Effect of artificial closure materials on crack growth retardation

Premature crack closure plays a dominant role in affecting the crack driving force during fatigue. This work is focused on artificial infiltration of closure materials into a crack, promoting premature crack closure thereby depressing crack growth rate. Thus, service life is extended for cracked members. The test program was performed in 5083-O Al-alloy and AISI 4130 alloy steel, 9.8 and 3.6 mm in thickness, respectively. Pressurized nitrogen was utilized in boosting different closure materials into the crack. These materials include (i) epoxy resin modified with fine (0.05 mu m) and coarse (1 mu m) alumina powders, respectively; (ii) epoxy resin containing 1 mu m silicon carbide powder; and (iii) silver paste. Experimental results indicated that, with the exception of silver paste, all the other closure materials work well in giving rise to different levels of crack closure and the accompanying growth retardation. The silicon carbide reinforced epoxy resin has the best retarding ability. The corresponding life extension exceeded 300 000 cycles. (C) 1998 Elsevier Science Ltd. All rights reserved.