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Stem structural failure, or lodging, affects many crops including sorghum, and can cause large yield losses. Lodging is typically caused by mechanical forces associated with severe weather like high winds, but exposure to sub-catastrophic forces may strengthen stems and improve lodging resistance. The responses of sorghum internodes at different developmental stages were examined at 2 and 26h after initiating moderate mechanical stimulation with an automated apparatus. Transcriptome profiling revealed that mechanical stimulation altered the expression of over 900 genes, including transcription factors, cell wall-related and hormone signaling-related genes. IAA, GA

Summary Intercalation-induced phase transformations in Li-ion battery electrode materials give rise to multi-phase coexistence regimes within individual particles, generating significant lattice coherency strain across dynamically evolving interfaces. We demonstrate here that the lattice coherency strain can be alleviated by leveraging the coupling of electrochemistry, mechanics, and particle geometry to achieve controllable nucleation and deterministic ion transport. Here, we contrast singular kinks and continuous curvature as a means of enabling homogeneous lithiation without developing large stresses within a model cathode material, V2O5. The singular kink confirms that local curvature facilitates lithiation but also exacerbates lithiation inhomogeneities and elastic misfit strain. In contrast, the incorporation of continuous curvature enables homogeneous single-phase lithiation, mitigating lattice coherency strain. The studies provide a direct view of the coupling of mechanics and electrochemistry within crystalline electrodes and suggest that mesoscale architectures can help resolve key failure mechanisms limiting the performance of energy-storage systems without sacrificing charge/discharge kinetics.

Inconel alloy 718 is a high-strength and corrosion resistant alloy that is commonly used as a beamline vacuum window. The accumulation of irradiation-induced damage substantially decreases the window’s service lifetime, and replacing it engenders significant beamline downtime. With this application in mind, herein we examine whether post-irradiation annealing can alleviate irradiation-induced damage of Inconel alloy 718. Inconel alloy 718 was received in a solution annealed state. We then irradiated samples using two different modalities (1.5 MeV H+ and 5 MeV Ni2+) at three representative temperatures for beamline windows (room temperature, 100 °C, and 200 °C), followed by annealing at temperatures viable for in-situ annealing processes (no anneal, 300 °C, and 500 °C). Using nanoindentation, we determined that irradiation-induced hardening occurs but is largely mitigated by post-irradiation annealing. Overall, our results suggest that in-situ annealing of radiation damage in Inconel alloy 718 vacuum windows appears feasible, which could potentially decrease beam downtime and maintenance costs.

Despite renewed interest in lithium metal anodes, unstable electrodeposition of Li during operation has obstructed progress in practical battery applications. While deformation mechanics likely play a key role in Li's mechanical stability as an anode material, reports of Li's mechanical properties vary widely, perhaps due to variations in testing procedures. Through bulk tensile testing and nanoindentation, we provide a comprehensive assessment of the strain-rate and length-scale dependent mechanical properties of Li in its most commonly used form: high purity commercial foil. We find that bulk Li exhibits a yield strength between 0.57 and 1.26 MPa for strain rates from 5E-4 s−1 to 5E-1 s−1. For indentation tests with target P ˙ / P = 0.05 s−1, the hardness decreases precipitously from nearly 43 MPa to 7.5 MPa as the indentation depth increases from 250 nm to 10 µm. The plastic properties measured from bulk and nanoindentation testing exhibit strong strain-rate dependencies, with stress exponents of n = 6.55 and 6.9, respectively. We implement finite element analysis to relate the indentation depth to length scales of relevance in battery applications. Overall, the results presented herein may provide important guidance in designing Li anode architectures and charging conditions to mitigate unstable growth of Li during electrochemical cycling.

Beginning with the outbreak of COVID-19 at the dawn of 2020, the continuing spread of the pandemic has challenged the healthcare market and the supply chain of Personal Protective Equipment (PPE) around the world. Moreover, the emergence of the variants of COVID-19 occurring in waves threatens the sufficient supply of PPE. Among the various types of PPE, N95 Respirators, surgical masks, and medical gowns are the most consumed and thus have a high potential for a serious shortage during such emergencies. Considering the unanticipated demand for PPE during a pandemic, re-processing of used PPE is one approach to continue to protect the health of first responders and healthcare personnel. This paper evaluates the viability and efficacy of using FDA-approved electron beam (eBeam) sterilization technology (ISO 11137) to re-process used PPE. PPEs including 3M N95 Respirators, Proxima Sirus gowns, and face shields were eBeam irradiated in different media (air, argon) over a dose range of 0-200 kGy. Several tests were then performed to examine surface properties, mechanical properties, functionality performance, discoloration phenomenon, and liquid barrier performance. The results show a reduction of filtration efficiency to about 63.6% in the N95 Respirator; however, charge regeneration may improve the re-processed efficiency. Additionally, mechanical degradation was observed in Proxima Sirus gown with increasing dose up to 100 kGy. However, no mechanical degradation was observed in the face shields after 10 times donning and doffing. Apart from the face shield, N95 Respirators and Proxima Sirus gown both show significant mechanical degradation with ebeam dose over sterilization doses (25 kGy), indicating that eBeam technology is not appropriate for the re-processing these PPEs.

Owing to their enormous capacities, Li-S batteries have emerged as a prime candidate for economic and sustainable energy storage. Still, potential mechanics-based issues exist that must be addressed: lithiation of sulfur produces an enormous volume expansion (~ 80%). In other high capacity electrodes, large expansions generate considerable stresses that can lead to mechanical damage and capacity fading. However, the mechanics of electrochemical cycling of sulfur is fundamentally distinct from other systems due to solid-to-liquid, liquid-to-liquid, and liquid-to-solid phase transformations, and thus remains poorly understood. To this end, we measure the evolution of stresses in composite sulfur cathodes during electrochemical cycling and link these stresses to structural evolution. We observe that nucleation and growth of solid lithium-sulfur phases induces significant stresses, including irreversible stresses from structural rearrangements during the first cycle. However, subsequent cycles show highly reversible elastic mechanics, thereby demonstrating strong potential for extended cycling in practical applications.

Sorghum [Sorghum bicolor (L.) Moench] is a tropical grass that can be used as a bioenergy crop but commonly suffers from stem structural failure (lodging) when exposed to mechanical stimuli, such as rain and wind. Mechanical stimulation can trigger adaptive growth in plant stems (thigmomorphogenesis) by activating regulatory networks of hormones, proteins, transcription factors, and targeted genes, which ultimately alters their physiology, morphology, and biomechanical properties. The goals of this study are 1) to investigate differences in the morpho-anatomical-biomechanical properties of internodes from control and mechanically-stimulated plants and 2) to examine whether the changes also depend on the plant developmental stages at the time of stimulation. The sweet sorghum cultivar Della was grown in a greenhouse under two growth conditions: with and without mechanical stimulation. The mechanical stimulation involved periodic bending of the stems in one direction during a seven-week growth period. At maturity, the anatomical traits of the stimulated and non-stimulated stems were characterized, including internode lengths and diameters, and biomechanical properties, including elastic (instantaneous) modulus, flexural stiffness, strength, and time-dependent compliance under bending. The morpho-anatomical and biomechanical characteristics of two internodes of the stems that were at different stages of development at the time of mechanical stimulation were examined. Younger internodes were more responsive and experienced more pronounced changes in length due to the stimulation when compared to the older internodes. Statistical analyses showed differences between the stimulated and non-stimulated stems in terms of both their anatomical and biomechanical properties. Mechanical stimulation produced shorter internodes with slightly larger diameters, as well as softer (more compliant) and stronger stems.

There is a growing need for increased efficiency in the sterilization of single use medical devices and other products that contain polymer components. Gamma radiation is widely used for devices suited for radiation sterilization; however, safety, throughput and cobalt-60 source availability are challenging the prospect of relying on gamma radiation to meet the anticipated needs of the industry. Use of electron beam (e-beam) and X-rays as alternatives to gamma for radiation sterilization have been hampered in part by a concern that these modalities may adversely affect polymer integrity and performance relative to the gamma method, for which the industry has had much more experience. To address this concern, the effects of sterilization-relevant doses of e-beam, X-ray and gamma radiation were directly compared using common medical device polymers found in two prototypical commercial devices currently sterilized using cobalt-60 gamma irradiation. The Becton, Dickinson and Company (BD) Vacutainer™ Plus tube contains low-density polyethylene and chlorobutyl rubber components, while the BD Vacutainer™ Push Button Blood Collection Set contains polypropylene homopolymer and polyolefin elastomer components. Injection-molded samples prepared from the polymers used in these products were exposed to target doses of 15, 35, 50 and 80 kGy using gamma, e-beam and X-ray radiation. Changes in coloration, tensile properties and hardness were measured for each condition, and the effects of e-beam and X-ray irradiation compared with the effects of gamma irradiation on these properties. Both e-beam and X-ray appear as viable alternatives to gamma irradiation for sterilization of the polymers tested.

Liquid that resides in a soft elastomer embedded between wearable electronics and biological tissue provides a strain-isolation effect, which enhances the wearability of the electronics. One potential drawback of this design is vulnerability to structural instability, e.g., roof collapse may lead to partial closure of the liquid-filled cavities. This issue is addressed here by overfilling liquid in the cavities to prevent roof collapse. Axisymmetric models of the roof collapse are developed to establish the scaling laws for liquid-overfilled cavities, as well as for air- and liquid-filled ones. It is established that the liquid-overfilled cavities are most effective to prevent roof collapse as compared to air- and liquid-filled ones.

Effective sterilization methods for single-use devices are a growing need for the medical industry. Concerns with safety, throughput and source availability, however, prompt prudent contingency planning for gamma irradiation of devices suited for radiation sterilization. Electron beam (e-beam) and X-ray represent two alternatives to gamma radiation if they can be confirmed to be compatible with sterilization of the devices. To address this question, the effects of sterilization-relevant doses of e-beam and X-ray radiation are directly compared to the effects of gamma radiation using two prototypical commercial devices currently sterilized using cobalt-60 gamma radiation. These devices include components that comprise six distinct polymer materials commonly used in the medical device industry. The devices investigated are the Becton, Dickinson and Company (BD) VacutainerTM Plus tube, comprised of low-density polyethylene, chlorobutyl rubber, and polyethylene terephthalate components; and the BD VacutainerTM Push Button Blood Collection Set, containing polypropylene, polyolefin elastomer, and polyvinyl chloride components. Changes in functionality, discoloration and select mechanical properties of components of each device were measured following exposure to targeted doses of 15, 35, 50 and 80 kGy. A statistical analysis was performed to determine if the effects of e-beam or X-ray radiation differ from the effects of gamma radiation for the properties considered. No devices were found to fail the functional performance tests at any of the doses considered. Small, but statistically significant differences were observed in device discoloration from e-beam, X-ray and gamma radiation following processing for certain materials at certain dose levels. Both e-beam and X-ray irradiation appear as viable alternatives to gamma irradiation for sterilization of the medical devices and materials considered.

We measure stresses that develop in sputter-deposited amorphous Ge thin films during electrochemical lithiation and delithiation. Amorphous LixGe electrodes are found to flow plastically at stresses that are significantly smaller than those of their amorphous LixSi counterparts. The stress measurements allow for quantification of the elastic modulus of amorphous LixGe as a function of lithium concentration, indicating a much-reduced stiffness compared to pure Ge. Additionally, we observe that thinner films of Ge survive a cycle of lithiation and delithiation, whereas thicker films fracture. By monitoring the critical conditions for crack formation, the fracture energy is calculated using an analysis from fracture mechanics. The fracture energies are determined to be Γ = 8.0 J m−2 for a-Li0.3Ge and Γ = 5.6 J m−2 for a-Li1.6Ge. These values are similar to the fracture energy of pure Ge and are typical for brittle fracture. Despite being brittle, the ability of amorphous LixGe to flow at relatively small stresses during lithiation results in an enhanced ability of Ge electrodes to endure electrochemical cycling without fracture.

Elastomers often exhibit large stretchability but are not typically designed with robust energy dissipating mechanisms. As such, many elastomers are sensitive to the presence of flaws: cracks, notches, or any other features that cause inhomogeneous deformation significantly decrease the effective stretchability. To address this issue, we have dispersed voids into a silicone elastomer matrix, thereby creating a “negative” composite that provides increased fracture resistance and stretchability in pre-cut specimens while simultaneously decreasing the weight. Experiments and simulations show that the voids locally weaken the specimen, guiding the crack along a tortuous path that ultimately dissipates more energy. We investigate two geometries in pre-cut specimens (interconnected patterns of voids and randomly distributed discrete voids), each of which more than double the energy dissipated prior to complete rupture, as compared to that of the pristine elastomer. We also demonstrate that the energy dissipated during fracture increases with the volume fraction of the voids. Overall, this work demonstrates that voids can impart increased resistance to rupture in elastomers with flaws. Since additive manufacturing processes can readily introduce/pattern voids, we expect that applications of these elastomer–void​ “composites” will only increase going forward, as will the need to understand their mechanics.

Grasses represent the most productive and widely grown crop family across the globe but are susceptible to structural failure (lodging) during growth (e.g., from wind). The mechanisms that contribute to structural failure in grass stems are poorly understood due to a lack of systematic studies of their biomechanical behavior. To this end, this study examines the biomechanical properties of sweet sorghum (Sorghum bicolor (L.) Moench), focusing on the time-dependent behavior of the stems. Specifically, we conducted uniaxial compression tests under ramp and creep loading on pith and stem specimens of the sorghum cultivar Della. The tests demonstrated significantly nonlinear and time-dependent stress-strain behavior in all samples. We surmise that this behavior arises from a combination of poroelasticity due to migration of water through the plant and viscoelasticity due to rearrangement of macromolecular networks, such as cellulose microfibrils and lignin matrices. Overall, our measurements demonstrate that sorghum is not a simple reversible elastic material. As such, a complete understanding of the conditions that lead to stem lodging will require knowledge of sorghum's time-dependent biomechanical properties. Of practical importance, the time-dependent biomechanical properties of the stem influence its mechanical stability under various loading conditions during growth in the field (e.g., different wind speeds).

We have measured the fracture energy of lithiated silicon thin-film electrodes as a function of lithium concentration using a bending test. First, silicon thin-films on copper substrates were lithiated to various states of charge. Then, bending tests were performed by deforming the substrate to a pre-defined shape, producing a variation of the curvature along the length of the electrode. The bending tests allow determination of the critical strains at which cracks initiate in the lithiated silicon. Using the substrate curvature technique, we also measured the elastic moduli and the stresses that develop in the electrodes during electrochemical lithiation. From these measurements, the fracture energy was calculated as a function of lithium concentration using a finite element simulation of fracture of an elastic film on an elastic–plastic substrate. The fracture energy was determined to be Γ = 12.0 ± 3.0 J m−2 for amorphous silicon and Γ = 10.0 ± 3.6 J m−2 for Li3.28Si, with little variation in the fracture energy for intermediate Li concentrations. These results provide a guideline for the practical design of high-capacity lithium ion batteries to avoid fracture. The experimental technique described in this paper also provides a simple means of measuring the fracture energy of brittle thin-films.

highlights g rap hical a bstract � Increasing the charging rate results in an increase in stresses measured in a- LixSi. � Observations indicate that rate- sensitive plasticity occurs in a-LixSi. � A model of concurrent lithiation and rate-sensitive plasticity is developed. � Rate-sensitive material parameters are quantified for a-LixSi. � Results have important ramifications for rate-capabilities of silicon electrodes. abstract Silicon is a promising anode material for lithium-ion batteries due to its enormous theoretical energy density. Fracture during electrochemical cycling has limited the practical viability of silicon electrodes, but recent studies indicate that fracture can be prevented by taking advantage of lithiation-induced plasticity. In this paper, we provide experimental insight into the nature of plasticity in amorphous LixSi thin films. To do so, we vary the rate of lithiation of amorphous silicon thin films and simultaneously measure stresses. An increase in the rate of lithiation results in a corresponding increase in the flow stress. These observations indicate that rate-sensitive plasticity occurs in a-LixSi electrodes at room temperature and at charging rates typically used in lithium-ion batteries. Using a simple mechanical model, we extract material parameters from our experiments, finding a good fit to a power law rela- tionship between the plastic strain rate and the stress. These observations provide insight into the un- usual ability of a-LixSi to flow plastically, but fracture in a brittle manner. Moreover, the results have direct ramifications concerning the rate-capabilities of silicon electrodes: faster charging rates (i.e., strain rates) result in larger stresses and hence larger driving forces for fracture.

We report observations of microstructural changes in {100} and {110} oriented silicon wafers during initial lithiation under relatively high current densities. Evolution of the microstructure during lithiation was found to depend on the crystallographic orientation of the silicon wafers. In {110} silicon wafers, the phase boundary between silicon and LixSi remained flat and parallel to the surface. In contrast, lithiation of the {100} oriented substrate resulted in a complex vein-like microstructure of LixSi in a crystalline silicon matrix. A simple calculation demonstrates that the formation of such structures is energetically unfavorable in the absence of defects due to the large hydrostatic stresses that develop. However, TEM observations revealed micro-cracks in the {100} silicon wafer, which can create fast diffusion paths for lithium and contribute to the formation of a complex vein-like LixSi network. This defect-induced microstructure can significantly affect the subsequent delithiation and following cycles, resulting in degradation of the electrode.

Enhancing the electrochemical performance of lithium-sulfur batteries requires improved fundamental understanding of the reduction and oxidation of the soluble lithium polysulfide species. To this end, we have designed a ‘donut-shaped’ cell to enable direct optical observation of phase transformations of a liquid polysulfide catholyte to solid lithium sulfide during electrochemical cycling. We use this technique to image the spatio-temporal distribution of the solid lithium sulfide as it deposits on a carbon matrix at different charging rates. These experiments indicate that the reduction and oxidation of polysulfide catholyte occurs as a thin film deposition and growth process during both lithiation and delithiation. We then investigate the ramifications of these morpological changes in terms of mechanical stability by measuring the evolution of stress during discharge of the polysulfide catholyte. The stress measurements indicate that the average stress during discharging decreases with increasing the charging rate, which we attribute to less dense deposition of lithium sulfide at high discharge rates.

In a novel design of lithium-ion batteries, hollow electrode particles coated with stiff shells are used to mitigate mechanical and chemical degradation. In particular, silicon anodes of such core–shell nanostructures have been cycled thousands of times with little capacity fading. To reduce weight and to facilitate lithium diffusion, the shell should be thin. However, to avert fracture and debonding from the core, the shell must be sufficiently thick. This tradeoff is considered here by calculating the stress fields resulting from concurrent insertion reaction and plastic flow for both spherical and cylindrical hollow core–shell nanostructures. Conditions to avert fracture and debonding are identified in terms of the radius of the core, the thickness of the shell, and the state of charge. The effect of the stress on the electrochemical reaction is also discussed.