SiCp/ZL101AI复合材料中的层裂微损伤演化行为

对ＳｉＣｐ／ＺＬ１０１Ａｌ复合材料进行了层裂损伤演化实验，得到了试样的层裂损伤演化图像．通过对这些微损伤演化图像的微观观察和对微损伤的统计定量分析，发现在层裂损伤演化过程中，微损伤的形成和发展不仅与应力水平、作用时间相关，而且还与材料中的微结构分布密切相关．通过层裂损伤演化实验，得到了在这种复合材料中，微裂纹在基体中的扩展速度及其与宏观应力水平的关系     

层裂的分形机理及分维和连接阈值的关系

通过对微裂纹连接的动力学分析，提出了描述层裂损伤演化的统计分形模型，指出分形层裂面的形成机理与层裂中微裂纹级串连接的动力学过程密切相关，由此，得到了一种单峰的分维－连接阈值关系，定性解释了分维随专心韧性单峰变化的实验现象。     

爆轰加载下金属材料的微层裂现象

通过在LiF窗口撞击镀膜面增加一薄层LiF和对LiF窗口反光面进行漫反射面镀膜处理的方法，对传统Asay窗诊断技术进行了改进，获得了微层裂物质高质量的实验信号。将改进后Asay窗技术与中能X射线照相及激光干涉测速技术相结合，实验给出了熔化状态下Sn材料微层裂物质不同时刻的密度空间分布图像及演化特征，且不同测试技术诊断结果半定量吻合。得到Sn材料微层裂物质的清晰物理图像，可为微层裂物理机理的认识和物理建模提供实验数据。     

微孔洞有核长大损伤演化模型研究

针对材料的层裂问题,从细观角度出发,提出微孔洞有核长大损伤演化模型假说。该模型包含损伤开始、演化和终止三个阶段,共有4个材料参数,分别是代表损伤开始发展的阈值应力的σ_0,损伤演化时损伤率对超阈值应力的依赖指数λ,损伤终止时材料发生层裂时的极限损伤D_c,和损伤持续的时间参数Ψ。通过对D6AC钢和45钢层裂实验进行计算分析,验证了本文提出的损伤演化模型假说的合理性。并结合试验,给出了模型中4个材料参数物理内涵、取值方法及影响规律。损伤发展的过程量λ对损伤影响最大,表明损伤演化过程并非简单的能量累积,其次是损伤阈值应力σ_0,极限损伤D_c和损伤持续的时间参数Ψ对损伤影响最小。     

45#钢的损伤演化方程和层裂准则研究

通过唯象分析和细观物理统计相结合的方法建立了一种韧性材料的损伤演化方程。在试验结果和内变量理论的基础上得到了45#钢的含损伤热—粘塑性本构关系。用有限差分方法计算了45#钢平板撞击所产生的应力波传播规律、损伤演化规律及层裂进程。通过自由面速度历史的数值模拟,并基于计算结果与试验结果间的最佳一致性,得到了损伤演化方程中的材料参数和极限损伤数值,并以此为依据建立了材料的应力率层裂准则。     

晶粒尺寸对高纯铝板材层裂特性的影响

采用不同热处理工艺制备了3种晶粒尺寸（60、100、500 μm）的高纯铝板材,利用平板撞击实验研究了其层裂行为。通过改变飞片击靶速度,在靶板中实现初始层裂状态和完全层裂状态。基于自由面速度时程曲线和微损伤演化及断口显微形貌分析,讨论了晶粒尺寸对高纯铝板材层裂特性的影响规律。实验结果显示:（1）晶粒尺寸对高纯铝板材层裂特性的影响强烈依赖于冲击加载应力幅值,在低应力条件下,层裂强度与晶粒尺寸之间表现出反Hall-Petch关系,而在高应力条件下,晶粒尺寸对层裂强度几乎没有影响;（2）随着晶粒尺寸的增大,靶板损伤区微孔洞的尺寸和分布范围均增大,但数量显著减少,在微孔洞周围还发现比较严重的晶粒细化现象;（3）随着晶粒尺寸的增大,层裂微观机制从韧性沿晶断裂向准脆性沿晶断裂转变,且在断口上观察到少量随机分布的小圆球,归因于微孔洞长大和聚集过程中严重塑性变形引起的热效应。     

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。     

延性金属层裂自由面速度曲线特征多尺度模拟研究

以延性金属钽为研究对象,对钽在平板撞击下的层裂行为进行了多尺度下的数值模拟研究,从微观视角对自由面速度曲线上的典型特征进行了新的解读。在宏观尺度,对比分析了光滑粒子流体动力学法（smootfied particle hydrodynamics, SPH）与Lagrange网格法以及几种本构模型的模拟结果及其适用性。通过与实验数据的对比表明,Steinberg-Cochran-Guinan本构模型在层裂模拟中与实验数据吻合较好,通过改变加载条件获得了不同应变率下的自由面速度曲线,分析了不同应变率下的自由面速度曲线中的典型特征。在微观尺度,采用分子动力学方法获得层裂区域内损伤演化情况,揭示了宏观尺度自由面速度曲线典型特征所蕴含的物理内涵。分析表明,层裂表现为材料内部微孔洞形核、长大和聚集的损伤演化过程,自由面速度曲线上的典型特征与层裂区域的损伤演化过程存在密切关联。Pullback信号是层裂区域内微孔洞形核的宏观表征;自由面速度曲线的下降幅值在一定程度上反映了微孔洞的形核条件,由此计算得到的层裂强度实际上是微孔洞的形核强度。此外,Pullback信号后的速度回跳速率反映了微损伤演化的速率。     

平纹编织陶瓷基复合材料面内剪切细观损伤行为研究

采用约西佩斯库(Iosipescu)纯剪切试件,研究了平纹编织SiC/SiC和C/SiC复合材料的面内剪切应力-应变行为和细观损伤特性.通过试验获得了材料不同方向上的单调和迟滞应力-应变行为,对比分析了两种材料的剪切损伤特性,结果表明材料的剪切损伤演化规律受热残余应力水平影响严重.由试件断口电镜扫描结果发现剪切加载状态下桥连纤维承受显著的弯曲载荷和变形,据此提出了纤维弯曲承载机制,并结合裂纹闭合效应分阶段阐释了材料的剪切迟滞环形状.基于材料的剪切细观损伤机制,通过两个损伤变量表征了材料的剪切损伤演化进程,得到了材料的面内剪切细观损伤演化模型.对比发现2D-C/SiC复合材料45°方向基体裂纹的起裂应力明显小于2D-SiC/SiC复合材料,而两者0°/90°方向裂纹的起裂应力基本相同.      

延性金属层裂模型比较

在平面一维弹塑性流动有限差分计算程序中加入4种延性金属层裂模型，对平板撞击层裂实验进行数值模拟。结果表明:简单最大拉伸应力模型和简单损伤累积模型能定性反映层裂的物理现象，由于忽略损伤对本构的影响，计算结果和实验有偏差，但模型要求参数较少，对于一些精度要求不是很高的工程问题，可以采用；从材料损伤断裂物理本质出发，采用微损伤统计方法得到的NAG模型和封加波损伤度函数模型，能很好地再现实测的自由面速度剖面,数值计算结果与实验吻合很好。     

Microdamage of a nonlinear elastic material in combined stress state

The structural theory of short-term damage is used to study the coupled processes of deformation and microdamage of a physically nonlinear material in a combined stress state. The basis for the analysis is the stochastic elasticity equations for a physically nonlinear porous medium. Damage in a microvolume of the material is assumed to occur in accordance with the Huber-Mises failure criterion. The balance equation for damaged microvolumes is derived and added to the macrostress-macrostrain relations to produce a closed-form system of equations. It describes the coupled processes of nonlinear deformation and microdamage of the porous material. Algorithms are developed for calculating the dependence of microdamage on macrostresses and macrostrains and plotting stress-strain curves for a homogeneous material under either biaxial normal loading or combined normal and tangential loading. The plots are analyzed depending on the type of stress state __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 11, pp. 30–39, November 2006.     

Weibull modulus for diverse strength due to sample-specificity

By sample specificity it is meant that specimens with the same nominal material parameters and tested under the same environmental conditions may exhibit different behavior with diversified strength. Such an effect has been widely observed in the testing of material failure and is usually attributed to the heterogeneity of material at the mesoscopic level. The degree with which mesoscopic heterogeneity affects macroscopic failure is still not clear. Recently, the problem has been examined by making use of statistical ensemble evolution of dynamical system and the mesoscopic stress re-distribution model (SRD). Sample specificity was observed for non-global mean stress field models, such as the cluster mean field model, stress concentration at tip of microdamage, etc. Certain heterogeneity of microdamage could be sensitive to particular SRD leading to domino type of coalescence. Such an effect could start from the microdamage heterogeneity and then be magnified to other scale levels. This trans-scale sensitivity is the origin of sample specificity. The sample specificity leads to a failure probability Φ_N with a transitional region 0<Φ_N<1, so that globally stable and catastrophic modes could co-exist. It is found that the scatter in strength can fit the Weibull distribution very well. Hence, the Weibull modulus is indicative of sample specificity. Numerical results obtained from the SRD for different non-global mean stress fields show that Weibull modulus increases with increasing sample span and influence region of microdamage.     

Coupled processes of deformation and long-term damage of layered materials under thermal loading

The failure criterion for a microvolume is characterized by its stress-rupture strength. It is determined by the dependence of the time to brittle fracture on the difference between the equivalent stress and its limit, which is the ultimate strength, according to the Schleicher–Nadai failure criterion, and assumed to be a random function of coordinates. An equation of damage (porosity) balance in the layers at an arbitrary time is formulated taking into account the thermal component. Algorithms of calculating the time dependence of microdamage and macrostresses are developed. Corresponding curves are plotted. The effect of temperature on the deformation and microdamage of the layers is studied     

Coupled processes of deformation and long-term damage of fibrous materials under thermal loading

A theory of long-term damage of fibrous composites under thermal loading is set up. The damage of the matrix is modeled by randomly dispersed micropores. The failure criterion for a microvolume is characterized by its stress-rupture strength. It is determined by the dependence of the time to brittle fracture on the difference between the equivalent stress and its limit, which is the ultimate strength, according to the Schleicher–Nadai failure criterion, and assumed to be a random function of coordinates. An equation of damage (porosity) balance in the matrix at an arbitrary time is formulated taking into account the thermal component. Algorithms of calculating the time dependence of microdamage and macrostresses are developed. Corresponding curves are plotted. The effect of temperature on the deformation and microdamage of the material is studied     

Deformation and long-term damage of orthotropic composites with limited stress-rupture microstrength

The theory of long-term microdamage of homogeneous materials based on the mechanics of stochastically inhomogeneous materials is generalized to a composite with orthotropic inclusions. The damage of the composite components is modeled by randomly dispersed micropores. The damage criterion for a microvolume is characterized by its stress-rupture strength. It is determined by the dependence of the time to brittle failure on the difference between the equivalent stress and its limit, which is the tensile strength, according to the Huber–Mises criterion, and assumed to be a random function of coordinates. Given macrostresses or macrostrains, an equation of damage (porosity) balance in the composite components at an arbitrary time is derived. The time dependence of microdamage and macrostresses or macrostrains in a discrete-fiber-reinforced composite with limited stress-rupture microstrength described by a fractional-power function is plotted     

Long-term damage of discrete-fiber-reinforced composites with transversely isotropic inclusions and stress-rupture microstrength described by an exponential power function

The theory of long-term damage of homogeneous materials, which is based on the equations of the mechanics of stochastically inhomogeneous materials, is generalized to discrete-fiber-reinforced composite materials. The microdamage of the composite components is modeled by randomly dispersed micropores. The failure criterion for a microvolume is characterized by its stress-rupture strength. It is determined by the dependence of the time to brittle failure on the difference between the equivalent stress and its limit. Given macrostresses and macrostrains, an equation of damage (porosity) balance in the composite components at an arbitrary time is formulated. The time dependence of microdamage and macrostresses or macrostrains is established in the case of stress-rupture microstrength described by an exponential power function Translated from Prikladnaya Mekhanika, Vol. 45, No. 2, pp. 19–29, February 2009.     

Mesomechanics of deformation and short-term damage of linear elastic homogeneous and composite materials

The structural theory of microdamage of homogeneous and composite materials is generalized. The theory is based on the equations and methods of the mechanics of microinhomogeneous bodies with stochastic structure. A single microdamage is modeled by a quasispherical pore empty or filled with particles of a damaged material. The accumulation of microdamages under increasing loading is modeled as increasing porosity. The damage within a single microvolume is governed by the Huber-Mises or Schleicher-Nadai failure criterion. The ultimate strength is assumed to be a random function of coordinates with power-law or Weibull one-point distribution. The stress-strain state and effective elastic properties of a composite with microdamaged components are determined using the stochastic equations of elasticity. The equations of deformation and microdamage and the porosity balance equation constitute a closed-form system of equations. The solution is found iteratively using conditional moments. The effect of temperature on the coupled processes of deformation and microdamage is taken into account. Algorithms for plotting the dependences of microdamage and macrostresses on macrostrains for composites of different structure are developed. The effect of temperature and strength of damaged material on the stress-strain and microdamage curves is examined __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 6, pp. 3–42, June 2007.     

Coupled processes of deformation and damage of composites with orthotropic inclusions and unbounded rupture-stress function

The theory of long-term damage of homogeneous materials, which is based on the equations of the mechanics of stochastically inhomogeneous materials, is generalized to composite materials reinforced with orthotropic ellipsoidal inclusions. The microdamage of the composite components is modeled by randomly dispersed micropores. The failure criterion for a microvolume is characterized by its stress-rupture strength. It is determined by the dependence of the time to brittle failure on the difference between the equivalent stress and its limit, which is the tensile strength, according to the Huber–Mises criterion, and assumed to be a random function of coordinates. Given macrostresses or macrostrains, an equation of porosity balance in the composite components at an arbitrary time is formulated. The time dependence of microdamage and macrostresses or macrostrains is established in the case of unlimited stress-rupture microstrength described by an exponential power function     

Interfacial friction in the debonded structural cell of particulate rubber composites

The role of the interface friction in formation of mechanical behavior of structural cells is examined. A method for calculation of the stress–strain state induced by the interface friction within the debonded structural cells is presented. Features of the structural stresses and strains are presented and the localities of the microdamage onsets are established. Effective properties of cells are determined and their dependence on the interface friction is demonstrated.