This paper presents a 3D simulation of damages and cracks growth in composite material using Discrete Element Method (DEM). Fiber/matrix debonding and ply to ply delamination, cracks matrix, rupture of fibers are addressed. Matrix and fiber are supposed to be brittle materials and follow a linear fracture model. Cohesive contact laws are implemented to model interfaces behavior for both debonding (fiber/ matrix) and delamination (ply/ply). Piecewise linear elastic laws usually used in cohesive zone models are retained in this work. A Double Cantiliver Beam (DCB) test is first experimented using the present DEM with Cohesive Contact Models (CCM). Then, based on De Borst's works [1], a single fiber composite under transverse traction is modeled to study debonding and matrix cracks propagations depending on the matrix and the fiber/matrix interface strengths ratio. A bi-disperse medium for matrix and fiber is specifically elaborated to reduce the discrete elements number. The analysis is extended to a so-called multi-fibers composite specimen, also called Statistical Elementary Volume (SEV), made of several fibers embedded in the matrix. Finally, the results are compared with DeBorst's works and qualitatively discussed.
We propose a discrete element model for brittle rupture. The material consists of a bidimensional set of closed-packed particles in contact. We explore the isotropic elastic behavior of this regular structure to derive a rupture criterion compatible to continuum mechanics. We introduce a classical criterion of mixed mode crack propagation based on the value of the stress intensity factors, obtained by the analysis of two adjacent contacts near a crack tip. Hence, the toughness becomes a direct parameter of the model, without any calibration procedure. We verify the consistency of the formulation as well as its convergence by comparison with theoretical solutions of tensile cracks, a pre-cracked beam, and an inclined crack under biaxial stress.
In the absence of initial cracks, the material behavior is limited by its strength, usually defined in homogeneous conditions (of stress and strain). Beyond this limit, in quasi-brittle case, cracks may propagate and the material behavior tends to be well described by fracture mechanics. Discrete element approaches show consistent results dealing with this transition during rupture. However, the calibration of the parameters of the numerical models (i.e., stiffness, strength, and toughness) may be quite complex and sometimes only approximative. Based on a brittle rupture criterion, we analyze the biaxial response of uncracked samples. Thus, tensile and compressive strengths are analytically identified and become direct parameters of our discrete model. Furthermore, a physically reliable crack initiation (and subsequent propagation) is shown to be induced during rupture and verified by the simulation of three-point bending and diametral compression tests.
Purpose -The purpose of this paper is to use the discrete element method (DEM) to model the fracture behaviour of brittle materials in 2D. Design/methodology/approach -The material consists of a set of particles in contact with a close-packed structure. It allows the derivation of an expression for the stress intensity factor as a function of the contact forces near the crack tip. A classical failure criterion, based on the material's toughness, is then adopted for the analysis of crack propagation, represented by the contact loss between particles. Findings -The DEM approach is compared to two tensile cases (mode I); both presenting a monotonous convergence towards classical solutions for more precise discretization. Originality/value -The paper proposes a DEM approach in fracture mechanics of isotropic brittle materials entirely compatible with continuous classical theory. Hence the toughness value is directly introduced as a parameter of the material without any previous calibration of the DEM.
This paper presents a fracture behavior modeling of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) slabs under contact blast loading using the finite element method. The UHPFRC is supposed to be brittle material and follow the Johnson–Holmquist-II(JH-2) model. The steel rebar is modeled using the elasto-plastic model. The Emulsion Explosive has been used and modeled by the SPH method. UHPFRC slabs with the dimensions 1000mm of length, 800mm of width and 120mm of thickness is considered. The steel fibers with a volume fraction of 2% is used. The UHPFRC material is fabricated in laboratory using the material available in Vietnam. The concrete crater and spall damage of UHPFRC slab under contact blast loading are considered. The numerical results are compared with experiment. These results allow to evaluate the resistance against blast load of UHPFRC fabricated in lab.
A promising way to model fracture mechanics with the use of an original Discrete Element Method (DEM) is proposed. After proving the ability of the method to capture kinetic damage induced by cracking phenomena in brittle materials such as silica [1], taking advantage of the method for composite materials applications is the main purpose of this work. This paper highlights recent and current developments to prove abilities of the DEM to give some answers to challenges : i) use the present DEM to model damage mechanisms (matrix cracking, debonding, fiber break and delamination) in a composite material ii) deal with impact applications on dry fabrics using the DEM. All developments are made in the home made software GRANOO (GRANular Objet Oriented) [2]. The promising results are commented and the on going developments are exposed.
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