METHODOLOGY FOR RESIDUAL STRENGTH EVALUATION OF CRACKED STRUCTURES

Residual strength evaluation is playing a significant role in damage tolerance analysis of structures. Available methods to determine residual strength of engineering structures are those similar to Feddersen's, in which the strength evaluated on the basis of linear elastic fracture criterion must be limited by flow stress at short crack length and by net section yielding stress as crack ligament is getting quite narrow. Major deficiencies of such methods are that smooth curve of elastic fracture strength vs. crack length must be available before any modifications going along with it, and they are not applicable, or inconvenient to use for some situation. A simple procedure for evaluating residual strength of structures with cracks was developed based on the consideration that the strength of a cracked body is controlled by the mechanism of both linear elastic fracture and net section static failure. The linear elastic fracture strength is determined in terms of apparent fracture toughness criterion and the static failure strength equals the ultimate load that would result in entire breaking of ligament beyond crack tips. According to present method, it is convenient to obtain residual strength value at any given time. Two kinds of specimens, center cracked LY12CZ aluminum alloy plates (CCT specimens) and pin loaded straight lugs separately made of LD5CS aluminum alloy forging and 30CrMnSiNi2A steel alloy forging materials, were tested to obtain their residual strength. Good agreement was achieved between the results of residual strength predictions according to derived formula and test results. Nowadays, lack of fracture toughness data has become the major impediment for the application of residual strength evaluation methodologies.