PHASE-STRESS PARTITION DURING UNIAXIAL TENSILE LOADING OF A TIC-PARTICULATE-REINFORCED AL COMPOSITE

Using neutron diffraction, we measured during in situ loading the latt ice elastic mean phase (LEMP) strains in the matrix and reinforcement of a 15 vol pct TiC-particulate-reinforced 2219 Al composite. From the strain components longitudinal to and transverse to loading, the in s itu normal phase stresses (average normal stresses in the constituent phases) were obtained through Hooke's law. The internal stress partiti on between the matrix and reinforcement, i.e., load sharing, can then be inferred. Internal stress development was also modeled using the fi nite-element method (FEM), showing good agreement with the experimenta l: results. Both indicate that the relationship between the LEMP strai ns/phase stresses and the applied load noticeably deviates from linear ity during composite microyielding, long before the nominal 0.2 pct pr oof stress is reached. The nonlinearity arises (despite the linear ela stic relationship between phase stresses and LEMP strains) because the applied traction is not synonymous with the phase stresses, and the r atio of phase stresses may vary during loading. Notably, the morpholog y of the LEMP strain development with applied load differs in the dire ctions parallel to or perpendicular to the load. The differences are e xplained by considering the evolution of local matrix plasticity. Ther mal residual stresses and inelastic stress relaxation, driven by inter facial diffusion, are also discussed.