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在应力作用下, 材料的力学参数随着微观结构的变化而变化, 需要考虑参数的时间效应. 利用黏滞系数随时间变化的黏性元件, 构造出非定常Maxwell模型、非定常Kelvin模型和非定常Zener模型. 求解非定常模型的微分型本构方程得到它们的松弛模量、蠕变柔量和卸载方程. 结果表明, 可以把常见的经验松弛函数和经验蠕变函数视为非定常微分型本构模型. 相似文献
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硅锰合金扭簧应力松弛行为研究 总被引:4,自引:0,他引:4
研制了矩形截面扭簧应力松弛试验装置并进行了多组高温实验;提出了可动位错密度函数,结合现有应力松弛位错理论提出了新的硅锰合金弹簧钢扭转应力松弛动力学方程;利用ABAQUS二次开发接口CREEP子程序,实现了将新的应力松弛动力学方程转化为基于隐式有限元法的修正时间硬化蠕变模型,对400℃下的硅锰合金弹簧钢扭转应力松弛行为进行了数值模拟;模拟结果表明,修正的时间硬化蠕变模型与试验结果吻合,扭簧表面的Von Mises应力随时间变化规律与试验中的扭矩随时间变化规律一致。 相似文献
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用振动梁方法测量粘弹性材料的复模量和粘弹性参数 总被引:2,自引:0,他引:2
本文利用共振梁方法,通过对一点响应、相位滞后和共振频率的测量,可以获得粘弹性材料的复模量以及标准线性固体模型的三个参数,即松弛模量、松弛系数和蠕变系数.实验结果表明,实验原理正确,测试系统可靠而且简单实用. 相似文献
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利用三维Voronoi模型和有限元方法分析了胞壁材料具有粘弹特性的低密度开孔泡沫的蠕变和应力松弛行为.采用了三参量标准线性固体模型来描述胞壁材料的粘弹特性.所得结果表明.低密度开孔泡沫具有与其胞壁材料相同的松弛时间,当相对密度较低时(低于1%)开孔泡沫的松弛模量与胞壁材料的松弛模量和泡沫相对密度平方成正比.此外,计算结果还表明,低密度开孔泡沫在较小的初始应力条件下具有与其胞壁材料相同的延迟时间.其蠕变柔度与胞壁材料的蠕变柔度和泡沫相对密度平方倒数基本成正比.但随着初始应力值的增大,泡沫的延迟时间将会显著增加. 相似文献
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针对几种经典和新发展的蠕变-疲劳寿命模型开展综述介绍,并建立预测航空涡轮盘在循环热-机蠕变-疲劳载荷谱下蠕变-疲劳行为的数值流程,对某型航空涡轮盘的蠕变-疲劳损伤和寿命进行预测和对比.结果表明:等效应变法与临界平面法得出的疲劳损伤差距较小,等效应变法由于数值计算简单,工程适用性更强.寿命-时间分数(TF)法由于无法考虑应力松弛效应,给出了最为保守的蠕变损伤预测,其对盘体应力三轴度引起的损伤不敏感;延性耗竭法(DE)法仅以蠕变应变率作为损伤因素,虽考虑多轴蠕变因子的影响,但是给出的蠕变损伤过小;修正应变能密度耗竭(MSEDE)法综合考虑蠕变应变与应力松弛,并且考虑多轴蠕变因子与弹性跟随效应的影响,结合疲劳损伤模型可以给出合理的蠕变、疲劳损伤比例,其预测结果更加合理. 相似文献
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本文提出用三维光弹性应力冻结法模拟分析预应力钢筋混凝土结构中的应力。通过模拟体与实体结构的相似性研究,给出了模型载荷比例系数Cq参数,通过参数合理的选取,有效的解决了应力冻结水平预测这一技术关键;用光弹性应力二次冻结法,将结构预应力和负载应力冻结在同一试件中;应分析精度对模型尺寸的要求,采用了精密浇铸的方法制作模型。此外,还研制了受力清晰明确的加载系统。对这些涉及应力冻结的若干关键问题结合工程实例进行探讨。实验应力分析结果与有限元数值法一致性较好。 相似文献
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为了研究粘性效应作用下的动态扩展裂纹尖端渐近场,建立了可压缩粘弹性材料II型动态扩展裂纹的力学模型,推导了可压缩材料Ⅱ型动态扩展裂纹的本构方程.在稳态蠕变阶段,弹性变形和粘性变形同时在裂纹尖端场中占主导地位,应力和应变具有相同的奇异量级r-1/(n-1).通过渐近分析求得了裂纹尖端应力、应变和位移分离变量形式的渐近解,并采用打靶法求得了裂纹尖端应力、应变和位移的数值结果,给出了应力、应变和位移随各种参数的变化曲线.数值计算表明,弹性变形部分的可压缩性对Ⅱ型裂尖应力场影响甚微,而对应变场和位移场影响较大.裂尖场主要受材料的蠕变指数n和马赫数M的控制.当泊松比ν =0.5时,可以退化为不可压缩粘弹性材料Ⅱ型动态扩展裂纹. 相似文献
9.
胶凝原油蠕变的时间-温度-应力等效性 总被引:2,自引:0,他引:2
黏弹性蠕变是胶凝原油重要的流变特性,要描述胶凝原油的黏弹性蠕变行为,必须同时考虑
应力、时间和温度等参数. 于是对胶凝原油进行了不同应力和不同温度下的蠕变实验,利用
时间-温度-应力等效原理分析了胶凝原油的非线性蠕变行为,得到了参考应力和参考温度下
的蠕变主曲线,并用黏弹性流变模型拟合得到了蠕变主曲线的表达式. 从而可以分别通过较
高温度和应力水平下的短期蠕变行为来预测较低温度和应力水平下的长期蠕变行为. 相似文献
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针对混凝土构件耐久性试验环境的腐蚀性和多变性、试验设备容量的限制、混凝土的徐变及加载杆件的松弛等影响,对持荷试件加载装置进行了设计与研究。通过自平衡加载装置对紧固件施加扭矩来控制持荷试件的应力水平,并实时监测不同材质及环境下的扭矩系数、混凝土徐变和紧固件的应力松弛,以此获得扭矩的衰减规律,为试件应力补偿提供理论依据。采用两套加载装置对8根(套)试件进行了测试,试验结果表明,自平衡加载装置适用性强、加载及其补偿简便且能够满足试验要求,持荷试件应力损失在六周后趋于稳定。该装置及其应用技术可用于荷载与环境共同作用下混凝土构件的耐久性试验。 相似文献
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Konstantin Naumenko Holm Altenbach Yevgen Gorash 《Archive of Applied Mechanics (Ingenieur Archiv)》2009,79(6-7):619-630
Many materials exhibit the stress range dependent creep behavior. The power law creep observed for a certain stress range changes to the viscous type creep as the stress value decreases. Recently published experimental data for advanced heat resistant steels indicate that the high creep exponent (in the range 7–12) may decrease to the low value of approximately unity within the stress range relevant for engineering structures. The aim of this paper is to analyze the influence of the stress range dependent power-law-viscous creep transition on the behavior of structures at elevated temperature. A constitutive model for the minimum creep rate is introduced to describe both the linear and the power law creep depending upon the stress level. To demonstrate basic features of the stress range dependent creep modeling, several elementary examples from structural mechanics are presented. They include a stress relaxation problem, a beam subjected to pure bending and a pressurized thick-walled cylinder. Based on the uni-axial transition stress the transition value of the external load is estimated such that above this value the power law can be applied. For the loading levels below this value the character of the stress distribution as well as the stress values are essentially influenced by the viscous creep. 相似文献
14.
J. Stickforth 《International Journal of Plasticity》1986,2(4):347-357
Recently the author published a time-dependent theory of plasticity including recovery which treats creep strain and plastic strain as mathematically indistinguishable. After presenting a sketch of this theory, we establish the differential equation of low-temperature stress relaxation on the basis of a Mises-type material with kinematic hardening. Then we discuss high-temperature transient creep, steady-state creep, and Norton's rule results as an approximation with Sherby's exponent n = 5. 相似文献
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在大体积混凝土结构中,徐变应力的分析是个十分重要的问题。本文在线性徐变条件下,(1)导出了关于徐变度和松弛系数的两个定理;(2)提出了直接由徐变度求松弛系数的一种递推公式;(3)对求解徐变问题的初应变法和初应力法,导出了对于任意的松弛系数和徐变度表达式的一般递推公式,从而简化了计算方法,避免了应变或应力历史资料的存贮,节省计算机的大量存贮量。 相似文献
16.
An intermediate model method for obtaining a discrete relaxation spectrum from creep data 总被引:2,自引:0,他引:2
A convenient method is described for obtaining a discrete stress relaxation spectrum from linear viscoelastic creep data by means of a three-stage process. In stage one, a discrete retardation spectrum is fitted to the creep data using a least squares procedure, subject to the constraint that the discrete spectrum must be a specified order of polynomial function of the retardation time. In stage two, the resulting generalised Voigt model is solved numerically for an imposed step in strain, to determine the stress relaxation modulus function of time. In stage three, a discrete relaxation spectrum is fitted to the calculated stress relaxation modulus function. Although three stages are involved instead of the usual two, the procedure has been found to have certain practical advantages. These advantages make it suitable for the generation of relaxation spectra needed in viscoelastic stress analyses of solids, for example by the finite element method. In order to illustrate the proposed procedure it is applied to both artificial data and experimental creep data for poly(methyl methacrylate) at 70°C and at the glass transition. 相似文献
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《International Journal of Plasticity》2003,19(7):1069-1095
The inelastic deformation behaviors of metals and polymers are discussed with the aim of finding a common base that would simplify academic and engineering analyses. Only monotonic loading conditions at room temperature are considered. For loading at different rates, nonlinear relations between loading rate and stress level, creep stress level and creep strain, and relaxation rate and stress were common to both type of materials. There are, of course, significant differences in elastic properties, strength levels and the strains involved. Special properties such as relaxation behaviors and creep anomalies can be qualitatively and quantitatively reproduced by the state variable model VBO (viscoplasticity theory based on overstress). Since experimental investigations typically concentrate on one particular aspect of inelastic deformation behavior such as creep or strain-rate dependence, it is often difficult to gather a comprehensive data set for a given material. In spite of this, considerable similitude in the deformation behavior of metals and polymers in various test conditions has nevertheless been established. 相似文献
18.
《Journal of the mechanics and physics of solids》1986,34(3):191-212
Transient crack growth in an elastic/power-law creeping material is investigated under antiplane shear loading and small-scale-yielding conditions. At time t = 0 the solid is suddenly loaded far from the crack by tractions that correspond to the elastic crack-tip stress distribution. At that time the crack begins to propagate at a constant velocity. The stress fields evolve in a complex manner as the crack propagates due to the competing effects of stress relaxation due to constrained creep and stress elevation due to the instantaneous elastic material response to crack growth. From detailed finite element calculations it is shown that these fields can be approximated by a simple matching of three asymptotic singular crack-tip solutions. A characteristic stress, distance and time are defined for this problem which provide a normalization that accounts for any crack velocity, loading and all material properties for a given creep exponent n. Results are presented for crack-tip stresses, strains, crack opening displacements and creep zones. 相似文献
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Yize Wang Fengming Li Kikuo Kishimoto Yuesheng Wang Wenhu Huang 《Acta Mechanica Solida Sinica》2008,21(6):529-535
The elastic wave localization in disordered periodic piezoelectric rods with initial stress is studied using the transfer matrix and Lyapunov exponent method. The electric field is approximated as quasi-static. The effects of the initial stress on the band gap characteristics are investigated. The numerical calculations of localization factors and localization lengths are performed. It can be observed from the results that the band structures can be tuned by exerting the suitable initial stress. For different values of the piezoelectric rod length and the elastic constant, the band structures and the localization phenomena are very different. Larger disorder degree can lead to more obvious localization phenomenon. 相似文献