A Micro—Macro Approach to Modeling Progressive Damage in Composite Structures

Abstract

Modeling progressive damage in composite materials and structures poses considerable challenges because damage is, in general, complex and involves multiple modes such as delamination, transverse cracking, fiber breakage, fiber pullout, etc. Clearly, damage in composites can be investigated at different length scales, ranging from the micromechanical to the macromechanical specimen and structural scales. In this article, a simple but 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, i.e., because the stiffness matrix of the element is not changed, computational convergence is theoretically guaranteed, resulting in a robust modeling tool. The EFM, when employed with suitable micromechanicsbased failure criteria, may be a practical method for mapping damage initiation and propagation in composite structures. In this article, we present a micromechanical analysis for a new failure criterion called the strain invariant failure theory and the application of the EFM in the modeling of open-hole tension specimens. The micromechanical analysis yields a set of amplification factors, which are used to establish a set of micromechanically enhanced strain invariants for the failure criterion. The effects of material properties and volume fraction on the amplification factors are discussed.KEY WORDS: progressive damage, multiscale damage, element-failure method, strain invariant failure theory, micromechanical amplification.

Finite fracture mechanics analysis of crack onset at a stress concentration in a UD glass/epoxy composite in off-axis tension

“…The accuracy could be further improved by treating the characteristic distance as a function of notch size and geometry, but at the cost of increasing the number of model parameters [9,15]. Further development of strength-based analyses employed finite element method (FEM) that allowed progressive ply-by-ply and/or element-by-element failure modeling [16][17][18][19][20]. Such models incorporate specific assumptions concerning strength criteria of the plies and stiffness reduction upon element failure [21], and are capable of yielding generally accurate prediction of progressive damage.…”

Finite Element Analysis and Experimental Characterisation of SMC Composite Car Hood Specimens under Complex Loadings

“…Liu and Zheng [15] and Padhi et al [21] addressed this issue by separating the three stress components to give a better understanding and identify the failure modes. New failure theories have also being developed; some notable theories are the strain invariant failure theory [22][23][24], the multi-continuum theory [25,26], and the micromechanics-based failure theory [27,28].…”

“…This also means that the material properties have to be recalculated simultaneously, while holding the same load to remain in equilibrium, causing instability in some simulations due to numerical convergence issues [3]. This problem was later resolved by Tay et al [22,23,46], at which point the element failure method was proposed. This method allowed for more rapid convergence and computational robustness by manipulating the nodal forces of elements to simulate damage, while leaving the material stiffness unaffected; although subsequently, this method struggles to predict damage evolutions due to stiffness degradation.…”

A Damage Mechanics Model for Porous Media

“…Damage mechanics provides an average measure of material degradation due to microcracking, interfacial debonding, nucleation and coalescence of voids. Consequently, the influences of micro-void generation in the porous medium are accounted for in a phenomenological sense by adopting the damage mechanics approach (Cheng and Chen 2008;Karel et al 2008;Tay et al 2008).…”