平面应变脆性损伤裂纹场分析

根据Ｂｕｉ的脆性损伤理论，本文研究Ｉ型拉伸裂纹的平面应变过程区及其力学场。计及裂尖材料的有限变形，细致的有限元分析给出了小范围屈服条件下两种典型的损伤区形貌。     

脆性损伤材料裂纹尖端的局部解

本文利用Mazars和Lemaitre提出的混凝土脆性损伤模型,求得了裂纹尖端应力、应变及损伤的局部解.对手Ⅲ型及不可压缩平面应变Ⅰ型裂纹,其尖端场的构造和理想塑性材料相类似.指出由于丧失了应力全连续条件,从而损伤边界不能由局部解定出.     

一种固体推进剂破坏的细观实验研究

固体推进剂是一种颗粒填充高能聚合物,其破坏时所表现出的一些行为和金属的破坏相比,有明显不同之处。本文利用扫描电镜,给出了受载情况下固体推进剂试件的损伤发展以及裂纹扩展过程。结果表明,损伤的发展过程也就是微裂纹区扩展及微裂纹密度加大的过程,而裂纹扩展过程中的慢速扩展和亚临界扩展的最大区别则是其裂尖损伤区范围不同,同时也表明,裂纹尖端和边缘的微裂纹损伤区尺寸已不容忽略。     

非晶态高聚物裂尖银纹损伤场

在非晶态高聚物裂端塑性区引入银纹损伤，提出了一个修正的Dugdale模型，并由它确定塑性区的大小，算例表明，银纹损伤导致了塑性区深度的增加。此外，在Dugdale模型下研究了稳态扩展的端塑性区，在裂纹缓慢扩展、小范围银纹化以及材料为线粘弹性等假定下，由能量原理得到了控制裂纹生长的一个非线性微分一积分方程，从中看到银纹损伤的影响十分显著。     

偏心裂纹板在裂纹面受一对集中拉应力作用时弹塑性解析解

利用裂纹线场方法对理想弹塑性材料偏心裂纹板在裂纹面受一对集中拉力问题进行了弹塑性分析,并且获得了理论解．这个解包括：裂纹线附近弹塑性边界上的单位法向矢量,裂纹线附近的弹塑性解析解、最大塑性区长度、裂纹线上的塑性区长度随荷载的变化规律及其承载力．该分析不受小范围屈服假设的限制,并且不附加假使条件．结果在裂纹线附近足够精确．     

考虑应力松驰复合型裂纹顶端塑性区分析

Ｓｈｉｈ［１］应用奇异单元，获得了不考虑应力松驰小范围屈服条件下复合型裂纹尖端塑性区形状。Ｚ．Ｚ．Ｚｕ等［２］采用Ｒｉｃｅ［５］给出的裂纹尖端应力关系式，利用有限元分析获得了不考虑应力松驰下复合型裂纹尖端塑性区，本文基于静力学中内力与外力平衡条件，用线弹性的全场解代替局部解，给出了考虑应力松驰下复合型裂纹尖端塑性区边界方程，获得了考虑应力松驰下的任意方向的塑性区尺寸及塑性区形状     

裂纹起始扩展的弹塑性场

本文分析了裂纹扩展之前Ⅰ、Ⅱ混合型应力应变场演变的自相似性,并采用理想弹塑性模型给出了自相似解基本方程及边界条件.对v=1/2情况给出了尖端附近小范围应力应变的渐近解,同时讨论了满塑性区的存在条件.     

基于压电振动能量俘获的弯曲结构损伤监测研究

建立了含裂纹损伤的曲梁压电能量俘获系统在强迫振动下的动力学模型. 基于Prescott型压电曲梁力电耦合振动方程的解析解和裂纹截面处的连续性条件, 求解了含裂纹损伤的压电曲梁的格林函数. 根据线性叠加原理, 对含裂纹的力电耦合模型的系统方程解耦, 得到强迫振动下含裂纹损伤的曲梁压电俘能器的输出电压. 在得到模型的强迫振动解析解后, 提出逆方法检测结构中的裂纹损伤, 这一检测方法适用于处于振动状态下的结构. 在数值计算中, 令裂纹深度为零, 通过对比本文的解析解与现有文献中的解析解, 验证了本文解的有效性. 分别分析了含裂纹损伤的压电曲梁的电压响应与裂纹深度、裂纹位置、材料的几何参数以及阻尼之间的关系. 研究结果表明: 裂纹的存在对曲梁式压电俘能器的影响比直梁式更加复杂; 裂纹出现时, 损伤曲梁在健康曲梁的一阶频率值处一定会出现波动并被激励出二阶频率, 此时的二阶频率是开路中健康压电曲梁的一阶频率值; 通过对电压响应的检测可以确定的损伤裂纹的深度和在结构中出现的位置范围; 利用振动问题的解来检测压电曲梁的健康状况是可行且准确的.      

关于理想弹塑性介质中Ⅲ型稳恒扩展裂纹位移场

Chitaley与McClintock给出了理想弹塑性介质中Ⅲ型稳恒扩展裂纹的应力渐近解和小范围屈服情况的数值解。Rice曾指出文献[1]数值解所给出的位移是错误的。本文将给出变形与位移的渐近解。     

改进的Irwin模型及裂尖塑性区对断裂行为的影响

本文研究了小范围屈服条件下I型裂纹尖端塑性区对断裂行为的影响.Irwin模型假设塑性区外奇异应力场分布是弹性解的平移,并将塑性区的一部分加上原有裂纹视为等效裂纹.这样得到的等效应力强度因子总是大于相应的线弹性解的应力强度因子,这与塑性区的增韧作用相悖.为了考察塑性区对裂纹尖端附近应力分布的影响,本文提出在塑性影响区内,裂纹延长线上奇异应力分布与线弹性奇异应力场静力等效的原则.在此基础上建立了改进的Irwin模型,并导出了衡量塑性区屏蔽效应的显式表达式,定量地解释了塑性区的屏蔽效应,本文结果与基于相变增韧理论的方法得到的结果在趋势上一致.     

The anti-plane shear field in an infinite slab of elasto-damaged material with a semi-infinite crack

This paper deals with an infinite slab with a semi-infinite crack, which is subjected to the anti-plane sheark _III field at infinity. The slab is made of an elasto-damaged material. Analytical solution is obtained by use of conformal mapping. The shape of damaged-zone, the dissipative energy, the shear opening displacement on the crack surface and several stress distribution curves are given. The far field condition is checked, The asymptotic behavior near the crack-tip is given. The project supported by National Natural Science Foundation of China     

桁架式钢筋混凝土叠合板式墙抗爆性能实验

为研究桁架式叠合板式墙的抗爆性能,进行了2块桁架式叠合板式墙和2块现浇板式墙在多次冲击荷载作用下的对比实验,分析了各试件的破坏过程、变形(刚度)、承载力、强度及裂缝分布形态。结果表明:桁架式叠合板式墙与现浇板式墙相比,爆炸破坏过程相似;爆炸荷载小时,试件处于弹性状态,两者刚度基本一致;开裂后,现浇板式墙比叠合板式墙刚度降低明显快,桁架钢筋能有效抑制裂缝扩展,且试件并未出现剪切破坏。说明桁架式叠合板式墙的整体性能较好,叠合板式墙的抗爆性能优于现浇板式墙。     

On the damage field near crack tips in a filled polymer

Dynamic-acoustic imaging techniques have been used to delineate, in terms of specific acoustic attenuation, the dewetting damage field near the tips of extending cracks in uniaxially strained thin sheets of an inert-solid rocket-propellant composition. The results show that before crack extension begins, the material damage near the crack tips extends over a large volume of the specimen. From the geometry of the damage field it is deduced that shear strains contribute to the volume dilatation observed near crack tips. The implications of the results for judging the validity of commonly used fracture mechanics models for crack propagation in solid rocket propellants are discussed.     

Elastoplastic near field solution for mode II crack loaded by remote shear stress in an infinite plate

A suitable elastic stress field near the crack line which satisfied the far field boundary conditions and the boundary conditions of the crack surfaces has been obtained and successful analysis has been made of a near crack line field for an infinite elastic-perfectly plastic medium containing a quasi-statically propagating plane stress crack subjected to far field shear stress. It is shown that the solutions of the problem of mode II crack loaded by remote shear stress from the Westergaard method in some previous papers is used as the elastic stress field near the crack line, are inappropriate.     

Intersonic crack propagation in homogeneous media under shear-dominated loading: theoretical analysis

The mechanics of cohesive failure under mixed-mode loading is investigated for the case of a steadily propagating subsonic and intersonic dynamic crack subjected to a follower tensile and shear distributed load. The cohesive failure model chosen in this study is rate independent but accounts for the coupling between normal and tangential damage. Special emphasis is placed here on mixed-mode cases with predominantly shear loading. The analysis shows that the size of the mixed-mode cohesive zone is smaller than that obtained in the pure shear case. The relative extent of the shear and tensile cohesive damage zones depends on the crack speed and the mode mixity. In the intersonic regime, the failure process takes place exclusively in shear, even under remote mixed-mode loading conditions.     

The singular elastostatic field due to a crack in rubberlike materials

Within the framework of finite-strain elastostatics an asymptotic analysis is carried out in order to calculate the singular field near the crack tip in a slab under conditions of plane deformation. A class of Ogden-Ball hyperelastic rubberlike materials and general loading conditions ensuring vanishing tractions on the crack faces near the crack tip are considered. It is shown that the singular deformation field near the crack tip can be specified by applying a rigid body rotation with a subsequent parallel translation to a so-called canonical field. The adjective canonical is adopted here to denote the field with symmetrically opening crack faces, just resembling the displacement field of the symmetric mode in linear elastic fracture mechanics. No analogy with the antisymmetric mode is possible, and the crack equilibrium criterion requires only one stress intensity factor to be determined.     

Crack shielding and material deterioration in damaged materials: an antiplane shear fracture problem

Summary A simple damage evolution model is proposed for a quasibrittle material in the framework of continuum damage mechanics. The model is used to obtain a closed form solution for a mode-III stationary crack under small scale damage conditions. It is found that the crack tip stress intensity factor is reduced, i.e., the crack is shielded by the damage. However, this shielding effect is completely offset by the material deterioration caused by the damage. It also holds for steady state crack growth. When the most effective shielding is reached for the stationary crack, the zone dominated by the stress intensity factor shrinks to the crack tip. The results for the antiplane shear problem should shed some light on the in- plane fracture problem. Received 4 August 1997; accepted for publication 7 October 1997     

基于裂纹附加模态Timoshenko梁的裂纹损伤识别

将梁中横向裂纹等效为无质量扭转弹簧，并忽略其对梁剪切变形的影响，得到的具有任意裂纹数目Timoshenko 梁自振模态的统一显示解析表达式．将裂纹梁的自振模态分为基本模态和裂纹附加模态，利用最小二乘拟合，建立了利用裂纹附加模态函数的梁裂纹损伤识别方法．通过数值模拟开展了简支单裂纹梁以及悬臂和固支双裂纹梁等的裂纹损伤识别，考察了测量误差对损伤识别的影响，数值结果表明本文所提出的裂纹损伤识别方法对裂纹位置的识别精度高于对裂纹损伤程度的识别精度；随着测量误差的增加，裂纹位置及裂纹损伤程度的识别误差增加，但仍在可接受的范围内，故该裂纹损伤识别方法在实际工程中具有一定的应用价值．     

The dynamic stress intensity factor analysis of adhesively bonded material interface crack with damage under shear loading

This paper studies the dynamic stress intensity factor (DSIF) at the interface in an adhesive joint under shear loading. Material damage is considered. By introducing the dislocation density function and using the integral transform, the problem is reduced to algebraic equations and can be solved with the collocation dots method in the Laplace domain. Time response of DSIF is calculated with the inverse Laplace integral transform. The results show that the mode Ⅱ DSIF increases with the shear relaxation parameter, shear module and Poisson ratio, while decreases with the swell relaxation parameter. Damage shielding only occurs at the initial stage of crack propagation. The singular index of crack tip is -0.5 and independent on the material parameters, damage conditions of materials, and time. The oscillatory index is controlled by viscoelastic material parameters.     

A rate-dependent damage model for brittle materials based on the dominant crack

A rate-dependent, continuum damage model is developed for brittle materials under dynamic loading. This model improves on the approach (ISOSCM) of [Addessio, F.L., Johnson, J.N., 1990. A constitutive model for the dynamic response of brittle materials. Journal of Applied Physics 67, 3275–3286] in several respects. (1) A new damage surface is found by applying the generalized Griffith instability criterion to the dominant crack (having the most unstable orientation), rather than by averaging the instability condition over all crack orientations as done previously. The new surface removes a discontinuity in the damage surface in ISOSCM when the pressure changes sign. (2) The strain due to crack opening is more consistent with crack mechanics, with only the tensile principal stresses contributing to the crack opening strain. This is achieved by incorporating a projection operator in the equation for the crack opening strain. One consequence of incorporating the projection operator is a prediction of shear dilatancy, which is not accounted for in ISOSCM. (3) The evolution of damage, which is based on the energy-release rate for the dominant crack, has a physical basis, whereas in the previous approach the damage growth rate was assumed to be an exponential function of the distance from the stress state to the damage surface without specific physical justification.An implicit algorithm has been developed so that a larger time step can be used than with the explicit algorithm used in ISOSCM. The numerical results of a silicon carbide (SiC) ceramic under several loading paths (hydrostatic tension/compression, uniaxial strain, uniaxial stress, and shear) and strain rates are presented to illustrate the main features of the model.