Collapse of Thick Hollow Cylinders by External Pressure T. Thomas Indiana University Mathematics Journal 1968 text pdf 10.1512/iumj.1968.17.17061 10.1512/iumj.1968.17.17061 en Indiana Univ. Math. J. 17 (1968) 987 - 1004 state-of-the-art mathematics http://iumj.org/access/