Mechanical Response of Materials Investigated through Novel In-situ Experiments and Modeling: Session VI
Sponsored by: TMS Structural Materials Division, TMS: Thin Films and Interfaces Committee
Program Organizers: Saurabh Puri, VulcanForms Inc; Amit Pandey, Lockheed Martin Space; Dhriti Bhattacharyya, Australian Nuclear Science and Technology Organization; Dongchan Jang, KAIST; Jagannathan Rajagopalan, Arizona State University; Josh Kacher, Georgia Institute of Technology; Minh-Son Pham, Imperial College London; Robert Wheeler, Microtesting Solutions LLC; Shailendra Joshi, University of Houston
Thursday 2:00 PM
February 27, 2020
Room: 32A
Location: San Diego Convention Ctr
Session Chair: Alessandro Piglione, Imperial College London
2:00 PM Keynote
Examination of Local Microscale-microsecond Temperature Rise in HMX-HTPB Energetic Material under Impact Loading: Ayotomi Olokun1; Bing Li1; Chandra Prakash2; Zhiwei Men3; Dana Dlott3; Vikas Tomar1; 1Purdue University; 2Johns Hopkins University; 3University of Illinois Urbana-Champaign
Energetic material (EM) with solid oxidizer material and polymeric binder can experience abrupt temperature rise or even explosion when exposed to dynamic impact due to its complex microstructure. Such unintended detonation could result in severe accidents. It has been noticed that there are hot-spots within the EM, which are prone to initiate the chemical reaction and detonation under dynamic loads. The behavior of hot-spots during detonation initiation under impact is influenced by the EM microstructure, including oxidizer particle size, volume fraction, etc. It is important to capture the local temperature rise and relate it with material microstructure during the detonation for improvement of safety management. Infrared imaging technique was employed in this work to provide visualization of temperature change during EM detonation, and high time and special resolution were both achieved. This related the behavior of hot-spots with material microstructure and the observation agreed well with existing numerical simulation work.
2:40 PM Keynote
Impact of the Architecture / Texture on the Mechanical Behavior of Ni-microwires: How to Drive the Strength and Ductility: Ravi Raj Purohit Purushottam Raj Purohit1; Alla Ndiaye Dieng1; Celine Gerard2; Loic Signor3; Abhinav Arya4; Girish Bojjawar4; Satyam Suwas4; Atul H. Chokshi4; Ludovic Thilly1; 1Pprime Institute - Poitiers University; 2Pprime Institute - CNRS; 3Pprime Institute - ENSMA; 4Indian Institute of Science
Severely cold drawn Ni micro-wires mechanical behavior has been intensively studied showing the architecture key-role in the observed significant size effects [Purushottam et al, Sc Rep, 2019], where their tensile strength approaches the theoretical strength with a reduction of diameter from 120 µm down to 20 µm [Warthi et al, Script Mat, 2013]. In-situ deformation study under synchrotron radiation allowed to achieve a fundamental understanding of the observed size effect by monitoring the evolution of microstructure (including dislocation storage) and detecting elastic-plastic transition in the different grain families. Realistic 3D microstructures were generated using EBSD maps and texture information. Crystal plasticity FE simulations were performed, both with semi-phenomenological and physical-based models fed by dislocations densities experimentally obtained during TEM observations. The influence of different microstructural parameters was investigated. The feasibility of driving the micro-wires strength and ductility by the architecture design is discussed.
3:20 PM
In-situ TEM Investigation of the Electroplasticity Phenomenon in Metals: Xiaoqing Li1; John Turner2; Karen Bustillo2; Rohan Dhall2; Andrew Minor1; 1University of California, Berkeley; 2Lawrence Berkeley National Laboratory
Electroplasticity is a phenomenon in which applied pulsed electric fields during deformation result in reduced flow stress and increased formability in metals. In this work, in situ TEM electromechanical tests of Nickel dog-bone shaped samples on electrical push-to-pull device were performed in order to correlate direct observations of nanostructure change with both mechanical data and applied electrical pulses in an effort to provide clarity on the true origin of this phenomenon. By analyzing the frame-by-frame videos with collected mechanical and electrical data, we found that deformation mechanisms and dislocation behaviors were changed during the pulsing period. Relatively large slip traces with dislocations nucleated from the edges could be triggered by the pulses, and dislocations tend to move with a faster speed and a longer distance compared to the purely mechanically-triggered movement. Results such as local joule heating which was measured indirectly through lattice expansion by diffraction will also be discussed.
3:40 PM Break
4:00 PM
In-situ Mechano-electrochemical Coupling of Structural Supercapacitor Electrodes: Dimitrios Loufakis1; James Boyd1; Zachary Powell1; Alejandro Martinez1; Jodie Lutkenhaus1; Dimitris Lagoudas1; 1Texas A&M University
Mechano-electrochemical coupling performance of structural supercapacitor electrodes was explored using a novel testing method, providing new insights for structural energy and power materials. Structural energy and power combines load-bearing and energy storage functions into a single multifunctional material. Studying mechano-electrochemical coupling of such materials is vital, since the energy storage capabilities may be affected by mechanical loads, and vice versa. However, there are few such studies in the literature. In this work, a custom-built instrument was developed to perform in-situ electrochemical measurements under tension, i.e., independently controlled cyclic voltammograms and stress-strain curves were acquired simultaneously. Additionally, tensile tests were performed under various states of charge. The mechano-electrochemical coupling experiments were performed on nanocomposite structural supercapacitor electrodes consisting of reduced graphene oxide (rGO) and aramid nanofibers (ANF). This study shows minimal degradation in specific capacitance until mechanical failure, indicating that the mechanical deformation does not impede electric double layer formation.
4:20 PM
A Novel Approach to Join Large Coefficient of Thermal Expansion (CTE) Mismatched Thermoelectric (TE) Materials for High Temperature Applications: Michell Aranda1; Ike Chi1; Ravi Vilupanur1; Obed Villapando1; Brooke Singleton1; Fivos Drymiotis1; Billy Li1; Jean-Pierre Fleurial1; 1Jet Propulsion Laboratory
Radioisotope thermoelectric generators (RTGs) have been used to enable deep space exploration where solar power is insufficient. Heritage RTGs have reliably provided power throughout the lifetime of various missions but thus far have been relatively inefficient and convert less than 10% of heat to electricity. A method to achieve higher conversion efficiencies is via the segmentation of advanced thermoelectric (TE) materials. Though advantageous to achieve high performance, segmentation can be challenging. Thermal stresses induced by large coefficient of thermal expansion (CTE) mismatch can cause cracking at the bonded interface, these stresses need to be minimized in order to reduce the probability of cracking at the joint interface. In this study, two TE materials with dissimilar CTE were joined by using a graded-CTE bonding approach. Preliminary results of a stress model showed a reduction of stress at the bonded interface and is in agreement with experimental results.
4:40 PM
Synthesis and Mechanical Behavior of Freestanding NiTi Films with Varying Grain Sizes: Paul Rasmussen1; Jagannathan Rajagopalan1; 1Arizona State University
Here, we describe a new process to synthesize thin films with precise microstructural control via systematic, in-situ seeding of nanocrystals, and subsequent crystallization of amorphous precursor films. Based on this process, we synthesized Cr-seeded NiTi films with nanocrystalline and submicron grain sizes, and different phase compositions by methodically varying the annealing treatments. We then co-fabricated freestanding samples of the films with MEMS testing stages and performed cyclic tensile load-unload experiments. While all samples exhibited the shape-memory effect, the underlying deformation mechanisms were notably different. Films with submicron grains that initially had a mixed austenite/martensite microstructure deformed via a combination of phase transformation of austenite grains alongside detwinning of martensite grains. The nanocrystalline films initially had a fully austenitic microstructure and deformed via combination of phase transformation and plasticity. Preliminary in-situ TEM straining suggest that inelastic strain recovery in these films is caused by both reverse phase transformation and reverse plasticity.
5:00 PM Concluding Comments