10 - Time-dependent damage evolution in unidirectional and multidirectional polymer composite laminates

Abstract

Damage modes such as fiber cracks, matrix yielding, matrix cracks, and fiber-matrix interfacial debonding can develop within a lamina. These are referred to as intrinsic damage modes to contrast them with the extrinsic damage modes that develop within a laminate, such as delamination between the plies and repeated cracking of a ply (matrix cracks also known as transverse cracks) due to constraints applied by surrounding plies. Due to viscoelasticity and viscoplasticity of the polymer matrices used in structural composites, the evolution as well as sequence of evolution of these damage modes may vary with loading rate (quasistatic loading), time (static loading, i.e., creep), and number of cycles (cyclic loading). These in turn will influence how the properties degrade with loading rate, time, and number of cycles. Due to increasing use of polymer composites in load-bearing structural applications, a comprehensive review of the state of the art in this area is essential and would be timely, to help designers as well as researchers in this area. Hence, this chapter includes (a) an introduction to various intrinsic and extrinsic damage modes, (b) a review of experimental studies of time-dependent evolution of these damage modes during quasistatic, static, and cyclic loading including characterization methods, (c) a review of published criteria to predict the time-dependent initiation and evolution of intrinsic and extrinsic modes, and (d) concluding remarks based on the review.