ABSTRACT Soldier termites of the dampwood species Neotermes castaneus defend their colonies with crushing‐type mandibles that generate bite forces near the upper end of the range for insects of comparable head width, imposing substantial mechanical demand on a non‐mineralized cuticle. Using a combination of microscopy, spectroscopy, and modeling, we demonstrate how this cuticle accommodates the combined contact and bending loads during defensive biting. Finite element models partition the mandible into two mechanical environments: compressive contact stresses at the convex regions of teeth and bending‐induced tensile stresses in the concave regions between the teeth. These regions coincide with distinct load‐bearing regions and higher hardness at the convex marginal teeth, which contain localized domains of preferentially aligned out‐of‐plane α‐chitin within an otherwise Bouligand‐like lamellar architecture; Atomic Force Microscopy ‐ Infrared Spectroscopy (AFM‐IR) and elemental mapping reveal a through‐thickness sclerotization gradient with relative zinc enrichment confined at the crushing interface, providing contact durability. These findings indicate that a predominantly organic mandible achieves crushing performance through regionally coordinated fiber architecture, sclerotization‐driven stiffness gradients, and surface‐localized chemical hardening and thus offers design principles for lightweight organic composites that rely on regional reinforcement rather than uniform bulk stiffening.

Confidently predicting high-temperature deformation, including creep and creep rupture, is paramount for the design and commercialization of candidate materials for advanced nuclear energy systems. To accelerate creep quantification, we introduce a framework that enables rapid, cost-effective, and reliable prediction of creep rup ture lifetimes, minimizing reliance on time-intensive bulk creep testing. Unlike conventional creep analysis, which requires extensive time and resources, our method leverages a maximum of four short-term bulk creep tests as training data for prediction. This framework combines high-throughput nanoindentation up to 700 degrees C with these targeted bulk tests to inform our creep rupture model in order to predict rupture lifetimes. The strong agreement between our predictions and conventional experimental data demonstrates the effectiveness of our approach foraccelerated creep analysis and lifetime prediction of structural components in high-temperature applications. Our multi-pronged approach motivates further integration of computational tools and advanced instrumentation to establish a universal framework for understanding high-temperature material responses.

Journal Article Mechanical Spectroscopy: Machine Learning and High Speed Nanoindentation for High Throughput Material Evaluation Get access Eric D Hintsala, Eric D Hintsala Bruker Nano Surfaces & Metrology, Eden Prairie MN, United States Search for other works by this author on: Oxford Academic Google Scholar Bernard R Becker, Bernard R Becker Bruker Nano Surfaces & Metrology, Eden Prairie MN, United States Search for other works by this author on: Oxford Academic Google Scholar Benjamin Stadnick, Benjamin Stadnick Bruker Nano Surfaces & Metrology, Eden Prairie MN, United States Search for other works by this author on: Oxford Academic Google Scholar Ude Hangen, Ude Hangen Bruker Nano Surfaces & Metrology, Aachen, Germany Search for other works by this author on: Oxford Academic Google Scholar Moujhuri Sau, Moujhuri Sau Chemical Engineering & Materials Science, U Minnesota, Minneapolis MN, United States Search for other works by this author on: Oxford Academic Google Scholar Nathan Mara, Nathan Mara Chemical Engineering & Materials Science, U Minnesota, Minneapolis MN, United States Search for other works by this author on: Oxford Academic Google Scholar Douglas D Stauffer Douglas D Stauffer Bruker Nano Surfaces & Metrology, Eden Prairie MN, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 774–775, https://doi.org/10.1093/micmic/ozad067.383 Published: 22 July 2023

Coated nuclear fuel particles, most commonly tri-structural isotropic (TRISO), are intended for use in advanced high temperature reactors. It is vital to understand the mechanical properties of each coating layer to accurately predict the performance of these fuel particles and how these might change at each stage of their lifecycle. This paper reports results of in-situ nanoindentation, with an emphasis on the structural SiC layer, along with microcantilever testing of the critical SiC-IPyC interface. At 1000 C-degrees the hardness of the SiC layer is similar to 75% lower than at room temperature implying significantly more plasticity at the reactor operating temperature. The elastic modulus was slightly lower at 1000 C-degrees than at room temperature. Microcantilever fracture at the SiC-IPyC interface shows that failure occurs within the pyrolytic carbon layer rather than an interfacial "debonding" with a strength similar to that of bulk pyrolytic carbon.

Journal Article Pearlite Size Effects on Ductility at Cryogenic Temperature via In-Situ Cantilever Loading Get access Jarod Robinson, Jarod Robinson The University of Alabama, Tuscaloosa, AL, United States Search for other works by this author on: Oxford Academic Google Scholar Eric D Hintsala, Eric D Hintsala Bruker Nano Surfaces and Metrology, Eden Prairie, MN, United States Search for other works by this author on: Oxford Academic Google Scholar Douglas D Stauffer, Douglas D Stauffer Bruker Nano Surfaces and Metrology, Eden Prairie, MN, United States Search for other works by this author on: Oxford Academic Google Scholar Sanjit Bhowmick, Sanjit Bhowmick Bruker Nano Surfaces and Metrology, Eden Prairie, MN, United States Search for other works by this author on: Oxford Academic Google Scholar Eric R Homer, Eric R Homer Brigham Young University, Provo, UTUnited States Search for other works by this author on: Oxford Academic Google Scholar Gregory B Thompson Gregory B Thompson The University of Alabama, Tuscaloosa, AL, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 1521–1522, https://doi.org/10.1093/micmic/ozad067.783 Published: 22 July 2023

Twins play an important role in modern defect engineering.They can increase the strength of a material as well as provide superior electrical conductivity [1].However, under specific loading conditions, the removal of twins (detwinning) can occur in FCC, HCP, and BCC metals [2][3][4].Even more interesting is that atomistic simulations have demonstrated that the incoherent twin boundary (ITB) migration responsible for detwinning in FCC systems has a higher mobility at lower temperatures [5][6].To study this effect experimentally, a Cu-2Al alloy was sputter deposited at a high rate of 1.45 nm/s, which has been well established as a method to produce a high density of nanotwins in a columnar grain structure through the thickness of the film [7].Using a Xenon plasma focus ion beam (PFIB), individual pillars were shaped out of the film.These pillars were then compressed in-situ a scanning electron microscope using a flat punch indenter at 23 °C, and -150 °C.The evolution of the pillar deformation was linked to a quantitative load-displacement response with post-mortem TEM imaging of the nanostructures within the column.The load-displacement curves are plotted in Fig. 1.At 23 °C, the load curve shows a response with an initially linear regime that then transitions into a relatively small amount of work hardening with a work hardening coefficient of 0.18.Similar to the ambient temperature condition, the -150 °C shows an initial linear response whereupon it transitions with a clear rise in the loaddisplacement response.Here the work hardening coefficient was measured to be 0.41.Additionally, minor serrations are present in the load curve at -150 °C.The final deformed shape of the compressed pillars at 23 °C and -150 °C are seen in Figures 2 a) and c).At 23 °C, plastic flow at the top of the pillar is observed.In addition, bulging in the pillar is present near the bottom of the pillar resulting in an overall 'hourglass' shape.In contrast, the pillar deformed at -150 °C resulted in a near cylindrical shape indicating that the pillar accommodated deformation relatively uniformly.TEM foils were extracted from each post-compressed pillar using a Gallium focused ion beam (FIB) lift out technique.The microstructures, viewed as a brightfield image, are shown in Fig. 2 b) andd).Beginning with the pillar compressed at 23 °C, Fig. 2 b), a clear equiaxed grain structure at the top of the film is observed and denoted as region (i).This region has a thickness on the order of 100 nm which correlates with the depth of the initial linear region.This top region, both in the SEM and TEM images, reveals significant plastic flow forming a 'smeared' surface.This surface is linked to the initial conical shape of the top of the pillar that formed during milling and shaping of the pillar from the ions.Investigating region (ii) from Fig. 2 b), a nanotwinned columnar structure is retained in the pillar, which is the initial as-deposited structure [7].Finally, in region (iii), a complete loss of nanotwins (a known strengthening mechanism) and the columnar grain morphology is observed [1].Here, the microstructure has evolved into a refined, equiaxed granular structure that spans to the base of the film.Since the Si substrate is harder than the Cu film, there is a strong plastic strain concentration at this interface.Consequently, the film at the substrate likely evolved the microstructure from the interface upwards since region (ii) had not changed.Due to this microstructural evolution at the base of the pillar, the pillar barreled into the hourglass shape.This evolution also appears to reduce the extent of work hardening in the pillar's response.This highlights the asymmetric deformation evolution in the pillar.Examining the pillar compressed at -150 °C, the top region of the pillar plastically deformed and evolved into a smeared morphology, Fig. 2 c), but, at this temperature, it was not as severe.The linear region for the cryogenic loading in Fig. 1 has a slightly greater slope than the ambient temperature response.This portion of the curve is a combination of the elastic and early plastic response from stress concentrations and preexisting defects which begin moving before the overall plasticity begins.The modestly higher slope for the -150 °C condition in this linear region is attributed to the lower dislocation mobility at this temperature.The overall pillar structure remained relatively homogenous, Fig. 2 c), indicating uniform deformation and a higher work hardening response.The TEM cross-section, Fig. 2 d), largely retains the granular columnar morphology; however, the nanotwin density is lower when one compares this image to region (ii) in Fig. 2 b).This supports computational findings that such detwinning is promoted at cryogenic temperatures [5][6].While a high density of nanotwins can provide a strengthening mechanism, the retention of the columnar grain structure appears to be more significant in strengthening the material.This is evident in that the cryogenically loaded sample where it had a reduced twin density but retained a columnar structure and had a higher work hardening response.In contrast, the ambient temperature pillar microstructure where nanotwins and the columnar morphology was lost.This sample barreled and had a lower work hardening coefficient.Collectively, this gives insights into the stability of nanostructure strengthening mechanisms as a function of loading temperature [8].

In this project, we demonstrated stable nanoscale fracture in single-crystal silicon using an in-situ wedge-loaded double cantilever beam (DCB) specimen. The fracture toughness KIC was calculated directly from instrumented measurement of force and displacement via finite element analysis with frictional corrections. Measurements on multiple test specimens were used to show KIC = 0.72 ± 0.07 MPa m1/2 on {111} planes and observe the crack-growth resistance curve in <500 nm increments. The exquisite stability of crack growth, instrumented measurement of material response, and direct visual access to observe nanoscale fracture processes in an ideally brittle material differentiate this approach from prior DCB methods.

This work aims to adapt nanoindentation mapping combined with a k-means algorithm as a high-throughput technique to study the nano-scale spatial changes in mechanical properties for a heterogeneous material. This technique can also classify the individual data points based on their properties. Hundreds to thousands of indents were performed on additively manufactured T91 at room temperature, 300°C, 400°C, and 500°C across a square area with a side length of 120 μm to 400 μm. From this data, the hardness and reduced modulus at each point could be calculated and mapped. Using k-means clustering, we were able to arrange the data into three or four clusters corresponding roughly to the ferritic and martensitic phases as well as one or two intermediate clusters sampling both the phases. The hardness of these two phases appears to be quite stable as a function of temperature. Nanoindentation mapping and the k-means algorithm can therefore be used to rapidly assess the feasibility of heterogeneous materials under extreme conditions, such as nuclear reactor steels.

Journal Article Advanced In Situ TEM Nanomechanical Testing Options with the PI-95 Get access Sanjit Bhowmick, Sanjit Bhowmick Bruker Nano, Minneapolis, MN, USA Corresponding author: sanjit.bhowmick@bruker.com Search for other works by this author on: Oxford Academic Google Scholar Eric Hintsala, Eric Hintsala Bruker Nano, Minneapolis, MN, USA Search for other works by this author on: Oxford Academic Google Scholar Douglas Stauffer Douglas Stauffer Bruker Nano, Minneapolis, MN, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Pages 3174–3175, https://doi.org/10.1017/S1431927622011783 Published: 01 August 2022

In this letter, we demonstrated stable nanoscale fracture in single-crystal silicon using an in-situ wedge-loaded double cantilever beam (DCB) specimen. The fracture toughness KIC was calculated directly from instrumented measurement of force and displacement via finite element analysis with frictional corrections. Measurements on multiple test specimens were used to show KIC = 0.72 ± 0.07 MPa m1/2 on {111} planes and observe the crack-growth resistance curve in <500 nm increments. The exquisite stability of crack growth, instrumented measurement of material response, and direct visual access to observe nanoscale fracture processes in an ideally brittle material differentiate this approach from prior DCB methods.

Materials are needed that can tolerate increasingly harsh environments, especially ones that retain high strength at extreme temperatures. Higher melting temperature alloys, like those consisting primarily of refractory ele-ments, can greatly increase the efficiency of turbomachinery used in grid electricity production worldwide. Existing alloys, including Ni-and Co-based superalloys, used in components like turbine blades, bearings, and seals, remain a performance limiting factor due to their propensity, despite extensive optimization efforts, for softening and diffusion-driven elongation at temperatures often well above half their melting point. To address this critical materials challenge, we present results from integrating additive manufacturing and alloy design to guide significant improvements in performance via traditionally difficult-to-manufacture refractory alloys. We present an example of a multi-principal element alloy (MPEA), consisting of five refractory elements and aluminum, that exhibited high hardness and specific strength surpassing other known alloys, including super -alloys. The alloy shows negligible softening up to 800 degrees C and consists of four compositionally distinct phases, in distinction to previous work on MPEAs. Density functional theory calculations reveal a thermodynamic expla-nation for the observed temperature-independent hardness and favorability for the formation of this multiplicity of phases.

Journal Article Mechanical Properties of Bond Coatings and Ni-based Superalloys at Extreme Temperatures Get access Sanjit Bhowmick, Sanjit Bhowmick Bruker, Minneapolis, Minnesota, USA Search for other works by this author on: Oxford Academic Google Scholar Eric Hintsala Eric Hintsala Bruker, Minneapolis, Minnesota, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Pages 1810–1812, https://doi.org/10.1017/S1431927622007152 Published: 01 August 2022

High throughput nanoindentation techniques can provide rapid materials screening and property mapping and can span millimeter length scales and up to 106 data points. To facilitate rapid sorting of these data into similar groups, a necessary task for establishing structure–property relationships, use of an unsupervised machine learning analysis called clustering has grown in popularity. Here, a method is proposed and tested that evaluates the uncertainty associated with various clustering algorithms for an example high entropy alloy data set and explores the effect of the number of data points in a second Damascus steel data set. The proposed method utilizes the bootstrapping method of Efron to resample a modeled probability distribution function based upon the original data, which allows the uncertainty related to the clustering to be evaluated in contrast to the classical standard error on the mean calculations. For the Damascus, it was found that results data from a 104 point subsample are comparable to those from the full 106 set while representing a significant reduction in data acquisition.

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The brittle to ductile transition (BDT) is difficult to predict without extensive fitting parameters or tuning to a particular material. Currently, predicting fracture through extensive fitting or computationally expensive algorithms is high in both cost and time required to capture the relevant deformation physics. Presented here is analysis using a comparatively high throughput analytical model to predict fracture behavior using relatively few key experimentally determined parameters: activation volume, shear stress, and activation energy. This approach could reduce the time scale to predict fracture and thus accelerate new materials discovery. The current work utilizes seminal studies to provide the inputs for validating our approach via two single crystal materials, Si and W, which both have marginal toughness at low temperatures. It is shown that knowledge of underlying deformation mechanisms (still in progress) coupled to rapid determination of physical quantities (shear stress, activation volumes, and dislocation shielding) promotes unique discovery and opportunities, including future application to polycrystalline materials and phenomena. The technique, using literature values for physical parameters, correlates well to experimental fracture behavior for these two different classes of materials, semiconductors and metals, offering new opportunities for broader study.