Fracture Of Composite Structures Research Articles

An efficient peridynamics-based statistical multiscale method for fracture in composite structures

This paper proposes a peridynamics-based statistical multiscale (PSM) framework to simulate the macroscopic structure fracture with high efficiency. The heterogeneities of composites, including the shape, spatial distribution and volume fraction of particles, are characterized within the representative volume elements (RVEs), and their impact on structure failure are extracted as two types of peridynamic parameters, namely, statistical critical stretch and equivalent micromodulus. At the microscale level, a bond-based peridynamic (BPD) model with energy-based micromodulus correction technique is introduced to simulate the fracture in RVEs, and then the computational model of statistical critical stretch is established through micromechanical analysis. Moreover, based on the statistical homogenization approach, the computational model of effective elastic tensor is also established. Then, the equivalent micromodulus can be derived from the effective elastic tensor, according to the energy density equivalence between classical continuum mechanics (CCM) and BPD models. At the macroscale level, a macroscale BPD model with the statistical critical stretch and the equivalent micromodulus is constructed to simulate the fracture in the macroscopic homogenized structures. The algorithm framework of the PSM method is also described. Two- and three-dimensional numerical examples illustrate the validity, accuracy and efficiency of the proposed method.

Evaluation of the frictional effect on the energy release rate in doubly end-notched tension test for mode II delamination

Fracture of composite structures is frequently caused by delamination, and evaluation of the interlaminar fracture toughness is thus important. A new double-lap joint-like fracture toughness test, that is, the doubly end-notched tension (DENT) test, achieves stable mode II delamination growth in a simple tensile test. This study numerically investigated the influence of friction between delamination surfaces on the perceived energy release rate in the DENT test. The virtual crack closure technique was adapted with considering friction for the DENT models, as well as the three-point-bend and four-point-bend end-notched-flexure models for comparison. Despite the tensile loading in the DENT test, the frictional effect was significant when the thickness ratio of the surface to the middle layers was high. A corrected equation for evaluating the energy release rate successfully eliminated the frictional effect in the DENT test. An analysis of the full DENT model revealed that the crack length difference alleviated the contact and frictional effects.

A polymorphic element formulation towards multiscale modelling of composite structures

This paper presents a new polymorphic element modelling approach for multi-scale simulation, with an application to fracture in composite structures. We propose the concept of polymorphic elements; these are elements that exist as an evolving superposition of various states, each representing the relevant physics with the required level of fidelity.During a numerical simulation, polymorphic elements can change their formulation to more effectively represent the structural state or to improve computational efficiency. This change is achieved by transitioning progressively between states and by repartitioning each state on-the-fly as required at any given instant during the analysis. In this way, polymorphic elements offer the possibility to carry out a multiscale simulation without having to define a priori where the local model should be located.Polymorphic elements can be implemented as simple user-defined elements which can be readily integrated in a Finite Element code. Each individual user-defined polymorphic element contains all the relevant superposed states (and their coupling), as well as the ability to self-refine.We implemented a polymorphic element with continuum (plain strain) and structural (beam) states for the multiscale simulation of crack propagation. To verify the formulation, we applied it to the multiscale simulation of known mode I, mode II andmixed-mode I and II crack propagation scenarios, obtaining good accuracy and up to 70% reduction in computational time —the reduction in computational time can potentially be even more significant for large engineering structures where the local model is a small portion of the total.We further applied our polymorphic element formulation to the multiscale simulation of a more complex problem involving interaction between cracks (delamination migration), thereby demonstrating the potential impact of the proposed multiscale modelling approach for realistic engineering problems.

An extended element-free Galerkin method for thermo-mechanical dynamic fracture in linear and nonlinear materials

In this manuscript, an extended element-free Galerkin (XEFG) method for dynamic thermo-mechanical fracture is proposed. The crack is considered adiabatic and the discontinuous displacement field and temperature field is modeled by partition-of-unity enrichment of the test and trial functions. The coupled thermo-mechanical formulation is implemented for static and dynamic problems and applied to fracture in composite structures in two dimension. The method is verified through comparison to analytical and experimental results. Where available, the results are also compared to reference solutions. The proposed method models thermo-mechanical efficiently and robustly with few degrees of freedom. Therefore, an h-adaptive refinement procedure is employed that inserts nodes based on the temperature gradient.