Session: 16-01-01: Poster Session: NSF-Funded Research (Grad & Undergrad)

Paper Number: 100089

100089 - Multiscale Analysis of the Thermomechanical Fatigue Behavior of Additively Manufactured Metals 

Following the widespread development of polymer-based additive manufacturing (AM), Laser Powered Bed Fusion (L-PBF) techniques have evolved considerably in recent years for the fabrication of additively manufactured metals. As a consequence, additively manufactured metals are increasingly being considered as structural components in a number of industries, including the aerospace and nuclear industries. Room temperature mechanical properties of such materials have been widely investigated and currently form the basis for their usage. However, many applications in these industries involve both mechanical and thermal loads over a wide range of time scales. Thus, there is also a need to study their fatigue behavior when subjected to high temperatures. In addition, it is of interest to establish the influence of material microstructure on this mechanical response since L-PBF is known to produce significantly different microstructures depending on processing conditions. The residual stresses caused by thermal history of the additively manufactured components can cause distortions at part scale, as well as microstructural effects which is one of the influential factors for the material properties. The local microstructural features as well as the residual stresses at the macroscale add an extra level of complexity to the already complicated fatigue failure predictions of metals. At the same time, it is difficult to directly measure the residual stresses.

In this work, the effect of thermal processing history of additively manufactured metals (nickel-based and titanium-based alloys) on the residual stresses are investigated. Finite elements analysis is used to determine the influence of the complex thermal processing history of AM metals on the residual stresses and deformations. The results of the analysis are validated with our previous in-situ force and full-field strain measurements of AM parts. The results of the analysis are also used as a guide for compensating geometrical distortions in the AM tensile coupons. Uniaxial tensile experiments on L-PBF samples fabricated from AM parts are performed to study cyclic material plasticity at the macroscale and the microscale. By applying appropriate speckle patterns at two length scales, we use multiscale Digital Image Correlation to measure the plastic strain fields developed. Cyclic plasticity experiments are performed at high temperatures (up to 1,000°C) and the results are correlated to microstructural observations obtained by Electron Back Scatter Diffraction (EBSD), as well as room temperature to allow for comparison of the results and conclusions about the influence of temperature. Following isothermal cyclic plasticity experiments we then investigate fatigue life and fatigue crack growth in these materials under combined thermal and mechanical loading. Of particular interest in the fatigue experiments is the influence of residual stresses on crack growth rates of the different AM metals at high temperatures.

Presenting Author: Elisabeth Funck University of Illinois at Urbana-Champaign

Presenting Author Biography: Elisabeth Funck is a Graduate Research Assistant at the University of Illinois at Urbana Champaign.<br/>She received her Bachelor&#39;s degree in Mechnical Engineering from the University of Rostock in Germany and is now studying Aerospace Engineering. Her current research is focussed on additively manufactured metals and she is working in the High Strain Rate Mechanics Lab.

Authors:

Elisabeth Funck University of Illinois at Urbana-Champaign
Pouria Khanbolouki University of Illinois at Urbana-Champaign
Eann Patterson University of Liverpool
Chris Sutcliffe University of Liverpool
John Lambros University of Illinois at Urbana-Champaign