塑性应力分布以及塑性极限弯矩均有较大影响.研究结果可为功能梯度材料梁的弹塑性分析提供一定的参考.     

Timoshenko梁弯曲分析的一种新方法

本文给出了Ｔｉｍｏｓｈｅｎｋｏ梁弯曲的混合状态方程及其解的一般表达式．算例表明：本文方法求解简单，明显优于以往的分析方法．     

一种用于蠕变损伤失效概率计算的分层抽样方法

根据蠕变损伤试验和相关的研究资料,确定出影响材料蠕变损伤的随机参数;建立了蠕变损伤失效的概率模型.其次根据分层抽样法的基本思想,建立了一种考虑对蠕变损伤失效概率区间分情况抽样的蒙特卡洛分层抽样方法.并且在蠕变损伤模型中选择等效应力作为一个分层抽样变量.随后根据工程实际情况,提出了一种在统计意义下确定抽样变量的安全区域和失效区域的分层抽样的策略,以减少抽样次数.并推导出确定分层抽样区间的计算方法.然后对选择区间大小进行了讨论,可知如果所选择的分层抽样区间太小,会漏掉许多导致蠕变损伤失效的等效应力抽样值,从而使计算结果误差增大;但是如果分层抽样区间选择太大,会增加无效抽样次数,因而降低抽样效率.最后的算例表明了该方法在同样的计算精度下,其计算效率比直接抽样法的效率要高.     

矩形板非线性蠕变损伤屈曲特性分析

基于Von Karman非线性板理论和Kachanov-Rabotnov损伤理论,建立了在横向和面内载荷共同作用下考虑蠕变损伤效应的矩形板的非线性控制平衡方程,采用有限差分法和时间增量算法对未知变量进行离散,对整个问题进行迭代求解,分析了几何非线性、荷载等因素对板非线性蠕变损伤特性的影响。     

Damage Accumulation in Aluminum Alloys under Plastic Deformation and Creep

The accumulation of local and bulk damage in D16 AT and 1201 T1 aluminum alloys used in aircraft engineering is studied. The local damage level is calculated from data of thermoactivation analysis of the residual life of D16 AT alloy specimens after preliminary plastic deformation. The bulk damage level is determined from the elastic-modulus defect by measuring the natural frequency of 1201 T1 alloy specimens. Life tests of the specimens were performed at constant tensile loads and elevated temperatures. The dependence of the local damage on preliminary plastic strain at room temperature is obtained. The residual life of the specimens is calculated with allowance for the damage to the material in the initial stage of failure and compared with experimental results. Data are given on the kinetics of bulk-damage accumulation in various test regimes. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 172–182, January–February, 2006.     

Real-time Detection and Analysis of Damage in High-performance Concrete under Cyclic Bending

In order to quantitatively evaluate the damage level in high-performance concrete (HPC) with pozzolanic minerals under constant amplitude cyclic loads, three methods for real-time damage detection are employed in the present work, i.e., dynamic modulus instrument, real-time strain collector, and digital speckle correlative method (DSCM). Six mechanical parameters at different numbers of loading cycles are real-time captured by these three methods. For a maximum applied fatigue stress equal to 70% of the static flexural strength, a cohesive crack is detected on the specimen surface by the DSCM system from 10% of concrete fatigue life. The nucleation and propagation of the cohesive crack is reflected by the change of the strain concentration zone in 2-dimensional strain fields. The experimental results show that the admixtures of Class F Fly Ash (FA) and S95 Ground Granulated Blast-furnace Slag (GGBS) in high proportions increase the strain and cohesive-crack opening displacement as well as remarkably improve the fatigue performance of HPC.     

Calculating the Time to Creep Failure of Thin-Walled Pipes under Internal Pressure

The time to failure is calculated for thin-walled pipes subjected to internal pressure, to internal pressure and tension, and to internal pressure and bending. The problems are solved using the concept of equivalent stresses. The equivalent stresses are found from a mixed delayed-failure criterion relating the maximum normal stress and the intensity of tangent stresses. The criterion includes an additional material constant, which is determined experimentally. The calculated results and experimental data are compared and found to be in satisfactory agreement     

Determining the Thermoviscoplastic State of Shells of Revolution Subject to Creep Damage

A technique is developed for determining the thermoviscoplastic state of shells of revolution with allowance for creep damage. The technique is based on the hypotheses of rectilinear element and the theory of deformation along paths of small curvature. The equivalent stress appearing in the kinetic equations of damage and creep is determined using a creep-rupture criterion that accounts for the stress mode and the level of irreversible strains. The technique is tested by determining the thermoviscoplastic state and time to failure of tubular specimens under a tensile force and a torque