Solution

ID: past-exam-of-the-elasticity-and-plasticity-course-of-the-university-of-oxford/2011/2/f/solution

The material occupies , so its outward unit normal at the surface is . A free surface has zero traction, . Therefore
The third condition is automatic for the two-dimensional displacement field with zero third component and no dependence on the third coordinate. The first two impose zero shear and normal stress at the free surface.

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