Fracture Properties and Residual Stresses in Small Dimensions: In Situ Fracture Testing Methodologies
Sponsored by: TMS Structural Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Daniel Kiener, University of Leoben; Marco Sebastiani, Roma TRE university; Nagamani Jaya Balila, Max Planck Institut fuer Eisenforschung GmbH; William Gerberich, University of Minnesota; Siddhartha (Sid) Pathak, University of Nevada, Reno

Wednesday 2:00 PM
March 1, 2017
Room: 21
Location: San Diego Convention Ctr

Session Chair: Andrew Minor, UC Berkeley; Jeffrey Wheeler, ETH Zurich

2:00 PM Introductory Comments

2:05 PM  Invited
Nanoscale Strain Mapping of Individual Defects during In Situ Deformation: Thomas Pekin1; Colin Ophus2; Christoph Gammer3; Jim Ciston2; Andrew Minor1; 1UC Berkeley & LBNL; 2LBNL; 3Erich Schmid Institute
    Recent advances in local strain mapping using nanobeam electron diffraction (NBED) has demonstrated the ability to observe single defects and the strain fields around them at a resolution of single nanometers. In addition to measuring the strength of small-volumes, measuring the evolution of strain during plastic deformation is of great importance for correlating the defect structure with material properties. This work will highlight our latest results from in situ strain mapping in an Al-Mg alloy and stainless steel using both contact loading methods (such as in situ nanopillar compression and nanoindentation) as well as non-contact methods such as tensile straining. Our method of local strain mapping consists of recording large multidimensional data sets of nanodiffraction patterns during the test. The resulting dataset contains diffraction data for every point of the STEM image, from which strain maps can be extrapolated on a scale not previously possible during in situ deformation.

2:35 PM  
Studying Plasticity during Fracture at the Micron Scale by Means of Cantilever Experiments in Single-crystalline NiAl and W – HR-EBSD Analyses and Elevated Temperature Measurements: Johannes Ast1; Juri Wehrs1; Johann Michler1; Xavier Maeder1; 1EMPA
    In order to understand the elastic-plastic fracture process at the microscale in the temperature range from room temperature up to 400 C, we perform micro-cantilever experiments inside a scanning electron microscope. The materials we focus on, single-crystalline B2-NiAl and tungsten, have brittle to ductile transition temperatures in the investigated temperature range. In that way the fracture behavior and the fracture toughness can be studied in dependence of temperature. Additionally in-situ high resolution electron backscatter diffraction measurements of the area around the crack tip are performed at various loading states at room temperature. This enables the observation of stresses leading to crack growth in the samples. By analyzing the relative misorientations in the crystal, the plastic deformation in terms of geometrically necessary dislocations can be mapped, quantified and used to describe the effect of dislocations on the fracture behavior.

2:55 PM  
In Situ Stable Crack Growth at the Micron Scale: Giorgio Sernicola1; Tommaso Giovannini2; Punit Patel3; James Kermode3; Daniel Balint2; T Ben Britton1; Finn Giuliani1; 1Department of Materials, Imperial College; 2Department of Mechanical Engineering, Imperial College London; 3Warwick Centre for Predictive Modelling, University of Warwick
    Grain boundaries typically dominate the mechanical properties of ceramics. Therefore, measuring the properties of individual grain boundaries is useful if we want to promote mechanistically informed grain boundary engineering in ceramic processing. Extracting properties of individual boundaries is very difficult in conventional testing, as a large scale fracture experiment tests many grain boundaries and convolute microstructure, crack path and performance. Therefore, we have developed an in situ technique using micro double cantilever beam and direct measurements of stable crack growth to measure the surface energy of SiC and the fracture energy of a glassy interface in a SiC bicrystal. Our measurements of the surface energy are correlated to new DFT calculations of the same interface and match well.

3:15 PM  Invited
In Situ Micron Scale Fracture Toughness Testing and Modeling of a Chevron Notched Bowtie-shaped Beam: Fiona Yuwei Cui1; Richard Vinci1; 1Lehigh University
    The chevron Single Edge Notched three point bending test has many advantages for measuring fracture toughness in bulk system. However employing this technique at the micron scale is challenging. In this study, we are developing a micron-scale bowtie-shaped specimen with a chevron notch to create stable crack growth. In-situ fracture testing was carried out using a Hysitron PI 85 Pico-indenter inside FEI Scios DualBeam FIB. A multi-step loading function was utilized to generate information about compliance change with respective to crack length in each loading cycle. A 3D finite element analysis model was built in Altair Hypermesh and ANSYS to evaluate the compliance change with crack length. Finally, a fracture toughness value was calculated by combining both experimental and analytical results. In order to verify the FEA model, a TEM specimen was fabricated at the notch area after early cycles in a fracture test to measure a real crack length.

3:45 PM Break