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1.
根据界面剪胀与Ⅱ型断裂能间的关系,给出构造含剪胀效应张力-位移关系的新途径,该方法先假定Ⅱ型张力-位移关系,再计算界面剪胀函数,从而更易于应用。通过定义基于能量和界面不连续位移的4个损伤变量,给出含剪胀效应的损伤张力-位移关系表示形式,使模型不仅能模拟单调加载问题,而且可模拟反复加载问题。对界面在受压状态下的切向粘结强度、法向位移和摩擦作用分别进行了讨论,给出了相应的计算方法或取值建议。最后通过一个张力-位移关系的实例讨论了界面压力作用、复合模式开裂、卸载-再加载行为和接触罚刚度对法向位移的影响等模型性质。 相似文献
2.
Viggo Tvergaard 《Engineering Fracture Mechanics》2003,70(14):1859-1868
A cohesive zone model that describes tangential separation as well as normal separation along an interface is reviewed. The model is based on nonlinear traction-separation relations between the normal and tangential components of the interface tractions and relative displacements. To illustrate the application of the cohesive zone model in studies of material failure or crack growth, analyses of matrix-fibre debonding in metal matrix composites are presented, taking into account effects of residual stresses or of nonlocal plasticity for the matrix. Also studies of interface crack growth under mixed mode conditions are discussed. 相似文献
3.
Chinmaya R. DandekarYung C. Shin 《Composites Science and Technology》2011,71(3):350-356
Molecular dynamics simulations are carried out to study the effect of porosity and temperature on a ductile-brittle interface under tensile and shear loadings. Traditionally the interface is characterized by a cohesive zone model (CZM) with the traction-separation law assumed or parameterized through experiments, where the experimental determination of the shape of the CZM has proven to be difficult. In this study a traction-separation law is thus obtained for an alumina-aluminum composite system by conducting molecular dynamics simulations. A statistical approach is suggested to characterize the cohesive strength in the parameterized traction-separation law via the Weibull distribution, which consequently governs the interface behavior of the composite. 相似文献
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Randolph R. Settgast 《Engineering Fracture Mechanics》2009,76(11):1614-3241
Embedding cohesive surfaces into finite element models is a widely used technique for the numerical simulation of material separation (i.e. crack propagation). Typically, a traction-separation law is specified that relates the magnitude of the cohesive traction to the distance between the separating surfaces. Thus the characterization of fracture in such models is not directly coupled to the bulk constitutive response, in the sense that the cohesive traction does not explicitly depend on material stretching in the plane of the fracture surface. In this work, an initially-rigid cohesive-traction formulation that is coupled to the surrounding continuum is introduced as a further development of the cohesive zone idea. In this model, the traction-separation law - and therefore the fracture phenomenology - derives directly from the bulk constitutive law. The immediate goal is an improved cohesive zone framework that naturally and logically initiates cohesive separation behavior, and couples its evolution to the material state in the region of the crack tip. A cohesive element based on this model is implemented in an explicit three-dimensional finite element code. Proof-of-concept analyses using both linear elastic and Gurson void growth constitutive relations are presented. A three-point bend simulation is found to give good agreement with experimental results. 相似文献
6.
Ingo Scheider 《Engineering Fracture Mechanics》2009,76(10):1450-1459
The paper addresses the determination of the traction-separation law of the cohesive model on a micromechanical basis. For this task, a specific failure mechanism, i.e. ductile damage consisting of void nucleation, growth and coalescence, is investigated. An approach already described in the literature is to transfer the deformation behaviour of the simplest representative volume element, i.e. a single voided unit cell, to the cohesive interface. After reviewing the existing approach, its main drawback, namely that the unit cell contains both, deformation and damage of a material point whereas the cohesive model should contain the material separation only, is addressed. A new approach is presented, in which the behaviour of a unit cell is partitioned in its elasto-plastic deformation and damage, and only the damage contribution is applied as the traction-separation law for the cohesive model. Instead of modelling the voided unit cell, a single element with Gurson type plastic potential for the damage has been employed as a reference for the behaviour at the microscale. A study with fracture specimens, C(T) and M(T), made of an engineering Aluminium alloy shows that the new approach exhibits a better transferability than the existing one. 相似文献
7.
The purpose of this work was to examine the feasibility of using fracture process zone models for extracting the adhesive
fracture energy of thin films on a thick substrate from circular blister experiments that involve a substantial amount of
inelastic deformation in the thin film. The interface produced by vapor depositing polyimide on aluminum formed the basis
of the experiments that were conducted. The experiments were conducted in volume control while the pressure history and the
corresponding three dimensional blister shape were measured. The analysis accounted for the nonlinear kinematics and material
behavior of the polyimide film and included a traction-separation law for the interface. The traction-separation law for the
interface was calibrated in an iterative manner by comparing measured pressure-volume responses and crack opening displacements.
The adhesive fracture energy obtained from the selected traction-separation law was reasonable considering that fracture occurred
in an interphase region. It was bounded by values that were obtained from elastic analyses (with updated kinematics) of the
type performed by Gent and Lewandowski (1987) and Chu et al. (1992 a, b).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
For prediction of the fatigue crack growth (FCG) behavior under cyclic compression, a plasticity-corrected stress intensity factor (PC-SIF) range ΔKpc is proposed on the basis of plastic zone toughening theory. The FCG behaviors in cyclic compression, and the effects of load ratio, preloading and mean load, are well predicted by this new mechanical driving force parameter. Comparisons with experimental data showed that the proposed PC-SIF range ΔKpc is an effective single mechanical parameter capable of describing the FCG behavior under different cyclic compressive loading conditions. 相似文献
9.
An semi-analytical formulation based on the cohesive crack model is proposed to describe the phenomenon of fatigue crack growth
along an interface. Since the process of material separation under cyclic loading is physically governed by cumulative damage,
the material deterioration due to fatigue is taken into account in terms of interfacial cohesive properties degradation. More
specifically, the damage increment is determined by the current separation and a history variable. The damage variable is
introduced into the constitutive cohesive crack law in order to capture the history-dependent property of fatigue. Parametric
studies are presented to understand the influences of the two parameters entering the damage evolution law. An application
to a pre-cracked double-cantilever beam is discussed. The model is validated by experimental data. Finally, the effect of
using different shapes of the cohesive crack law is illustrated 相似文献
10.
为了研究异种材料界面的开裂过程,在Srensen等人工作的基础上,给出一种含剪胀效应张力-位移关系的构造方法。在界面受拉状态下,通过预先给定的剪胀函数及法向张力-位移关系导出切向张力-位移关系;在界面受压状态下,将切向张力分解为粘结力和摩擦力,摩擦力的大小与法向压力和粘结界面的破坏程度相关。该方法的结果解释了Srensen模型中切向张力-位移关系不连续及其不符合一致关联准则的原因。为便于进行数值计算,给出了用于三维有限元模型的界面刚度矩阵计算方法。选取了一种特定形式的剪胀函数,并将法向张力-位移关系假定为分段线性形式和指数形式,分别求得对应的切向张力-位移关系。最后给出了两个工程应用的例子,数值模拟结果与试验数据吻合较好。 相似文献
11.
A new technique for evaluating fatigue-damage accumulation in shot-peened (SP) carbon steel based on variations in residual stress is proposed. Using findings from previous studies, a fatigue damage parameter for a material treated with SP based on the change in induced compressive residual stress (CRS) is examined. A plastic replica method with the focused ion beam (FIB) technique is used to assess the relationship between the residual stress state and the fatigue crack growth (FCG) behavior of SP specimens over the fatigue lifespan. It is found that the residual stress relaxation phenomenon can be used as an effective parameter for determining the fatigue damage growth, provided the residual stress relaxation rate of each mechanical load and the critical threshold relaxation boundary of each material is known. 相似文献
12.
Solder alloys of lead-rich composition have been commonly used as joining materials in electronic package. However, because of environmental concerns, lead-free solders will replace lead-rich solders more and more in the future. The fatigue characteristics of the solders used are most important in assessing the reliability of joints in electronic packaging. In the present study, the fatigue crack growth (FCG) behavior of a wide variety of solders of both lead-rich and lead-free types has been investigated under a range of mean stresses and frequencies. Both time dependent and time independent (cyclic dependent) behaviors were observed. In the cyclic dependent crack growth regime, the FCG rates could be expressed as a function of either ΔKeff or ΔJ. Further, the lead-free solders were found to have a higher resistance to FCG than did the lead-rich solders. In the time dependent crack growth regime, the FCG rates were found to be a function of C∗. The point of transition between time dependent and time independent behavior was found to depend on the homologous temperature and strength of the alloys. 相似文献
13.
There is a major interest in replacing cobalt binder in hardmetals (cemented carbides) aiming for materials with similar or even improved properties at a lower price. Nickel is one of the materials most commonly used as a binder alternative to cobalt in these metal-ceramic composites. However, knowledge on mechanical properties and particularly on fatigue behavior of Ni-base cemented carbides is relatively scarce. In this study, the fatigue mechanics and mechanisms of a fine grained WC–Ni grade is assessed. In doing so, fatigue crack growth (FCG) behavior and fatigue limit are determined, and the attained results are compared to corresponding fracture toughness and flexural strength. An analysis of the results within a fatigue mechanics framework permits to validate FCG threshold as the effective fracture toughness under cyclic loading. Experimentally determined data are then used to analyze the fatigue susceptibility of the studied material. It is found that the fatigue sensitivity of the WC–Ni hardmetal investigated is close to that previously reported for Co-base cemented carbides with alike binder mean free path. Additionally, fracture modes under stable and unstable crack growth conditions are inspected. It is evidenced that stable crack growth under cyclic loading within the nickel binder exhibit faceted, crystallographic features. This microscopic failure mode is rationalized on the basis of the comparable sizes of the cyclic plastic zone ahead of the crack tip and the characteristic microstructure length scale where fatigue degradation phenomena take place in hardmetals, i.e. the binder mean free path. 相似文献
14.
Fatigue crack growth behaviour of Ti-6 Al-4 V metal matrix/continuous SiC and B4C/B fibre composites
The fatigue crack growth (FCG) behaviour of SiC and B4C/B reinforced Ti-6 Al-4 V metal matrix composites loaded in the transverse direction as a function of modifications of the interface between the fibre and matrix was studied. The interface chemistry, modified by sulphur diffusion during thermal cycling treatment, changed the FCG in air, dry nitrogen and hydrogen environments when compared with the as-received specimens. The FCG rates tend to be higher in a humid environment. The SEM fractrography indicates that the FCG in humid air was by an increased amount of fibre splitting. The FCG in dry nitrogen environment was more often by interface debonding with some fibre splitting and fiber fracture. The FCG rates in dry hydrogen for both as-received and heat-treated specimens were intermediate between the observed rates for dry nitrogen and humid air. During FCG in laboratory air, the sulphur-enriched interface of the specimens thermal cycled in a sulphur environment reacts with the humidity in air to degrade the interface cohesion, resulting in complete separation of the interface from the matrix and the fibre at low strains. This inability of the interface to sustain any strain further increases the FCG rates in the matrix. The results show that the interface does transfer load during fatigue cycling either in an inert environment or if the interface has a minimal amount of impurities. 相似文献
15.
Shravan Gowrishankar Haixia Mei Kenneth M. Liechti Rui Huang 《International Journal of Fracture》2012,177(2):109-128
Traction-separation relations have been used to represent the adhesive interactions at bimaterial interfaces for contact and fracture analyses. There are a variety of methods for determining these relations, which are broadly sorted into iterative and direct methods. Here we compare the traction-separation relations for a silicon/epoxy interface extracted by two such methods. Interferometric measurements of the normal crack opening displacements near the crack front in a double-cantilever beam specimen were exploited along with an augmented analytical solution for J-integral as an illustration of the direct method. As an example of the iterative method, we relied on comparisons of measured crack length and normal crack opening displacements with numerical simulations obtained from two types of candidate traction-separation relations. It was found that the shape of the traction-separation relation, in addition to the interfacial toughness and strength, was needed to bring the numerical solutions into optimal registration with the measurements. On the other hand, the direct method lived up to its name in terms of ease of parameter extraction while providing a reasonable set of parameters. 相似文献
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本文总结了作者近来研究金属低温疲劳取得的进展,主要内容包括:疲劳极限的热激活模型、应变疲劳公式、疲劳始裂寿命和裂纹扩展速率的定量预测方法、疲劳裂纹扩展机制脆转模型。当室温下的疲劳极限和门槛植ΔK_(th)确定后,应用本文的方法可根据拉伸性能定量预测材料在低温下的疲劳极限、应变疲劳寿命、疲劳始裂寿命和裂纹扩展速率,并且不需要低温疲劳试验和经验修正。 相似文献
18.
Microstructure and fatigue crack growth behavior in tungsten inert gas welded DP780 dual-phase steel
《材料与设计》2015
The purpose of this study was to evaluate microstructural and mechanical change of DP780 steel after tungsten inert gas (TIG) welding and the influence of notch locations on the fatigue crack growth (FCG) behavior. The tempering of martensite in the sub-critical heat affected zone (HAZ) resulted in a lower hardness (~ 220 HV) compared to the base material (~ 270 HV), failure was found to originate in the soft HAZ during tensile test. The fusion zone (FZ) consisted of martensite and some acicular ferrite. The joint showed a superior tensile strength with a joint efficiency of 94.6%. The crack growth path of HAZ gradually deviated towards BM due to the asymmetrical plastic zone at the crack tip. The FCG rate of the crack transverse to the weld was fluctuant. The Paris model can describe the FCG rate of homogeneous material rather well, but it cannot precisely represent the FCG rate of heterogeneous material. The fatigue fracture surface showed that the stable expanding region was mainly characterized by typical fatigue striations in conjunction with secondary cracks; the rapid expanding region contained quasi-cleavage morphology and dimples. However, ductile fracture mechanism predominated with an increasing stress intensity factor range (ΔK). The final unstable failure fractograph was subtotal dimples. 相似文献
19.
S.C. Wu Q.B. Qin Y.N. Hu R. Branco C.H. Li C.J. Williams W.H. Zhang 《Fatigue & Fracture of Engineering Materials & Structures》2020,43(5):1051-1063
The microstructure, mechanical strength, and fatigue response of metal active gas (MAG) butt‐welded G20Mn5 cast steel was thoroughly investigated for exploring the service safety and reliability of new‐generation railway bogie frames. The fatigue properties of the matrix and welded joints were determined by both low‐ and high‐cycle service regimes. On the basis of nanoindentation testing, the fatigue crack growth (FCG) was derived by correlating with cyclic plastic response of microdomain materials across the MAG joint. The results show that the MAG induces considerable changes in microstructures and hardness of the G20Mn5 matrix and resultantly produces an overmatching welded joint but show comparatively low‐ and high‐cycle fatigue properties to as‐received material. The calculated threshold FCG range based on the Murakami model indicates that the maximum 1.5‐mm defect might be the cracking site subjected to fatigue loading from the structural integrity viewpoint. 相似文献