Determination of Failure Characteristics of Materials and Structures
Final technical rept. 1 Jun 1975-30 Nov 1983
GEORGE WASHINGTON UNIV WASHINGTON DC SCHOOL OF ENGINEERING AND APPLIED SCIENCE
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A research program has been pursued with the objective of examining failure characteristics of materials and structures analytically and experimentally. The expression for the nonlinear energy toughness was rederived for a generalized instability condition and new expressions were derived for biaxial loading situations. The geometry dependence of the nonlinear energy toughness was studied experimentally using center-cracked thin sheet specimens and thicker compact tension specimens of several alloys and compared with other nonlinear toughness parameters. The nonlinear energy toughness can be used as a useful failure criterion under certain geometrical variations in semi brittle materials. Its geometry dependence is similar to that of JIc. Experimental and finite element studies have shown that the plastic energy dissipation is a linear function of the plastic energy dissipation is a linear function of the stable crack growth, but the slope of the curve has been found to change considerably with changes in crack length-to-specimen width ratio. Singular solutions of cracked bodies predict no biaxial effect when one load axis is parallel to the crack plane. However, it has been shown analytically that including the second term reveals changes in stresses and strains in the vicinity of the crack tip due to biaxiality. Finite element studies show larger dependence of stresses and strains on biaxiality on ductile materials. Pulse duration has a significant effect on buckling under dynamic loading. Plastic deformation has a significant effect in buckling only when the imperfection is small, and creep plays an important role in long term loading.
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