Growth of a penny-shaped crack with a nonsmall fracture process zone in a composite

The paper studies the stress rupture behavior of a reinforced viscoelastic composite through which a penny-shaped mode I crack propagates under a constant load. The composite has hexagonal symmetry and consists of elastic isotropic fibers and viscoelastic isotropic matrix. The material is modeled as a transversely isotropic homogeneous viscoelastic medium with effective characteristics. The crack is in the isotropy plane. The ring-shaped fracture process zone at the crack front is modeled by a modified Dugdale zone with time-dependent stresses. The viscoelastic properties of the matrix are characterized using a resolvent integral operator. Use is made of Volterra's principle, the method of operator continued fractions, and the theory of precritical crack growth in viscoelastic bodies. The problem is reduced to nonlinear integral equations. Numerical results are obtained for certain components of the composite, constant volume fractions, and different fracture strengths Translated from Prikladnaya Mekhanika, Vol. 44, No. 8, pp. 45–51, August 2008.     

Lattice model applied to the fracture of large strain composite

An improved lattice model is developed to simulate the fracture behavior of large strain composite. Based on equivalent relation between the continuum and the lattice model for small deformation, the equivalent relation between large strain continuum and improved lattice model is established by introducing large strain elastic law into the lattice system. The theory can simulate large deformation. The program of large strain lattice model simulates several representative problem of large strain elasticity. The results agree with the theoretical results. Assumed failure criterion is used to describe the fracture process of large strain elasticity and large strain composite. The improved lattice model provides an effective method for fracture simulation of large strain composite.     

Stability of plates made of a particulate composite with nonlinear elastic matrix and damaged inclusions

The bifurcation instability problem for rectangular plates made of particulate composites with nonlinear elastic matrix and damaged inclusions is formulated and solved __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 7, pp. 79–89, July 2007.     

Stability of cylindrical shells made of a particulate composite with nonlinear elastic inclusions and damageable matrix

The bifurcation instability problem for cylindrical shells made of particulate composites with nonlinear elastic inclusions and damageable matrix is formulated and solved __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 10, pp. 68–79, October 2007.     

Stability of cylindrical shells made of a particulate composite with nonlinear elastic matrix and damaged inclusions

The bifurcation instability problem for cylindrical shells made of particulate composites with nonlinear elastic matrix and damaged inclusions is formulated and solved __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 8, pp. 80–91, August 2007.     

Stability of shells of revolution made of a particulate composite with nonlinear elastic inclusions and damageable matrix

The bifurcation instability problem for shells of revolution made of particulate composites with nonlinear elastic inclusions and damageable matrix is formulated and solved __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 11, pp. 55–65, November 2007.     

Growth of a mode II crack in an orthotropic plate made of a viscoelastic composite material

The growth of a straight mode II crack in a viscoelastic orthotropic plate is examined. The plate material is modeled by a viscoelastic anisotropic medium. The shear displacement in the fracture process zone is determined as a function of time using the corresponding elastic solution, the Volterra principle, and the method of operator continued functions. The time dependence of the crack length is constructed as integral equations of three phases of stable growth. The solution of these equations gives kinetic curves __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 9, pp. 89–97, September 2006.     

Stress wave interference effects during fracture of silicon micromachined specimens

We report on unique measurements of multiple microsecond-duration arrest periods during the propagation of high speed (>1 km s⁻¹) cracks in micromachined single-crystal silicon specimens. These events were recorded electronically and in physical features remaining on the fracture plane. Using time-of-flight calculations, we have determined that these arrest patterns are due to the interference of boundary-reflected stress waves with the propagating crack tip. The specimen size, the measurement method, and the low acoustic attenuation in cyrstalline silicon facilitated the observation of these phenomena.     

Inelastic material behavior and fracture mechanics: a variational approach

Summary A variational principle is presented, which relates the macroscopic fracture response of a mechanical component to its microscopic, inelastic material behavior. The principle allows a comparison between the crack driving force, expressed by the J-integral, and an integral expression of the fracture resistance. On this basis, the critical values of J are calculated for a Griffith crack under mixed-mode loading. The preliminary check with data available in literature shows a fairly good agreement. Received 18 July 1998; accepted for publication 9 February 1999     

Weight function theory and variational formulations for three-dimensional plane elastic cracks advancing

The weight function theory for three-dimensional elastic crack analysis received great attention after the work of Rice (1985, 1989). Several applications have been considered since then, particularly in the context of configurational stability, crack path prediction, stress intensity factor expansions, perturbation approaches. In all cases, a specific hypothesis has been made on the variation of crack shape, in order to formulate the problem in terms of Cauchy principal value. In the present note, such hypothesis is further investigated and consequences discussed. A variational statement given in Salvadori and Fantoni (2013a) is thus rephrased in terms of weight functions. Its discrete formulation shows the potential to accurate approximation of crack front propagation.     

一种碳纤维织物增强复合材料应变率相关的各向异性强度准则

为了获得一种碳纤维二维正交平纹机织布增强树脂基复合材料在一维应变状态下的强度准则,在已完成的准静态和动态压缩实验的基础上,拟合出了单轴压缩下三个主方向上的计及应变率的应力-应变关系式,进而得到初始屈服应力和压缩破坏强度与应变率相关性表达式。依据该表达式,得到了该复合材料在一维应变下考虑应变率效应的Tsai-Hill屈服强度和破坏强度准则方程。通过计算,考察了Tsai-Hill屈服强度和破坏强度准则随应变率的变化规律。结果表明,本文中研究的复合材料的强度性能,不但存在应变率效应,而且这种效应是各向异性的。     

Simulation of size effects by a phase field model for fracture

In phase field fracture models the value of the order parameter distinguishes between broken and undamaged material. At crack faces the order parameter interpolates smoothly between these two states of the material, which can be regarded as phases. The crack evolution follows implicitly from the time integration of an evolution equation of the order parameter, which is coupled to the mechanical field equations. Among other phenomena phase field fracture models are able to reproduce crack nucleation in initially sound materials. For a 1D setting it has been shown that crack nucleation is triggered by the loss of stability of the unfractured, spatially homogeneous solution, and that the stability point depends on the size of the considered structure. This work numerically investigates to which extend size effects are reproduced by the 2D phase field model. Exemplarily, a finite element study of the hole size effect is performed and the simulation results are compared to experimental data.     

空心微珠/Al复合材料的动态压缩力学性能和吸能特性

利用分离式霍普金森压杆（split Hopkinson pressure bar,SHPB）系统对空心微珠体积分数为0.4的空心微珠/1199Al复合泡沫在1 700~2 900s^-1应变率范围内的动态压缩力学性能、吸能性能进行了研究,还利用SEM扫描电镜对压缩试件断口进行微观组织分析,与准静态条件下材料的压缩力学性能及压缩变形机制进行了对比。结果表明,空心微珠/1199Al复合泡沫是一种应变率敏感材料,与准静态结果相比,在高应变率下复合材料的流动应力和塑性应变有明显的增大,应变率硬化效应对复合材料的流动应力的影响明显大于应变硬化的影响。复合材料的准静态和动态压缩变形机制存在一定差异,动态载荷作用下,空心微珠/1199Al复合泡沫内部空心微珠的压缩和基体材料的充填同时发生,组分之间具有良好的协调变形能力。

     

Fractal geometry concerned with stable and dynamic fracture mechanics

Fractal modeling of the rugged crack geometry is considered for the stable and dynamic fracture mechanics characterizing the morphology of a fracture surface and the influence of its growth. It is shown that the fractal dimension has a strong influence on the rising of the R-curve in brittle materials. For the unstable Griffith–Mott’s approach or dynamical crack growth the fractal dimension has a strong influence on the velocity limit of the crack growth. It is also shown that the limit of crack velocity lowers with increasing surface ruggedness (higher fractal dimension D = 2 − H) explaining the intangibility of the Rayleigh wave velocity by the cracks.     

Impact response of a piezoelectric layered composite plate with a crack

The dynamic response of a central crack in a piezoelectric layered composite plate under normal impact is analyzed. The crack is oriented normally to the interfaces. The Laplace and Fourier transform techniques are used to formulate the problem in terms of a singular integral equation. The order of stress singularity around the tip of the terminated crack is also obtained. Numerical calculations are carried out, and the main results presented are the variations of the dynamic stress intensity factor and the dynamic energy density factor versus time as functions of the geometric parameters and the piezoelectric material properties of the layered composite plate.     

Experimental and numerical investigation of concrete properties effects on fracture toughness under complex loading

Abstract

This article is presenting the common experimental specimen for determining the fracture toughness of the first pure mode and second pure mode. The Notched beam is chosen from a presented common specimen in the form of three-point flexure beam and four-point flexure beam that were built in the concrete laboratory. For prevention of cracks growth, a critical load of first pure mode and the second pure mode of each specimen computed. Obtained results are used for computing the fracture toughness. For the purpose of investigating the effective fracture parameters in the suggested specimen, finite element analysis on the mentioned geometry is performed. Obtained results show that different parameters are effective on the fracture toughness including crack length, cement percentage, water and the thickness of biggest used aggregate in the sand. Also with changing each of these parameters, the fracture mechanic properties are changed. Each of these effects is examined separately in this article and the conclusions presented in tables and figures.

Communicated by Dumitru Caruntu.