| The delamination fracture toughness of graphite, glass, and aramid-epoxy composite laminates were determined as a function of loading rate for unidirectional and woven fibrous reinforcements. In addition, the in-situ fracture toughness of the epoxy matrix was obtained by determining the strain energy release rate during the delamination fracture of thin epoxy films.;The results show that increasing the loading rate as well as the use of woven reinforcements increases the fracture toughness. The fracture surfaces were investigated using scanning electron microscopy. A fracture toughness model is developed which provides information on micro and macrofailure processes, and estimates the relative contributions for the fiber-matrix interface and the matrix itself to the overall delamination fracture toughness.;Microcracking-induced acoustic emission (AE) during Mode I fracture was monitored to study microfailure processes involved during fracture. In addition, AE was used to determine whether a correlation exists between the strain energy release rate and acoustic emission parameters. These experiments were conducted for the in-situ epoxy matrix, woven graphite, glass, and aramid-epoxy composite laminates.;The results show that there are at least five separate stages present in the Mode I delamination fracture: elastic region, microcracking initiation, microcracking growth, macrocracking initiation, and macroscopic delamination. The macroscopic delamination stage also consists of several microcracking stages. In addition, each microcracking stage itself contains all the five stages present in delamination fracture.;A correlation was obtained between the total AE counts per unit crack area during delamination (steady-state macrocrack propagation) and a strain energy release rate (G... |
