Fracture toughness of the + 45° / – 45° interface of a laminate composite

Abstract

Experiments are carried out to determine the delamination toughness for a crack along the interface between two transversely isotropic materials. The material chosen for study consists of carbon fibers embedded within an epoxy matrix. A crack is introduced between two layers of this material, with fibers in the upper layer along the +45 • -direction and those in the lower layer along the −45 • -direction both with respect to the crack plane. The Brazilian disk specimen is employed in the testing. To calibrate the specimens, stress intensity factors are obtained which result from the applied load, as well as residual curing stresses. It may be noted that all three modes are coupled, leading to a three-dimensional problem. The finite element method and a mechanical M-integral are employed to determine the stress intensity factors arising from the applied load. For the residual stresses, a three-dimensional conservative thermal M-integral is presented for stress intensity factor determination. The stress intensity factors found for the applied load and residual stresses are superposed to obtain a local energy release rate, together with two phase angles. From the load at fracture, the critical interface energy release rate or interface toughness G ic as a function of phase angles ψ and φ is determined. Results are compared to a fracture criterion.

Fracture Mechanics Analyses for Interface Crack Problems - A Review

“…Banks-Sills, with several co-workers, focused on computational fracture mechanics using finite element analysis to study bimaterial interface fracture and compute complex stress intensity factors [64][65][66][67][68][69][70]. Over the past decade their research has also included the study of interlaminar fracture in composite laminates.…”

“…Over the past decade their research has also included the study of interlaminar fracture in composite laminates. An approach for calculating the energy release rate and the phase angles along the delamination front as well as measuring the interface fracture properties of a composite materials [68][69][70] was developed.…”

Behavior of a flat internal delamination within a fiber reinforced cross-ply composite

“…The latter approach is taken in this investigation. For all interfaces, the criterion is given by Banks-Sills et al (2006) …”

Delamination Tests of DCB Specimens Composed of Woven Composites

“…To this end, the Stroh formalism [3] was used to determine the first term of the asymptotic expressions for the stress and displacement fields in the neighborhood of the delamination front. Similar methods have been used for straight through delaminations in cross-plies [4,5].The experimental set-up consists of an Instron loading machine (no. 8872) with a load cell of maximum load 250 N. This small load cell is required since the maximum load at fracture is approximately 60 N. The Instron measures the load as a function of time.…”

“…To this end, the Stroh formalism [3] was used to determine the first term of the asymptotic expressions for the stress and displacement fields in the neighborhood of the delamination front. Similar methods have been used for straight through delaminations in cross-plies [4,5].…”