Damage Progression in Open-hole Tension Laminates by the SIFT-EFM Approach

Abstract

Predicting and modeling progressive damage in fiber-reinforced composite structures up to and including final failure is a considerable challenge because damage in composite materials is extremely complex, involving multiple modes, such as delamination, transverse microcracking, fiber breakage, fiber pullout, etc. Indeed, damage in composites should be studied at different length scales, ranging from the micromechanical to the macromechanical specimen and structural scales. The challenge, however, is in finding theories and methodologies that will faithfully reflect the structural effects of damage progression without involving an inordinate amount of detail (and effort) in the model, so that designers and engineers will have practical tools. In this article, a novel finite element-based method for modeling progressive damage in fiber-reinforced composites is presented. The element-failure method (EFM) is based on the simple idea that the nodal forces of an element of a damaged composite material can be modified to reflect the general state of damage and loading. This has an advantage over the usual material property degradation approaches in that because the stiffness matrix of the element is not changed, computational convergence is guaranteed, resulting in a robust modeling method. When employed with a suitable micromechanics-based failure criterion, it may evolve into an engineering tool for mapping damage initiation and propagation in composite structures. Here, we have utilized the micromechanical information contained in a new strain invariant failure theory (SIFT) to guide the nodal force modification scheme to model progressive damage. As an application of the SIFT-EFM approach, we present a rational nodal force modification scheme for the modeling of progressive damage in quasi-isotropic composite laminates with open holes, subjected to remote tensile loads. The proposed nodal force modification scheme assumes loss of load-bearing capability in the direction transverse to the fibers for the case of local transverse microcracking, and assumes total loss of load-bearing capability when both transverse microcracking and fiber rupture occur. The study investigates the effect of stacking or layup sequence and shows that it is important to refine the model in the through-thickness dimension and includes nodal force modification for the out-of-plane component. It reinforces the view that damage propagation in composites is a complex three-dimensional event. When compared with experimental data, the predicted damage maps and final failure loads show correct trends and reasonable agreement.

Comparison of Damage Path Predictions for Composite Laminates by Explicit and Standard Finite Element Analysis Tools

“…From the data presented, only about one third of the experimentally observed damage path was predicted near peak loading [18]. An alternative approach was adopted by Tay, Liu and Tan where the element forces are degraded rather that the stiffness matrix when a strain invariant theory predicts damage [19]. This method is called the SIFT-EFM approach (Strain Invariant Failure Theory-Element Failure Method) and is used by the authors to predict damage path.…”

Long-term Open-hole Compression Strength of CFRP Laminates based on Strain Invariant Failure Theory

“…The failure criterion and critical parameters used in this research is the SIFT. Here, brief description of the SIFT is included according to the literatures Gosse and Christensen [7] and Tay et al [8]. The SIFT is a micromechanics-based 3D failure criterion for constituents matrix and fiber, separately.…”

“…A unique feature of this failure theory of the SIFT is that information at the micromechanical scale is extracted from FEM analyses of the representative micromechanical block to amplify strain invariant quantities which are in turn used as criteria to determine failure. The strains in fiber and matrix are amplified through the use of representative micromechanical block, whereby individual fiber and matrix are modeled by 3D elements [8]. The micromechanical effect and thermal residual strains from curing temperature are considered.…”

“…With the SIFT, the progressive damage and delamination treated as 3D events can be analyzed. Tay [8,9] has developed new progressive damage analysis method, called SIFT/EFM, by combining the SIFT and element failure method (EFM). Other work with SIFT can be found in the research of the interfacial strain distribution of a unidirectional composite with randomly distributed fibers under transverse loading by Oh et al [10].…”

Measurement of hole damage characteristics in the glass fibre reinforced plastic composite using digital image correlation technique

“…A theoretical solution to the stress field around a circular and elliptical hole in an infinite orthotropic plate under tensile load using complex variable method was presented by Lekhnitskii, and some experimental techniques, such as ESPI (Electronic Speckle Pattern Interferometry) , Moire, Digital Image Correlation (DIC) and strain gages techniques, have been used in determining the stress and strain field around the hole . The strain concentration around a circular hole for a composite laminate with different fibre orientations was measured by Smith based on digital image correlation image measurements and the difference in strength compared to numerical analysis was 10% .…”