A method for estimation of critical stress intensity factor for welded sheet

Welded structures subjected to vibration loads in modern aerospace vehicles during practices have the hazard of undergoing fatigue. Critical stress intensity factor is the key parameter in the fatigue failure criterion. Usually fracture toughness is used as an approximation of the critical stress intensity factor in fatigue crack propagation calculation, however it can be seriously influenced by welding and thickness effects when applied to sheet metal welded joints. To solve the problem, this study analyzes these effects both experimentally and theoretically. The paper considers a method for estimation of the critical stress intensity factor based on crack size at the fatigue fracture location. Fatigue tests are conducted on welded specimens made of 2219-T87 aluminum alloy and critical stress intensity factors are calculated. The relationship for critical stress intensity factor results is determined from fracture crack sizes under different loading modes. Results reveal that the estimation method that was applied to measure the factor based on the fracture crack size excludes influences of welding and thickness effects in a convenient way of measurement and calculation. The method can be adopted for welded structures in spacecrafts subjected to vibration loads for fatigue failure analysis and reference of fracture toughness in engineering practice.