Marc A. Meyers

ABSTRACT The tensile strength of metals at extreme strain rates is a key predictor of their performance in ballistic and structural impact applications. An important experimental method to reach these extreme strain rates is the use of high‐amplitude, short‐duration pulsed lasers. The Jupiter Laser Facility at the Lawrence Livermore National Laboratory enabled probing for the first time the mechanical response of several promising High Entropy Alloys at times on the order of nanoseconds (strain rates of ∼10 7 and ∼10 9 s −1 ). The measured strength is in the range of 6 to 10 GPa, ten times the quasistatic value. The mechanisms of plastic deformation and failure were identified and quantified through analysis and molecular dynamics simulation. The reflected wave amplitudes, obtained by VISAR, were used to determine the tensile (spall) stress. The high tensile strength obtained is due to two factors: the strain‐rate dependence of plastic flow and the kinetics of void nucleation, growth, and coalescence. The experimental results are compared with an analytical prediction considering both grain‐interior and grain‐boundary void initiation. Molecular dynamics simulations, conducted at strain rates of 10 8 and 10 9 s −1 , rationalize the experimental results. They provide valuable information about the process of failure evolution, and reveal that grain boundary separation plays a pivotal role in spalling.

The JMRT Senior Career Award, established in 2022, honors a global leader in materials science that has made seminal contributions to the field. The 2025 recipient is Professor Robert O. Ritchie.

<title>Abstract</title> Iron (Fe) is a primary constituent of terrestrial planetary cores, yet its rheological properties under extreme conditions remain uncertain. Here we present direct measurements of Fe strength at 310-430 GPa pressures and 3700-5800 K temperatures, obtained using Rayleigh-Taylor (RT) instability experiments at the National Ignition Facility. Single-crystal α-Fe samples with [001] and [111] orientations are shock-ramp compressed past the α-ε transition along paths approaching Earth's inner core conditions. We find that ε-Fe derived from [001] α-Fe is consistently stronger (11-20 GPa), than that from [111] α-Fe (8-18 GPa), contrary to the trend at ambient conditions. Large-scale molecular dynamics simulations reproduce these values and attribute this anisotropy to microstructural evolution during the phase transition and subsequent ε-phase plasticity. Ripple growth analysis further constrains viscosities of 100-170 Pa·s under the driven conditions. Our results provide new experimental benchmarks for Fe rheology at inner-core conditions, with implications for seismic anisotropy and the geodynamo.

Abstract The mechanical behavior and microstructural evolution of a BCC‐phase NbTaTiV refractory multi‐principal element alloy (RMPEA) is studied over a wide range of strain rates (10 −3 to 10 3 s −1 ) and temperatures (room temperature to 850 °C). The mechanical property of present RMPEA shows less strain‐rate dependence and strong resistance to softening at high temperatures. Under high strain‐rate loading, the formation of thin type‐I twins is observed, which could lead to an increase in strain‐hardening rates. However, this hardening mechanism competes with adiabatic heating effects, resulting in the deterrence of strain‐hardening behaviors. In contrast, substantial strain‐hardening occurs at cryogenic temperatures due to the formation of twins, which act as stronger barriers to dislocation motion and interact with each other. To further understand the different strain‐hardening behaviors, density functional theory (DFT) calculations predict relatively low stacking fault energies and high twinning stress for the NbTaTiV RMPEA.

Fully revised and updated, the new edition of this classic textbook places a stronger emphasis on real-world test data and trains students in practical materials applications; introduces new testing techniques such as micropillar compression and electron back scatted diffraction; and presents new coverage of biomaterials, electronic materials, and cellular materials alongside established coverage of metals, polymers, ceramics and composites. Retaining its distinctive emphasis on a balanced mechanics-materials approach, it presents fundamental mechanisms operating at micro- and nanometer scales across a wide range of materials, in a way that is mathematically simple and requires no extensive knowledge of materials, and demonstrates how these microstructures determine the mechanical properties of materials. Accompanied by online resources for instructors, and including over 40 new figures, over 100 worked examples, and over 740 exercises, including over 280 new exercises, this remains the ideal introduction for senior undergraduate and graduate students in materials science and engineering.

Abstract The embira bark fiber is routinely used in Brazil to construct simple structures because of its ease of extraction, flexibility, and considerable strength. It plays an important role, somewhat similar to duct tape, and is commonly used for temporary repairs and tying objects. The flexible bark is removed from the tree by making two cuts into it and manually pulling off the fibrous structure. Three similar but distinct embira bark fibers are characterized structurally and mechanically: embira branca , embira capa bode , and embira chichá . The bark separates readily into strips with thicknesses between 0.3 and 1 mm, enabling it to be twisted and bent without damage. The structure consists of aligned cellulose fibers bound by lignin and hemicellulose. Thus, it is a natural composite. The tensile strength of the three fibers varies in the range of 25 to 100 MPa, with no clear difference between them. There is structural and strength consistency among them. The mechanical strength of embira branca is measured for different fiber bundle diameters and is found to increase with decreasing diameter. Thermogravimetric analysis showed that degradation of the fibers initiates at 250 °C, consistent with other lignocellulosic fibers. X-ray diffraction identifies two major components: the monoclinic crystalline structure of cellulose and an amorphous phase; the crystallinity index is approximately 50%. The tensile strength shows significant variation, a characteristic of biological materials; this can be significantly improved by selective growing of embira-bearing trees.

Critical engineering applications, such as landing gears and armor protection, require structural materials withstanding high strength and significant plastic deformation. Nanoprecipitate-strengthened high-entropy alloys (HEAs) are considered as promising candidates for structural applications due to their enhanced strength and exceptional work-hardening capability. Herein, we report a FeCoNiAlTi-type HEA that achieves ultrahigh gigapascal yield strength from quasi-static to dynamic loading conditions and superb resistance to adiabatic shear failure. This is accomplished by introducing high-density coherent L1 2 nanoprecipitates. Multiscale characterization and molecular dynamics simulation demonstrate that the L1 2 nanoprecipitates exhibit multiple functions during impact, not only as the dislocation barrier and the dislocation transmission medium, but also as energy-absorbing islands that disperse the stress spikes through order-to-disorder transition, which result in extraordinary impact resistance. These findings shed light on the development of novel impact-resistant metallic materials. By introducing high-density coherent L1 2 nanoprecipitates, the FeCoNiAlTi-type HEA achieves high quasi-static/dynamic mechanical properties. The hierarchical deformation mechanism provides various pathways for dissipating the impact strain energy, thereby endowing the HEA with extremely high impact resistance.

Keratinous materials found in the feather shafts of flying birds possess impressive mechanical attributes, combining excellent strength-to-weight balance, toughness, and more. In this study, we investigate the shape memory effect in bird feather shafts, examining its underlying design principles as templates for bioinspired shape memory composites. Through analytical and computational analysis, we aim to uncover the underlying rules and design guidelines based on stimulus-induced softening (pertaining to strength and/or stiffness) and swelling (pertaining to expansion in volume). More specifically, we study a one-dimensional case to examine the synergistic relationship between the matrix and fibers inside the feather structure. We propose three distinct micro-mechanical modeling approaches to evaluate the contribution of each hydration-induced effect-softening, swelling, and the combined action of both. In all models, the matrix is considered to be an elastic-perfectly plastic material that is sensitive to hydration, while the fibers are treated as purely elastic and unaffected by hydration. The findings of the study provide informative insights into the nuanced nature of swelling within the material, highlighting that its desirability is dependent on specific conditions and circumstances. Furthermore, we find that the softening component plays a large pivotal role in driving the process of shape recovery. Using the proposed analytical framework and design principles, we develop a conceptual feather shaft-like composite, followed by demonstrating its tunability in degree of shape recovery and its versatility in selecting constituent base material components. This research offers valuable core framework for exploring and designing advanced bioinspired shape memory materials while eliminating the need for traditionally active shape memory components, holding promising potential for actuation, deployment, and morphing purposes. STATEMENT OF SIGNIFICANCE: This study investigates the shape-memory effect in bird feather shafts, offering bioinspired strategies for designing advanced shape-memory composites. Unlike conventional materials, which often rely on external stimuli or active components, our research focuses on hydration-driven mechanisms-specifically, matrix softening and swelling. Through micro-mechanical modeling, we demonstrate that softening is the key driver of shape recovery, while swelling plays a secondary role under specific conditions. These insights provide new, passive design principles for creating tunable shape-memory composites without the need for traditional active components. The findings have broad implications for applications in actuation, morphing, and reconfigurable systems, where material adaptability is crucial.

This book presents the papers given at a conference on the impact testing of metals. Topics considered at the conference included dynamic consolidation, the analysis of dislocation kinetics across shocks, high-strain-rate deformation, adiabatic shear band phenomena, dynamic fracture, explosive metal working, shock synthesis and the property modification of materials, and novel concepts and applications of high pressure.

The objective of this research program was to determine the effect of metallurgical parameters on the development of dynamic fracture by a tensile pulse in OFHC copper. Spalling was produced by explosive experiments. Copper specimens with varying grain sizes (250 μm, 90 μm, and 20 μm), in the predeformed condition (by rolling), and with two degrees of purity (99.99 and 99.5 pet) were subjected to impact pressures of 3.0, 3.5, and 3.8 GPa, at a constant initial pulse duration of 2.8 μs. The void volume fraction was determined in the recovered copper specimens as a function of distance from the impact surface. It was found to increase significantly between 3.0 and 3.8 GPa impact pressure. The metallurgical condition (grain size, predeformation, and impurity content) was found to have a marked effect on the spall strength of copper. The relative spall resistance of the various specimens did not correspond to their microhardnesses, since different metallurgical conditions exhibited different nucleation sites. While the large and medium-grain annealed specimens exhibited intergranular spalling, the small-grain and rolled specimens exhibited transgranular spalling. The primary nucléation sites for large and medium-grain specimens were grain boundaries, while grain interiors were important for the small-grain predeformed specimens. In specimens with low purity (99.5 pet), second-phase particles were the main nucléation sites. It was possible to identify a void by high-voltage electron microscopy; this is the first report of the observation of a void formed by a tensile pulse. The void was found to be surrounded by a high density of dislocations.

Microstructures of adiabatic shear bands in commercially pure titanium and tempered AISI 4340 steel were investigated by high voltage transmission electron microscopy. The structure of shear bands in titanium consists of small (0.05-0.3 μm) grains with well-defined grain boundaries, while regions near the shear bands show a high density of dislocations. In the tempered 4340 steel, both the shear band and the surrounding regions consist of highly dislocated α′-martensite with a low density of {112} microtwins. χ(Fe5C2) carbides are found to occur along such microtwins in the shear bands. The martensite lath boundaries inside the 4340 steel shear band are not well defined.

There are three primary thrusts for the study of the response of materials to shock-wave and high-strain-rate phenomena: High-energy rate fabrication, encompassing the more established technologies of explosive welding, cladding, forming and hardening, and the new, “frontier” areas of dynamic consolidation, shock modification of properties, and shock synthesis of new materials. Defense-related applications encompassing impact, fragmentation, explosive-metal interactions, effects of directed energy beams. Fundamental understanding of the behavior of material under these conditions.

Martensite is the result of a diffusionless displacive phase transition. In Fe-based alloys it transforms the FCC to the BCC, BCT, or HCP structures and occurs at high strain rates. It has two typical morphologies, known as lath and plate. A quantitative constitutive description of the slip-twinning transition in the martensitic transformation is presented. It is based on the temperature and strain-rate sensitivities of slip, which are much higher than those for twinning. Thus, twinning becomes a favored deformation mechanism at low temperatures and high strain rates. The Hall-Petch coefficient, for the inclusion of grain size effects, is two times larger for twinning than slip. Constitutive relationships for slip and twinning are presented and applied to the martensitic transformation in steels; the lath-to-plate morphology change observed with increasing carbon content is successfully predicted as a function of grain size by calculations incorporating the two modes of deformation. A simple calculation of the strain rates during martensitic transformation is also provided. This methodology is applied to the Fe–C system and can be extended to the Fe–Ni–C system and to thermoelastic martensites, where twinning is favored over slip to enhance reversibility.

The equine hoof wall has outstanding impact resistance, which enables high-velocity gallop over hard terrain with minimum damage. To better understand its viscoelastic behavior, complex moduli were determined using two complementary techniques: conventional (∼5 mm length scale) and nano (∼1 µm length scale) dynamic mechanical analysis (DMA). The evolution of their magnitudes was measured for two hydration conditions: fully hydrated and ambient. The storage modulus of the ambient hoof wall was approximately 400 MPa in macro-scale experiments, decreasing to ∼250 MPa with hydration. In contrast, the loss tangent decreased for both hydrated (∼0.1-0.07) and ambient (∼0.04-0.01) conditions, over the frequency range of 1-10 Hz. Nano-DMA indentation tests conducted up to 200 Hz showed little frequency dependence beyond 10 Hz. The loss tangent of tubular regions showed more hydration sensitivity than in intertubular regions, but no significant difference in storage modulus was observed. Loss tangent and effective stiffness were higher in indentations for both hydration levels. This behavior is attributed to the hoof wall's hierarchical structure, which has porosity, functionally graded aspects, and material interfaces that are not captured at the scale of indentation. The hoof wall's viscoelasticity characterized in this work has implications for the design of bioinspired impact-resistant materials and structures. STATEMENT OF SIGNIFICANCE: The outer wall of horse hooves evolved to withstand heavy impacts during gallop. While previous studies have measured the properties of the hoof wall in slowly changing conditions, we wanted to quantify its behavior using experiments that replicate the quickly changing forces of impact. Since the hoof wall's structure is complex and contributes to its overall performance, smaller scale experiments were also performed. The behavior of the hoof wall was within the range of other biological materials and polymers. When hydrated, it becomes softer and can dissipate more energy. This work improves our understanding of the hoof's function and allows for more accurate simulations that can account for different impact speeds.

Stinger-like structures in living organisms evolved convergently across taxa for both defensive and offensive purposes, with the main goal being penetration and damage. Our observations over a broad range of taxa and sizes, from microscopic radiolarians to narwhals, reveal a self-similar geometry of the stinger extremity: the diameter ( d ) increases along the distance from the tip ( x ) following a power law <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>x</mml:mi> <mml:mo>∼</mml:mo> <mml:msup> <mml:mi>d</mml:mi> <mml:mi>n</mml:mi> </mml:msup> </mml:math> , with the tapering exponent varying universally between 2 and 3. We demonstrate, through analytical and experimental mechanics involving three-dimensional (3D) printing, that this geometry optimizes the stinger’s performance; it represents a trade-off between the propensity to buckle, for n smaller than 2, and increased penetration force, for n greater than 3. Moreover, we find that this optimal tapering exponent does not depend on stinger size and aspect ratio (base diameter over length). We conclude that for Nature’s stingers, composed of biological materials with moduli ranging from hundreds of megapascals to ten gigapascals, the necessity for a power-law contour increases with sharpness to ensure sufficient stability for penetration of skin-like tissues. Our results offer a solution to the puzzle underlying this universal geometric trait of biological stingers and may provide a new strategy to design needle-like structures for engineering or medical applications.

The non-equiatomic FeNiCoAlTaB high-entropy alloy exhibits outstanding quasi-static mechanical properties. Here, we investigate the microstructural evolution and mechanical response of this alloy subjected to dynamic loading, which has not been done before. A novel strategy combining extensive microbanding and martensitic transformation improves the resistance to the plastic instability by deterring the formation of adiabatic shear bands, that only occur beyond a critical shear strain larger than 4. The aged alloy, with grain sizes up to 400 μm, exhibits a dynamic yield stress over 1300 MPa with good deformability in this regime. This investigation sheds light on potential strategies for the enhancement of dynamic mechanical properties of structural materials through the use of a stress-induced martensitic transformation.

The equine hoof wall has a complex, hierarchical structure that can inspire designs of impact-resistant materials. In this study, we utilized micro-computed tomography (μ-CT) and serial block-face scanning electron microscopy (SBF-SEM) to image the microstructure and nanostructure of the hoof wall. We quantified the morphology of tubular medullary cavities by measuring equivalent diameter, surface area, volume, and sphericity. High-resolution μ-CT revealed that tubules are partially or fully filled with tissue near the exterior surface and become progressively empty towards the inner part of the hoof wall. Thin bridges were detected within the medullary cavity, starting in the middle section of the hoof wall and increasing in density and thickness towards the inner part. Porosity was measured using three-dimensional (3D) μ-CT, two-dimensional (2D) μ-CT, and a helium pycnometer. The highest porosity was obtained using the helium pycnometer (8.07%), followed by 3D (3.47%) and 2D (2.98%) μ-CT. SBF-SEM captured the 3D structure of the hoof wall at the nanoscale, showing that the tubule wall is not solid, but has nano-sized pores, which explains the higher porosity obtained using the helium pycnometer. The results of this investigation provide morphological information on the hoof wall for the future development of hoof-inspired materials and offer a novel perspective on how various measurement methods can influence the quantification of porosity.

Abstract The equine hoof wall has a complex, hierarchical structure that can inspire designs of impact-resistant materials. In this study, we utilized micro-computed tomography (μ-CT) and serial block-face scanning electron microscopy (SBF-SEM) to image the microstructure and nanostructure of the hoof wall. We quantified the morphology of tubular medullary cavities by measuring equivalent diameter, surface area, volume, and sphericity. High-resolution μ-CT revealed that tubules are partially or fully filled with tissue near the exterior surface and become progressively empty towards the inner part of the hoof wall. Thin bridges were detected within the medullary cavity, starting in the middle section of the hoof wall and increasing in density and thickness towards the inner part. Porosity was measured using three-dimensional (3D) μ-CT, two-dimensional (2D) μ-CT, and a helium pycnometer, with the highest porosity obtained using the helium pycnometer (8.07%), followed by 3D (3.47%) and 2D (2.98%) μ-CT. SBF-SEM captured the 3D structure of the hoof wall at the nanoscale, showing that the tubule wall is not solid, but has nano-sized pores, which explains the higher porosity obtained using the helium pycnometer. The results of this investigation provide morphological information on the hoof wall for the future development of hoof-inspired materials and offer a novel perspective on how various measurement methods can influence the quantification of porosity.