A Method of Analyzing Fatigue Cracks in Cast Iron by Measuring Vibration Characteristics Caused by Impact Striking

This paper describes a technique for evaluating fatigue cracks in cast iron by analyzing vibration caused by hammer striking. The relationship between the vibration characteristics and cracking damage is quantitatively investigated for gray cast iron by using bending load tests and slitting. It is found that the resonant frequency decreases and the attenuation constant increases as cracks extend. The stage of crack extension can therefore be quantified by determining the typical relation between the attenuation constant and resonant frequency. We theoretically investigate the speed of crack growth and the destruction process of cast iron by determining the relationship between the reduction of resonant frequency caused by cracks to the stress intensity factor and stress cycles in the fatigue model. Based on the experimental results, we have devised a manhole cover diagnosis technique and we have developed a portable tester that can evaluate cracking damage of covers in the field.