Abstract
In the previous papers, the stability criterion of perfectly flat plate, made of perfectly elastic-plastic material was discussed. However, from practical viepoint, it is rare that plates are perfectly flat, and the average com pressive stresses of plates under tests can often reach the levels above yielding without losing stability. Therefore, we must now treat ahe stability of the plates with small initial imperfections, which are made of strain-hardening material. In this report, the stability of crusiform column is discussed as an example. It is the equivalent case of the long rectangular plate hinged along one edge and free on the other under uniform compressive stress at the ends. Afer investigating for the uniformly compressed crusiform column to fail by twisting, the following results are obtained; (1) The maximum stress of the compressed crusiform column without initial twisting is the same both in the elastic range and in the plastic range. It is called "elastic critical stress". (2) In the elastic range, the maximum stress of the column with initial twisting is the same as the elastic critical stress, independent of twisting magnitude. (3) In the plastic range, however, the maximum stress of the column with some initial twisting enormously descends as twisting angle increases. It is because of existing of shearing stress in addition to compressive stress. (4) The useful suggestions to design criteria of plastic hinges were obtained by examining the relation between the width-thickness ratio of column's wing and the possible twisting angle until losing stability in the plastic range. Moreover, the meaning of stability criterion and what kind of states of shearing stress to have the most influence on the maximum stress are discussed.
