100 Years and Still Cracking: A Griffith Fracture Symposium: Fracture and Modeling
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Megan Cordill, Erich Schmid Institute of Materials Science; William Gerberich, University of Minnesota; David Bahr, Purdue University; Christopher Schuh, Northwestern University; Daniel Kiener, Montanuniverstität Leoben; Neville Moody; Nathan Mara, University of Minnesota; Erica Lilleodden, Fraunhofer Insitute for Microstructure of Materials and Systems (IMWS)
Wednesday 2:00 PM
March 17, 2021
Room: RM 47
Location: TMS2021 Virtual
Session Chair: Megan Cordill, Erich Schmid Institute
2:00 PM
Characterization of a Novel Crack Growth Mechanism in Ti-6Al-4V Subjected to Dwell Fatigue at Elevated Temperature: Adam Pilchak; John Joyce-Rotella1; Nate Levkulich2; Sushant Jha3; Reji John4; Jim Larsen4; 1Purdue University and Air Force Research Lab; 2UES Inc.; 3University of Dayton Research Institute; 4Air Force Research Lab
Life-time debits in titanium alloys under dwell-fatigue conditions are well-documented for near-alpha Ti alloys, but less so for alpha/beta alloys like Ti-6Al-4V. These debits have been linked to microstructural features including microstructure, texture, and micro-texture. Cracks extension generally occurs by transgranular propagation through one large microtextured region in near-alpha alloys. However, in Ti-6Al-4V, we hypothesize that accelerated crack extension is aided by secondary nucleation ahead of the main crack front. To demonstrate this effect, dwell-fatigue crack growth experiments were performed with one interrupted at a specific crack length corresponding to that where we observe the acceleration. The crack morphology and crack surface are investigated via electron backscatter diffraction, white light interferometry, x-ray computed tomography and serial sectioning, to elucidate the complex features susceptible to and responsible for the accelerated crack growth rate.
2:20 PM
The Maximum Limit of Compressive Strength and Hardness of Nanocrystalline MgAl2O4 Spinel: Jessica Maita1; Jacob Davis2; James Wollmershauser3; Edward Gorzkowski3; Boris Feigelson3; Seok-Woo Lee1; 1University of Connecticut; 2University of Massachusetts Amherst; 3U.S. Naval Research Laboratory
Transparent materials are used extensively due to their ability to transmit light and provide physical protection from external chemical and mechanical interactions. Transparent nanocrystalline MgAl2O4 has been sintered with grain sizes ranging from 3.7 to 80 nm, the smallest currently reported. Nanoindentation and micropillar compression are performed to elucidate the effect of grain size on plasticity and fracture. We found that both the maximum hardness in nanoindentation and the maximum fracture strength in micropillar compression appear at 10.5 nm grain size. High-resolution transmission electron microscopy and molecular dynamics simulations revealed that grain boundaries play an important role in the determination of the critical grain size regardless of different deformation modes; as fracture initiators in uniaxial compression and plasticity barriers/carriers in nanoindentation. These results provide a better understanding of the mechanical behavior and help improve the design of transparent armor with superior protection capability.
2:40 PM
Reversing Griffith after 100 Years: Mechanics of the Solid-state Bonding: Yanfei Gao1; Zhili Feng2; 1University of Tennessee - Knoxville; 2Oak Ridge National Laboratory
Solid-sate-bonding techniques have been widely used and investigated in welding and joining community, and also recently in novel nanomanufacturing processes. Nevertheless, it is well known in the community of mechanics of materials that crack healing, an opposite process to Griffith fracture, does not usually take place at ambient conditions except for extremely flat surfaces. Traditionally, the solid-state-bonding mechanisms are believed to be dominated by atomic interdiffusion across the interface. In contrary, we propose that both lateral diffusion along the interface and creep deformation of surrounding materials dominate the gap closure and thus dictate the kinetics of bonding. Additionally, the competition between these two processes defines a length scale, on which various solid-state-bonding techniques find their characteristic parametric space.
3:00 PM
High-strength and Thermal Stability of Nanotwinned Al Alloys: Qiang Li1; Sichuang Xue1; Yifan Zhang1; Haiyan Wang1; Jian Wang2; Xinghang Zhang1; 1Purdue University; 2University of Nebraska-Lincoln
Lightweight Al alloys show widespread applications, but often have inherently low mechanical strength and low service temperature. Age hardened Al alloys have mechanical strength less than ~ 700 MPa and readily experience grain growth at low homologous temperature. We have used far-from-equilibrium approach to fabricate various nanotwinned Al solid solution alloys. Some of the selected Al alloys have flow stresses exceeding 1 GPa, making them one of the strongest Al alloys. Our in situ SEM studies show that the nanotwinned Al alloys possess anisotropy under both tension and compression tests. The solid solution Al alloys have superb thermal stability and mechanical stability at elevated temperatures. These studies shed lights on the design of lightweight high-strength Al alloys for applications in harsh environments.
3:20 PM
Nanomechanics of Amorphous Silica: From Mechanical to Fracture Properties: Pania Newell1; Truong Vo1; Bang He1; Michael Blum1; Angelo Damone2; 1The University of Utah; 2University of Brescia
Porous materials are typically heterogeneous containing pores of different shapes and sizes ranging from nanoscale to macroscale. In continuum scales, mechanical properties of porous materials are estimated by considering porosity, while the underlying variations in nano/micro pore structures are typically ignored. This presentation numerically investigates the effect of nanopore structure in addition to porosity on mechanical and fracture properties of amorphous silica (a-SiO2). Various pore shapes (e.g., circular, square, and triangular) and sizes were selected based on the experimental observation of pores in SiO2-based materials. Molecular dynamics simulations coupled with the-state-of-the-art reactive force field (ReaxFF) have been adopted for this investigation. The results revealed that the variation in the nanopore structure influences Young’s modulus and critical energy release rate (GIC) of a-SiO2. In particular, for the same exact porosity, the circular pore has the highest impact on Young’s modulus, while the square pore has the most influence on GIC.