CRACK MEASURING APPARATUS

PURPOSE:To enable automatic determination of relationship between the length of cracking and the frequency of vibration, by detecting change in the output voltage level of a cracking length detection element with a sampling pulse generation circuit. CONSTITUTION:Loading machines 11 and 12 of a fatigue testing machine 10 each vibrate vertically by a distance equivalent to a difference between the max. and the min. of a load control voltage signal Vs. The vibration is applied to a test piece 1 to develop a cracking on the test piece 1 with time. Consequently, an output voltage Vp appears according to the length of the cracking from a crack gauge 16. Level changes in the voltage Vp of the gauge 16 are judged by a sampling pulse generation circuit 17 and a sampling pulse Pr is sent output at each level change. This pulse Pr is sent to a counter 19 to determine the cracking length while the frequency of repeating a load to the test piece 1 is determined according to the cracking length and the results can be displayed. This enables automatic determination of relationship between the cracking length and the frequency of vibration accurately.