Apparatus for maximizing critical buckling loads for compression testing

摘要

Attempts to determine compression properties of materials from specimens having a thin cross-section or even specimens that have relatively large cross-sections and correspondingly large slenderness ratios, i.e., length-to cross-sectional-thicknesses, are thwarted, became failure will occur due to Euler buckling prior to the realization of the objective. The same problem exists when testing columns of various cross- sections and thin-walled cylinders as structural components, depending upon their slenderness ratios, or in situ specimens cut out of thin structural components. This invention presents an improved, but simple way to increase the critical buckling force while mechanically testing in compression laboratory specimens, in situ test specimens taken from structural components, or even structural components having large slenderness ratios. The invention allows the true compression load to be fully developed within the test piece such that the compression properties of the test material can be determined without buckling. This device can be operated at cryogenic, ambient, or elevated temperatures. The invention utilizes a hollow cylinder, termed a bending moment absorber, which is fitted and fixed to the ends of the test specimen. The test specimen can be a dumbbell type, a thin coupon, a thin hollow cylinder, or in situ a specimens cut out of structural components. The test piece can be either pinned or threaded and/or bonded at its ends to the bending moment absorber. The sample can be rectangularly-shaped or have a square-shaped cross-section, wherein semi-circular spacers, with appropriate cut-outs to fit and accommodate the particular cross-sections, which are employed at each end and pinned or threaded and/or bonded between the specimen and the bending moment absorber. These assemblies, in turn are clamped at each end by commercially available hydraulicly- operated grips within the load train. The combined cross-sections of the hollow cylinder and the specimen act in concert so as to markedly increase the moment of inertia of the system and will result in a corresponding increase in the critical buckling load.