用能量图形面积法计算非线性弹性材料任意加载方式的能量释放率

从能量释放率G的定义出发,用图解法,即能量图形面积法,分别对线弹性材料和非线性弹性材料,以及在固定位移,或固定载荷,或任意加载方式的情况下,推导出能量释放率的计算公式.证明不同加载方式下的非线性弹性材料的能量释放率,在用能量图形面积法极限求导时,其数值是一样的.     

功能梯度材料裂纹能量释放率

 提出一个评价功能梯度材料裂纹扩展能量释放率的简单方法， 用双悬臂梁柔度法推导了典型梯度材料内裂纹沿梯度方向扩展的能量 释放率解析表达式，用算例分析了裂纹扩展方向不同能量释放率的差 别.     

三维编织CMC的弯曲断裂研究

从界面断裂的角度出发，对三维编织CMC的断裂作了理论研究和数值分析，对于三点弯曲试件，通过数值拟合修正了能量释放率G的理论表达式中的自由常数A，同时也研究了材料的各个参变量对于断裂韧性的影响，由此得出了一个基本完善的三点弯曲试件断裂韧性G的理论公式，该能量释放率方法可以应用于单试件的试验计算，与断裂韧性的柔度标定方法相比，该方法一方面可以减少试验件数量；另一方面，试验结果显示出在试件切口尺雨处于0．4≤a/W≤0.5时，可以获得比较稳定的断裂韧性值。     

橡胶—钢粘接界面断裂韧性实验研究

采用双悬臂夹层梁试样,对橡胶—钢粘接界面的I型边缘裂纹的扩展情况及断裂韧性进行实验研究.通过声发射技术的监测将裂纹扩展划分为无损伤、开裂、失稳扩展三个阶段,把线弹性断裂力学中的柔度和能量释放率引入到橡胶—钢粘接界面断裂韧性的计算中,由实验测出裂纹的张开位移计算出夹层梁的柔度曲线,进而得到了能量释放率曲线,并对断裂韧性的变化规律进行了分析.     

仪器柔度标定误差对两种压入测试方法的精度影响

针对目前最具代表性的两种压入测试方法:Oliver-Pharr方法和Ma方法,通过有限元数值模拟分析了仪器柔度标定误差对测试精度的影响.结果表明仪器柔度的标定精度直接影响压入测试结果的准确度,尤其是当材料较软且压入深度较大时更为显著;对同一材料,压入载荷越大,由仪器柔度标定误差引入的压入测试结果误差越大;在同一压入深度下,针对不同材料,由仪器柔度标定误差引入的压入测试结果误差差别不大;就测试方法而言,Ma方法具有比Oliver-Pharr方法更高的精度和更低的仪器柔度敏感性.     

复合型断裂的非线性能量分析

对于复合型断裂的线弹性分析,根据最大能量释放率判据,得到了一般的G-K关系,对于带有任意取向的裂纹并受双向加载的有限板的非线性能量释放率,本文给出了理论表达式,同时,本文用数值结果表示了非线性能量释放率的双向加载影响。     

黏弹性功能梯度材料裂纹问题的有限元方法

针对组分材料体积含量任意分布的黏弹性功能梯度材料裂纹问题建立有限元分析途径. 通过Laplace变换,将黏弹性问题转化到象空间中求解,基于反映材料非均匀的梯度单元和裂纹尖端奇异特性的奇异单元计算象空间中的位移、应力和应变场,应用虚拟裂纹闭合方法得到应变能释放率,分别由应力和应变能释放率确定应力强度因子. 给出这些断裂参量在物理空间和象空间之间的对应关系,由数值逆变换求出其在物理空间的相应值. 文中分析两端均匀受拉的黏弹性边裂纹板条,首先针对松弛模量表示为空间函数和时间函数乘积的特殊梯度材料进行计算,结合对应原理验证方法的有效性. 然后分析组分材料体积含量具有任意梯度分布的情形,由Mori-Tanaka方法预测象空间中的等效松弛模量. 计算结果表明,蠕变加载条件下,应变能释放率随时间增加,其增大程度与黏弹性组分材料体积含量相关. 由于梯度材料的非均匀黏弹性性质,产生应力重新分布,导致应力强度因子随时间变化,其变化范围与组分材料的体积含量分布方式有关.     

电可通纳米尺度孔边均布多裂纹的电弹断裂分析

解析研究了面内电载荷和反平面机械载荷作用下压电体中纳米尺度圆孔边均布电可通多裂纹问题的断裂性能。基于Gurtin-Murdoch表面弹性理论,利用保角映射方法和复变弹性理论给出了裂纹尖端电弹场分布、电弹场强度因子及能量释放率的解析结果。阐述了无量纲电弹场强度因子、无量纲能量释放率的尺寸依赖效应,讨论了裂纹数量和缺陷几何参数对无量纲场强度因子和无量纲能量释放率的影响。结果表明：无量纲电弹场强度因子和无量纲能量释放率具有显著的尺寸依赖效应;考虑表面效应,孔径和裂纹长度相当时,电弹场强度因子达到最大;裂纹/孔径比对电弹场强度因子随裂纹数量变化的制约会随着裂纹数量的增加而逐渐消失;过大或过小的裂纹孔径比会削弱裂纹长度对能量释放率的影响。     

电可通纳米尺度孔边均布多裂纹的电弹断裂分析

解析研究了面内电载荷和反平面机械载荷作用下压电体中纳米尺度圆孔边均布电可通多裂纹问题的断裂性能。基于Gurtin-Murdoch表面弹性理论,利用保角映射方法和复变弹性理论给出了裂纹尖端电弹场分布、电弹场强度因子及能量释放率的解析结果。阐述了无量纲电弹场强度因子、无量纲能量释放率的尺寸依赖效应,讨论了裂纹数量和缺陷几何参数对无量纲场强度因子和无量纲能量释放率的影响。结果表明：无量纲电弹场强度因子和无量纲能量释放率具有显著的尺寸依赖效应;考虑表面效应,孔径和裂纹长度相当时,电弹场强度因子达到最大;裂纹/孔径比对电弹场强度因子随裂纹数量变化的制约会随着裂纹数量的增加而逐渐消失;过大或过小的裂纹孔径比会削弱裂纹长度对能量释放率的影响。     

能量释放率G的两种解法的统一

在线弹性断裂力学中,从能量的观点考察裂纹的扩展过程是研究破坏机理的一条有效途径.如果裂纹扩展过程中系统所释放出的能量,足以提供裂纹扩展所需要的能量,则裂纹便发生扩展.能量释放率G 就是描述裂纹扩展物体能量变化的一个参数,它是线弹性断裂力学中一个很重要的概念.在一些文献和断裂...     

On crack-tip strain energy release rate in non-principal directions of elasticity for simple layer plate of composite materials

In this paper,the fracture problem in non-principal directions of elasticity for a simple layer plate of linear-elastic orthotropic composite materials is studied.The formulae of transformation between characteristic roots,coefficients of elastic compliances in non-principal directions of elasticity and corresponding parameters in principal directions of elasticity are derived.Then,the computing formulae of strain energy release rate under skew-symmetric loading in terms of engineering parameters for principal directions of elasticity are obtained by substituting crack-tip stresses and displacements into the basic formula of the strain energy release rate.     

Fracture saturation and critical thickness in layered materials

Opening-mode fractures in layered materials are commonly found in a layer with uniform spacing that is nearly proportional to the thickness of the fractured layer. However, when fracture spacing reduces to a certain value, fracture density is saturated and no new fracture forms. If a loading condition is fixed, there exists a critical thickness of the layer, below which no fracture forms. This paper presents a three-layer model, containing a weak layer between two stronger layers, to interpret the fracture saturation and critical thickness of layered materials. Using elastic governing equations and a weak form stress boundary condition, a closed-form solution of elastic fields in the weak layer is derived and the energy release rate for opening-mode fracture is obtained. Interestingly, the normal stress between such fractures undergoes a transition from tensile to compressive with increasing applied tensile loading, which causes fracture saturation. Explicit expressions of critical fracture-spacing-to-layer-thickness ratio and critical thickness are derived for fracture saturation and fracture free conditions, respectively. Comparison with the existing numerical simulation results demonstrates the capability of this model. This explicit, analytical solution is useful to structural design and geosciences.     

Proposition d'un paramètre énergétique de rupture pour les matériaux dissipatifs

We suggest an energetic fracture parameter for non elastic materials. This one is presented in a domain integral, and founded on the release rate of the total mechanical energy received by a notched solid, using a domain derivation method. This parameter is proposed for a large class of loading and materials described by internal variables. It is shown that this parameter is reduced to the Rice–Cherepanov integral when the material is either elastic or elastoplastic and submitted to proportional loading.     

金属材料的强度与应力-应变关系的球压入测试方法

压入法获取材料单轴应力-应变关系和抗拉强度对服役结构完整性评价有重要的基础意义.假定材料均匀连续、各向同性、应力应变关系符合Hollomon律,基于能量等效假定,即代表性体积单元(representativevolume element, RVE)的vonMises等效和有效变形域内能量中值等效假定,本文提出了关联材料载荷、深度、球压头直径和Hollomon律的四参数半解析球压入(semi-analyticalspherical indentation,SSI)模型.通过球压入载荷-深度试验关系获得材料的应力-应变关系和抗拉强度.考虑压入过程中的损伤效应,针对金属材料提出了用于球压入测试的材料弹性模量修正模型.对11种延性金属材料完成了球压入试验,采用本文提出的球压入试验方法测到的弹性模量、应力-应变关系和抗拉强度与单轴拉伸试验结果吻合良好.      

Channel cracking in inelastic film/substrate systems

Studies on channel cracking are generally limited to elastic films on elastic or inelastic substrates. There are important applications were the cracking process involves extensive plasticity in both the film and substrate, however. In this work steady-state channel cracking in inelastic thin-film bilayers undergoing large-scale yielding from thermal or mechanical loading is studied with the aid of a plane-strain FEA. The plasticity of the film and substrate, represented by a Ramberg–Osgood constitutive law, each increases the energy release rate (ERR) relative to the linearly-elastic case. This effect is more pronounced under mechanical loading where the entire bilayer undergoes large-scale yielding. To help assess the analytic approach some fragmentation tests are performed using a well-bonding epoxy/aluminum system. The analysis reproduced well the observed dependence of crack initiation strain on film thickness.Ultra-thin films may be well represented by an elastic-perfectly plastic response. For such films on a flexible support the ERR remains fixed as the applied strain exceeds the yield strain of the film. Accordingly, a critical coating thickness exists below which no channel cracking is possible. The explicit relations and graphical data presented may be used for optimal design of such structures against premature failure as well as for determining fracture energy of ductile thin films.     

The energy release rate for hygrothermal coupling elastic materials

In the fracture problems of hydrophilic elastic materials under coupling effects of heat conduction, moisture diffusion and mechanical deformation, the conventional J-integral is no longer path independent. The value of J is unequal to the energy release rate in hygrothermal coupling cases. In the present paper, we derived a general form of the energy release rate for hygrothermal fracture problems of the hydrophilic elastic materials on the basis of energy balance equation in cracked areas. By introducing the constitutive relations and the essential equations of irreversible thermodynamics, a specific expression of the energy release rate was obtained, and the expression can be reformmulated as path independent integrals, which is equivalent to the energy release rate of the fracture body. The path independence of the integrals is then verified numerically. The project supported by the Key Project of Chinese Ministry of Education (03145) and the Science Fund of Southwest Jiaotong University. The English text was polished by Yunming Chen.     

Effects of Seawater and Low Temperatures on Polymeric Foam Core Material

Polymeric composite sandwich structures, often manufactured using a thick foam core material and thin composite facings, are of significant interest in naval applications. This paper summarizes the coupled effect of sea water and low temperature on the mechanical properties of closed cell polymeric H100 foam core material. The study considers the effects of harsh sea environmental conditions on the fracture and deformation behavior of such a foam material under complex loading conditions that include tension, torsion, compression, and true-triaxial stress paths. Mechanical testing techniques are developed using coupon samples of suitable geometry that minimize grip effects on these low density complex foam materials, along with information associated with the observed cross-anisotropic behavior. Interfacial delamination fracture response for the sandwich structures due to the combined effects of sea water and low temperature are evaluated and the associated degradation in critical energy release rate for delamination is found to be substantial. Experimental data for H100 foam cores associated with moisture induced expansional strains are also included.     

EXPERIMENTAL INVESTIGATIONS OF STRENGTH,TOUGHNESS AND FAILURE MECHANISM OF THE METAL/EPOXY/METAL ADHESIVE SYSTEM

本文系统地开展了金属/环氧/金属胶结体系的强韧机理及失效行为实验研究,针对铝合金圆棒与铝合金圆棒通过环氧树脂胶层的各种斜截面方向粘结,实验观测了该体系的拉伸变形和失效行为,测量了界面失效载荷对胶层厚度和粘结界面倾斜角的依赖关系;通过引入胶结界面平均正应力、平均剪应力、平均正应变、平均剪应变等概念,可对界面失效强度进行测量,获得界面强度与界面粘结角度以及胶层厚度的关系,进而获得了铝合金/环氧胶层/铝合金体系的强度失效面以及胶结界面的断裂能和胶结体系的能量释放率.上述研究结果为深入认识金属胶结体系的强韧性能和失效机制提供了科学依据,对金属胶结体系的优化设计和性能评判具有重要指导意义.研究结果表明,铝合金/环氧胶层/铝合金体系的拉伸失效总体呈弹脆性破坏特征,失效表现为胶层粘结界面的断裂,失效强度和界面断裂能在胶层厚度为百微米量级时表现出强烈的尺度效应：界面粘结强度随着胶层厚度的减小而显著增大,临界状态的平均正应力和平均剪应力在强度破坏面上近似位于同一圆上,界面断裂能随着胶层厚度的减小而显著减小;与此同时,界面失效强度和界面断裂能也密切依赖于界面粘结角度.     

花岗岩的加载速率效应及能量机制研究

加载速率对岩石的力学性质以及变形破坏方式具有重要的影响。基于MTS810电液伺服材料试验系统与PCI-2声发射仪对岩样进行不同加载速率作用下的单轴压缩和声发射试验。研究结果表明：（1）在各级加载速率作用下,岩样单轴压缩应力-应变曲线大致经历了压密、弹性、屈服、破坏四个阶段。岩样峰后曲线在加载速率为0.001~0.01 mm/s时出现台阶型分段跌落状,在加载速率为0.01~0.1 mm/s时呈现光滑、陡峭的连续曲线。（2）岩样峰值强度、弹性模量随加载速率的增加而增大,与加载速率对数均呈现三次多项式拟合关系。峰值应变随加载速率的增加而减小,与加载速率对数呈现线性拟合关系。（3）随着加载速率由0.001mm/s增加至0.1mm/s,岩样吸收的总应变能 具有波动性,可释放的弹性应变能 增幅60.42%,耗散应变能 降幅 66.38%, 增幅43.33%, 降幅66.67%,岩样破裂模式由拉剪破坏逐渐向张拉劈裂破坏过渡,岩样破裂块数增多。（4）加载速率为0.001~0.1 mm/s时,岩样破坏方式有所不同,但破坏为同一类损伤过程。单轴压缩状态下,能量耗散使得岩样损伤致使强度丧失,而能量释放使得岩样宏观破裂面贯通,并向着能量释放的方向张裂或弹射破坏。