Texas A&M researchers are challenging current theories behind the driving failure of metal alloys. Their findings could unravel the mystery of why load-bearing structures like commercial aircrafts and bridge suspension beams suddenly crack under physical stress.
The leading theory is porosity softening, which creates voids in the alloy that grow and join under constant tension. These cause shear fractures — the particular type of break that occurs in metal alloys.
Dr. Amine Benzerga and his colleagues noticed that most studies investigating the cause of shear fractures were based on experiments using rectangular-shaped alloys. For their experiments, Benzerga’s team turned to cylindrical-shaped alloys. With the new shape, they found their specimens less frequently had shear fractures.
“The fact that the shape of our specimens was influencing how often we saw shear fractures told us that something else is driving shear failure and that porosity softening was not the whole story,” Benzerga said.
To examine the cause, researchers built a sophisticated simulation model that considered porosity softening along with other potential causes, including plastic anisotropy — the property by which a pull or load on a material from one direction causes damage that is different from that in another direction.
“Our simulations were telling us something very different from the accepted theory for the cause of shear fractures,” Benzerga said.
The researchers speculate that plastic anisotropy causes internal damage to the material, leading to voids. As damage continues, these voids become larger naturally, then coalesce over time and cause failure.
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