填药柱壳在内部爆炸载荷下的变形和破坏

采用一种计及三轴因子的损伤模型,以本构关系的内变量理论为基础得到了热塑性本构关系的普适显武表达式;得到了改进的Johnson-Cook本构模型的增量形式; 考虑温度和损伤对材料参数的影响,计入温度和损伤对材料塑性变形发展的耦合作用,给出完备的计算方程组;用Lagrange显示差分的方法对填药柱壳在内部爆炸载荷下的变形和破坏进行了数值模拟,并对结果进行分析,与实验结果进行了比较.     

含损伤材料的热粘塑性本构关系和柱壳破裂研究

以含内变量的本构关系理论为基础 ,结合材料损伤演化方程 ,并考虑了温度和损伤对材料参数的影响 ,得到了增量形式的热粘塑性本构关系的普适显式表达式。然后使用Bodner幂函数型粘塑性模型 ,具体推导了其增量形式的热粘塑性本构方程。接着结合在实践中有重要意义的内部爆炸载荷作用下的柱壳破裂问题 ,建立了含损伤热粘塑性柱壳破裂问题的完备方程组 ,使用有限差分方法 ,完成了对问题的数值模拟 ,并对结果进行了分析。计算结果与实验结果符合良好。     

内爆炸载荷下圆管变形、损伤和破坏规律的研究

以物理统计和唯象研究相结合的方法,建立了微孔洞型的损伤函数模型和损伤演化方程,以变形热力学,Ｄｒｕｃｋｅｒ公设和内变量理论为基础建立了含损伤热塑性材料的增量型本构关系,用所建立的本构关系及损伤演化方程对内部爆轰作用下的圆管破坏过程完成了系列数值模拟,数值结果与实验结果相比较,在圆管变形过程,破坏时间,破坏速度,破坏应变,破坏应变率等信息方面都是基本一致的。     

考虑损伤效应的开孔浅球壳的非线性动力响应与动力屈曲

研究损伤对开孔浅球壳非线性动力响应与动力屈曲的影响.基于Talreja张量内变量损伤模型,建立了纤维增强复合材料板壳弯曲问题的损伤本构关系,导出了考虑损伤效应的具轴对称变形正交各向异性开孔浅球壳的非线性运动控制方程.对未知函数在空间域采用正交点配置法离散,时间域采用Newm ark-β方法离散.数值结果表明,由于损伤导致结构刚度不断削弱,结构振幅增大而频率减小,结构的动力临界屈曲载荷降低.     

微孔洞唯象损伤力学模型及其应用

基于微损伤发展的NAG(nucleation and growth)模型,从唯相角度,得到了一种微孔洞损伤演化方程。在考虑损伤软化和温度软化的基础上得到了材料含损伤本构关系。将损伤演化方程和材料本构关系引入ABAQUS有限元软件对D6AC和921两种钢板撞击层裂问题进行数值模拟。模拟结果与实验结果吻合。     

混凝土静力与动力损伤本构模型研究进展述评

对混凝土材料在静力和动力载荷作用下的损伤本构关系模型进行了评述.梳理了混凝土本构关系研究的历史脉络和逻辑脉络;归纳总结了在混凝土本构关系研究发展过程中具有代表性意义、并且对重大工程建设具有参考意义的若干混凝土静力和动力损伤本构模型.基于对混凝土材料非线性及随机性的理解和诠释,阐述了混凝土静力和动力本构关系研究的发展趋势.      

钢方管截面柱考虑损伤的滞回性能分析

结构钢本构关系的精度直接影响分析结果的可靠度.根据能量等效性假设、热力学第二定律,推出损伤材料的弹性本构方程;采用混合强化准则,考虑Bauschinger效应、屈服平台、硬化(软化)效应及损伤和损伤演化影响,建立了的结构钢弹塑性各向异性损伤本构关系.结合构建的本构关系,采用八节点超参数壳体单元,推导了用U.L.格式及Cauchy应力描述的板壳双重非线性有限元方程,并编制了计算程序.利用U.L.格式的壳体大挠度双重非线性有限元分析方法,对钢方管截面短柱进行面内拉压循环荷载作用下的滞回性能分析.     

横观各向同性超弹性球壳的有限振动

应用有限变形动力学理论研究了一种横观各向同性不可压超弹性材料球壳在表面突加均布拉伸载荷作用下的有限振动问题．给出了球壳振动的振幅和外加载荷之间的关系,得到了,球壳振动的相同和近似的周期,讨论了球壳振动的振幅、相图及振动的周期和材料各向异性程度的关系．     

圆柱壳的塑性膨胀和变形

根据材料不可压缩假设,适当选取材料塑性本构关系,将圆柱壳塑性膨胀运动简化为以圆柱壳内 半径为因变量的常微分方程初值问题。对3种初始内外半径比纯铜厚壁圆柱壳膨胀过程的计算表明,应变率 硬化阻碍圆柱壳的塑性膨胀运动,应变硬化和温度效应的影响可以忽略,而与圆柱壳的厚度无关。     

爆炸力学数值模拟中本构建模问题的讨论

就爆炸力学数值模拟中的本构建模问题的有关内容作了讨论,包括:波传播研究与材料的动态特性研究的相互依赖、容变律与畸变律的解耦与耦合、率型本构关系与失效准则、应变率效应与温度效应的等效性、加载本构关系与卸载本构关系以及流变过程与损伤演化过程的耦合等,并展望了今后的有关发展动向。     

Using the scanning infrared camera in experimental fatigue studies

Materials under cyclic loading dissipate energy in the form of heat due to hysteresis effects in the material. At locations of high stress levels, more heat is released than elsewhere, resulting in a local temperature rise in those areas. The scanning infrared camera has been used in this study to visualize the surface-temperature field on steel and fiberglass-epoxy composite samples during fatigue tests. The information achieved in this manner allows one to predict the probable location of the greatest fatigue damage well before such damage becomes visible in the form of a crack. The use of the scanning infrared camera for monitoring traveling cracks and mapping the temperature fields resulting from stress concentrations in cyclically loaded materials is also demonstrated. The results indicate that this instrument is of value in both nondestructive testing and crack-propagation studies.     

The near tip fields and temperature distribution around a crack in a body of hardening material containing small damage

In this paper, the following conclusions are reached: The influence of damage on the stress and strain feilds can be neglected in an asymptotic sense for the solutions of damage field in a plastic solid containing small damage. The formulation of the problem is simplified with an uncoupled approach. Based on experimental results of plastic damage, most of the damage in the material are considered as small damage with the critacal damage variable ω _c ≪1. Using this approach, closed form expressions of the near tip damage fields for mode III, mode I and the temperature distribution induced by plastic dissipation in a hardening material containing damage are deduced. We point out that the temperature distribution in the process zone is strongly dependent on the damage of materials even for the small damage case. The results of the predicted value of the temperature rise near the tip region ignoring the damage effect is appreciably higher than the observed data. The main reason of this discrepancy is the presence of damage dissipation and the fact that its influence on the calculation of plastic dissipation have not been appropriately taken account of. The calculation is improved by taking into account the damage effect on the temperature rise, then theT _max value is in better accord with the experimental value. The project supported by the National Natural Science Foundation of China.     

On the effect of temperature gradient on the stability of circular tubes made of hyperelastic entropic material

Rubber-like materials are very applicable in almost all fields of industries, but due to their large deformation characteristic, they can exhibit a variety of instabilities. Accordingly, many researchers have been motivated to investigate the effects of different parameters on the stability of hyperelastic cylindrical tubes under finite deformation, while the effects of temperature gradient have not been considered. In this paper, the effects of temperature variation on the stability and thermo-mechanical behavior of the cylindrical tubes made of the entropic materials such as rubber-like materials and elastomers are investigated via an effective strain energy density function. To this purpose, an Ogden-type strain energy density with only integer powers is applied in order to determine an analytical solution, not involving the integral form, for the stress distribution through the wall thickness of cylindrical tubes at finite deformation thermoelasticity. This problem is examined in two cases including (i) a thick-walled cylindrical tube under internal pressure and uniform variation of temperature and (ii) a thick-walled cylindrical tube under internal pressure and temperature gradient, simultaneously. It was observed that the positive temperature gradients in comparison with environment temperatures improve the stability of the circular tubes made of the entropic materials.     

A note on the thermal effects upon a Gurson-type material model

Gurson-type material models are based on concepts of porous materials and have been largely used to describe mechanical degradation under inelastic deformation. In addition to mechanical damage, temperature evolution is also relevant to this class of problems owing to thermal softening effects. This work addresses a finite strain thermo-elastic-plastic formulation fully coupled to the energy conservation equation and investigates the sensitivity of the mechanical response with respect to the temperature evolution based on tensile tests for small to moderate temperatures. The results indicate that the initial temperature, sensitivity of the yield stress to temperature and the heat transfer coefficient at the specimen surface play an important role on the evolution of the void fraction, stress distribution and, ultimately, the load-bearing capacity.     

High-Rate Progressive Failure of Borosilicate Glass under Mechanical Confinement at High Temperatures

In this study, we experimentally determined the dynamic response of a damaged borosilicate glass at different temperatures, damage levels and confinement pressures. The initiation and evolution of damage during the loading process were also examined. An improved double-pulse loading Kolsky compression bar, integrated with a non-contact high temperature testing system and a single loading momentum trap system, was used to characterize the high-rate mechanical behavior of a damaged borosilicate glass. Specimen deformation was interrupted at different strain levels to reveal damage evolution with increasing strain. The results show that the equivalent flow strength of damaged borosilicate glass depends linearly on the hydrostatic pressure; however the variation of temperature has little effects on the strength. Through post-mortem SEM analysis, the failure in an intact specimen was found to be initiated in the form of axial splitting. Further loading on the splitted specimens induced catastrophic buckling of the columns which converted the specimens into small fragments. Shear zones became evident in the compacted fragments as deformation further accumulated. The propagation of the shear zones to the entire specimen eventually led to full comminution of the borosilicate glass material.     

Modeling of diffusion in the presence of damage in polymer matrix composites

It is now well known that Fick’s Law is frequently inadequate for describing moisture diffusion in polymers and polymer composites. Non-Fickian or anomalous diffusion is likely to occur when a polymer composite laminate is subjected to external stresses that could give rise to internal damage in the form of matrix cracks. As a result, it is necessary to take into account the combined effects of temperature, stress, and damage in the construction of such a model. In this article, a modeling methodology based on irreversible thermodynamics applied within the framework of composite macro-mechanics is presented, that would allow characterization of non-Fickian diffusion coefficients from moisture-weight-gain data for laminated composites. A symmetric damage tensor based on continuum damage mechanics is incorporated in this model by invoking the principle of invariance with respect to coordinate transformations. For tractability, the diffusion-governing equations are simplified for the special case of a laminate, with uniformly distributed matrix cracks, that is subjected to a uniaxial tensile stress. The final form for effective diffusivity obtained from this derivation indicates that the effective diffusivity for this case is a quadratic function of crack density. A finite element procedure that extends this methodology to more complex shapes and boundary conditions is also presented. Comparisons with test data for a 5-harness satin textile composite are provided for model verifications.     

Deformation behaviour in advanced heat resistant materials during slow strain rate testing at elevated temperature

In this study, slow strain rate tensile testing at elevated temperature is used to evaluate the influence of temperature and strain rate on deformation behaviour in two different austenitic alloys. One austenitic stainless steel (AISI 316L) and one nickel-base alloy (Alloy 617) have been investigated. Scanning electron microscopy related techniques as electron channelling contrast imaging and electron backscattering diffraction have been used to study the damage and fracture micromechanisms. For both alloys the dominante damage micromechanisms are slip bands and planar slip interacting with grain bounderies or precipitates causing strain concentrations. The dominante fracture micromechanism when using a slow strain rate at elevated temperature, is microcracks at grain bounderies due to grain boundery embrittlement caused by precipitates. The decrease in strain rate seems to have a small influence on dynamic strain ageing at 650°C.     

升温热冲击环境下超高温陶瓷材料抗热震性能的热-损伤模型

在现有的抗热震理论基础上考虑到超高温陶瓷材料热物理性能对温度的敏感性及损伤在其使役历程中随温度的演化,建立了适用于升温服役环境下表征超高温陶瓷材料抗热震性能的热-损伤模型。该模型考虑了微裂纹尺寸、密度、热冲击环境温度等因素对材料抗热震性能的影响。利用此模型研究了超高温陶瓷材料在升温服役环境下损伤以微裂纹形核规律演化时对其抗热震性能的影响。从理论上验证了基于材料微结构设计思想在制备超高温陶瓷材料时,引进一定密度一定尺寸的微裂纹并控制其随温度演化规律以形核方式进行,既可以使材料保持较高的强度又能大幅度提升材料的抗热震性能。     

Transverse vibrations in micro-scale viscothermoelastic beam resonators

In this article, the closed form expressions for the transverse vibrations of a homogenous isotropic, thermally conducting, Kelvin–Voigt type viscothermoelastic thin beam, based on Euler– Bernoulli theory have been derived. The effects of relaxation times, thermomechanical coupling, surface conditions, and beam dimensions on energy dissipation induced by thermoelastic damping in MEMS (micro-electromechanical systems) resonators are investigated for beams under clamped and simply supported conditions. Analytical expressions for deflection, temperature change, frequency shifts, and thermoelastic damping in the beam have been derived. Some numerical results with the help of MATLAB programming software in case of Silicon Nitride have also been presented. The computer-simulated results in respect of damping factor and frequency shift have been presented graphically.     

高温环境下纤维复合材料蠕变损伤的细观机理研究

首先利用复合材料纤维断裂单胞模型，编制蠕变损伤子程序，对单胞模型进行蠕变损伤分析。分析了纤维／基体弹性模量比对蠕变变形、蠕变损伤以及应力场的影响。从计算结果发现，蠕变损伤首先在纤维断裂尖端起始，然后沿着一定的角度向基体外围延伸，直至完全损伤，而且纤维／基体模量比对高温环境下的复合材料蠕变损伤产生很大的影响；纤维与基体的模量相差越大，复合材料越容易变形，抵抗蠕变变形的能力就越小，蠕变损伤越严重。经过对不同韧性的基体材料进行研究，发现基体韧性低的复合材料蠕变损伤明显高于高韧性基体复合材料，表明低韧性基体复合材料抵抗蠕变破坏的能力较低。