Mechanical Response of Materials Investigated through Novel In-situ Experiments and Modeling: Session V
Sponsored by: TMS Structural Materials Division, TMS: Thin Films and Interfaces Committee, TMS: Advanced Characterization, Testing, and Simulation Committee
Program Organizers: Saurabh Puri, VulcanForms Inc; Amit Pandey, Lockheed Martin Space; Dhriti Bhattacharyya, Australian Nuclear Science and Technology Organization; Dongchan Jang, Korea Advanced Institute of Science and Technology; 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
Wednesday 8:30 AM
March 17, 2021
Room: RM 17
Location: TMS2021 Virtual
Session Chair: Dongchan Jang, Korea Advanced Institute of Science and Technology
8:30 AM
Complementary In-situ Methods for Crack Evaluation within High-temperature Materials at Ambient Conditions
: Michael Burtscher1; Markus Alfreider1; Michael Wurmshuber1; Klemens Schmuck1; Helmut Clemens2; Svea Mayer1; Daniel Kiener1; 1Montanuniversität Leoben; 2 Montanuniversität Leoben
In modern technological applications the introduction of innovative material concepts, e.g. WCu or intermetallic TiAl alloys, strongly depends on their damage tolerance and fracture behavior. Therefore, the evaluation and determination of fracture processes along distinct interfaces during in situ micron scaled cantilever experiments are investigated. Continuous stiffness measurement was used to calculate the crack length by applying a new analytical approach. Furthermore, digital image correlation is used as a complementary method to validate the determined crack length. The in situ recorded SEM video signal can thus be analyzed semi-automatically. This enables a fast and reproducible data evaluation during fracture experiments. Besides this, the complementary use of two independent methods allows to determine the respective fracture toughness and J-integral values of the investigated materials precisely. The knowledge of the fracture properties of distinct interfaces in turn can be used to modify the alloy and thus to enhance the materials damage tolerance.
8:50 AM
In-situ Experimental Evaluation of Residual Stresses in Composites during Autoclave Manufacturing: Sandeep Chava1; Sirish Namilae1; Marwan Al-Haik1; 1Embry-Riddle Aeronautical University
Residual stresses are generated within a thermosetting composite laminate during autoclave cure due to the differences in thermal expansion properties of fibers and matrix as well as cure shrinkage of the matrix. These stresses can be significant enough to distort the dimensions of the laminate, which could result in processing induced defects. It is essential to understand the evolution of these residual stresses during processing to optimize the manufacturing process to reduce processing defects. In this research, processing induced residual stresses in the composite laminates are evaluated by devising a novel in-situ experimental approach. Composite laminates are cured in a custom-designed autoclave with viewports. The residual strains during the cure are characterized in-situ using Digital Image Correlation (DIC) through the viewports. The resulting residual stresses are calculated using laminate theory. Methods for altering residual stresses including modifying carbon fiber surfaces with ZnO nanorods will be discussed.
9:10 AM
In-situ Investigation of Intergranular Crack Initiation in Hydrogen Embrittled Inconel 725: Mengying Liu1; Lai Jiang1; Emmeline Sheu1; Michael Demkowicz1; 1Texas A&M University
We perform an in situ investigation of hydrogen-assisted crack initiation at grain boundaries in initially flaw-free samples of polycrystalline Inconel 725. We design specialized tensile specimens, introduce hydrogen into them using electrochemical charging, and perform in situ tensile tests in a scanning electron microscope (SEM). We used electron backscattered diffraction to correlate crack initiation processes with the underlying microstructure. Cracks are found to initiate at twin boundaries, including coherent twin boundaries. To elucidate the role of hydrogen and the effect of plasticity on the crack initiation process, we use digital image correlation (DIC) to characterize surface plastic strain distributions. Potential mechanisms for hydrogen-assisted crack initiation will be discussed.
9:30 AM
Advanced In-situ Electrochemical Nanoindentation Testing for Understanding Hydrogen-materials Interactions: Verena Maier-Kiener1; Anna Ebner1; Helmut Clemens1; Reinhard Pippan2; 1Montanuniversitaet Leoben; 2Austrian Academy of Sciences
Hydrogen embrittlement mechanisms are still controversially discussed, Especially the role of plasticity itself is often underestimated. Hence, the investigation of deformation processes under hydrogen influence is a broad field of research. In-situ electrochemical nanoindentation became a versatile tool for probing the impact of electrochemical charging on the mechanical properties. Besides measuring hardness and Young’s modulus, deeper insights in the acting deformation mechanisms can be gained by advanced nanoindentation testing methods. The advantages and possibilities of these methods are demonstrated on a precipitation hardened nickel-based alloy. Generally, a hydrogen-induced hardness increase was visible for all applied strain-rates. The measured increase in strain-rate sensitivity and the decrease in activation volume could be related to short range effects, which can lead to a more localized deformation. Furthermore, the evaluation of the remaining imprints with laser scanning confocal microscopy showed a clear change in the evolution of the plastically deformed zone during hydrogen charging.
9:50 AM
Size Effects in Barium Titanate: Nidhin George Mathews1; Ashish Saxena2; Christoph Kirchlechner2; N Venkataramani1; Gerhard Dehm2; Balila Nagamani Jaya1; 1Indian Institute of Technology Bombay; 2Max-Planck-Institut für Eisenforschung GmbH
Barium Titanate (BTO) is a widely accepted lead-free piezoelectric ceramic used at micron length scales and in thin film forms in applications. Our micropillar compression studies on single crystal BTO show that the elastic limit (σe) increases by 400% at sub-micron length scales. The strain accommodation mechanism at smaller length scales is by plastic flow, with size exponent of 0.96 ± 0.09. These results are then extended to understand the behaviour of BTO thin films. From microcantilever fracture measurements, it is seen that single crystal possess 45% higher KIC than the bulk while polycrystalline film has 60% lower KIC due to the weak inter-columnar boundaries. The miniaturized compression and fracture tests provide the requisite benchmarking but require expensive micromachining. This is replaced by nanoindentation combined with finite element modelling as a high throughput method to study the effect of film thickness, microstructure and residual stress on the mechanical behaviour of BTO thin films.
10:10 AM
Size Effect, Friction and Adhesion in Small-scale Cutting of Metals: Gan Feng1; Parth Dave1; Dinakar Sagapuram1; 1Texas A&M University
We present an experimental study of cutting of metals at sub-micron to nano-scales. An instrumented ultramicrotomy technique employing "ideally" sharp glass and diamond knives is developed to achieve small cutting depths (30 nm to a few um) under controlled plane-strain conditions and measure corresponding forces. A striking observation from the study is the existence of a strong size effect, manifested by multi-fold increases in the specific energy with decreasing chip size, with this effect being most prominent in soft metals. This effect has its origin in the tool-chip contact mechanics and arises due to the non-linear scaling of the contact area with the characteristic length scale. The results are interpreted from the viewpoint of adhesion theory, where surface forces play an important role in determining the contact area and friction at small scales. Implications for using cutting as a novel means to explore small-scale mechanical behavior will be discussed.
10:30 AM
The Effect of Material Volume on Impact Energy Absorption for Protective Equipment Applications: Kendra Hartley1; Prasad Tennakoon2; John Nychka1; 1University of Alberta; 2Superior Glove Works, Ltd.
Hand injuries from impact are common in the workplace; therefore, gloves with bumpers on the back of the hand were created to prevent these injuries. Limitations created by impact performance standards as well as limitations from human factors, such as dexterity and the surface area of the back of the hand, create a challenge when designing these gloves. Elastomers are frequently used as they are able to meet both criteria; however, there is limited knowledge regarding size effects and absorbed energy of the bulk polymer material. This presentation will detail results of drop test experiments and Abaqus modelling that reveal a threshold of specimen size above which no significant gains were found in impact performance (transmitted force). Moreover, the volume of material required to meet the threshold was significantly smaller than hypothesized. In addition, some materials performed better at the smaller volumes than in the larger volumes.