Design Analysis and Testing for Mixed-Mode and Mode II Interlaminar Fracture of Composites

Abstract

This paper presents the design analysis and results of an experimental program that was conducted to evaluate mixed-mode and Mode II interlaminar fracture behavior of a resin matrix composite material system. A double cracked-lap-shear specimen was designed utilizing a simple, new analysis method. The specimen was made of AS4/3502 graphite/epoxy material with a [±45, 0, 90]6s quasi-isotropic balanced symmetric layup. The lap interface studied was at ±45° orientations to the loading direction. A fundamental feature of the designed specimen is its ability to be tested under net tensile and compressive loadings. The specimen exhibits mixed-mode or Mode II behavior depending on the loading direction. This paper summarizes the tension testing only. The crack growth during testing was monitored by observing the isochromatic fringes in photoelastic coatings mounted on the two lap surfaces. Preliminary results indicate that the fracture behavior follows a resistance curve. In order to assess the double cracked-lap-shear specimen data and test, a comparison was made with results obtained with single cracked-lap-shear specimens. Less scatter in the data from the double cracked-lap-shear specimens was found.

Mechanics and fracture of crack tip deformable bi-material interface

“…The existing sub-laminate model (Armanios et al, 1986;Chatterjee and Ramnath, 1988;Zou et al, 2001;Wang and Qiao, 2004c) is a special case of Eqs. (4) and (5) by assuming the interface compliance coefficients are zero, implying a semi-rigid joint condition, in which only the root rotation is permitted.…”

“…Excellent agreements with numerical finite element analysis and experimental testing results could be reached by this method. However, for a general bi-layer cracked beam, a sub-layer (or sub-laminate in composite laminates) model (Armanios et al, 1986;Wang and Qiao, 2004b,c) is more suitable. In this type of model, each layer of the virgin beam at the joint is modeled as a single sub-beam, instead of only modeling the whole uncracked portion as a composite beam in the conventional way (Suo and Hutchinson, 1990;Schapery and Davidson, 1990).…”

Analysis of beam-type fracture specimens with crack-tip deformation

“…The concept of the interface compliance was first introduced by Suhir (1986) to study the stresses in the bi-metal thermostats. In this way, the existing sub-laminate model (Armanios et al, 1986;Chartterjee and Ramnath, 1988;Zou et al, 2001;Wang and Qiao, 2004a) is a special case of Equations (4) and (5) by assuming that the two interface compliance coefficients are zero, which is equivalent to a semi-rigid joint case (Qiao and Wang, 2005, in press). As recently demonstrated by Wang and Qiao (2004b), a good estimation of these two compliances is given by…”

“…However, the beam on elastic foundation model could only be employed to model one sub-beam. In case of a general bi-layer beam-type interface fracture specimen, a sub-layer (or sub-laminate in composite laminates) model (Armanios et al, 1986;Wang and Qiao, 2004a) is more suitable. In this type of model, each layer of the virgin beam near the crack tip was modeled as a single sub-beam, instead of only considering the whole uncracked portion as a composite beam in the conventional way (Schapery and Davidson, 1990;Suo and Hutchinson, 1990).…”