Committee Members: 

• Prof. Naresh Thadhani, Co-advisor, MSE
• Prof. Josh Kacher, Co-advisor, MSE
• Saryu Fensin, Ph.D., LANL
• Prof. Aaron Stebner, ME/MSE
• Prof. David McDowell, ME/MSE

The Effects of Controlled Porosity on the Dynamic Compression and Tensile Failure of Additively Manufactured 316L Stainless Steel

Abstract:

Additive manufacturing (AM) techniques are powerful processing tools that provide control over the material microstructure and, as such, the resulting mechanical properties under complex loading conditions.  To take full advantage of the processes and the relationship between heterogeneities within the material, it is imperative to understand the unique microstructure, and the ensuing changes in properties such as strength and failure mechanisms.  The proposed research focuses on understanding the effect of heterogeneities, such as process-inherent and intentionally tailored porosity on the shock compression and eventually dynamic failure of AM fabricated steels investigated using plate impact experiments. 

The research will be conducted using Powder Bed Fusion (PBF) printed 316L SS to generate a better understanding of how the process-inherent porosity can be controlled and utilized to tailor the material properties. The understanding developed will enable us to design additively manufactured parts containing specific porosities to meet desired strength and fracture criteria, allowing for replacement of standard wrought stainless steel or for further performance improvement, e.g., to handle higher or more targeted loads. A high-throughput experimental method involving multiplexed PDV diagnostics to study multiple samples per experiment will be utilized to simultaneously investigate the effects of porosity and other directional heterogeneities on dynamic failure of these materials. The experiments will include multiple PDV probes mounted off of the back surface of disc-shaped samples to measure the free-surface particle profile. Signatures associated with the spall pull-back and recompression rates will be used to determine the spall strength as well as void nucleation and growth characteristics, representative of the spall failure process. Additionally, samples will be soft recovered, and the fracture surfaces will be analyzed using electron microscopy to identify stress and strain accommodation as well as void nucleation and growth processes affected by variations in microstructure.  The combined PDV and microstructure analysis will be correlated to generate the process-structure-property mapping of AM-fabricated steels.