Extraction of EAC crack growth rates and stress intensity factors from slow strain rate tests data for 5xxx and 7xxx series aluminum alloys
July 15-20, 2018
A knowledge of crack propagation rate as a function of the applied stress intensity factor (K) to generate crack velocity-K (cv-K) curves for aluminum alloys is desired due to their propensity for environment-assisted cracking (EAC). However, to do this has historically required the use of standard fracture mechanics test specimens requiring several days to months per test. In addition, most data obtained in this way involves the use of fixed-displacement double-cantilever-beam (DCB) or compact-tension-specimens (CTS). Here, the applied K during testing decreases with increasing EAC crack length, and the K-factor measured at the end of testing is a ‘crack arrest’ parameter, as opposed to an EAC threshold factor, K1SCC as assumed in most studies, which may become invalidated by crack branching and in some environmental conditions by secondary stresses generated in the crack-tip region due to local wedging from corrosion products.
A method of extracting information to construct EAC crack velocity-K curves under raising load (and K) conditions from slow strain rate test taking only a few hours is provided. Verification of assumptions made with regards to EAC crack initiation and growth is presented based on 3D computed Tomography data from interrupted slow-strain rate tests and information from 4D computed Tomography data from slow-strain rate experiments conducted on the Diamond Light Source Synchrotron.
Henry Holroyd, "Extraction of EAC crack growth rates and stress intensity factors from slow strain rate tests data for 5xxx and 7xxx series aluminum alloys" in "Stress-Assisted Corrosion Damage V", A.K. Vasudevan, ONR (retired) Ronald M. Latanision, Exponent, Inc. N. J. Henry Holroyd, Luxfer Eds, ECI Symposium Series, (2018). http://dc.engconfintl.org/sacd_v/28