Real-Time Characterization of Damage Growth in Graphite/Epoxy Laminates

Abstract

The damage growth and failure mechanism in graphite/epoxy composite specimens were characterized by using a modified X-ray nondestructive evaluation ( NDE) technique. The NDE monitoring was conducted in real- time while the fracture specimens were under tensile ramp loading and constant amplitude cyclic loading. Tetrabromoethane ( TBE) was applied as an opaque additive at the tips of a slit in the center of the specimens to enhance the flaw image. Damage initiation, growth and failure mechanism were observed from sequences of X-ray pictures recorded during testing. Limited results indicated that matrix failure appeared to precede delamina tion between plies in the failure mechanism study. The NDE technique allowed the actual stress redistributions in the composite laminates to be observed.

3-Dimensional Response of Composites

“…Subsequently, various authors have conducted investigations on this problem by using various techniques such as finite difference, finite element and series solutions. References (2,3,4,14] lead to an understanding of various failure modes that 4 have been shown to occur in composite laminates. The bending and stretching of laminate deformation and Reissner-Mindlin plate theory have been incorporated [5,6] and higher order classical laminate theory [9,10] was applied to evaluate the interlaminar normal stress distribution, but only at a plane of symmetry.…”

“…However, the analytical investigation of the nature and magnitude of the free edge stresses by various researchers has lead to disparate conclusions. As an extension, a reliable analytical procedure for solving the free edge problem may also lead to an understanding of the various failure modes that have been shown to occur in composite laminates [1,2,3,4]. Also, in practical applications of composite materials, a large number of anisotropic layers are usually present.…”

Failure Strength and Damage Mechanisms of E-Glass/Epoxy Laminates under In-Plane Biaxial Compressive Deformation

“…More recently, attention has been focused on composite compressive failure mechanisms because compressive failure modes are more sensitive to the constitutive materials, interface properties, material processing variables, composite lamination parameters, manufacturinginduced flaws, structure shape, and size and loading conditions than the tensile failure modes. A variety of test methods have been used to investigate the composite failure mechanisms, including SEM observation [1], surface and subsurface optical microscopy [2,3], ultrasonic scanning [4], acoustic imaging [5], Xray analysis [6], and surface replication. Both microand macromechanisms have been studied using these methods.…”