School of Mechanical Engineering: Alan Needleman

~~

SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Monday, December 30 2019 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Identification of Plastic Properties from Indentation using a Bayesian-Type Statistical Approach

Alan Needleman
Texas A&M University

A mechanical property of a material is a quantity associated with a constitutive theory that purports to represent its mechanical behavior, at least in some range of circumstances. Measured properties are used to predict the mechanical response of a material under loading conditions that differ from those in the test. Quite generally, the directly measured response in a test depends on the geometry of the test specimen and the nature of the applied loading. In some circumstances, relating quantities measured in a test to material properties can be complex and may not even be unique. For example, in indentation, the force versus indentation depth response does not uniquely determine the uniaxial stress-strain response. Materials with very different uniaxial stress strain curves can give indistinguishable force versus indentation depth curves, the so called “mystical” materials. In order to uniquely identify the uniaxial stress-strain response from indentation measurements additional data is needed. Work exploring the use of a Bayesian-type statistical approach to identify the values of plastic material properties from the surface profiles as well as from the indentation force versus indentation depth response will be discussed. The indentation responses in conical indentation for three “mystical” materials are analyzed and used to identify their plastic properties. The effects of superposed fluctuations (“noise”) on the measured data and of the presumed functional form of the stress-strain response on the accuracy of the material characterization are investigated.