Biologically inspired design—natural convex joints reduce stress concentrations

Finite element stress analysis and corner optimization of a tree-steel railing interface/joint (Mattheck, 1998) showed that the naturally formed tree/railing joint was very effective in reducing stress concentration. Using this principle, we designed and tested convex interfacial joints of dissimilar engineering materials, and find that these new joints will significantly increase ultimate failure load and even reduce material volumes.  Click here to read two related papers (a. Xu, et al., Experimental Mechanics, 2004; b. Wang and Xu, Mechanics of Materials, 2006).

Our In-situ photoelasticity experiments on polycarbonate-aluminum joints showed that the free-edge stress singularity (leading to stress/fringe concentration) existed in the straight-edge joint (first movie).© Dr. L. R. Xu (Vanderbilt University)

However, for our proposed convex joint, free-edge stress singularity was successfully removed so no fringe concentration was observed at the specimen edges (second movie). © Dr. L. R. Xu (Vanderbilt University)