The steady state fracture toughness of elastic visco-plastic materials is studied numerically, using both a conventional and a higher order model. Focus is on the combined effect of strain hardening, strain gradient hardening and strain rate hardening on cracking in layered material systems, and predictions for the crack tip shielding ratio is brought forward. Included is a novel procedure for extracting information on the rate-independent toughness without approaching this numerically cumbersome limit.
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