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1. Solid‐state shear pulverization of post‐industrial ultra‐high molecular weight polyethylene: Particle morphology and molecular structure modifications toward conventional mechanical recycling

   https://doi.org/10.1002/pen.26207  

   Johnson, Riggs W. ; Scopelliti, Haley R. ; Herrold, Nathan T. ; Wakabayashi, Katsuyuki ( December 2022 , Polymer Engineering & Science)

   Ultra‐high molecular weight polyethylene (UHMWPE) is one of the most prominent high‐performance thermoplastics for biomedical, leisure, and coating applications. Large‐scale recycling of UHMWPE is extremely difficult due to the high melt viscosity of the material as well as its exceptional chemical resistance and impact strength. There is a need for a commercially scalable methodology that can process the waste feedstock for mechanical recycling while sustaining the outstanding physical properties of the material. Solid‐state shear pulverization (SSSP) is a continuous, twin‐screw extruder‐based processing technique in which the low‐temperature application of shear and compressive forces impart changes in structure at different length scales to overcome the challenges of difficult‐to‐recycle polymers. This paper investigates the use of SSSP in mechanically recycling post‐industrial scrap UHMWPE (rUHMWPE) material from a local ski and snowboard manufacturer. The SSSP‐processed particles are flat, micron‐scale flakes with enhanced surface area, which can sinter very quickly when compression molded. The molded rUHMWPE samples in turn exhibit enhanced ductility and toughness compared to the as‐received scrap material, based on the tunable mechanochemical modification of the ethylene chains.
2. Effect of Negative Poisson's Ratio on the Tensile Properties of Auxetic CFRP Composites

   https://doi.org/10.12783/asc37/36413  

   Lin, Wenhua ; Wang, Yeqing ( September 2022 , 37th American Society for Composites (ASC) Technical Conference)

   Carbon fiber reinforced polymer (CFRP) matrix composites have become increasingly popular across industries such as aerospace and automotive industries due to its outstanding mechanical properties and significant weight saving capability. CFRP composites are also widely known to be highly tailorable. For instance, different laminate-level mechanical properties for CFRP composites can be achieved by varying the individual carbon fiber laminar arrangements, among one of them is the Poisson’s ratio. Conventional materials have a positive Poisson’s ratio (PPR), visualize any conventional materials in a 2D block shape, when stretching that material in longitudinal direction, contraction follows on the transverse direction, whereas for materials with a negative Poisson’s ratio (NPR), stretching in the longitudinal direction leads to expansion in the transverse direction. Materials with NPRs have been shown to improve the indentation and impact resistances, when compared to equivalent materials with PPRs. However, producing NPRs could potentially compromise other properties, such as tensile properties, which has not been reported. The current work investigates the effects of NPR on the tensile properties of CFRP composites. Specifically, a laminatelevel NPR of -0.4094 in the in-plane direction is achieved through ply arrangement of CFRP composites using classical lamination theory (CLT). The non-auxetic counterpart CFRP composites aremore »designed to produce an PPR of 0.1598 in the in-plane direction while simultaneously match their elastic moduli in three directions with those of the auxetic composites. Results show that the predicted tensile modulus and in-plane Poisson’s ratio were in excellent agreement with the experiment results. It was found that the ultimate tensile strength and failure strain or ductility of auxetic specimens were on average 40% lower than those of the conventional CFRP composites.

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3. Micromechanical origins of remarkable elongation-to-fracture in AHSS TRIP steels via continuous bending under tension

   https://doi.org/141876  

   Sharma, Rishabh ; Poulin, Camille M. ; Knezevic, Marko ; Miles, Michael P. ; Fullwood, David T. ( August 2021 , Materials science engineering)

   Continuous bending under tension (CBT) is known to achieve elongation-to-failure well above that achieved under a conventional uniaxial simple tension (ST) strain path. However, the detailed mechanism for supplying this increased ductility has not been fully understood. It is clear that the necking that occurs in a typical ST specimen is avoided by constantly moving the region of plastic deformation during the CBT process. The volume of material in which the flow stress is greatest is limited to a moving line where the rollers contact the sheet and superimpose bending stress on the applied tensile load. Hence the condition of a large volume of material experiencing stress greater than the material flow stress, leading to strain localization during ST, is avoided. However, the magnitude of the contribution of this phenomenon to the overall increase in elongation is unclear. In the current set of experiments, an elongation to fracture (ETF) of 4.56x and 3.7x higher than ST was achieved by fine-tuning CBT forming parameters for Q&P 1180 and TBF 1180, respectively. A comparison of maximum local strains near the final point of fracture in ST and CBT sheets via digital image correlation revealed that avoidance of localization of plastic strain duringmore »CBT accounts for less than half of the increased elongation in the CBT specimens for two steels containing different amounts of retained austenite (RA). Geometrically necessary dislocation evolution is monitored using high-resolution EBSD (HREBSD) for both strain paths, indicating a lower hardening rate in the CBT samples in the bulk of the sheet, potentially relating to the cyclical nature of the stress in the outer layers of the sheet. Interestingly, the GND evolution in the center of the sheet, which does not experience the same amplitude of cyclic stress, follows the ST behavior more closely than the sheet edges. This appears to contribute to a precipitous drop in residual ductility for the specimens that are pulled in ST after partial CBT processing. The rate of transformation of RA is also tracked in the steels, with a significantly lower rate of transformation during CBT, compared to ST. This suggests that a slower transformation rate achieved under CBT also contributed to higher strain-to-failure levels.« less
4. Fabrication of Cu-CNT Composite and Cu Using Laser Powder Bed Fusion Additive Manufacturing

   https://doi.org/10.3390/powders1040014  

   Ladani, Leila ; Razmi, Jafar ; Sadeghilaridjani, Maryam ( December 2022 , Powders)

   Additive manufacturing (AM) as a disruptive technique has offered great potential to design and fabricate many metallic components for aerospace, medical, nuclear, and energy applications where parts have complex geometry. However, a limited number of materials suitable for the AM process is one of the shortcomings of this technique, in particular laser AM of copper (Cu) is challenging due to its high thermal conductivity and optical reflectivity, which requires higher heat input to melt powders. Fabrication of composites using AM is also very challenging and not easily achievable using the current powder bed technologies. Here, the feasibility to fabricate pure copper and copper-carbon nanotube (Cu-CNT) composites was investigated using laser powder bed fusion additive manufacturing (LPBF-AM), and 10 × 10 × 10 mm3 cubes of Cu and Cu-CNTs were made by applying a Design of Experiment (DoE) varying three parameters: laser power, laser speed, and hatch spacing at three levels. For both Cu and Cu-CNT samples, relative density above 90% and 80% were achieved, respectively. Density measurement was carried out three times for each sample, and the error was found to be less than 0.1%. Roughness measurement was performed on a 5 mm length of the sample to obtain statisticallymore »significant results. As-built Cu showed average surface roughness (Ra) below 20 µm; however, the surface of AM Cu-CNT samples showed roughness values as large as 1 mm. Due to its porous structure, the as-built Cu showed thermal conductivity of ~108 W/m·K and electrical conductivity of ~20% IACS (International Annealed Copper Standard) at room temperature, ~70% and ~80% lower than those of conventionally fabricated bulk Cu. Thermal conductivity and electrical conductivity were ~85 W/m·K and ~10% IACS for as-built Cu-CNT composites at room temperature. As-built Cu-CNTs showed higher thermal conductivity as compared to as-built Cu at a temperature range from 373 K to 873 K. Because of their large surface area, light weight, and large energy absorbing behavior, porous Cu and Cu-CNT materials can be used in electrodes, catalysts and their carriers, capacitors, heat exchangers, and heat and impact absorption.« less
5. Lightweight, Thermally Conductive Liquid Metal Elastomer Composite with Independently Controllable Thermal Conductivity and Density

   https://doi.org/10.1002/smll.202104762  

   Krings, Ethan J. ; Zhang, Haipeng ; Sarin, Suchit ; Shield, Jeffery E. ; Ryu, Sangjin ; Markvicka, Eric J. ( November 2021 , Small)

   Lightweight and elastically deformable soft materials that are thermally conductive are critical for emerging applications in wearable computing, soft robotics, and thermoregulatory garments. To overcome the fundamental heat transport limitations in soft materials, room temperature liquid metal (LM) has been dispersed in elastomer that results in soft and deformable materials with unprecedented thermal conductivity. However, the high density of LMs (>6 g cm⁻³) and the typically high loading (⩾85 wt%) required to achieve the desired properties contribute to the high density of these elastomer composites, which can be problematic for large‐area, weight‐sensitive applications. Here, the relationship between the properties of the LM filler and elastomer composite is systematically studied. Experiments reveal that a multiphase LM inclusion with a low‐density phase can achieve independent control of the density and thermal conductivity of the elastomer composite. Quantitative design maps of composite density and thermal conductivity are constructed to rationally guide the selection of filler properties and material composition. This new multiphase material architecture provides a method to fine‐tune material composition to independently control material and functional properties of soft materials for large‐area and weight‐sensitive applications.