The caustics method is a useful measurement for determining the value of the stress intensity factor, K. The method mainly has been applied to isotropic materials. For anisotropic materials, however, it does not appear that this method has been studied much. In this paper, the method of caustics is examined for a highly orthotropic unidirectionally reinforced carbon-epoxy composite under mode I loading by using a coating technique. The results are compared with those of finite element analysis. The main results are summarized as follows:
It is possible to apply the method of caustics to orthotropic CFRP laminate materials. A measurement technique suggest by this study is useful in case the initial curve radius, ro, is larger than the minimum initial curve radius, romin.
The magnitude of the minimum initial curve radius, romin, is the specimen half-thickness in the case of orthotropic CFRP laminate material. This is identical to the results of isotropic materials.
The distribution of displacement by two-dimensional and three-dimensional finite element analyses near the crack tip for CFRP laminate materials correspond to the distribution of a three-dimensional field.
Composite materials have many mechanical advantages as 264 structural members. The investigation from a fracture mechanics point Of view is essential to the safe use of composite materials. The optical method of caustics is a useful technique for determining the stress intensity factor, K, experimentally [M. Shozu, 1995, 1996], [S. Suzuki, 1989]. This method has been applied mainly to isotropic materials. For anisotropic materials, however, it does not appear that this method has been studied much. In this study, the method of reflected caustics is applied to specimens with a highly orthotropic, unidirectionally-reinforced carbon-epoxy composite under mode I loading by using a coating technique.
