Abstract
An effect of per-loading on fracture toughness was studied by using a three-point bending test method on a steel of 50kgf/mm2 strength. Results are summerized as follows.
(1) In the case of low fracture toughness, preloading gave little influence on the critical COD, so that preloading is beneficial to safety.
(2) In the case of high fracture toughness, perloading made the critical COD decrease by the nearly same amount as COD produced by preloading. Preloading is not necessarily beneficial.
A possible mechanism was discussed as to why preloading gives the effect on the critical COD.
