When a copper plated specimen is subjected to cyclic stress, grown grains appear in the plating zone. In this investigation, the relation between the density of grown grains and the stress amplitude has been examined. The result showed that the relation between the grown grain density r and the stress amplitude τ was expressible by the equation, τ=A+B·ln(1/r-1), where A and B are constants determined by the number of stress cycles and the plating solution. Thus, when the coefficients A and B are obtained in advance for the plating solution to be used, the stress at the measuring portion can be found from the above equation by measuring the density of grown grains at the portion. By using the above method, the stress concentration factor of the shaft with a semi-circular groove in torsion was measured. It was found that this method was an accurate way for stress analysis.
