A SIMPLE EXPERIMENT TO FIND PARIS EQUATION CONSTANT OF SHIP BUILDING STEEL

Abstract

Aim: The present work attempts to conduct fatigue testing on Shipbuilding steel. And find the Paris equation constant for the same. Methodology: The procedure involves application of constant amplitude pulsating stress on cantilever specimens, starting from zero to a maximum value. A simple test rig has been designed and fabricated and installed. To study the crack growth phenomenon in ship building steel experimental programme was planned. Long specimens with Rectangular cross section with size 50mm x12mm were cut
and machined form ship building steel. Those specimens are pre-cracked at very low stress levels to obtain test specimens with initial cracks. The testing machine essentially consists of a eccentric cam assembly mounted on a shaft fitted on to the frame by two plummer blocks. This shaft is driven by an electric motor of 5HP, 1440 rpm using a V -belt speed reduction drive. Crack initiates near the fixed end of the specimen and the growth of the crack occurs both along the width and along the depth directions. The growth along the width direction observed during frequent intervals. The full inside view of the fatigue crack in specimens after the cycling is made possible by breaking the specimen along the plane of crack. After completing the desired number of cycles the specimens which are removed from the test rig are dipped in liquid nitrogen immersing the cracked surface area for a short duration. Later the specimens were taken out and broken to observe the crack profile clearly. A load load-point deflection records were made at various stages of crack growth. Paris equation is utilized for analyzing the crack growth rate during the propagation of the crack. Result: From the experimental data available constants of Paris equation are calculated for the material. Conclusion: the value obtained for the Paris equation constant are very much tally with the available values from the literature.