Papers by Keyword: Matrix Crack

Abstract: Fiber-reinforced plastic (FRP) composites are subjected to micro-level defects such as fiber-matrix debond and/or matrix cracks after a period of their service due to the increasing brittleness of matrix material. Prediction of the degraded elastic properties of a lamina through micromechanical studies by incorporating micro-level defects gives an idea of the health condition of such structures. Due to the limitations of classical mathematical approaches in solving complex structures, numerical mathematical methods like the finite element method (FEM) can be employed. The present investigation deals with the micromechanical analysis of Glass fiber-reinforced plastic (GFRP) composite with micro-level defects to predict some of the elastic properties. The composite is idealized as an array of square unit cells, and the micromechanical behavior of one such unit cell is simulated in ANSYS software using the three-dimensional finite element method to predict Young’s moduli and Poisson’s ratios in principal material directions. The converged finite element solution for longitudinal modulus is validated by the rule of mixtures and the other properties using the Maxwell–Betti reciprocal theorem. Variations of Young’s moduli and Poisson’s ratios due to an incremental internal failure of composite such as low-level, medium-level, and high-level defects at an expected range of fiber volume fractions (50% - 60%) are evaluated and estimated the percentage degradation with respect to a corresponding defect-free composite.

Abstract: In this paper, the single ply fiber breakage model is established based on the distribution function of fiber static strength, and on this basis, the acting process of fiber breakage in FRP laminate is analyzed in detail. According to the experiment data, a method is devised to identify the parameters of the static strength distribution function. Through the references to the classical laminate theory, a computation model of the laminate stiffness degradation process is developed which takes the fiber breakage damage into consideration. The analysis of the results shows that this model can employ only several parameters to describe very well the laminate stiffness degradation process under different stresses.

Abstract: The eigen-values problem of matrix cracks is studied in this paper. The stress field and displacement field of plane matrix crack is setup at first. The eigen-equation of matrix cracks is founded on the basis of the stress field and displacement field. The factors to affect the eigen-values are discussed. The effect of shearing modulus and Poisson ratio of matrix material and attaching material on eigen-values are analyzed. The results show that the bigger shearing modulus of material should be selected for attaching material and the shearing modulus of attaching material should bigger than that of matrix material in fracture design.

Abstract: Matrix crack and fibre breakage are the main damage models of the fibre reinforced polymer (FRP) laminates under cyclic loading. In this paper, meso-mechanical analysis is used and a two-parameter model is developed to describe the stiffness reduction. Based on the probability distribution function of fiber strength, the evolution of fibre breakage is deduced. Then with the help of the damage evolution, the stiffness reduction of laminates can be predicted. As an example, the stiffness reduction of grass fibre reinforced polymer (GFRP) laminate is made and the simulation results show that the proposed model has good capacity to describe the stiffness reduction of FRP laminates resulted in the combination of matrix crack and fibre breakage.

Abstract: The eigen-equation of bi-materials cracks was founded on the basis of the stress field and displacement field. The influence of shearing modulus and Poisson’s ratio of matrix material and additive material to eigen-values were analyzed through the results of calculating. The stress intensity factors at the tip of matrix crack were calculated. The suitable parameters of bi-steel materials crack in fracture design were obtained. The results show that the effect of Poisson’s ratio on eigen-values is not obviously and the effect of shearing modulus is obviously. The shearing modulus of additive material should bigger than that of matrix material.

Abstract: The fracture designs of metallic matrix crack for bi-materials were studied. The stress field and displacement field of plane matrix crack was setup at first. Then the finite element method is used to analyses the stress singularity of matrix cracks between different materials. The solutions of stress singularity of a cracked bi-materials beam under uniform tension, and the three-point bending of bi-materials specimen were computed. The result lays a theoretic and applied foundation for the practical engineering application of metallic matrix crack for bi-materials.

Abstract: To evaluate the damage of composite laminate structures which are consist of maraging steel, rubber and carbon fiber reinforced composite subjected to low velocity impact, the drop weight was used to impact the specimens and nondestructive evaluation using the C-scan was performed. After experiments, impact damages were compared with respect to various temperatures and impact energies. In case of circular plate, the damage characteristics such as delamination, matrix cracking, and fiber breakage were observed at the interface of rubber and carbon fiber reinforced composite. These results were found to be correlated with the deflection of specimen.