100 Years and Still Cracking: A Griffith Fracture Symposium: Fracture in Complex Materials
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)
Tuesday 2:00 PM
March 16, 2021
Room: RM 47
Location: TMS2021 Virtual
Session Chair: Neville Moody, Sandia National Laboratories - Retired
2:00 PM Invited
Fracture Resistance of Hierarchical Metallic Nanocomposite Thin Films: Amit Misra1; Y. Cui1; B. Derby1; N. Li2; 1University of Michigan; 2LANL
Nanolayered metallic materials exhibit ultra-high strengths as the composition modulation wavelength decreases below approximately 10 nm but fail via shear localization resulting in limited toughness. In a model Cu-Mo system synthesized via co-sputtering at elevated temperatures, a hierarchical morphology of a matrix of phase-separated Cu-Mo with nanoscale ligaments dispersed with sub-micron scale Cu-rich islands containing Mo nano-precipitates was discovered. Fracture experiments conducted via in situ 3-point bend testing of pre-notched microbeams in SEM revealed that the nanoscale hierarchical morphology exhibits superior crack growth resistance as compared multilayer morphology. The toughening mechanisms in hierarchical microstructures involved crack bridging by the Cu-rich layer, crack deflection via shear along the Cu/Mo interface, and multiple cracking. This work demonstrates an approach to increase toughness in high strength nanocomposites through interface micro-structure design.
2:40 PM
In-situ Fracture along Distinct Interface Types: Michael Burtscher1; Markus Alfreider1; Michael Wurmshuber2; Klemens Schmuck1; Helmut Clemens3; Svea Mayer1; Daniel Kiener1; 1Montanuniversität Leoben, Austria; 2Department Materials Science, Chair of Materials Physics, Montanuniversität Leoben, Austria; 3Department Materials Science, Chair of Physical Metallurgy and Metallic Materials, Montanuniversität Leoben, Austria
The determination of fracture processes on micron-scale enables to identify material's shortcomings. Therefore, interfaces within a WCu and an intermetallic TiAl alloy are investigated. By applying continuous stiffness measurement, the fracture toughness, J-integral, and crack propagation within different high-temperature alloys are determined in situ. Hence, fracture behavior of ordered interfaces and large-angle grain boundaries are evaluated and compared with known fracture parameters from the literature. In contrast to macro-mechanic fracture experiments, distinct interfaces are selected within the backscattered contrast of a scanning electron microscope and tested using a picoindenter from type Hysitron PI-85. Therefore, strengthening mechanisms are identified and linked to the presence of precipitates, or other surface modifications along distinct interfaces. Complimentary digital image correlation is used to verify determined crack length and outlines the limitations of the used experimental setup. Based on this, microstructural designs are proposed to enhance the fracture behavior of the alloying systems under investigation.
3:00 PM
The Clamped Beam Bending as a Length Scale Compatible Fracture Test Geometry: Balila Nagamani Jaya1; Ashwini Kumar Mishra1; Hrushikesh Sahasrabuddhe1; Neha Kumari1; Deepesh Yadav1; Tanmayee More1; Tejas Chaudhari1; 1Indian Institute of Technology Bombay
Knowing a material’s fracture toughness is the first step towards preventing or delaying or at least predicting failure of a component. Over the past two decades, various size effects have been documented by several groups, which show ‘materials not really behaving themselves’ with respect to their mechanical response to applied loads. This naturally implies that the fracture toughness of their bulk counterparts cannot be exploited directly. Our group has been working on development of the clamped beam and clamped wire bending as a fracture test geometry that works for both macro and micro-length scales. Two such examples of its applications for multilayered and architectured structures will be shown. Analytical solutions of stress intensity factor or energy release rate will be provided where applicable. The use of clamped beam in R-curve determination and in interface fracture energy measurement will also be elaborated upon.
3:20 PM
A Griffith's Theory-based Model for Strength of Silicon Nitride Nanoporous Membranes from Atomistic Simulation Perspective: Ali Shargh1; Gregory Madejski1; James McGrath1; Niaz Abdolrahim1; 1University of Rochester
Silicon nitride nanoporous membranes are extremely permeable ceramics that were first developed at University of Rochester. It was shown that range of working pressure and size of those nanostructures in biomedical applications are limited by their mechanical properties. We use molecular dynamics simulations to investigate mechanical behavior of amorphous nanostructures with porosity range of 5-40% and different pore arrangement and diameter. It is found that pore separation distance ratio (L1/L2) along with porosity play major role in controlling strength and fracture behavior of nanostructures. Depending on L1/L2 value, different networks of shear bands form in the nanostructure which further change its mechanical properties. A mathematical model based on Griffith’s theory is calibrated on MD results to predict the strength of nanostructure, which is further used to estimate burst pressure. The proposed model can be used as guideline for future manufacturing of robust nanostructures with enhanced mechanical properties at larger sizes.
3:40 PM Invited
Transformation-induced Cracking in ZrO2 Shape-memory Ceramics: towards Cyclic Stability in Polycrystals: Edward Pang1; Isabel Crystal1; Christopher Schuh1; 1Massachusetts Institute of Technology
A new class of shape memory materials has been proposed based on ZrO2-based ceramics, which offer higher martensitic transformation stresses, work output, transformation temperatures, and possibly environmental resistance compared to metallic shape-memory alloys. Despite these potential benefits, shape memory ceramics (SMCs) have not yet lived up to their potential because they are limited by catastrophic cracking during the martensitic transformation. Recent work in the group has focused on characterizing and understanding transformation-induced cracking in bulk specimens. In this talk, we will present recent results evaluating the effect of grain structure on crack evolution during thermal cycling of single- and poly-crystalline bulk specimens. We will also overview our recent efforts to suppress transformation cracking by compositional tuning to minimize mismatch stresses in polycrystals. Together, these studies aid our understanding of transformation-induced cracking and pave the way towards repeatable shape memory and superelastic behavior in polycrystalline SMCs.