SEDL / STP / STP1280-EB / STP16221S

Plane Stress Crack Resistance Curves of an Inclined Crack Under Biaxial Loading

Donne, CD
Research engineer and section head, German Aerospace Research Establishment DLR, Institute of Materials Research, Cologne, D

Döker, H
Research engineer and section head, German Aerospace Research Establishment DLR, Institute of Materials Research, Cologne, D

Pages: 21    Published: Jan 1997

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Abstract

Elastic-plastic stable crack growth under Mixed-Mode I and II loading in thin cruciform specimens of aluminum, Al2024-T3, and structural steel, StE 550, was investigated using a biaxial test rig. Two cruciform specimen types were considered, one containing an inclined through thickness crack, the other with inclined short cracks emanating from a hole (precrack length to hole radius ratio, á⁰/R = 0.286). It is shown that predominant Mode II loading drove the stable crack in the direction almost parallel to the fatigue pre-crack (maximum shear strain criterion). High (steel) or moderate (aluminum) Mode I crack-tip-opening components caused a crack path deviation, that is, the stable crack grew normal to the maximum tensile stress. The mixed-mode crack resistance curves are presented in the form of the magnitude of a crack-tip-displacement vector, δ^s = (δ^I2 + δ^II2)^0.5, and compared with conventional R-curves of standard compact-tension (C(T)) and center-cracked-tension (M(T)) specimens. The effect of the load biaxiality is discussed with regard to previous experiments with Mode I loaded cruciform specimens.