The Use of Eigenfunction Expansions in the General Solution of Three-Dimensional Crack Problems R. HartranftG. Sih Indiana University Mathematics Journal 1970 text pdf 10.1512/iumj.1970.19.19012 10.1512/iumj.1970.19.19012 en Indiana Univ. Math. J. 19 (1970) 123 - 138 state-of-the-art mathematics http://iumj.org/access/