Abstract
Two-dimensional off-axis ratcheting behavior of unidirectional CFRP laminates at high temperature has been examined for different fiber orientations on the basis of strain field measured by means of a digital image correlation (DIC) method with two CCD cameras. The accuracy of strain measurement with DIC is first evaluated by comparing the stress-strain curves identified with DIC and strain gauge, respectively, indicating that in-plane strains and their distributions can adequately be measured with DIC. Then, accumulation of in-plane strains in off-axis specimens at high temperature under an asymmetric cyclic loading at a constant stress ratio is observed for different fiber orientations. Non-uniform strain field in off-axis specimen during ratcheting that depends on fiber orientation is successfully visualized by DIC. It is shown that two-dimensional off-axis ratcheting behavior depends on fiber orientation, and the magnitude of ratchet strain tends to become larger than that of creep strain at the constant stress with a magnitude equal to the maximum stress of cyclic loading. It is also revealed that the time dependence of off-axis ratcheting behavior is similar to that of off-axis creep behavior.
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