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Size effects in copper whiskers Moore, Zelma Esther

Abstract

Whiskers were grown by the hydrogen reduction of cupric chloride. Tensile tests were performed on the whiskers, some of which were long enough to divide into two or three parts. After the whisker yielded ("primary tests") they were retested ("secondary tests") after removal of the deformed region. In order to see if length had any effect on yield stress, a normalizing proceedure was established to convert the yield stress measured at any diameter d to an equivalent whisker with d = 10 μ. No observable length dependence of yield stress was found for either primary tests or secondary tests. The diameter dependence of yield stress was found to depend on the type of tests. For primary tests, the yield stress was inversely proportional to d¹‧⁶, while for secondary tests, inversely proportional to d²‧⁵. A dislocation mechanism to explain this was proposed in terms of only a part of the cross-sectional area (a small annular ring at the periphery of the whisker) taking part in the deformation. This mechanism was suitable only if the whiskers were assumed to be initially free of dislocations. A decrease in the value of Young's Modulus of about 30% from the normal values was observed for whiskers subjected to a secondary test.

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