Plastic Flow and Fracture in a Torsionally Stressed Planetary Sphere Hugh Rance Indiana University Mathematics Journal 1968 text pdf 10.1512/iumj.1968.17.17059 10.1512/iumj.1968.17.17059 en Indiana Univ. Math. J. 17 (1968) 953 - 974 state-of-the-art mathematics http://iumj.org/access/