Papers by Keyword: Fiber Breakage (FB)

Abstract: The ultimate objective of the current work is to examine the effect of thickness on fiberglass reinforced epoxy matrix subjected to high velocity impact loading. The composite material chosen for this research was from type C-glass/epoxy 200 g/m² and type C-glass/epoxy 600 g/m². This material is used as a composite reinforcement in high performance applications since it provides certain advantages of specific high strength and stiffness as compared to metallic materials. This study investigates the mechanical properties, damage characterisation and impact resistance of both composite structures, subjected to the changes of impact velocity and thickness. For mechanical properties testing, the Universal Testing Machine (UTM) was used while for the high velocity impact, a compressed gas gun equipped with a velocity measurement system was used. From the results, it is found that the mechanical properties, damage characterisation and impact resistance of type C-glass/Epoxy 600 g/m² posses better toughness, modulus and penetration compared to type C-glass/Epoxy 200 g/m². A general trend was observed on the overall ballistic test results which indicated that as the plate specimen thickness continues to increase, the damage at the lower skin decreases and could not be seen. Moreover, it is also found that, as the plate thickness increases, the maximum impact load and impact energy increases relatively. Impact damage was found to be in the form of perforation, fibre breakage and matrix cracking. Results from this research can be used as a reference in designing structural and body armour applications in developing a better understanding of test methods used to characterise impact behaviour.

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: Damage and failure of the fiber reinforced composites remain as a challenging research subject in the area of material science and engineering. In this study a novel particle assembly model is developed using two dimensional Discrete Element Method (DEM) for the purpose of simulating the damage and failure process of the single-fiber composite (SFC) under axial tension. Fiber (SiC) and matrix (Epoxy) are represented by particles bonded together through elastic parallel bonds which are calibrated by a series of numerical tests. The contacts between the fiber particles and matrix particles are directly accounted for the fiber/matrix interface which is represented by the contact softening model similar to the cohesive zone model (CZM) in the continuum mechanics. The single-fiber composite tensile test is carried out using the developed DEM model in order to evaluate the interactions between fiber breakage, interfacial debonding and matrix cracking. The numerical results have demonstrated the capability of the developed DEM model in simulating the entire failure process of each individual constituent of the single fiber composite. This study has also confirmed that the DEM model has unique advantages over the conventionally numerical models in terms of dealing with the evolution of microscopic damages in composite materials.

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: Apparent fracture strength of notched fiber-reinforced composite laminates depends on the notch tip radius even if it is evaluated in terms of the local parameters such as the stresses at a notch tip or the stress intensity factors. Although numbers of phenomenological explanations have been made, this phenomenon has not yet been physically clear enough. In order to elucidate its key mechanism, our interest is here focused on the interlaminar crack extension from a notch tip in cross-ply laminates subjected to mode-I loading. We find a stochastically expected upper bound of interlaminar crack length due to the probabilistic breakage process of fibers in load-bearing laminas inside the delaminated zone. This upper bound, i.e., the critical length of interlaminar crack, is inherent to the laminate and corresponds to its notched strength. The well-known variation in apparent fracture strength of notched fiber-reinforced composite laminates with respect to the notch tip radius is clearly explained as the scale effect of this constant critical length in different displacement distributions ahead of notch tips of different radii.

Abstract: This paper focuses on the effect of different fiber content on the mechanical properties of specimens with and without weld lines. The effect of three different melt temperatures and holding pressures were also investigated. For the experiments dumbbell shaped standard tensile specimens with and without weld lines were injection molded from PP (TVK’s H116F homopolymer) and short glass fiber (0, 10, 20, 30, 40 wt%). The mechanical properties of these composites were determined by quasi-static (standard tensile testing) and dynamic (Charpy impact test) testing methods and the corresponding weld line factors were calculated. The fracture surfaces were analyzed with the help of scanning electron microscopy (SEM). From the results of the tensile and Charpy-impact tests, it was ascertained that the temperatures and the holding pressures during injection molding did not affect the tensile and impact properties, but fiber length had a major impact on the mechanical properties of this specific composite. By increasing the fiber content, the tensile strength increased until a peak and declined after. Whereas the impact resistance decreased by the increasing fiber content in the whole examination window. Comparing the weld lined and weld line free specimens, it was concluded that weld lines did significantly decrease the tensile strength and impact properties due to the unfavorable fiber orientation beside the weld line which was visualized by scanning electron microscopy.