Compressed block to indentation

Values of indentation force N for a given small indentation, from Eq. (1.27), are plotted in Figure 1.13 against the equibiaxial strain e parallel to the surface, where e = X — I. (No denotes the value for an initially unstrained block, when f(X) = 2.) The resistance to indentation is seen to decrease sharply as the compressive strain is increased, becoming zero at a compressive strain of 0.333, in agreement with Biot s result. 

When a block is subjected to a sufficiently large equibiaxial compression in the surface plane it becomes unstable to small indentations. Green and Zema [29] expressed the relation between indentation force N and amount of indentation d as ... 

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