Papers by Keyword: Cohesive Zone Model (CZM)

Abstract: As dual-phase (DP) steel sheet is widely used in automotive manufacture, researches on failure mode of DP steel have been carried out experimentally and numerically in recent years. In this paper, failure mode of DP 780 steels with geometrical imperfection, which was assumed as a consequence of previous process, was investigated via a microstructure approach utilizing RVE technique. Multiple damage models were applied on characteristic microstructures and the modified pointed-ended geometrical imperfection was ingrained. Considering the progress of crack evolution, the depth and the location of geometrical imperfection were critical factors in determining the mode of crack initiation and propagation. Essentially, geometrical imperfection influenced the failure mode of investigated DP steel via aggravating the structural heterogeneity.

Abstract: Composite solid propellant is a particulate composite with high volume fraction and wide size distribution, macroscopic mechanical behavior of SP is strongly depended on its mesostructure. This work presents a numerical analysis of mesostructure damage for SP based on XFEM and CZM method. A simplified physical model is used for the validation of the proposed method. It is shown that the result of crack extension agrees with experiment of Micro CT scan on the whole. Numerical simulations also indicate the fact that initiation of SP damage takes place at the interface of particle and matrix. At last, the relations of macroscopic strain and stress of SP with 55% volume fraction and 65% volume fraction AP are predicted based on mesostructure simulation and compared with experiments.

Abstract: Cracking in the surface layer of asphalt pavement has been shown to be a major source of distress in roadways. Asphalt mixture is typically a heterogeneous material composed of aggregates, binder and air voids. Previous cracking studies have not considered the material heterogeneity. Digital Image Processing techniques is a powerful tool to describe the microstructure of the material. A micromechanical cohesive zone model that introduces ductility at the crack tip has been used to simulate the cracking of asphalt mixtures. ABAQUS software is a convenient finite element method to conduct simulations of particular laboratory specimens such as Indirect Tensile Tests(IDT) considering the micromechanical model. Simulation results of the IDT compared favorably with experimental results. Even though this study presented a attempt of a numerical simulation of a simple IDT test, the theory and methods adopted by the study can be applied to the fatigue damage study under the complicated loading considering the material heterogeneity, and then would effectively allow researchers link the micro-scale damage observed on the local scale with the real pavements fail on the global scale.

Abstract: Adhesive joints are largely employed nowadays as a fast and effective joining process. The respective techniques for strength prediction have also improved over the years. Cohesive Zone Models (CZM’s) coupled to Finite Element Method (FEM) analyses surpass the limitations of stress and fracture criteria and allow modelling damage. CZM’s require the energy release rates in tension (G_n) and shear (G_s) and respective fracture energies in tension (G_n^c) and shear (G_s^c). Additionally, the cohesive strengths (t_n⁰ for tension and t_s⁰ for shear) must also be defined. In this work, the influence of the CZM parameters of a triangular CZM used to model a thin adhesive layer is studied, to estimate their effect on the predictions. Some conclusions were drawn for the accuracy of the simulation results by variations of each one of these parameters.

Abstract: In this paper, flatwise tensile test (FWT) and modified double cantilever beam (DCB) experiment were conducted to investigated the debond fracture of sandwich plate with corrugated core. In the experiment, the crack always stays at the face/core interfacial. Tensile bond strength of face core can be given from the flatwise tensile test and we can get the mode I fracture toughness G_IC from DCB tests. It is found that the trends of curves change greatly at the beginning, with the propagation of crack, load against open displacement curves change smoothly. In order to simulate the face/core failure of sandwich plate with corrugated core, the cohesive element model is used. Tensile strength and strain energy release rate measured by the experiments presented in this paper are used in as parameters for simulation of the debond fracture. By comparing with the experiment results, the model can express the face/core failure of sandwich plate with corrugated core validly.

Abstract: Firstly, the parameters of cohesive zone model in ABAQUS software are calibrated through the cohesive constitutive model determined by cohesive potential energy, which is provided by Oriz and Pandofi（1999）. Then, the validity and liability are verified by the single element example which compares extended finite element simulation with experimental results. Lastly, it puts forward the model of FEM based on the highway pre-sawed cracks. The curve of CMOD with changing temperature is obtained, and the curve can be divided into three stage segments. The middle stage segment changes dramatically for the local cracking in the crack tip field between asphalt surface and base. The research results illustrate the cracking mechanisms of asphalt pavement under changing temperature.

Abstract: The research methods of Cohesive Zone Model (CZM) are introduced and the parameters of cohesive zone model in ABAQUS software are calibrated based on the cohesive constitutive model determined by the fracture energy. Besides adopting exponential cohesive zone model, this paper applies a bilinear one to simulate the crack propagation of a simply supported single-edge notched concrete beams SE(B) (Mode I) and make comparisons with experimental result. Finally, the results represent effectiveness of the effective modulus and the special advantage in term of failure of fracture based on the cohesive zone model, which is of directly guiding significance for achieving a deep going understanding of crack propagation.

Abstract: Natural short fiber reinforced composite is promising in motor industry, it is meaningful to study the tensile property of spruce short fiber reinforced polypropylene (PP) composite. In this paper, the finite element model is developed with the consideration of the fiber random orientation, random distribution, fiber volume content and interphase effect, especially the cohesive zone model to simulate the interphase property. The tensile behaviors of the short spruce/PP composite with kinds of fiber volume content are predicted. The results show that both strength or stiffness and experimental data are well identical.

Abstract: The theoretical analysis and numerical study focused on the delamination onset of composites in drilling are presented. An analytical model considering the form of loads distribution is built. The formulas based on the fracture mechanics theory are given for predicting the critical drilling force of delamination onset. A finite element model is used to simulate the process of interfacial crack growth between layers. The interface elements are employed to account for delamination based on cohesive zone model. Some numerical results are given for verifying the validity of the distribution loading model and discussing the delamination onset and growth in drilling composites.

Abstract: The main objective of the study is to understand the mechanisms of the preform reinforcement (2D, stitched and 2.5D) in laminated composite materials. The study is focusing on the mode I interlaminar fracture toughness for glass/vinylester based composites. Starting from DCB tests we quantify the critical energy release rate for the various cases of reinforcement, conclusive that 2.5D reinforcement can increase resistance x7 in comparison with the standard composite. Moreover, the existence of z-fibres made the fracture more complex and caused several characteristic phenomena, so that the required fracture energy for crack propagation was strongly increased. It is shown that a finite element model is successful in reproducing qualitatively the cracking initiation and propagation through the un-reinforced and 3D reinforced sample provided that the action of the through-thickness reinforcement is modelled by discrete nodal forces so as to replicate the physical phenomena.