A study on flaw detection method for CFRP composite laminates. (1st report). The measurement of crack extension in CFRP composites by electrical potential method.

An in-service flaw detection and estimation method for CFRP composites using electrical potential drop is developed. It involves passing a constant current through composites and measuring the electrical potential, which changes as the crack advances. The resister network analysis of the random lattice model of CFRP composites shows that even in the plane normal to the fiber direction, CFRP composites can be considered as electrically homogeneous on a gross scale, i. e., on a scale of dimensions dozens of times large compared with the fibre radius. The analysis also shows that the method can detect the small increment of crack growth in CFRP composites with only a fraction of current that is required for metals. The relation between the amount of the crack growth and the potential change is expressed by a broken line composed of two straight lines. The method is applied to the delamination test of the DCB composite laminate specimen and the results are compared with the FEM solutions. The present method can provide accurate and inexpensive means for flaw detection and crack growth measurement in CFRP composite structures.