A micromechanical study of stress concentrations in composites

Abstract

Random and periodic representations of composite microstructures are inherently different both in terms of the resultant range of stresses that each phase carries as well as the total load over the entire volume comprising both matrix and fiber phases. In this study, an algorithm was developed to generate random representative volume elements (RVE) with varying volume fractions and minimum distances between fibers. The random microstructures were analyzed using finite element models (FEM) and the results compared to those for periodic microstructured RVEs in terms of the range of stress values, maximum stress, and homogenized stiffness values. Using a large number of random RVE analyses, a meaningful estimation for range and average maximum stress in the matrix phase was achieved. Results show that random microstructures exhibit a much larger range of stress values than periodic microstructures, resulting in an uneven distribution of load and distinct areas of high and low stress concentration in the matrix. It is shown that the maximum stress in the matrix phase, often responsible for failure initiation, is largely dependent on the random morphology, minimum distances between fibers, and volume fraction. Moreover, it is shown that the predicted overall load-carrying capacity of the matrix changes depending on the use of random or periodic microstructures.

Numerical analysis of resin-rich areas and their effects on failure initiation of composites

“…An acceptable size of RVE is one that is statistically representative of both the morphology and behavior of the material [26,27,28,29]. For the purpose of this study the ratio of δ = 40 was chosen, which has been shown to be representative of carbon epoxy composite materials [12,28].…”

“…The current study focuses on failure in the transverse direction (perpendicular to the fibres), and examines the effects of resin rich areas on failure initiation in the matrix phase. It has been shown that a realistic representation of the non-uniform distribution of fibers within the matrix of fiber-reinforced composites can have a significant impact on the magnitude and distribution of stress concentrations in finite element models of the unit cell [12]. Similarly, one could expect that this non-uniform microstructural morphology will also affect failure initiation and progression.…”

Micromechanical modeling of the mechanical behavior of unidirectional composites – A comparative study

“…Ghayoor et al. 94 investigated the influence of stress concentration and distribution in the epoxy matrix phase for the damage analysis of a composite material with random and periodic microstructure. Table 4 provides a summary of the main methodologies along with their capabilities.…”

“…Praud et al 93 developed a new model accounting for anisotropic damage and an elasticity induced by microcracks in UD composite using continuum damage mechanics and RVE concept. Ghayoor et al 94 investigated the influence of stress concentration and distribution in the epoxy matrix phase for the damage analysis of a composite material with random and periodic microstructure. Table 4 provides a summary of the main methodologies along with their capabilities.…”

Effects of spinning conditions on structure and properties of aramid-based hollow fiber blend separation membranes

“…However, due to the great difference in thermodynamic properties between reinforced fibers and resin matrix, the poor bonding strength at their interface makes the comprehensive properties of composites far from the expected values [2]. Stress concentration resulting from long-term use leads to serious performance degradation and short life [3].…”