Virtual testing for fracture toughness, fatigue crack growth and fatigue life data estimation of metallic components

Evaluating fracture and fatigue life properties of structural components involves tests that are costly and time consuming. To estimate total life of engineering parts, high cycle fatigue data (S-N) for the material under study is needed. In many cases the S-N data is not available to the analyst and both the time and budget required for testing prevent engineers to meet the deadline imposed on the program. An analytical combined Progressive Damage and Fracture Mechanics based approach is proposed that estimates the S-N data for components that have stress concentrations. The proposed methodology starts from a full engineering tensile stress-strain curve of the material under study and ends up with the estimation of fracture toughness, fatigue crack growth and fatigue S-N curves. The methodology is presented and validated for two aerospace alloys, Aluminum 7050T-7451 and Titanium Ti-6Al-4V MA, for different geometries and stress ratios. AlphaSTAR's MCQ-Metals and GENOA virtual testing tools implement this methodology and perform the prediction sequentially: 1) Fracture Toughness Determination (FTD) module estimates fracture toughness vs. specimen thickness, 2) Fatigue Crack Growth (FCG) module predicts da/dN vs. Delta K curves, 3) Progressive Failure Analysis (PFA) module evaluates crack initiation life through a damage based approach and crack propagation life through the Virtual Crack Closure Technique (VCCT).