PREDICTION OF CRACK INITIATION IN UNIDIRECTIONAL COMPOSITE BEAMS SUBJECT TO 4-POINT BENDING

The local stress field near a support is analyzed as a contact stress problem in an infinite half plane. The results are utilized to explain the influence of focal stresses on crack initiation in a four-point b ending test on unidirectional graphite/epoxy composite beams. Also, nu merical simulations are carried out using the finite element method. C rack-initiation phenomena at the bottom surface of the beam are explai ned with the aid of the stress distribution and strain-energy release rates. The initiation location for various fiber angles is predicted a nd compared with the experimental results reported in the literature. The existence of two distinct ranges of fiber angles for which the cra cking phenomena is different is verified.