NOVEL SERR-CONTROLLED ENVIRONMENTAL FATIGUE TEST METHODOLOGY FOR ADHESIVE-BONDED LAMINATES
In this paper a novel environmental fatigue test methodology is presented, in which the strain energy release rate (SERR) was controlled during the cyclic experiment at an elevated temperature in humid air. Therefore, an electrodynamic testing machine equipped with a custom-built environmental chamber along with a compatible calculation and controlling software package was used. To determine the crack length based on force and displacement data a compliance-based calibration method was implemented. SERR values were deduced for individual load cycles employing an user defined control channel. The control channel allows for definition of a specific starting point (e.g., 10 J/m²) and an increase rate (e.g., +5 J/m² after 50,000 cycles). By holding the SERR constant over many cycles confidence bands were deduced for the measured crack propagation rates accounting for measurement uncertainties. To corroborate the novel methodology, experiments were conducted on double cantilever beam laminates bonded with soft adhesives in both, a SERR and a displacement controlled mode.