A NUMERICAL STUDY OF DYNAMIC CRACK-GROWTH IN ELASTIC-VISCOPLASTIC SOLIDS

Dynamic crack growth is analyzed numerically for a plane strain block with an initial central crack subject to impact tensile loading. The m aterial is characterized as an isotropically hardening elastic-viscopl astic solid. A cohesive surface constitutive relation is also specifie d that relates the tractions and displacement jumps across the crack p lane. In this formulation crack initiation, crack growth and crack arr est emerge naturally as outcomes of the imposed loading, without any a d hoc assumptions concerning crack growth criteria. Full transient ana lyses are carried out using two characterizations of strain rate harde ning; power law strain rate hardening and a combined power law-exponen tial relation that gives rise to enhanced strain rate hardening at hig h strain rates. The effects of the strain rate hardening characterizat ion on crack initiation, crack growth and crack arrest are investigate d. Enhanced strain rate hardening is found to lead to higher crack spe eds, to lower toughness values and to crack tip fields that are more l ike those of an elastic solid than for the power law rate hardening so lid. Additionally, some parameter studies varying the cohesive surface strength and the material flow strength are carried out. The effectiv e stress intensity factor is found to increase dramatically at a certa in value of the crack speed that depends on the cohesive surface stren gth, the material Bow strength, the characterization of strain rate ha rdening and the impact velocity, but there is a range where the crack speed at which the increase in effective stress intensity factor occur s is not very sensitive to impact velocity. (C) 1997 Elsevier Science Ltd. All rights reserved.