Implementation of a Viscoplastic Model to Predict the Stress Distribution Measured Using Nano-Mechanical Raman Spectroscopy

Vignesh Vivekanandan, Purdue University

Abstract

Nano-mechanical Raman spectroscopy(NMRS) is a novel technique designed for temperature, stress, and chemistry mapping at micro to nano-scale for different temperature and loading conditions.This study focuses on comparing the direct measurements of stresses during mesoscale micro-structural deformation of nickel based super alloy(IN - 617) during 3-point bending tests at elevated temperatures using NMRS with the dislocation density based visco-plastic model. During the 3-point bending test, notch tip plastic stresses as a function of micro structure, load, and temperature with micron scale resolution were measured. A visco-plastic model is used in this work to capture the stress contours of the 3-point bending sample of IN-617. In this project, we use a viscoplastic model to establish a microstructure dependent relation to the mechanical properties of IN 617. The constitutive model used in this work incorporates the Taylor's Dislocation Model, wherein the dislocation density is used as the internal variable of flow stress function. An user-defined material behavior(UMAT) is written based on the above mentioned constitutive model and is used to simulate the 3-point bending test in ABAQUS. Local material properties of the notch sample is extracted using nano-indentation. These material properties are then incorporated into the model and the stress distribution of the 3-point bending sample is calculated. It is then compared and analyzed with the experimental results obtained from Nano Mechanical Raman Spectroscopy.

Degree

M.S.A.A.

Advisors

Tomar, Purdue University.

Subject Area

Mechanics

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