THE LAGRANGIAN MULTIPLIER METHOD OF FINDINGnUPPER AND LOWER LIMITS TO CRITICAL STRESSES OF CLAMPED PLATES

摘要

The theory of Lagrangian multipliers is applied to the problem of finding both upper and lower limits-to the true compressive buckling stress of a clamped rectan¬gular plate. The upper and lower limits thus bracket the true stress, which cannot be exactly found by the differential-equation approach. The procedure for obtaining the upper limit, which is believed to be new, presents certain advantages over the classical Rayleigh-Ritz method of finding upper limits. The theory of the lower-limit procedure has been given by E. Trefftz but, in the present application, the method differs from that of Trefftz in a way that makes it inherently more quickly convergent. It is expected that in other buckling problems and in some vibration problems, the Lagrangian multiplier method of finding upper and lower limits may be advantageously applied to the calculation of buckling stresses and natural frequencies.