Modeling of Bonding at an Interface Crack

A mechanical and mathematical model is suggested for an interface crack with bonding in its end zones. Normal and shear bond tractions occurring under the action of the external loads are searched for by solving a system of two singular integrodifferential equations. The stress intensity factors at the crack tip are calculated taking the compensating action of the bonds into account. Energetic characteristics of the interface crack (the deformation energy release rate and the rate of the energy absorption by the bonds) are analyzed. A sensitivity analysis is performed of the force and energetic characteristics of the interface crack to the end zone size, bond compliance and limit stretching. This revised version was published online in July 2006 with corrections to the Cover Date.     

复合材料的界面强度及测定方法

研制出一种显微脱粘法界面强度的测定仪，在０－０．９８Ｎ范围内可以匀速连续加载，精度为０．９８ｍＮ。用它测定了Ｎｉｃａｌｏｎ ＳｉＣ纤维增强７７４０硅硼酸盐玻璃复合材料的界面强度，研究了纤维直径，相邻纤维间距对界面强度和界面强度对复合材料断裂韧性的影响。     

50th Anniversary Article: Review on Interface Fracture and Delamination of Composites

In this review paper, a methodology for measuring the interface fracture toughness of a crack between two isotropic, homogeneous materials and a delamination between two laminae of unidirectional composite materials of differing directions is presented. Four cases are considered. Two isotropic material pairs are described: glass/epoxy and two ceramic clays. Similar studies are presented for two cross‐ply laminates: 0°/90° and +45°/?45. The Brazilian disk specimen was used to carry out mixed mode fracture tests. The load and crack or delamination length at fracture were measured and used in a finite element analysis to determine the displacement field. An interaction energy or M‐integral was used to obtain the stress intensity factors at failure. These in turn were employed to calculate the critical interface energy release rate and two phase angles ψ and φ, which measure the mode mixity. For the M‐integral and for each interface crack or delamination, the first term of the asymptotic solution of the fields is required. For two isotropic materials, these solutions are well known. For the laminates described here, they were determined by the Stroh and Lekhnittski formalisms. A failure criterion determined from first principles is presented. The values of , ψ and φ are used to specify the criterion for each material pair. A statistical analysis is presented, which predicts a 5% probability of failure.     

Interface fracture of polymer films: blister test experiments and modelling

The interface fracture between a rigid substrate and polymer film is investigated in this work using pressurised blister test experiments and modelling. The interface crack growth is studied for two different types of polymer films: stiff and compliant ones. The pressurised blister test is used to provide critical pressure-crack length curves for different loading media (water and electrolyte solutions) and loading rates. Two different analytical approaches and a numerical modelling concept are used to determine the critical total energy release rate as a function of the crack length (crack resistance curve or R-curve). A relatively flat R-curve is observed for the system with the stiff polymer film, whilst R-curve for the compliant film system exhibits an increasing tendency. The mixed-mode fracture behaviour occurs for both investigated polymer film systems, as shown by the value of the mixed-mode angle that is constant for all investigated crack lengths. R-curves are nearly unaffected by different loading media, whereas the loading rate has a strong influence on the interface fracture of the compliant file system. Finite element method-based prediction of the total energy release rate is in good agreement with that obtained from analytical expressions.     

Constraint effects on the elastic–plastic fracture behaviour in strain gradient solids

ABSTRACT Crack‐tip constraint effects (or T‐stress effects) on the elastic–plastic fracture behaviour in strain gradient materials are analysed in the present study. The T‐stress effects on the stress distributions along the plane ahead of the stationary and growing crack tip, respectively, are analysed by using the Fleck and Hutchinson strain gradient plasticity formation. For a steadily growing crack, the T‐stress effects on the steady‐state fracture toughness are analysed by adopting the embedded fracture process zone model. In addition, the analysis for the growing crack is applied to an interfacial cracking experiment for a metal/ceramic system, and the material length‐scale parameter appearing in the strain gradient plasticity theory is predicted. In the present analyses, a new finite element method specially designed for strain gradient problems by Wei and Hutchinson is adopted.     

The effect of plasticity on dynamic crack growth across an interface

The effect of plasticity on the growth of a crack originating in an elastic solid across an interface and into an elastic-viscoplastic solid is analyzed numerically. The analyses are carried out within a framework where the continuum is characterized by two constitutive relations; one relating the stress and strain in the bulk material and the other relating the traction and separation across a specified set of cohesive surfaces. Crack initiation, crack growth and crack arrest arise naturally as a consequence of the imposed loading, without a priori assumptions concerning criteria for crack growth and for crack path selection. Full transient analyses are carried out. Various values of initial flow strength and cohesive strength of the elastic-viscoplastic solid and of cohesive strength of the interface are considered. With the ratio of cohesive strength of the elastic-viscoplastic solid to cohesive strength of the interface fixed, increasing the ratio of cohesive strength to initial flow strength for the elastic-viscoplastic solid is found to promote crack deflection into the interface.     

过渡层对含氢非晶碳膜生长的影响

本文利用射频等离子体增强化学气相沉积（RFPECVD）工艺在不锈钢基底上制备了含氢非晶碳膜（a-C：H膜）。在沉积碳膜之前，首先在基底表面预先沉积了Ti／TiC、Ti／TiN和Ti／TiN／TiC等过渡层以提高膜基结合力。利用激光Raman光谱分析了过渡层对a-C：H膜生长过程及膜中sp^3含量的影响。实验结果表明，采用Ti／TiN／TiC过渡层时所制备的a-C：H膜中sp^3含量最多，同时膜基结合力最大。     

Crack-tip Caustics at a bi-Material Interface

The size and the shape of crack-tip caustics, at a bi-material interface, under static load, are studied. When the crack-tip, which is perpendicular to interface, is at the interface of the bi-material, the caustic depends on the properties of the two materials. Thus, the caustic is divided into two branches. The size of the two branches of the caustic mainly depends on the elastic modulus and Poisson's ratios of the two materials. This revised version was published online in July 2006 with corrections to the Cover Date.     

First-Principles Study of the Polar TiC／Ti Interface

The interface structure, work of adhesion, and bonding character of the polar TiC/Ti interface have been examined by the first-principles density functional plane-wave pseudopotential calculations. Both Ti- and C-terminated interfaces including six different interface structures were calculated, which present quite different features. For the Ti-terminated interface, the interfacial Ti-Ti bond has a strong metallic and weak covalent character; while for the C-terminated interface, the interfacial bond is a strong polar covalent interaction between the Ti-3d and C-2p orbital.The work of adhesion of C-terminated interface is nearly 9 J/m2 stronger than that of the Ti-terminated. It is found that each termination has relatively large work of adhesion, which is consistent with other polar interfaces.     

Mixed-mode fracture analyses of plastically-deforming adhesive joints

A mode-dependent embedded-process-zone (EPZ) model has been developed and used to simulate the mixed-mode fracture of plastically deforming adhesive joints. Mode-I and mode-II fracture parameters obtained from previous work have been combined with a mixed-mode failure criterion to provide quantitative predictions of the deformation and fracture of mixed-mode geometries. These numerical calculations have been shown to provide excellent quantitative predictions for two geometries that undergo large-scale plastic deformation: asymmetric T-peel specimens and single lap-shear joints. Details of the deformed shapes, loads, displacements and crack propagation have all been captured reasonably well by the calculations.     

界面监测系统对复合材料界面最佳性能的评价

本文采用自行建立的纤维增强复合材料界面监测系统研究了纤维/树脂基体间的界面强度及其与复合材料力学性能的关系。结果表明,界面剪切强度是决定复合材料层间剪切强度与断裂韧性的一个关键的临界参数。     

(SiCP/Cu)-铜箔叠层复合材料的制备与组织性能

采用浸涂法和热压烧结法制备了（SiC_P/Cu）-铜箔叠层复合材料,研究了SiC_P含量对材料组织结构、拉伸性能和断裂韧性的影响。结果表明,制备的（SiC_P/Cu）-铜箔叠层复合材料层间厚度均匀,界面结合力良好,增强颗粒SiC能够弥散分布于黏结相中和界面处。随着SiC_P体积分数的增加,（SiC_P/Cu）-铜箔叠层复合材料的抗拉强度和屈服强度都先增加后降低,当SiC_P的体积分数为20vol%（总体积为100）时,其抗拉强度和屈服强度达到最大值,分别为226.5 MPa和113.1 MPa,断裂方式主要为韧性断裂和部分脆性解理断裂。裂纹扩展方向平行于层界面时,材料的断裂韧性随SiC_P体积分数的增加略有减小,SiC_P体积分数为15%时达到最大值16.96 MPa·m^1/2;裂纹扩展方向垂直于层界面时,（SiC_P/Cu）-铜箔叠层复合材料的断裂韧性随SiC_P体积分数的增加逐渐减小,SiC_P体积分数为15%时达到最大值12.51 MPa·m^1/2。     

Crack Growth Across a Strength Mismatched Bimaterial Interface

Crack growth across an interface between materials with different strength is examined by a cohesive zone model. The two materials have identical elastic properties but different fracture process properties, or different yield stresses, which is modeled by different cohesive stresses. The fracture criteria is a critical crack opening displacement. Load is represented by a stress intensity factor defining a remote square root singular stress field. The results show that the ratio between the cohesive stresses of the two materials primarily determines the behavior of the critical stress intensity factor. When the crack approaches a material with a higher cohesive stress the crack tip is shielded, but if the crack approaches a material with smaller critical crack opening displacement the maximum level of shielding is determined by the ratio between the critical crack opening displacements. When a crack approaches a material with a lower cohesive stress it is exposed to an amplified load. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interface Corner Failure Analysis of Joint Strength: Effect of Adherend Stiffness

The strength of cylindrical butt joints, fabricated by bonding either aluminum or steel adherends together with an epoxy adhesive, has been determined for a wide range of bond thicknesses. Joint strength varied significantly with bond thickness. The measured strength of joints with steel adherends varied as the inverse cube root of bond thickness, while the strength of joints with aluminum adherends varied as the inverse fourth root of bond thickness. This bond thickness dependence is accurately predicted by an analysis that assumes failure occurs at a critical value of the interface corner stress intensity factor. The difference in the measured joint strength-bond thickness relation for joints with aluminum and steel adherends is a consequence of the difference in the order of the interface corner stress singularity.     

显微镜的放大倍数对陶瓷材料断裂韧性测量的影响

压痕法是测量材料断裂韧性一种经济实用的方法 ,该方法的最大缺点是测量的准确性受压痕裂纹长度测量精度的影响较大。本文详细讨论了显微镜放大倍数对材料断裂韧性测量结果的影响。研究发现 :在光学显微镜的分辨率之内 ,其放大倍数越大 ,测得的裂纹长度越长 ,材料的断裂韧性越低 ,反之则越高。因此要使测量结果具有可比性应规定显微镜的放大倍数     

Interface fracture properties of a bimaterial ceramic composite

In this investigation, the interface fracture toughness is measured for a pair of ceramic clays which are joined together. The Brazilian disk specimen, which provides a wide range of mode mixity, is employed to measure these properties. Calibration equations relating the stress intensity factors to the applied load and geometry are determined by means of the finite element method and the M-integral. The effect of residual stresses is accounted for by employing a weight function to obtain the contribution to the stress intensity factors. Total stress intensity factors are obtained by superposition. These are employed to determine the critical interface energy release rate as a function of mode mixity from critical data obtained from tests carried out on the Brazilian disk specimens. An energy release rate fracture criterion is compared to the experimental results for .     

A methodology for measuring interface fracture properties of composite materials

A methodology is presented for measuring interface fracture properties of composite materials. A bimaterial Brazilian disk specimen with a crack along the interface is employed. The specimen is analyzed by means of the finite element method and a conservative integral to determine stress intensity factors as a function of loading angle and crack length. A weight function is employed to determine the effect of residual curing stresses on the stress intensity factors. These are combined to determine the critical interface energy release rate _ic as a function of stress intensity phase angle for tests carried out on a glass/epoxy material pair.     

激光层裂法测量复合材料界面拉伸强度研究进展

本文介绍激光层裂法检测复合材料界面拉伸强度的基本原理与实验方法 ,并从该测量方法的几个关键技术 ;应力波生成与传播的数学模型、应力波形的测量与临界值的判定 ,评述该技术及其研究进展的情况。     

VARI成型泡沫夹芯壁板结构界面性能

针对真空辅助成型工艺(VARI)制备的泡沫夹芯壁板面-芯界面粘接强度较低的问题, 提出铺放本体树脂胶膜和对芯材进行打孔两种解决方案。通过无损检测、三点弯曲力学性能测试、计算机模拟树脂充模流动以及微观界面结构观察, 探究两种方案的可行性及改善效果, 分析了胶膜的有无和厚度、打孔工艺参数对界面性能的影响。结果表明, 在不加入胶膜时界面强度最高, 胶膜厚度在0.5 mm时, 无损检测显示的界面缺陷最少, 胶膜厚度达到2 mm后界面质量下降; 合理设计芯材的打孔行、间距可以促进树脂充模流动, 形成质量好的连续界面, 同时还能提高结构刚度。