Trial Manufacture and Performance Evaluation of Fatigue Crack Growth Restraining Sheets Using a High Water Content Gel

A simple technique of restraining fatigue crack growth utilizing wedge effects of electrodeposition products was newly proposed and experimentally tested.Crack growth restraining sheets, which consist of a high water content gel and an anode layer, were manufactured by way of trial and applied to notched plate specimens of a steel and an aluminium alloy, and the efficacy of the sheets was evaluated by fatigue tests.In the fatigue tests, the crack growth restraining sheet was renewed at proper timing to maximize its performance.In order to find a most suitable electrochemical environment for the crack growth restraint by wedge effects of electrodeposition products on the crack surfaces, water components absorbed in the gel and effects of an anode layer as promoting factors of the electrodepositon were comparatively examined.For the steel specimens, it was found that all the proposed crack growth restraining sheets were effective and extend the failure life in the range of 1.6 6.0 times as compared with the base metal specimen, and the efficacy of the gel sheet impregnated with synthetic sea water covered by an anode layer of zinc-leaf tape was maximum.Also for the aluminium alloy specimens, it was found that almost all the proposed crack growth restraining sheets were effective and extend the failure life in the range of 3.66.8times as compared with the base metal specimen, and the efficacy of the gel sheet impregnated with synthetic sea water covered by an anode layer of aluminium-leaf tape connected to an external DC power supply was maximum.From fracture mechanical analyses with FEA, it was found that the crack restraining effect of the gel sheet greatly depends on the water gel content.In situ observations around the cracks and microscopic observations of the fracture surfaces were also performed for a comparative study.