Direct Tensile Test: Stability and Bifurcationby Zdeněk P. Bažant, Civil Engineering Northwestern Univ, Evanston, United States,
Luigi Cedolin, Civil Engineering Northwestern Univ, Evanston, United States,
Abstract: Unnotched specimens of quasibrittle materials that exhibit post-peak strain softening do not deform symmetrically in a direct tension test. The phenomenon (which is similar to the recently discovered behavior of notched tensile fracture specimens) is illustrated using a simple model in which the specimen consists of two bars of unequal length, joined by a strain-softening link. The equilibrium path bifurcates and the thermodynamic criterion of stable path requires the specimen to flex to one side, even if the geometry is perfect and if the straightening effect of the moment of the axial force about the centroid of the deflected cross section is taken into account. The bifurcation behavior is analogous to Shanley's bifurcation in elastoplastic columns. In absence of rotational restraints at the ends, the specimen fails right after the peak load. The lateral flexing can be retarded by providing rotational restraints at the specimen ends.
Subject Headings: Material tests | Strain hardening and softening | Bifurcations | Ultimate strength | Thermodynamics | Model tests | Cracking
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