Anil Saigal

Commercialization of energy-dense lithium metal batteries relies on stable and uniform plating and stripping on the lithium metal anode. In electrochemical-mechanical modeling of solid-state batteries, there is a lack of consideration of specific mechanical properties of battery-grade lithium metal. Defining these characteristics is crucial for understanding how lithium ions plate on the lithium metal anode, how plating and stripping affect deformation of the anode and its interfacing material, and whether dendrites are suppressed. Recent experiments show that the dominant mode of deformation of lithium metal is creep. This study measures the time and temperature-dependent mechanics of two thicknesses of commercial lithium anodes inside an industrial dry room, where battery cells are manufactured at high volume. Furthermore, a directional study examines the anisotropic microstructure of 100 µm thick lithium anodes and its effect on bulk creep mechanics. It is shown that these lithium anodes undergo plastic creep as soon as a coin cell is manufactured at a pressure of 0.30 MPa, and achieving thinner lithium foils, a critical goal for solid-state lithium batteries, is correlated to anisotropy in both lithium’s microstructure and mechanical properties.

Lithium dendrites are protruding growths that form via ionic flow into and out of the lithium metal throughout the use cycle of a battery. Many more changes occur in the cell during this process, including increase of pressure and temperature, which have been shown to alter the mechanics of the materials inside the battery. The increase of pressure deforms the lithium metal

A physician palpates a tissue to detect an embedded tumor nodule by sensing an increase in local tissue stiffness and nodule size. The Hertz contact model, however, is unable to predict the material or physical properties of a tumor nodule embedded in a healthy tissue of finite thickness. In this study, utilizing a hyperelastic material model, we propose a general methodology to analyze the extent to which the stiffness, size, and depth of a nodule embedded in a tissue affect its detectability. Using dimensional analysis, we generate simple power-law relations to predict physical and material properties of tumor nodules embedded in healthy tissue during indentation. Our results indicate that indenter radius and indentation depth are critical parameters in nodule detection and a thin indenter and large indentation depth increase detection sensitivity of an embedded tumor nodule. Our results also show that anisotropic material properties of either a tissue or an embedded nodule render the embedded tumor nodule undetectable using indentation. We define palpation sensitivity maps that can be used to predict material and physical properties of tumor nodules in healthy tissues. The analysis and results presented in this study might increase accuracy and precision in instrumented probe-based laparoscopic or robotic surgeries.

Microscale holes were punched at cryogenic conditions in polycaprolactone (PCL) membranes to create synthetic three-dimensional (3D) tissue scaffolds through multilayer stacking of two-dimensional (2D) porous membranes. Punching forces were experimentally measured, and finite element modeling of the punching process was validated by comparing punching force results. Holes of nominal diameter of 200 μm were punched in PCL films of two different thicknesses: 40 μm and 70 μm. Die clearances used for holes in 40 μm thick films were 15.0%, 30.0%, and 45.0%. Die clearances used for holes in 70 μm films were 8.6%, 17.1%, and 25.7%. All holes were punched while the PCL film was in thermal equilibrium with a bath of boiling liquid nitrogen. Punching forces were analyzed to study the effect of die clearance and film thickness. A 3D finite element simulation of the punching process was done using deform 3d software. Cryogenic material properties of PCL used in the simulation were determined experimentally. It was concluded that finite element simulation for the cryogenic micropunching process can be used to predict peak punching forces with reasonable accuracy, which is a key factor to be considered while designing the punching dies. The finite element simulations did not predict an optimal die clearance to minimize peak punching force. However, the measured peak punching forces for 70 μm thick film seem to favor the smallest die clearance to minimize peak punching force.

Main Menu Session 1463 INDUSTRY-UNIVERSITY PARTNERSHIPS IN MECHANICAL AND MANUFATURING ENGINEERING AT TUFTS UNIVERSITY Anil Saigal and Vincent P. Manno Department of Mechanical Engineering Tufts University Medford, MA 02155 Tel: 617-627-2549 Fax: 617-627-3058 email: anil.saigal@tufts.edu Abstract The Department of Mechanical Engineering at Tufts University has a long history of industry-university partnerships. Up until the late 1960’s, these interactions focused on education programs such as apprenticeships leading to associates degrees. Growing emphasis on government-sponsored research and full-time undergraduate study directly after high school reduced the organization and substance of industrial interactions during the 1970’s and the early 1980’s. This paradigm began to change around 1985 and new partnerships have continued to expand to this day. One major influence that stimulated this reengagement was the growth and integration of manufacturing engineering within the mechanical engineering curriculum, instigated by renewed industrial interest in sponsoring employees for continuing education to keep current with changing technology. The need for practical relevancy led to the establishment of our Industrial Advisory Council with members from several companies and the US government. New programs emerged such as the Certificate Program in Manufacturing Engineering and a part-time Masters of Engineering degree program with a project focus. Other collaborative activities include joint responsibility for the Annual Thermal Manufacturing Workshop, industrial sponsorship of senior design projects and providing outside feedback as part of our ABET EC2000 continuous improvement process. The current level of collaboration is good but can be improved. For a university in which most of the students attend classes full-time during the day, meeting the needs of the students from industry and part -time students requires not only additional commitment of resources but also fundamental infrastructure changes. Finally, on the research side, the differing time scales and priorities of academe and industry always pose a challenge. Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright © 2002, American Society for Engineering Education Main Menu

In pursuit of research to create a synthetic tissue scaffold by a micropunching process, material properties of Polycaprolactone (PCL) in liquid nitrogen were determined experimentally. Specimens were prepared using injection molding and tested under compression to determine the stress-strain relationship of PCL below its glass transition temperature. Cryogenic conditions were maintained by keeping the PCL specimens submerged in liquid nitrogen throughout the loading cycle. Specimens of two different aspect ratios were used for testing. Yield Strength, Strength Coefficient, and Strain Hardening Exponent were determined for different specimen aspect ratios and extrapolated for the case with zero diameter to length ratio. Material properties were also determined at room temperature and compared against results available in the literature. Results demonstrate that PCL behaves in a brittle manner at cryogenic temperatures with more than ten times increase in Young’s modulus from its value at room temperature. The results were used to predict punching forces for the design of microscale hole punching dies and for validation of a microscale hole punching model that was created with a commercially available finite element software package, DEFORM 3D. The three parameters Yield Strength, Strength Coefficient, and Strain Hardening Exponent used in Ludwik’s equation to model flow stress of PCL in DEFORM 3D were determined to be 94.8 MPa, 210 MPa, and 0.54, respectively.

Liquid crystal polymers (LCP's) comprise a class of materials that derive favorable mechanical, chemical, and electrical behavior from long‐range molecular ordering. This unique microstructure gives rise to anisotropic bulk properties that can be problematic for industrial applications, and thus the ability to model the polymer texture is essential to the design of manufacturing processes for isotropic material production. Previous efforts to model LCP directionality have been primarily restricted to structured grids and simple geometries that demonstrate the underlying theory, but fall short of simulating the polymer flow and orientation through realistic manufacturing geometries. In this investigation, a practical methodology is proposed to simulate the 3D director field in full‐scale melt‐processing domains for the prediction of the bulk material orientation state. The hybrid approach utilizes separate simulations for the polymer flow and directionality, using commercial CFD software and a user‐defined post‐processing script, respectively. Wide‐angle X‐ray scattering is used to experimentally validate the directions and degree of order calculated by the model. It is shown that the model is capable of predicting not only the bulk orientation state but also the intricacies of the hierarchal structure produced during manufacturing. POLYM. ENG. SCI., 59:E414–E424, 2019. © 2019 Society of Plastics Engineers

Liquid crystalline polymers (LCP's) make up a class of performance materials that derive favorable mechanical, chemical, and electrical characteristics from their long-range molecular ordering. This unique microstructure gives rise to anisotropic bulk behavior and an understanding of the driving forces behind this morphology is essential to the design of manufacturing processes for isotropic material production. In this investigation, the preferred crystal orientation in injection molded LCP plaque samples was measured using wide-angle x-ray scattering (WAXS) and the degree of order in the material was quantified using an order parameter and an anisotropy factor. Additionally, the dielectric constant of the samples was measured with respect to the mold direction (MD) and transverse direction (TD). Specimens were analyzed both as-injection-molded and with the skin layer removed, to investigate the effects of hierarchal structure on material properties. It is shown that preferred orientation along the shear direction in the LCP samples corresponds to dielectric anisotropy, and mechanically removing the shear-aligned layer results in a more isotropic dielectric response.