Fatigue damage assessment of particle-reinforced metal matrix composite materials under uniaxial & multiaxial loading conditions

The proposed study intended to investigate the fatigue damage of Particle Metal Matrix (PMM) composites under uniaxial and multiaxial loading conditions. Five damage models of SmithWatson-Topper (S.W.T), Ellyin, Brown-Miller, Fatemi-Socie and Varvani were tested for various PMM composite materials for their ability to correlate the uniaxial, torsional and combined tension-torsion damage-life data. Four PMM composite materials of Al6061 I Ah03 I 20p-T6, Al 6061 I Ah03 I 22p-T6, Al 6061 I SiC I 17w-T6 and Ti-6Al-4V I TiC I lOp were evaluated for damage-life based on their strain-life fatigue data. The results of the fatigue damage correlation of uniaxial, torsional and combined tension-torsion fatigue damage versus life for the four PMM composites were investigated in this thesis. The critical plane approaches of Brown-Miller and Fatemi-Socie should almost have the same degree of success in damage assessment of composite materials. These strain based critical plane approaches scaled damage values versus fatigue life data as the lowest range (0.001-0.01) over low-cycle and high-cycle fatigue regimes. While energy based models of S.W.T and Ellyin holding both the stress and strain terms correlated damage data at the highest range (1-1 0) with a relatively larger scatter band for various fatigue lives as compared with other damage approaches. Varvani critical plane-energy approach incorporated the critical plane as the plane of crack initiation and damage growth as well as the strain energy density as a function of stress and strain components acting on the critical plane, which successfully evaluated fatigue damage values within a narrow band. Damage values based on this approach ranged between the highest (S.W.T and Ellyin) and the lowest (Brown-Miller and Fatemi-Socie) ranges and presented an intermediate range of (0.05- 0.1 ). Varvani damage model was further enhanced by means of material dependent terms of a and p to account for the magnitude of difference between Coffin-Manson coefficients for the metallic matrix and PMMC. Terms a and~ enables to estimate fatigue damage ofPMMCs if the strain-life curve for the base metal matrix is known. A finite element unit cell model was also developed to simulate stress-strain responses of Al 6061 I Ah03 I 1 Op-T6 and Al 6061 I Ah03 I 20p-T6 under monotonic tensile loading. The simulated numerical results of stress-strain showed good agreement with the experimental data and prove to be a good tool in the estimation of stress-strain behaviour of PMM composites with various volume fractions.