The Woodruff School

SUMMARY

It can take up to 20 years from the discovery of a new material to its ultimate deployment for commercial use. Repeated experimental testing and characterization loops must be conducted to develop, optimize the properties of the alloy and generate process-structure-property (PSP) linkages. There is a need to create high throughput (HT) material property characterization techniques to accelerate this process.

One such method is spherical indentation, which has been shown to reliably capture the complete elastic-plastic response of polycrystalline metal alloys when using the Pathak-Kalidindi (P-K) protocol. This test method also has the distinct advantage of being both high throughput (HT) and able to test small volumes of the material. The strength of a material is higher in indentation than uniaxial loading due to the constraint of the elastically deforming material surrounding the subsurface plastic zone. The indentation yield strength is often related to the uniaxial yield strength by a scaling factor, referred to as the constraint factor. This factor depends on the material, hence the depth of loading and contact radius. In the current work, finite element analysis (FEA) is used to provide a better understanding of the constraint factor and the influence of the elastic and plastic properties on it. Using the FEA data, an inverse method is developed to obtain uniaxial stress-strain curves from indentation data. The method is then demonstrated experimentally on indentation stress-strain curves for a set of Al7050 that have undergone several different solution and aging treatments.

One of the more challenging mechanical properties to assess with HT methods is fatigue, yet for uncertainty quantification of life-critical structural materials and components, experimental data on the influence of the variability of the microstructure on fatigue resistant and good damage tolerance is needed. This entails conducting multiple fatigue tests, which can take many days or even several months. This work explores the current state of the art for HT fatigue testing by providing a comprehensive literature review. As an exercise, a novel multiple specimen HCF test fixture that can be used on a single-axial fatigue test system is conceived, designed, built, and demonstrated. Perspectives on approaches to deal with this challenging problem are given.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Anirudh Srinivas Bhat

TIME:	Thursday, June 4, 2020, 12:00 p.m.

PLACE:	https://bluejeans.com/877824024, Online

TITLE:	High Throughput Mechanical Property Characterization for Structural Alloys

COMMITTEE:	Richard W. Neu, Chair (ME, MSE) Surya Kalidindi (ME, MSE) Antonia Antoniou (ME) David McDowell (ME, MSE) Meisha Shofner (MSE)

SUMMARY It can take up to 20 years from the discovery of a new material to its ultimate deployment for commercial use. Repeated experimental testing and characterization loops must be conducted to develop, optimize the properties of the alloy and generate process-structure-property (PSP) linkages. There is a need to create high throughput (HT) material property characterization techniques to accelerate this process. One such method is spherical indentation, which has been shown to reliably capture the complete elastic-plastic response of polycrystalline metal alloys when using the Pathak-Kalidindi (P-K) protocol. This test method also has the distinct advantage of being both high throughput (HT) and able to test small volumes of the material. The strength of a material is higher in indentation than uniaxial loading due to the constraint of the elastically deforming material surrounding the subsurface plastic zone. The indentation yield strength is often related to the uniaxial yield strength by a scaling factor, referred to as the constraint factor. This factor depends on the material, hence the depth of loading and contact radius. In the current work, finite element analysis (FEA) is used to provide a better understanding of the constraint factor and the influence of the elastic and plastic properties on it. Using the FEA data, an inverse method is developed to obtain uniaxial stress-strain curves from indentation data. The method is then demonstrated experimentally on indentation stress-strain curves for a set of Al7050 that have undergone several different solution and aging treatments. One of the more challenging mechanical properties to assess with HT methods is fatigue, yet for uncertainty quantification of life-critical structural materials and components, experimental data on the influence of the variability of the microstructure on fatigue resistant and good damage tolerance is needed. This entails conducting multiple fatigue tests, which can take many days or even several months. This work explores the current state of the art for HT fatigue testing by providing a comprehensive literature review. As an exercise, a novel multiple specimen HCF test fixture that can be used on a single-axial fatigue test system is conceived, designed, built, and demonstrated. Perspectives on approaches to deal with this challenging problem are given.