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The use of decohesion elements for the simulation of delamination in composite materials is reviewed. The test methods available to measure the interfacial fracture toughness used in the formulation of decohesion elements are described initially. After a brief presentation of the virtual crack technique most widely used to simulate delamination growth, the formulation of interfacial decohesion elements is described. Problems related with decohesion element constitutive equations, mixed-mode crack growth, element numerical integration and solution procedures are discussed. Based on these investigations, it is concluded that the use of interfacial decohesion elements is a promising technique that avoids the need for a pre-existing crack and pre-interfacial decohesion elements is a promising technique that avoids the need for a pre-existing crack and predefined crack paths, and that these elements can be used to simulate both delamination onset and growth.
Written by leading authorities in the field of damage and micromechanics of composites, this book deals mainly with the damage impaired in composites due to different types of loading. It examines the different types of damage in composites in the fiber, matrix, debonding and delamination. It also reviews the theoretical characterization of damage, its experimental determination as well as the numerical simulation of damage.
The objective of this work was to investigate the fatigue damage mechanisms and to identify the influence of skin stacking sequence in carbon epoxy composite bonded skin/stringer constructions. A simple 4-point-bending test fixture originally designed for previously performed monotonic tests was used to evaluate the fatigue debonding mechanisms between the skin and the bonded frame when the dominant loading in the skin is flexure along the edge of the frame. The specimens consisted of a tapered flange, representing the stringer, bonded onto a skin. Based on the results of previous monotonic tests two different skin lay-ups in combination with one flange lay-up were investigated. The tests were performed at load levels corresponding to 40%, 50%, 60%, 70%, and 80% of the monotonic fracture loads. Microscopic investigations of the specimen edges were used to document the onset of matrix cracking and delamination, and subsequent fatigue delamination growth. Typical damage patterns for both specimen configurations were identified. The observations showed that failure initiated near the tip of the flange in the form of matrix cracks at one of two locations, one in the skin and one in the flange. The location of the 90 deg flange and skin plies relative to the bondline was identified as the dominant lay-up feature that controlled the location and onset of matrix cracking and subsequent delamination. The fatigue delamination growth experiments yielded matrix cracking and delamination onset as a function of fatigue cycles as well as delamination length as a function of the number of cycles.