International Journal of Fracture最新文献

CT-based finite element analysis (FEA) of human bones helps estimate fracture risk in clinical practice by linking bone ash density ((rho _{ash})) to mechanical parameters. However, phase field models for fracture prediction require the heterogeneous fracture toughness (G_{Ic}), which can be derived from the critical stress intensity factor (K_{Ic}), determined through various experimental methods. Due to a lack of standards for determining cortical bone’s (K_{Ic}), an experimental campaign is presented using 53 cortical specimens from two fresh frozen femurs to investigate whether a correlation exists between (K_{Ic}) and (rho _{ash}). We investigated various experimental techniques for correlating (K_{Ic}) with (rho _{ash}). We conducted FEAs employing the phase field method (PFM) to determine the most suitable correlation among the five possible ones stemming from the experimental methods. The ASTM standard using displacement at force application point was found to be the recommended experimental method for the estimation of (K_{Ic}) perpendicular to osteons’ direction

The corresponding statistical critical energy release rate bounds were determined:

with a standard deviation (SD= 0.30) representing a 95.4% confidence interval. The average (G_{Ic}) resulted in good correlations between the predicted fracture force by PFM-FEA of four representative specimens and experimental fracture forces. The proposed correlations will be used in CT-based PFM FEA to estimate the risk of hip and humeral fractures.

This article introduces a novel method for investigating crack propagation in porous quasi-brittle structures. The method combines isogeometric analysis (IGA) with higher-order phase-field theory. IGA is particularly useful for representing complex geometries through high-order Non-Uniform Rational B-Spline (NURBS)-based elements. It gives it an advantage over conventional methods that rely on enriched nodes. The phase-field approach uses a scalar field to implicitly define the trajectory of cracks, eliminating the need to predefine an initial crack location. The study was conducted on a porous plate model with multiple perforations. The porosity level significantly affects the structural integrity of the domain under consideration. The degradation functions that characterize material softening concerning porosity are obtained through careful examination. These degradation functions are further implemented into numerical problems to observe the effect of porosity on crack initiation and propagation behavior. The results have demonstrated the proposed approach’s efficiency and accuracy in analyzing porous concrete’s failure behavior. The analysis results contribute to advancing our understanding of crack propagation and showcase the efficacy of the presented methodological framework in enhancing predictive capabilities in structural mechanics.

Many engineering structures are subjected to variable amplitude loading. A number of studies investigate the effects of post overload, even-though it is crucial to describe what occurs during the overloading. The aim of this paper is to provide effective independent descriptors based on purely kinematic measurements for the analysis of overloading. Fatigue tests were conducted on a SENT specimen. Investigating crack propagation was through direct measurements using Digital Image Correlation and Linear Elastic Fracture Mechanics via Williams’ series expansion. The higher terms in Williams’ series expansion, referred to as crack features were analyzed in cycles with and without overload. In a case without overload, all features exhibit a proportional regime. Singular value decomposition (SVD) analysis confirms that a single feature is adequate to characterize the mechanism. In a cycle with overload, the regime changes during the overloading phase, making it a signature of this phase. In this case, the SVD analysis reveals that two descriptors are needed for these cycles. A subsequent analysis allows the definition of two physically interpretable features. This work presents a robust method to identify, based on kinematic measurements and SVD analysis, independent descriptors for the processes that occur during a cycle with overload.

Unraveling the material behavior at the microscale is one of the challenges of this century, demanding progress in experimental and computational strategies. Among the latter, two approaches are commonly applied for predicting crack nucleation. The Coupled Criterion (CC) and the Phase Field (PF) model, both depending on a material length parameter. In brittle materials at the macroscale, this parameter is significantly smaller than the specimen size. However, when the scale decreases, this material length might approach the structural dimensions. In this context, a comprehensive comparison between the two models is conducted, changing the ratio between the material length parameter and the dimensions of the specimen. Results indicate that when this ratio is sufficiently small predictions from both models coincide, otherwise both the CC and the PF model predict different results. Despite their differences, an agreement with experiments reported in the literature have been observed.

As a remedy to pathological sharp crack configurations such as strong singularities or anti-plane shear cracks, where crack initiation is driven solely by energy, a regularized crack description can be adopted to study crack initiation. The nucleation of a regularized crack at a V-notch is studied using the coupled criterion through matched asymptotic expansions. The process zone around the crack is described by crack regularization usually employed in phase-field models. The effective crack length increases with increasing regularization length so that the incremental energy release rate decreases, which in turn increases the critical generalized stress intensity factor at initiation. Decreasing incremental energy release rate is also obtained with increasing Poisson’s ratio. For a given material characteristic length, it is shown that the initiation crack length only depends on the V-notch angle and Poisson’s ratio. For a given geometry and Poisson’s ratio, the initiation length is proportional to the regularization length. The proposed description of regularized crack initiation shows good correspondence to the generalized stress intensity factor obtained by phase-field calculation, the only difference being in the description of the process zone prior to crack initiation.

Soft materials are an important class of materials. They play critical roles both in nature, in the form of soft tissues, and in industrial applications. Quantifying their mechanical properties is an important part of understanding and predicting their behavior, and thus optimizing their use. However, there are often no agreed upon standards for how to do so. This also holds true for quantifying their fracture toughness; that is, their resistance to crack propagation. The goal of our work is to fill this knowledge gap using blood clot as a model material. In total, we compared three general approaches, some with multiple different implementations. The first approach is based on Griffith’s definition of the critical energy release rate. The second approach makes use of the J-Integral. The last approach uses cohesive zones. We applied these approaches to 12 pure shear experiments with notched samples (some approaches were supplemented with unnotched samples). Finally, we compared these approaches by their intra- and inter-approach variability, the complexity of their implementation, and their computational cost. Overall, we found that the simplest method was also the most consistent and the least costly one: the Griffith-based approach, as proposed by Rivlin and Thomas in 1953.

The dynamic fracture properties of porous ceramics were studied using single bunch synchrotron X-ray phase contrast imaging. The modified brazilian geometry was used to initiate and propagate a pure mode I crack. The specimen was compressed using the Split Hopkinson bars at strain rates of the order of (10^2) s(^{-1}). Main cracks were isolated for four different grades of (Al_2O_3), one dense alumina, and three porous grades with (20~%) to (60~%) porosity. The maximum measured crack velocities for three grades is of the order of (0.6c_R) and (0.4c_R) for the most porous. The fracture energy was estimated using a FE numerical simulation to quantify the influence of inertial effects induced by crack propagation. The results show that these inertial effects are far from negligible (up to (80~%) of the stored energy) and that the dynamic correction factors known from the literature tend to overestimate the fracture energy. The values obtained vary from 22 J/m(^2) for the densest to 5 J/m(^2) for the most porous.

Predicting the mechanical response and damage evolution of elastomers under large deformation is of great significance in engineering applications. In this work, a finite element (FE) scheme is formulated and used to simulate rate-dependent damage in elastomers. While based on the theoretical model of Lavoie et al. (Extrem Mech Lett 8:114–124, 2016) and maintaining the key features such as kinetics of chain scission and polydispersity, the FE scheme presented here includes the consideration of finite compressibility. Both implicit and explicit algorithms are derived and implemented as user subroutines in ABAQUS. Validated against existing numerical results as well as experimental data on homogeneous deformation, the capability of the FE scheme to solve problems involving inhomogeneous deformation is further explored by simulating samples with pre-existing defects. The numerical results can successfully capture several interesting phenomena, such as crack blunting, stress reduction near defect caused by damage, and rate-dependent damage evolution. Good agreement is also found with experimental data on the strain field near a crack tip.

Peel tests are commonly used to characterize the performance of adhesive tapes. The force required to peel a tape from a substrate depends on not only interface adhesion but also mechanics of the tape. Typically, adhesive tapes consist of a stiff backing film and a layer of adhesive material that is soft and viscoelastic. While mechanics of the backing film has been extensively studied, mechanics of the soft adhesive layer is less understood. In this work, finite element simulations are carried out to study large deformation of the soft adhesive layer during 90-degree peeling and its implication on the peel force. We find that debonding can occur ahead of the peel front when the peel front is still adhered to the substrate. This phenomenon, referred to as “interfacial cavitation”, causes the peel front to advance in a stepwise manner despite that a constant peeling velocity is prescribed. Consequently, the peel force follows an oscillatory history resembling the “stick–slip” behavior widely observed in peel tests. Further investigations reveal that interfacial cavitation originates from a non-monotonic distribution of interfacial traction ahead of the peel front. Moreover, emergence of interfacial cavitation can be controlled by three factors: interfacial slip, adhesive layer thickness and peeling velocity. These results can provide insights towards designing adhesive tapes with desired adhesion performance or release mechanisms.

Ti6Al4V is a widely used titanium alloy known for its excellent combination of mechanical properties, corrosion resistance, and biocompatibility. However, to ensure its effectiveness in various applications, it is important to understand the mechanical and fracture behavior of the alloy in the presence of a notch. In the present study, the effect of notch root radius on mode I fracture toughness of Ti6Al4V alloys with a nearly bimodal microstructure has been investigated. Fracture toughness tests were conducted on compact tension (CT) specimens with five different notch root radii. The experimental results demonstrate that the apparent fracture toughness, (K_{IA}), increases linearly with the square root of the notch root radius. Further to elucidate the results, a 2D elastoplastic finite element analysis is performed on the CT specimens using cohesive zone model. The simulation results are in good agreement with the experimental data. The study also reveals that the apparent fracture toughness is independent of the notch root radius below a critical value, estimated to be approximately (50 mu m). Finally, the scanning electron microscopy of the fracture surfaces has been examined. The micrographs reveal void coalescence and dimple regions indicating the ductile nature of the fracture process.