Quantification of degraded constitutive coefficients of composites in the presence of distributed defects

Abstract

Effect of distributed defects on effective material properties of composites is required for the progressive failure models. Although the degradation of the effective material properties due to the presence of the lower scale damages is well investigated, how each material coefficient should be compromised in a progressive failure model is still a dilemma. Percentage of defects, the shape of the defects and their stochastic distribution may affect the individual material coefficients in a unique way and may not be uniform across the constitutive matrix. Hence, to find how the individual material coefficients in a constitutive matrix changes due to the presence of the voids and fiber breakage, all material coefficients in a constitutive matrix were studied herein. Representative volume element of a unidirectional fiber-matrix composite was studied with appropriate boundary conditions and respective material coefficients were calculated. It was found that the local gradients of the degradation curve obtained for each material coefficient are not linear with the increasing percentage of degradation and not uniform for all material coefficients. The shape and different locations of the defects with constant defect percentage were found to be inert towards affecting the material coefficients.

Effect of Defects Part II: Multiscale Effect of Microvoids, Orientation of Rivet Holes on the Damage Propagation, and Ultimate Failure Strength of Composites

“…The time step was selected as ∆t = 2 × 10 −8 s. The material properties of the carbon/carbon unidirectional composite are listed in Table 1. The engineering material along and perpendicular to the fiber direction were calculated using the micromechanics concept [41]. The elasticity modulus along and perpendicular to the fiber direction were E 1 = 116 Gpa and E 2 = 8.5 Gpa, respectively.…”

“…This can be performed by quantifying the local material properties degradation of composite plates using micromechanics. According to established literature [41], the effective material properties for the unidirectional (UD) carbon/carbon composite materials were calculated fordifferent percentages, shapes, sizes, and locations of voids. Figure 10 shows the location of rhw considered material degradation around the hole and the different types of voids in the composite materials.…”

“…They found that the pentagonal inter-fiber decreased the strength of composite materials more than other void shapes. Tavaf et al [41,42] developed a framework to quantify the degraded material properties for the carbon/carbon unidirectional composite materials due to manufacturing defects such as microvoids and fiber breakage. They considered the RVEs with multiple fibers and used the finite element method to calculate the effective material properties (EMPs).…”

Effect of Defects Part I: Degradation of Constitutive Coefficients as an Input to the Composite Failure Model with Microvoids and Porosity

“…Failure of composite materials starts with distributed defects or local degradation, which is known as early-stage damage. The initial damages may significantly influence the local material properties of composite materials due to local compliance [1]. Local degradation of material properties leads to damage evolution in a unique way and ultimately causes the failure of the structures [2].…”

Predictions of the axial tensile property of the unidirectional composite influenced by microfiber breakage defects

“…Tavaf et al. 28 have adopted a multi-fiber representative unit cell (RUC) model to study the effect of fiber breakage defects on the elastic constants of the UD. However, they did not give the prediction tendency of the elastic constants of the UD influenced by different volume fractions of fiber breakage defects.…”