Effects of mixed-mode I/III loading on environment-induced cracking

Many materials that exhibit ductile, tough behavior during conventional Mod e I testing exhibit reduced toughness when loaded with combinations of Mode s I and III. A minimum in the energy for crack initiation and stable crack growth has been demonstrated for ductile metals with mixed-mode loading wit h crack planes at angles between 40 degrees and 60 degrees relative to Mode I loading. Internal hydrogen further reduces these energies in a ferritic/ martensitic steel with the effect being relatively equal in pure Mode I and mixed-mode loading conditions. Hydrogen effects can rationalize a number o f observations of Mode I crack growth rates being faster than Mode III rate s for environment-induced cracking. Where hydrogen is not a factor, cracks loaded in Mode I and mixed-Mode I/III grow at similar rates. (C) 2001 Elsev ier Science Ltd. All rights reserved.