EVALUATION OF THE PERTURBATION PARAMETERS IN BUCKLED RECTANGULAR PIN-ENDED EULER STRUTS BY CAUSTICS

The optical method of reflected caustics was applied to beam buckling problems. The reflected rays of a light beam (either parallel, or conv ergent, or divergent) on the flanks of the strut create caustics which consist of two strongly illuminated straight lines, confining the lum inous region of the strut. By measuring the distance between the extre mities of the caustics, the perturbation parameter s of the buckled be am can be defined. The accurate experimental evaluation of s allows th e solution of the respective Euler expansion equations for the critica l buckling load and its higher order terms in the post-buckling state of the strut. The method is a versatile and sensitive technique for ex perimentally defining the mode of elastic buckling of struts and can b e extended to study plastic buckling cases.