Seminars

Deformation and failure of materials under dynamic conditions is a topic of interest because of its relevance in various applications from manufacturing to crashworthiness assessments of vehicles to impact and blast. In this presentation, I will present results of an experimental investigation involving direct in situ observations of plastic flow and failure in ductile metals. Metal cutting is used as a tool for examining the material behavior under high strains and strain rates. The main innovation in our experiments is the use of high-speed photography to directly observe the plastic flow at high spatial resolution, combined with the use of common low melting point alloys to capture the transition between laminar flow, localization, and fracture with increasing strain rate. Our high-speed photography observations reveal that localization (shear band) precedes fracture and cracks nucleate where the shear band meets the surface; this is followed crack propagation along the band, eventually resulting in the formation of a fragment. Localization and fracture related aspects such as the time of shear band nucleation, evolution of localized strain, crack nucleation and propagation are quantified through image correlation analysis of the high-speed video recordings.
In the second part of the presentation, I will describe how time-resolved full-field measurements of the plastic flow can be exploited to calibrate plasticity models. The inverse problem of estimating constitutive model parameters from full-field observations is solved using the principle of work and optimization techniques. An advantage of this method is that it neither makes any assumptions about the flow nor requires computational simulations. Its application to determine the plastic response of copper, subjected to different pre-strain levels, will be described. The results suggest new opportunities for using cutting to study material behavior under extreme plastic strains and strain rates that may be difficult to achieve using conventional methods.

Dinakar Sagapuram is an Associate Professor in the Wm Michael Barnes ‘64 Department of Industrial and Systems Engineering at Texas A&M University. His research and teaching interests are in manufacturing, tribology, and mechanical behavior of materials with a focus on metals and alloys. His group at Texas A&M specializes in the development of high-speed imaging techniques for in situ characterization of materials under processing relevant conditions. He was the recipient of the Texas A&M Innovation Award (2023), TEES Engineering Genesis Award (2023), Breakthrough Energy Fellowship (2021), and the SME Outstanding Young Manufacturing Engineer Award (2021).