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1. On the Bonding Characteristics of Clays and Biopolymers for Sustainable Earthen Construction

   Mikofsky, R.A. ; Armistead, S.J. ; Srubar, W.V. ( June 2023 , International Conference on Bio-Based Building Materials)

   Amziane, S. ; Merta, I. ; Page, J. (Ed.)

   Sustainable earthen building materials provide a pathway to mitigating the environmental impacts of the modern construction sector. While the application of these materials has been limited due to the inherent heterogeneity, erosivity, and weak mechanical properties of soil, the physical and thermal properties can be improved through the addition of ubiquitous, non-toxic, sustainable biopolymers. Yet, the fundamental understanding of the physiochemical bonding mechanisms between clays and biopolymers in this system is limited. In this work, a ‘micro to macro’ methodological approach was applied to investigate the bonding characteristics of common clays and clay-stabilizing biopolymers. At the micro-scale, fundamental interactions of clays (i.e., kaolinite, bentonite) with biopolymer additives (i.e., xanthan gum, guar gum, sodium alginate, microcrystalline cellulose) were assessed through mineral binding characterization techniques, including Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The findings were used to interpret unconfined compressive strength (UCS) tests results for macro-scale soil-biopolymer composites samples (1% biopolymer by soil mass). The results from this study illustrate the utility of understanding the mechanisms of clay-biopolymer interactions for improving the design of strong and durable earthen materials and structures. 

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2. Quantification of age-related changes in the structure and mechanical function of skin with multiscale imaging

   https://doi.org/10.1007/s11357-024-01199-9  

   Woessner, Alan_E ; Witt, Nathan_J ; Jones, Jake_D ; Sander, Edward_A ; Quinn, Kyle_P ( May 2024 , GeroScience)

   The mechanical properties of skin change during aging but the relationships between structure and mechanical function remain poorly understood. Previous work has shown that young skin exhibits a substantial decrease in tissue volume, a large macro-scale Poisson’s ratio, and an increase in micro-scale collagen fiber alignment during mechanical stretch. In this study, label-free multiphoton microscopy was used to quantify how the microstructure and fiber kinematics of aged mouse skin affect its mechanical function. In an unloaded state, aged skin was found to have less collagen alignment and more non-enzymatic collagen fiber crosslinks. Skin samples were then loaded in uniaxial tension and aged skin exhibited a lower mechanical stiffness compared to young skin. Aged tissue also demonstrated less volume reduction and a lower macro-scale Poisson’s ratio at 10% uniaxial strain, but not at 20% strain. The magnitude of 3D fiber realignment in the direction of loading was not different between age groups, and the amount of realignment in young and aged skin was less than expected based on theoretical fiber kinematics affine to the local deformation. These findings provide key insights on how the collagen fiber microstructure changes with age, and how those changes affect the mechanical function of skin, findings which may help guide wound healing or anti-aging treatments.

    

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3. Deep learning for quantitative dynamic fragmentation analysis

   https://doi.org/10.1063/5.0233739  

   Cazares, Erwin ; Schuster, Brian_E ( January 2025 , APL Machine Learning)

   We have developed an image-based convolutional neural network that is applicable for quantitative time-resolved measurements of the fragmentation behavior of opaque brittle materials using ultra-high speed optical imaging. This model extends previous work on the U-net model. Here we trained binary-, three-, and five-class models using supervised learning on experimentally measured dynamic fracture experiments on various opaque structural ceramic materials that were adhered on transparent polymer (polycarbonate or acrylic) backing materials. Full details of the experimental investigations are outside the scope of this manuscript, but briefly, several different ceramics were loaded using spatially and time-varying mechanical loads to induce inelastic deformation and fracture processes that were recorded at frequencies as high as 5 MHz using high-speed optical imaging. These experiments provided a rich and diverse dataset that includes many of the common fracture modes found in static and dynamic fractures, including cone cracking, median cracking, comminution, and combined complex failure modes that involve effectively simultaneous activation and propagation of multiple fragmentation modes. While the training data presented here were obtained from dynamic fragmentation experiments, this study is applicable to static loading of these materials as the crack speeds are on the order of 1–10 km/s regardless of the loading rate. We believe the methodologies presented here will be useful in quantifying the failure processes in structural materials for protection applications and can be used for direct validation of engineering models used in design.

    

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4. Nano-Scale and Macro-Scale Characterizations of the Effects of Recycled Plastics on Asphalt Binder Properties

   https://doi.org/10.3390/buildings14030642  

   Al-Hosainat, Ahmad ; Nazzal, Munir D ; Kaya, Savas ; Reza, Toufiq ( March 2024 , Buildings)

   This paper summarizes the results of one of the first comprehensive laboratory studies that was conducted to evaluate the effects of adding different contents of recycled polyethylene terephthalate (rPETE) as a modifier to an asphalt binder on the rheological and mechanical properties of the modified binder as well as on the agglomeration behavior between the rPETE and asphalt binder at a multiscale level. The high-temperature and low-temperature performances of the modified binder were investigated at the macro-scale and compared with those of the unmodified binder using dynamic shear rheometer (DSR) and bending-beam rheometer (BBR) rheological tests, as well as asphalt binder cracking device (ABCD) testing. The nano-scale evaluation of the binder properties, including the surface roughness, bonding energy, and reduced modulus, was accomplished using atomic force microscopy (AFM). The results indicated that the addition of rPETE enhanced the high- and intermediate-temperature rheological properties of the modified PG 64-22 binder. The low-temperature rheological properties and resistance to cracking decreased slightly with increasing rPETE content in the asphalt binder. However, this reduction was not remarkable when adding 4%, 8%, and 10% rPETE contents. The asphalt binder modified with 4% rPETE had a low-temperature grade of −22, similar to that of the unmodified binder, indicating that 4% rPETE can be added to the binder to improve its high- and intermediate-temperature properties without reducing its resistance to low-temperature damage. The AFM tapping-mode results indicated that the inclusion of rPETE in the asphalt binder improved the stiffness properties of the modified binder as compared with those of the control asphalt binder. In addition, the rPETE-modified binders showed rougher surfaces than the control binder. The addition of rPETE to the binder increased the values of the reduced modulus and bonding energy compared with those of the control binder.

    

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5. Multi‐Scale In Situ Tribological Studies of Surfaces with 3D Textures Fabricated via Two‐Photon Lithography and Replica Molding

   https://doi.org/10.1002/admi.202000299  

   Afshar‐Mohajer, Mahyar ; Zou, Min ( May 2020 , Advanced Materials Interfaces)

   Surface texturing not only decreases friction by reducing the real area of contact but also is crucial for achieving multifunctionality. However, texturing a surface might undermine its deformation resistance due to increased sliding contact pressure. High resolution, 3D control over texture shapes can potentially address this issue. Utilizing a micro/nano‐scale additive manufacturing method based on two‐photon polymerization, textures are fabricated with precise shape, dimension, and position control. This allows for a systematic investigation of the effects of texture three‐dimensionality by comparing 3D textures (truncated cones) with 2.5D textures (cylinders and rods). Moreover, macro‐ and micro‐scale tribological testing and in situ monitoring of the experiments using a digital microscope at macro‐scale and a scanning electron microscope (SEM) at micro‐scale provides unique insights into the multi‐scale tribological properties of the textured surfaces by real‐time monitoring of the interplay between the forces and the sliding surfaces down to a single micro‐scale structure level. Macro‐scale tests show that cones not only have a lower coefficient of friction due to their reduced area of contact but also slide more smoothly and are more durable. Micro‐scale tests shed new light on the relationship between friction and the microstructure deformation by in situ SEM monitoring of texture‐counterface interactions.

    

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