In research pub­lished in the March 4 issue of the journal Nature, North­eastern Uni­ver­sity physi­cists have pio­neered the devel­op­ment of large-​​scale com­puter sim­u­la­tions to assess how cracks form and pro­lif­erate in mate­rials ranging from steel and glass to nanos­truc­tures and human bones.

For years, sci­en­tists have tried to under­stand the prop­a­ga­tion of cracks and how they affect the mate­rials in which they form, said Alain Karma, dis­tin­guished physics pro­fessor and lead inves­ti­gator on the project.

We now better under­stand what path cracks follow as they prop­a­gate in a stressed mate­rial,” said Karma, director of Northeastern’s Center for Inter­dis­ci­pli­nary Research on Com­plex Sys­tems. “This knowl­edge will allow us to develop new mate­rials — for advanced air­craft tur­bine blades, micro-​​electronic cir­cuits and arti­fi­cial bone — that better with­stand destruc­tion caused by cracks.”

Karma and the research team started out by exam­ining the com­bined effects of two types of stress on crack prop­a­ga­tion: shearing and ten­sion. Shearing occurs nat­u­rally when mate­rial is twisted out of shape while ten­sion occurs when mate­rial is pulled out of shape. The com­bi­na­tion of shearing and ten­sion causes crack insta­bility. The mech­a­nism for how this insta­bility develops and spreads, how­ever, remained elu­sive until Karma uti­lized the power of a computer.

Large-​​scale com­puter sim­u­la­tions yielded the sur­prising result that shearing and ten­sion cause cracks to take the shape of a helix. Based on the sim­u­la­tion results, Karma and his team devel­oped a the­o­ret­ical equa­tion to pre­dict how the helix would rotate, expand and mul­tiply in dif­ferent materials.

The fun­da­mental ques­tion we are answering is how these cracks grow inside mate­rials, said Karma. “Now that we have that infor­ma­tion, we can develop new mate­rials to with­stand cracks, as well as more effec­tively reduce the damage of cracks once they form.”

The research could yield inno­va­tions in the pro­duc­tion of lighter auto­mo­bile and air­craft parts that reduce energy con­sump­tion, and com­posite arti­fi­cial bones that will not frac­ture when inside the body. The results also have impli­ca­tions for under­standing the evo­lu­tion of geo­logic faults and frac­tures in the earth’s crust.