Joong-Choon Park

A Study on the Effect of Overload Ratio on Fatigue Crack Growth

A growing fatigue crack is known to be retarded on application of an overload cycle. The retardation may be characterized by the total number of cycles involved during retardation and the retarded crack length. The overload ratio plays an important role to influence the retardation behavior. The objective of the present investigation is to study the effect of different overload ratio on the retardation behavior. For ESET (eccentrically-loaded single edge crack tension) specimens, fatigue crack growth tests were conducted under cyclic constant-amplitude loading including a single tensile overloading with different overload ratios. The proposed crack retardation model predicted crack growth retardation due to a single tensile overloading. The predicted results were compared with the experimental ones to confirm the reliability of this model.

Fracture Characterization of MoSi2 Based Composites

This study dealt with the characterization of MoSi2 based composites containing three types of additive materials such as SiC, NbSi2 and ZrO2 particles have been investigated, based on the detailed examination of their microstructures and fracture surfaces. The effects of reinforcing materials on the high temperature strength of MoSi2 based composites have been also examined. MoSi2 based composites were fabricated by the hot press process under the vacuum atmosphere. The volume fraction of reinforcing materials in the composite system was fixed as 20 %. The microstructures and the mechanical properties of MoSi2 based composites were investigated by means of SEM, EDS, XRD and three point bending test.