Mechanical Response of Materials Investigated through Novel In-situ Experiments and Modeling: Session I
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
Tuesday 8:30 AM
February 25, 2020
Room: 33A
Location: San Diego Convention Ctr
Session Chair: Robert Wheeler, Microtesting Solutions LLC; Dongchan Jang, Korea Advanced Institute of Science and Technology
8:30 AM Keynote
Acoustic Emission Measurements During In-situ Scanning Electron Microscopy Experiments to Quantifying Damage Accumulation and Crack Initiation in Microcrystals: Mostafa Omar1; Steven Lavenstein1; Jaafar El-Awady1; 1Johns Hopkins University
We present a new methodology, coupling between acoustic emission measurements and in situ scanning electron microscopy experiments, to quantify the evolution of damage and crack initiation in microcrystals. The mechanical properties are continuously monitored during the loading using dynamic measurements and signal analysis. This new methodology is used to quantify the statistics associated with strain bursts in single crystal Ni microcrystals as predicted from the loading tip displacements and the acoustic emission measurements. Statistics associated with dislocation plasticity versus those associated with crack initiation and propagation are also quantified. Finally, the effect of the crystal size on the acoustic emission measurements are discussed.
9:10 AM
A Novel Fracture Observation in SiC-based Ceramics Through In-situ Double Torsion Testing: Pania Newell1; Robert Wheeler2; Matthew Dickerson3; 1The Unviersity of Utah; 2Microtesting Solutions LLC; 3Air Force Research Laboratory
In classical fracture mechanics, crack propagates rapidly, once it reaches the critical stress intensity factor. However, crack can propagate below this threshold called “subcritical crack growth” (SCG). This phenomenon is one of the main causes of time-dependent behavior of the crack. The double torsion (DT) test is a powerful fracture technique that can provide a constant stress intensity as crack length increases. DT test configuration consists of a symmetric four-point loading around a pre-existing crack on one end of a rectangular plate, which produces torsional deformation in the two plate halves. In this study, we investigate SCG in Scanning Electron Microscopy (SEM) using DT technique for a porous SiC-based ceramics. The degree of control of crack growth, with increments in crack length of less than micron allows to find the relationship between stress intensity factor and crack velocity and further characterize it as a function of the underlying pore network.
9:30 AM
Assessing Crack Propagation Along Brittle/Ductile Interfaces: Daniel Kiener1; Markus Alfreider1; Stefan Kolitsch2; Otmar Kolednik2; 1University of Leoben; 2Erich Schmid Institute
Interface failure is a common cause for functionality break down in heterogenous structures. This is driven by elastic and plastic material properties as well as differences in thermal expansion between the neighboring materials. In order to improve material performance and design damage tolerant components and systems, it is crucial to study the highly localized deformation and crack initiation processes at interfaces, both experimentally as well as numerically. Therefore, in the present work we utilize high-resolution in-situ SEM micromechanical testing methods in conjunction with advanced fracture modelling concepts in order to test and assess the local crack driving forces. Moreover, we can directly relate the predicted to the observed crack path with respect to the interface.Based on this, we suggest novel strategies for testing and analyzing local crack propagation along interfaces between stiff/compliant and strong/soft material combinations.
9:50 AM
Effect of Loading Rate on Fracture Behavior of Magnesium Alloys: Arjun Sreedhar S1; Suraj Ravindran2; Zev Lovinger2; G Ravichandran2; Narasimhan Ramarathinam1; 1Indian Institute of Science; 2California Institute of Technology
The static and dynamic fracture behavior of Mg AZ31 alloy are investigated using three-point bend specimens tested by loading with servo-hydraulic UTM and Hopkinson pressure bar, respectively. Displacement and strain fields are obtained in-situ using high-speed imaging and DIC technique. The strains along a cross-section away from crack plane are analysed to obtain the moment about the plastic hinge point. The energy release rate (J) history is determined using the moment-rotation data at the crack plane. SEM fractograph show transition from brittle (cleavage-like) features under static loading to ductile (fibrous) at high loading rate. Also, the dynamic fracture toughness increases with loading rate. The above behavior is attributed to inertia-driven loss of crack tip constraint with increase in loading rate which suppresses twin induced cracking and promotes void growth and coalescence. This corroborates with quasi-static experiments on effect of notch acuity on failure mechanisms and toughness of Mg alloys.
10:10 AM Break
10:30 AM Keynote
Fracture Across Length Scales in Tungsten: A Combined Experimental and Predictive Approach: Kevin Schmalbach1; Rajaprakash Ramachandramoorthy2; Manish Jain3; Siddharta Pathak3; Johann Michler2; William Gerberich1; Nathan Mara1; 1University of Minnesota; 2Empa-Thun; 3University of Nevada-Reno
Recent analytical models predict fracture behavior at the macroscale using physically-meaningful parameters from relatively simple uniaxial tension or compression tests. Here, we investigate application of these predictive capabilities to the micro/nanoscale in single crystal tungsten. In situ SEM micropillar compression and ex situ nanoindentation strain rate jump tests reveal deformation behavior over a range of temperatures (room to 400 °C) and strain rates (10-3 to 103 s-1); in situ SEM fracture experiments elucidate fracture behavior at similar conditions. Room temperature micropillar compression testing over these strain rates indicates a possible change in deformation mechanism at ~1 s-1, which is further studied through post-testing TEM. The links between plastic deformation and fracture will be discussed in terms of deformation mechanisms, degree of dislocation shielding ahead of the crack tip, and the brittle to ductile transition.
11:10 AM
Development of TiAl Alloys for High Temperature Applications: Seong-Woong Kim1; Jae-Kwon Kim1; Jong-Hoon Kim1; Ji Young Kim1; Seung-Hwa Ryu2; Dongchan Jang2; Jae Keun Hong1; Seung Eon Kim1; 1Korea Institute of Materials Science; 2Korea Advanced Institute of Science and Technology
Research on developing new TiAl alloys for high temperature (> 900oC) applications is introduced. At KIMS, we have developed new TiAl alloys which have excellent room temperature and high temperature properties. Especially, the new alloy showed excellent oxidation resistance in the temperature range from 900 to 1000oC by forming stable Al2O3 oxidation layer as well as room temperature ductility up to 0.78% solely by casting. The deformation behavior of -phase was investigated using in-situ transmission electron microscopy experiments and molecular dynamics simulation. The difference in deformation mode was explained by stacking fault energy of the TiAl alloys which was calculated by molecular dynamics. Furthermore, the role of lamellar orientation of tensile direction on deformation behavior was examined using Schmid factor of each orientation. Finally, we proposed the important microstructural factors to have room temperature ductility of TiAl alloys.
11:30 AM Cancelled
In-situ Micromechanical Characterization of Metallic Glass Microwires Under Torsional Loading: Sufeng Fan1; Yang Lu1; 1City University of Hong Kong
Small-scale metallic glasses have many applications in MEMS and sensors which require good mechanical properties. Bending, tensile, compression properties of metallic glasses at micro/nano-scale have been investigated previously. Here, by developing a micro robotic system, we investigated the torsional behavior of Fe-Co based metallic glass microwires inside a SEM. Benefiting from the in situ SEM imaging capability, the fracture behavior of metallic glass microwires has been uncovered clearly. It can be revealed that both spiral stripes and shear bands contributed to the fracture mechanism of the microscale metallic glass. Plastic deformation of the microwires included both homogenous and inhomogeneous plastic strain, which began with the liquidlike region, then a crack formed. Although the metallic glass microwire broke in brittle mode, the shear strain was not lower than that of conventional metal wires. Moreover, we found an inverse relationship between the plastic strain and the loading rates.