Date of Award

12-16-2013

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Michael A Sutton

Abstract

In this work, two separate research efforts are discussed. They include experimental studies in (1) Scaling and Blast Mitigation and (2) Scaling in Friction Stir Extrusion. In both studies, the primary experimental measurement method is three-dimensional digital image correlation (3D-DIC), a non-contacting full-field measurement method that is applicable for both high-rate loading and quasi-static loading conditions.

Scaling and Blast Mitigation Studies:

A series of properly scaled structures was subjected to buried blast loading conditions via detonation of a small explosive buried in saturated sand. Using high speed stereo-vision systems to record the deformations of selected regions on the upper surface of the structure, results clearly show that appropriate scaling of small specimens is adequate to compare responses from different size structures subjected to scaled levels of explosive loading, provided that the dominant physical processes remain the same in all cases.

Upon completion of the basic scaling studies, small scale models representing key vehicle structural elements, including (a) floorboards and bottom-mounted, downward V-shaped hulls in various configurations; (b) steel frames and steel structures with various frame connections and coatings, were subjected to buried blast loading. The results were used to compare various geometrical designs, with the primary metrics for the comparisons being vertical acceleration and the Head Injury Criterion. Results from these studies show that personnel on typical floorboard structures during blast loading will incur unacceptable shock loading conditions, resulting in either serious or fatal injury. However, results also show that an appropriate design using frame-mounted passenger seating could reduce the potential for injury to an acceptable level.

Scaling and Friction Stir Extrusion Studies:

With the goal of tracking particles in a highly viscous, transparent fluid under conditions that approximate the same Reynold's Number as expected in friction stir processing of a metallic material, a complete experimental apparatus was developed. Since 3D-DIC is used to track the particles within the viscous fluid during the flow and extrusion processes, software was written to account for the effects of refraction at the air-glass and glass-fluid interfaces so that the recorded image positions could be accurately converted to 3D locations within the fluid. Next, a series of baseline (known marker positions on rigid targets within the fluid) and extrusion experiments were performed. Results obtained from baseline experiments where the true positions of markers are known confirm that the method is quite accurate. Finally, through sparse seeding of the fluid with neutrally buoyant spherical particles, a series of rotational flow and extrusion experiments were performed. Rotational flow experimental results were in excellent agreement with simulations, while the extrusion data is in very good agreement with simulations in the latter part of the extrusion process.

Rights

© 2013, Xing Zhao

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