Date of Award

Fall 2020

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science

Committee Chair

Brahmananda Pramanik

First Advisor

Laurie Battle

Second Advisor

Erik Gumstrup

Third Advisor

Peter Lucon

Fourth Advisor

KV Dudhakar

Abstract

The characteristics of strain hardening of selective laser melting (SLM) processed AlSi10Mg under dynamic impact was investigated. The dynamic impact at high strain rate loading conditions occurs in many engineering applications, such as collisions of flying objects on aircraft engine components like bird impact, vehicle collisions, and impacts occur in sports events like club impact on golf balls and helmet impact. Among these various applications, the strength of the materials needs to characterize accurately for product quality, performance, and reliability.

AlSi10Mg is a lightweight metal alloy, and it has a growing demand in aircraft, military, and automotive applications. SLM is a manufacturing technique that uses a laser for the powder bed fusion-based product development process, and the method is applicable for producing AlSi10Mg parts. In the past few years, the microstructure, mechanical characteristics like quasi-static and toughness, and post-processing based on manufacturing parameters of the SLM built AlSi10Mg were studied by many researchers. However, the dynamic mechanical behavior, such as strain hardening behavior under different impact conditions, remains to be explored. For this work, split Hopkinson pressure bar (SHPB) and Charpy impact tester were used for the dynamic impact experimentation on the SLM built AlSi10Mg specimens.

The dynamic strain hardening response for the SLM built AlSi10Mg was investigated to explore the effects of manufacturing variables like the global energy density (GED) and the build orientation. The test specimens were produced at three GEDs of 37.1, 45.4, 49.9J/mm3, and two build orientations: 0° and 90°. The specimens were tested under dynamic compressive impact conditions at strain rates of 800 to 2555s-1 using a split Hopkinson pressure bar (SHPB). The pendulum (hammer) loading test was conducted by using a standardized Charpy impact tester (i.e., ASTM E23). It was found that, at more than 95% confidence limit, the maximum flow stress, which is related to the strain hardening behavior, was influenced by build orientation and global energy density. Also, at more than 95% confidence limit, the void growth, type of fractures, and roughness were affected by global energy density and build orientation. That influenced the strain hardenability of the SLM built AlSi10Mg specimens.

Comments

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy: Materials Science

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