Testing Method for Evaluation of Mode II Fatigue Delamination Growth Behaviors of Advanced Composite Materials

摘要

The crack shear displacement (CSD) is theoretically four times sensitive to the crack propagation than that of the load point displacement. In this paper based on CSD measurement, a new testing method for mode II fatigue Delamination growth of unidirectional CFRP laminates was developed. Mode II fatigue tests are conducted by applying the end-notched flexure (ENF) specimen and controlled by a computer through the parameter of maximum mode II energy release rate (G_IImax). The crack length and the G_IImax were measured through the CSD compliance. In order to measure the CSD with a high accuracy, experimental techniques, such as selection of the gage, mounting method of the gage and methods for preventing the ENF specimen from shifting during fatigue, were fully examined. Especially, with the solution of the friction problem which exists between the surfaces of the mode II crack, the accuracy and the stability of the CSD measurement have been greatly improved. As test conditions, the influence of the loading frequency and the suitable range of the normalized G_IImax gradient of the G_IImax-shedding test were also discussed.