|Analysis of residual stresses of layered nanostructured metallic plate
|Hong Kong Polytechnic University -- Dissertations
Metallic composites -- Testing
|Department of Mechanical Engineering
|xi, 124 leaves : ill. (some col.) ; 30 cm.
|The rapid process in construction and aerospace industry has proposed a high demand for structnral materials with higher strength and lower density. The surface mechanical attrition treatment (SMAT) process proposed recently can effectively generate a thin layered of nano-sized structures and a compressive residual stress profile on the near-surface of metals, thus leading to higher material strength without changing the material composition. The residual stress profile through the metal thickness has been proven to have significant influence on material strength. This thesis aims to investigate the magnitude and distributions of the residual stresses of metallic plates which are undergone the SMAT process. The metallic plates in this research are isotropic. And we assume that the metallic plates which are processed by the SMAT are still isotropic. To measure the residual stress profile of metal plates which are processed by the SMAT, both simulation work and experimental work have to been done. In this thesis, finite element method (FEM) simulation using the commercial software ABAQUS has been carried out. Both through-hole and blind hole cases are simulated. Different mesh generation schemes, materials properties, boundary conditions and loading status are employed. The numerical solutions obtained from FEM for through-hole case are also compared with analytical solution to verify the simulation results. The calibration coefficients are then determined for calculation of residual stress. In this simulation process, we simulate three kinds of materials which are the 7075 aluminum plates. the 6061 T6 aluminum plates and the steel plates. Incremental hole-drilling experiments are carried out on the 6061 T6 aluminum plates using milling machine. Strain data along different radial direction of the hole are determined using strain gage rosette. After each drilling step, strain data are recorded and plotted as a curve. The residual stress profiles through the thickness of the plate are then determined from the strain curve and the corresponding calibration coefficients. The 6061 T6 aluminum plates are processed by SMAT method with different processing time. The effect of varying processing time on the resulting residual stress profile is observed. The conclusion from this research work provides guidance for the design of residual stress profiles and the ways to achieve the desired residual stress profiles.
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