A Constant-G Double Cantilever Beam Fracture Specimen for Environmental Testing

Straight-sided double cantilever beam (DCB) fracture specimens have been used previously for long-duration environmentally assisted crack growth (EACG) testing. However, the applied strain-energy release rate G decreases with crack extension. In this study the width taper required to achieve constant-G during crack growth in a dou ble cantilever beam (DCB) fracture specimen is determined for the case of general load ing. The width taper b(a) is a function of the initial specimen compliance, C _o, the crack length, a, and the stiffness of the loading frame, κ. The compliance of DCB specimens tapered for testing under three loading conditions were verified experimentally. These were constant-load (κ → 0), constant-strain (k → ∞), and critical spring loading (κC _o → 0.5). Specimens designed for critical spring loading are suggested for use in long-term (EACG) experiment,, Limitations on the proposed test method related to nonlinear material behavior (e.g., crack bridging) are discussed.