Fatigue and fracture testing and analysis on four engineering materials

Fatigue and fracture testing and analyses were performed on four engineering materials: a low-strength aluminum alloy (D16CzATWH), a high-strength aluminum alloy (Al7050-T7351), a low-strength steel (A36 steel), and a high-strength steel (9310 steel). Large-crack testing included compression precracked constant amplitude and compression precracked load reduction over a wide range of stress ratios. Single- and multiple-spike overload tests were conducted on some of the materials. Fatigue and small-crack testing were also performed at constant amplitude loading at a constant load ratio on the newly designed single edge notch bend specimen. Using the FADD2D boundary element code, two-dimensional stress analysis was performed on the new specimen to determine the stress intensity factor as a function of crack size for surface and through cracks at the edge notch. Collected fatigue crack growth rate data was used to develop a material model for the FASTRAN strip-yield crack growth code. FASTRAN was used to simulate the constant amplitude and spike overload tests, as well as the small-crack fatigue tests. The fatigue crack growth simulation results have shown that both low-cycle and high-cycle fatigue can be modeled accurately as fatigue crack growth using FASTRAN and that FASTRAN can be used to accurately predict the acceleration and retardation in fatigue crack growth rates after a spike overload. The testing has shown that the starting fatigue crack growth rate of any load-shedding test has significant influence on load history effects, with lower starting rates yielding lower crack growth thresholds and faster rates. Through inspection of fatigue surfaces, it has been shown that beveling of pin-holes in the crack growth specimens is necessary to ensure symmetric crack fronts and that the presence of debris along the fatigue surfaces can cause considerable crack growth retardation