International Journal of Fracture最新文献

The present work aims to investigate the failure size effect on flattened disks containing an eccentric circular hole under mode I loading conditions. For this purpose, uniaxial compression tests are carried out on polymethyl methacrylate (PMMA) samples with holes. Depending on the hole radius and eccentricity, the energy release rate is either an increasing or decreasing function of the crack length, thus affecting the stability of crack propagation. Experimental results are interpreted and discussed through the coupled stress and energy criterion of Finite Fracture Mechanics. The approach lies on the assumption of a finite crack advance and it is implemented through the numerical estimation of the stress field and the Incremental Energy Release Rate functions. Finally, stability and crack speed propagation are discussed under the assumption of Linear Elastic Fracture Mechanics. Theoretical predictions reveal in agreement with experimental results thus demonstrating that the Coupled Criterion effectively captures the failure condition.

In the present paper, we extend results recently given by Ciavarella et al. (J Mech Phys Solids 169:105096, 2022) to show some actual calculations of the viscoelastic dissipation in a crack propagation at constant speed in a finite size specimen. It is usually believed that the cohesive models introduced by Knauss and Schapery and the dissipation-based theories introduced by de Gennes and Persson-Brener give very similar results for steady state crack propagation in viscoelastic materials, where usually only the asymptotic singular field is used for the stress. We show however that dissipation and the energy balance never reach a steady state, despite the constant propagation crack rate and stress intensity factor. Our loading protocol permits a rigorous solution, and implies a short phase with constant specimen elongation rate, but then possibly a very long phase of constant or decreasing elongation, which differs from typical experiments. For the external work we are therefore unable to use the de Gennes and Persson-Brener theories which suggested that the increase of effective fracture energy would go up to the ratio of instantaneous to relaxed modulus, at very fast rates. We show viscoelastic dissipation is in general a transient quantity, which can vary by orders of magnitude while the stress intensity factor is kept constant, and is largely affected by dissipation in the bulk rather than at the crack tip. The total work to break a specimen apart is found also to be possibly arbitrarily large for quite a large range of intermediate crack growth rates.

Williams asymptotic expansions are widely used to represent mechanical fields at the vicinity of crack-tips in plane elastic media. For practical applications, series solutions have to be truncated and it is believed that a better accuracy can be achieved by retaining more terms in the summations. The influence of the truncation on the accuracy can be quantified comparing truncated closed-form Williams series solutions available for some fracture configurations to their corresponding complex exact counterparts. The computation of 2D absolute error fields reveals astonishing patterns in which appear points with numerically zero error implying the existence of loci where truncated series can provide exact results. These loci of exactness gather on curves emanating from the crack-tips and pointing towards the outside of series convergence disks. An analytical investigation of this phenomenon allows to relate the number and tangency angle at the crack-tip of these curves to the number and values of the zeros of Williams series angular eigenfunctions. Beyond its analytical interest in the understanding of Williams series framework, this property of exactness for truncated series can also help to improve the accuracy of experimental and computational techniques based on Williams series.

The existing mechanical dicing process of single crystalline Silicon Carbide (SiC) is one of the main factors limiting the development of semiconductor process, which could be replaced by laser scribing potentially. To achieve efficient and low-damage SiC separation, the cracking behavior of SiC after laser grooving should be well understood and controllable. Since the laser grooving including thermal ablation and meltage solidification, the cracking behavior of the scribed SiC would be different to the original single crystal SiC. In this paper, cohesive zone model (CZM) is used to quantitively represent the cracking behavior of the nano-laser scribed SiC. The separation after scribing was conducted in a three-point bending (3 PB) fixture to characterize the cracking behavior. Therefore, by inverting the load–displacement curves of 3 PB with CZM embedded finite element model, the cohesive behavior is characterized by bilinear traction–separation law, which illustrated the whole cracking process numerically. The methodology established in current paper gives way to understand the SiC scribing and cracking process with quantitative cohesive parameters.

Construction of the Kitagawa–Takahashi (K–T) diagram requires inputs of two material properties, namely, endurance limit and threshold stress intensity range, ΔK_th. Both are sensitive to applied stress ratio. The effect of stress ratio on endurance limit is well known. Unfortunately, crack closure, associated with the nature of conventional testing practice obscures the effect of stress ratio on intrinsic, closure free ΔK_th that would apply to natural crack like defects and short cracks. This study was made possible by the development of a new test method to characterize closure free threshold conditions under controlled near-tip residual stress conditions that essentially determine near-tip stress ratio at threshold. A procedure is described to construct the K–T diagram, using ΔK_th values corrected for stress ratio and applicable to pre-existing defects and short cracks at notches that are unlikely to see closure. As a case study, a K–T diagram valid for different applied stress ratios is constructed for titanium alloy Ti-6Al-4V.

The global rubber industry is seeking alternatives to the widely-used antiozonant, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), due to its environmental toxicity concerns when used in automobile tires. These substantial research and development efforts on new antiozonants for rubber are hindered by a general inability to characterize the fundamental physical parameter of ozone-induced tearing energy threshold for crack growth, which underlies the practical ozone resistance of rubber products. Therefore, this paper presents, for the first time, a novel experimental–numerical combined approach to determine the tearing energy threshold in rubber exposed to ozone, which is a key criterion for assessing the resistance of rubber to ozone crack growth. The approach is based on in-situ optical analysis of ozone crack growth on the rubber surface and the determination of the crack growth rate when the rubber is stretched. Subsequently, the growth rates form the basis for calculating the energy release rates at the crack tips using the finite element method in Ansys software. By comparing the calculated energy release rates and experimentally measured crack growth rates, the energy release rate interval corresponding to the threshold tearing energy is determined. Based on this approach, the tearing energy threshold for carbon black reinforced natural rubber exposed to ozone was found to be a maximum of 2.12 J/m². This value is 96% lower than the threshold for the non-ozone-exposed specimens. In conclusion, this novel methodology was able to determine the ozone threshold tearing energy and represents a powerful, unique tool for an efficient future development of environmentally friendly antiozonants.

This research utilizes both single crystal and polycrystalline models to probe the fatigue crack propagation mechanism in pure silver via molecular dynamics (MD) simulations. A comprehensive validation approach at both micro and macro scales, incorporating transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and compact tension (CT) specimen fatigue testing, is developed to verify the reliability of simulation models and results. Simulation findings indicate that the initial crack orientation significantly influences crack propagation. As the crack advances within the crystal, two primary crack propagation mechanisms are discerned: (1) nano-voids appear at the crack tip, and the crack propagates by continuously aggregating with the nano-voids ahead; (2) the formation of Stair-rod dislocations and V-shape stacking faults due to dislocation reactions and slip band movements impedes crack propagation, accompanied by the dislocation reaction of Shockley partial dislocations ((tfrac{1}{6}) <112>) generating Hirth dislocations ((tfrac{1}{6}) <110>). The dislocation reaction is verified through the dislocation analysis of the crack tip area of the CT specimen after fatigue experiment by using TEM. In addition, the results of this study show that the angle between the direction of crack propagation and the grain boundary affects the fatigue crack propagation, e.g. when the angle is less than 60°, the crack rapidly propagates along the grain boundary. The orientation distribution function (ODF) results of EBSD can verify that the polycrystalline model containing 30 grains is a reliable model for the MD simulation of behavior of the crack tip of CT specimen. Lastly, the Paris law constants for pure silver are determined as m = 3.72 and lg C = − 10.77, providing a reference for the fatigue analysis and life prediction of silver components or silver soldering pots in engineering applications.

This article presents a novel two-dimensional quadrilateral solid finite element model, enhanced by incompatible modes and embedded strong discontinuity for simulation of localized failure in quasi-brittle heterogeneous multi-phase materials. The focus of interest lies in the development of discontinuities and cracks induced by both tensile and compressive loads, considering mesoscale material constituents and very complex meshes. Multiple cracks are initiated within elements using local Gauss-point criteria for crack initiation. Rankine and Maximum shear stress criteria control the crack initiation, location, and orientation depending solely on the stress state within the finite element. The model identifies distinct clusters of cracked elements and merges them into continuous cracks. A tracking algorithm ensures crack continuity, eliminating spurious cracks ahead of the crack tip to prevent crack arrest and stress locking. This approach ensures the formation of various types of cracks within the constituents of composite materials and their spontaneous coalescence forming the final failure mechanisms. The constitutive model for the crack representation is the damage softening model, which accounts for opening and sliding behavior. The efficacy of the proposed model is demonstrated through numerical simulations of heterogeneous 3-phase and 4-phase composites subjected to both tensile and compressive load cases.

Accurate fatigue life prediction of polycrystalline materials is crucial for many engineering applications. In polycrystalline materials, a significant portion of life is spent in the crack nucleation phase at the microstructural scale. Hence, the total fatigue life shows high sensitivity to the local microstructure. To predict fatigue life accurately, the microstructure models of polycrystalline material i.e., titanium alloy are virtually generated with the help of the Voronoi tessellation technique. These models incorporate critical microstructural features such as grain size, grain shape, and the volume fraction of different phases within the material. To efficiently predict microstructure sensitive fatigue life, the smooth finite element method (SFEM) is coupled with continuum damage mechanics (CDM). The SFEM provides flexibility in the meshing of complex microstructure geometries as it alleviates the need to use only triangular and quadrilateral elements. Moreover, there is no need of isoparametric mapping and explicit form of shape function derivatives in SFEM, hence it requires less computation time. To obtain the fatigue life (in number of cycles), jump in cycles algorithm is implemented using SFEM-CDM. The numerical results of fatigue life data obtained from simulations are compared with experimental data, which reveals the validity of the present approach. This approach is useful to find out the scatter in fatigue life data of polycrystalline materials along with the source of scatter.