Bicontinuous Microstructure Research Articles

Mechanical characterisation of a structural battery electrolyte

Structural battery composites require a structural electrolyte to work. The structural battery electrolyte has a bicontinuous microstructure which enables its dual roles: mechanical load transfer and ion transport between the electrodes. These structural electrolytes are difficult to characterise mechanically via bulk tests. For this reason, no extensive characterisation of the mechanical properties of the structural battery electrolyte has been performed to date. In this study, we highlight the many challenges of these types of tests, including the complexity of sample manufacturing, preparation and testing. We further demonstrate a method to prepare test samples and to perform mechanical tests on the structural battery electrolyte. The executed test campaign provides measures of Young's modulus (approximately 412 MPa) and Poisson's ratio (0.34), as well as tensile (4.85 MPa) and compressive strength (32.66 MPa) and strain to failure (2.49 % and 28.11 % in tension and compression, respectively). In addition, cure shrinkage is investigated and found insignificant. These results are crucial for the further development of structural battery composites as they allow for accurate prediction of their internal stress states.

Facile synthesis of hierarchically porous carbon monolith without templating agent for various applications in energy and catalysis

Monolithic carbon with hierarchically porous structure has a promising prospect for a wide range of applications in the fields of energy, environment, catalysis, etc. Due to the reliance on the utilization of templating agents, conventional preparation approaches often suffer from time-consuming preparation, complex post-processing, and uneconomical cost. Herein, we develop a novel strategy to match the sol-gel transition with the phase separation process for the direct preparation of hierarchically porous carbon monolith (HPCM) without templating agent. Resorcinol and resol are employed as carbon sources to adjust the polymerization for the formation of bi-continuous microstructure. Well-defined hierarchical pores and large specific surface area for fast mass diffusion enable the HPCM to be a prospective kind of electrode material in supercapacitor with an outstanding specific capacitance over 350 F g−1 (1.0 A g−1). After facile sulfonation, the modified HPCM can act as solid acid catalyst to realize a high-performance production of 5-hydroxymethylfurfural (5-HMF) in a 90 % yield with turnover frequency (TOF) value up to 155.9 h−1. Additionally, HPCM also exhibits an excellent Joule heating effect, which can be applied to the thermal management after compounding with phase change materials. The desirable integrated performance enables HPCM to be a valuable material suitable for various applications.

Ti/Mg dissimilar joining by eutectic-melting-induced liquid metal dealloying

Ti and Mg alloys, which have thermodynamically immiscible main components, have been chemically joined in previous work using a third element with high affinity for both elements. However, this strategy is challenging in precisely controlling brittle intermetallic compounds formed at a joint interface. In this study, we mechanically joined pure Ti and pure Mg without brittle layers by forming bicontinuous microstructure, 3D entanglement of immiscible phases, at the joint interface. We butt-joined pure Mg and Ti–Cu alloy interlayer, which we pre-diffusion bonded to the pure Ti and heated at 813 K and 20 MPa for 5 min. At the joint interface, Cu and Mg eutectic melted, which induced liquid metal dealloying of the interlayer. The entire Ti–Cu interlayer is dealloyed, and a byproduct (Mg–Cu phase) is removed by pressurization during melting. These brittle layer removal processes left only α-Ti/Mg–Cu phase bicontinuous microstructure at the joint interface, improving the joint strength. Ti/Mg joints fractured at the Mg base metal at ca. 90 MPa by tensile tests. The findings of this study provide the basis for achieving immiscible alloy joining, for which effective joining methods have not yet been established.

Reliability-Based Design Optimization of Additive Manufacturing for Lithium Battery Silicon Anode

Abstract With the blooming of the electric vehicle market and the advancement in the lithium-ion battery industry, silicon anode has shown great potential for the next-generation battery. Using the state-of-the-art additive manufacturing technique (three-dimensional (3D) holographic lithography), researchers have demonstrated that silicon anode can be fabricated as a three-dimensional bicontinuous porous microstructure. However, the volume fluctuation of the silicon anode caused by lithiation during the discharging process causes continuous capacity decay and poor cycling life. Besides, uncertainties are inherent in the manufacturing and usage processes, making it crucial to systematically consider them in the silicon anode design to improve its performance and reliability. To fill the gap between current silicon anode research and future industrial need, this study established a digital twin to investigate the optimal design for silicon anode under the uncertainties of additive manufacturing and battery usage. This study started with developing multiphysics finite element models of the silicon anode lithiation process to investigate the volume fluctuation of silicon. Then, surrogate models were built based on the results from the finite element models to reduce computational cost. The reliability-based design optimization (RBDO) was employed to find the best design point for the silicon anode, in which an outer optimization loop maximized the objective function and an inner loop dedicated to reliability analysis. Finally, the Pareto optimal front of the silicon anode designs was obtained and validated, which shows over 10% improvements in the silicon anode's total capacity and rate capability.

A FeCrAl-Al2O3 Composite Produced Via Laser Powder Bed Fusion of a Mixed Powder for Porous Catalyst Scaffolds

Abstract This study proposes a novel approach for synthesizing and etching bicontinuous FeCrAl-Al2O3 composites as a means for replacing FeCrAl foams as catalyst scaffolds in biodriven alcohol reactors for jet-fuel production. Conventional FeCrAl foams suffer from poor availability and consequent high costs. New additive manufacturing techniques provide an opportunity to produce tailored foams at reasonable times and at acceptable costs. This research aimed to generate a porous FeCrAl structure by etching a bicontinuous FeCrAl-Al2O3 composite produced by laser powder bed fusion of amalgamated FeCrAl and Al2O3 powders. The composite powder for laser powder bed fusion is created by ball-milling FeCrAl and Al2O3 powders. This research focuses on achieving a bi-continuous FeCrAl-Al2O3 structure, essential for the selective removal of the ceramic phase. The influence of laser processing parameters on the microstructure was examined across a range of laser powers (60–120 W) and scan speeds (100–400 mm/s), showing that higher powers and speeds produce finer metal struts. A bi-continuous microstructure was consistently obtained, marking a key achievement. The Al2O3 removal process involved a two-step etching method using hydrochloric and phosphoric acids, tested across various etching times. The alumina phase was reduced from 36 vol% to 17 vol% (corresponding to an increase in porosity from 24 vol% to 43 vol%), showing the potential for use as a porous catalyst scaffold. This research demonstrates the potential for using additive manufacturing to produce porous FeCrAl structures capable of replacing hard-to-source FeCrAl foams.

Peritectic solidification patterns in the Zn–Ag system captured in three- and four-dimensions

Microstructure selection in two-phase peritectic alloys has been a long-standing topic of fundamental importance. The bicontinuous microstructures arising from peritectic solidification have presented significant challenges for analysis due (in part) to our reliance on two-dimensional (2D) sections, which limits our ability to interpret the full three-dimensional (3D) complexity. Additionally, understanding growth mechanisms based solely on postmortem data has proven to be challenging because the extent of the solid-state peritectic transformation is unknown. Here, we employed X-ray imaging techniques to acquire detailed 3D data and visualize in real-time the dynamics of peritectic solidification in a model system of composition Zn-9.53 wt.% Ag. This paper offers a detailed examination of the origin of two-phase (Zn) + AgZn3 microstructures during directional solidification: specifically, our work investigates the influence of velocity, thermal gradient, and sample size on microstructure selection, namely, rod-like, singly-banded, and multiply-banded structures. Importantly, we find at low velocities V (0.07–0.1 μm/s) and a low thermal gradient G (3 K/mm) the emergence of peritectic (Zn) channels, interwoven within and between primary AgZn3 columnar grains. While these microstructures are suggestive of coupled growth morphologies, real-time imaging proves that the two solids are instead decoupled at the growth front. Meanwhile, at thermal gradients 10× higher, we observe a partially dendritic and partially banded structure that has not been reported before, to the best of our knowledge. We initiate a discussion on the formation of such structures, with broad implications to a wide range of metallic, semi-metallic, and organic peritectic alloys.

A Solid-Liquid Bicontinuous Fiber with Strain-Insensitive Ionic Conduction.

Stretchable ionic conductors are crucial for enabling advanced iontronic devices to operate under diverse deformation conditions. However, when employed as interconnects, existing ionic conductors struggle to maintain stable ionic conduction under strain, hindering high-fidelity signal transmission. Here, it is shown that strain-insensitive ionic conduction can be achieved by creating a solid-liquid bicontinuous microstructure. A bicontinuous fiber from polymerization-induced phase separation, which contains a solid elastomer phase interpenetrated by a liquid ion-conducting phase, is fabricated. The spontaneous partitioning of dissolved salts leads to the formation of a robust self-wrinkled interface, fostering the development of highly tortuous ionic channels. Upon stretch, these meandering ionic channels are straightened, effectively enhancing ionic conductivity to counteract the strain effect. Remarkably, the fiber retains highly stable ionic conduction till fracture, with only 7% resistance increase at 200% strain. This approach presents a promising avenue for designing durable ionic cables capable of signal transmission with minimal strain-induced distortion.

Composite material in the sea urchin Cidaris rugosa: ordered and disordered micrometre-scale bicontinuous geometries.

The sponge-like biomineralized calcite materials found in echinoderm skeletons are of interest in terms of both structure formation and biological function. Despite their crystalline atomic structure, they exhibit curved interfaces that have been related to known triply periodic minimal surfaces. Here, we investigate the endoskeleton of the sea urchin Cidaris rugosa that has long been known to form a microstructure related to the Primitive surface. Using X-ray tomography, we find that the endoskeleton is organized as a composite material consisting of domains of bicontinuous microstructures with different structural properties. We describe, for the first time, the co-occurrenceof orderedsingle Primitive and singleDiamond structures and of a disordered structure within a single skeletal plate. We show that these structures can be distinguished by structural properties including solid volume fraction, trabeculae width and, to a lesser extent, interface area and mean curvature. Indoing so, we present a robust method that extracts interface areas and curvature integrals from voxelized datasets using the Steiner polynomial for parallel body volumes. We discuss these very large-scale bicontinuous structures in the context of their function, formation and evolution.

Bicontinuous microstructure formation of immiscible phases by the liquid metal replacement method and its application to Ti/Mg dissimilar joining

We designed a new microstructure control method (liquid metal replacement method) that creates entirely new composites using the original microstructure as a template. This method selectively replaces a specific phase from a composite with another phase based on differences in atomic interactions. We applied this method to the dissimilar material joining of immiscible titanium and magnesium. After diffusion bonding one side of an interlayer consisting of α-Ti / α-Sc phases to Ti, we butted the opposite side with Mg and reheated. At this interface, selective interdiffusion of Mg and Sc results in the replacement of only the α-Sc phase by the α-Mg phase, forming a new α-Ti / α-Mg bicontinuous microstructure using the α-Ti / α-Sc monotectoid microstructure as a template. The Sc that diffused to the Mg side formed a reaction layer where the MgSc (B2) and (Mg, Sc) solid solution coexisted. These novel composite structures and reaction layers strengthened the joint area. As a result, we suppressed fracture at the joint interface, causing fracture at Mg and achieving a maximum joint strength of 116 MPa.

Surface-based anthropomorphic bone structures for use in high-resolution simulated medical imaging

Objective. Virtual imaging trials enable efficient assessment and optimization of medical image devices and techniques via simulation rather than physical studies. These studies require realistic, detailed ground-truth models or phantoms of the relevant anatomy or physiology. Anatomical structures within computational phantoms are typically based on medical imaging data; however, for small and intricate structures (e.g. trabecular bone), it is not reasonable to use existing clinical data as the spatial resolution of the scans is insufficient. In this study, we develop a mathematical method to generate arbitrary-resolution bone structures within virtual patient models (XCAT phantoms) to model the appearance of CT-imaged trabecular bone. Approach. Given surface definitions of a bone, an algorithm was implemented to generate stochastic bicontinuous microstructures to form a network to define the trabecular bone structure with geometric and topological properties indicative of the bone. For an example adult male XCAT phantom (50th percentile in height and weight), the method was used to generate the trabecular structure of 46 chest bones. The produced models were validated in comparison with published properties of bones. The utility of the method was demonstrated with pilot CT and photon-counting CT simulations performed using the accurate DukeSim CT simulator on the XCAT phantom containing the detailed bone models. Main results. The method successfully generated the inner trabecular structure for the different bones of the chest, having quantiative measures similar to published values. The pilot simulations showed the ability of photon-counting CT to better resolve the trabecular detail emphasizing the necessity for high-resolution bone models. Significance. As demonstrated, the developed tools have great potential to provide ground truth simulations to access the ability of existing and emerging CT imaging technology to provide quantitative information about bone structures.

Effect of mixture microstructure/compatibility on the properties of type-A gelatin-dextran edible films

The influence of phase separation behavior on bio-based film properties has attracted more and more attention. This work investigated the effects of microstructure and compatibility of the type-A gelatin (GE)-dextran (DE) mixtures on GE-DE edible film properties. Three kinds of GE-DE edible films with different textures were prepared via modulating the microstructure and compatibility of film-forming mixtures using the method of gelation-drying, e.g., homogeneous films, microphase separated films with relatively homogeneous texture, and microphase separated films with uneven texture. The optical, mechanical, water barrier, and thermal properties of films were characterized. Results showed that microstructure and compatibility significantly affected the film properties. In general, films with DE-in-GE microstructure exhibited the best film properties, followed by films with water-in-water-in-water/bicontinuous microstructure, and then films with GE-in-DE microstructure. And homogeneous films showed the best film properties, followed by films with relatively homogeneous texture, and then films with uneven texture. The weight loss results suggested the potential of GE-DE edible films for application in cherry tomato preservation. This work provided interesting information for the design of film with fabricated microstructure and properties.

Elastic microphase separation produces robust bicontinuous materials.

Bicontinuous microstructures are essential to the function of diverse natural and synthetic systems. Their synthesis has been based on two approaches: arrested phase separation or self-assembly of block copolymers. The former is attractive for its chemical simplicity and the latter, for its thermodynamic robustness. Here we introduce elastic microphase separation (EMPS) as an alternative approach to make bicontinuous microstructures. Conceptually, EMPS balances the molecular-scale forces that drive demixing with large-scale elasticity to encode a thermodynamic length scale. This process features a continuous phase transition, reversible without hysteresis. Practically, EMPS is triggered by simply supersaturating an elastomeric matrix with a liquid, resulting in uniform bicontinuous materials with a well-defined microscopic length scale tuned by the matrix stiffness. The versatility of EMPS is further demonstrated by fabricating bicontinuous materials with superior mechanical properties and controlled anisotropy and microstructural gradients. Overall, EMPS presents a robust alternative for the bulk fabrication of homogeneous bicontinuous materials.

Metrics for the characteristic length scale in the random bicontinuous microstructure of nanoporous gold

Nanoporous gold (NPG) made by dealloying exemplifies materials with random bicontinuous microstructures that can be approximated by leveled-wave type models. As a distinguishing feature, the characteristic length scale – often quantified by the “ligament size” L – of NPG may be tuned over several orders of magnitude while the microstructural geometry retains a high degree of self-similarity. It is therefore essential to have at hand accurate procedures for determining the size by experiment and to match it to analogous size metrics of model scenarios. Working with a set of NPG samples of widely different size, we compare ligament size distributions determined by analysis of scanning electron micrographs to those of the leveled-wave model. The model is representative of various material types with random bicontinuous microstructures. The size distribution is remarkably uniform over the cross-section of experimental samples. Furthermore, the distribution evolves self-similarly upon coarsening, and the normalized distribution width agrees closely to that of the model. A measure for size determined by the electrochemical capacitance ratio method correlates well with L. This supports a protocol for converting between the two measures. As a dimensionless factor characteristic of the microstructural geometry of random dual phase microstructures, the product of L and the specific surface area is found consistent between experiment and model. The findings suggest conversion factors between the various metrics, and they advertise the combination of NPG and the leveled-wave model as a showcase for characterizing the characteristic length scale of random bicontinuous microstructures.

Numerical verification of a nonlocal discrete model for anisotropic heat conduction problems

This paper presents the numerical study of a recently proposed nonlocal discrete model for anisotropic heat conduction problems. Both transient and steady-state heat conduction problems are studied. The solution schemes and applications of the temperature and flux boundary conditions are discussed in detail. Various benchmark problems are employed to demonstrate the convergence characteristic and the prediction accuracy of the proposed model. The proposed model is then applied to study the heat conduction in a bi-continuous composite microstructure. It is observed that the proposed model has an expected linear convergence rate and can accurately predict the solution with respect to finite element results. As demonstrated using the bi-continuous microstructure, the proposed model offers significant convenience to image-based modeling and simulation by directly take the digitized material voxels as discrete material particles without generating quality mesh.

Microstructure determined the gel properties of gelatin/dextran more than the macrophase separation

Hydrogels are important in foods. Although the hydrogel microstructure has been commonly reported, the effect of the microstructure before and after gelation on gel properties was rarely investigated. This work aims to explore the effects of micro- and macro-phase separation of type-A gelatin-dextran (GE A /DE) aqueous solutions on the rheological, texture, and hydration properties of GE A /DE hydrogels. Three types of phase separation microstructures at both pH 5.0 and 7.0, e.g., DE-in-GE A emulsion, bicontinuous microstructure, and GE A -in-DE emulsion, were designed by adding different DE concentrations. GE A /DE mixtures showed macro-stability at pH 5.0, but macroscopic phase separation at pH 7.0, in which the phase separation time increased with the increasing DE concentration. During cooling-gelation, microstructures of mixtures were almost unchanged at pH 5.0, but significantly changed at pH 7.0. Interestingly, the microstructure determined the gel properties of phase-separated gels more than the macrophase separation. Microstructures of continuous phase with the gelling ability, e.g., DE-in-GE A and bicontinuous phase, hardly changed the moduli ( G′ and G″ ) and hardness of GE A /DE mixed gels, while the microstructure of GE A -in-DE without the gelling ability for continuous phase greatly reduced the moduli and hardness. This might be due to the different GE A volume fractions in GE A /DE mixed gels with different microstructures, and the mixed gel strength decreased with decreasing GE A volume fractions. Water holding capacity and swelling ratio of GE A /DE mixed gels reduced with the increasing DE concentration. This work provides some new information on how microstructure and macro-stability affect the physical properties of mixed gels. Effect of microstructure of GE A /DE before and after gelation on G′ and G″ at pH 5.0 and 7.0. • Three microstructures were designed based on gelatin/dextran phase separation. • Microstructures of macro-stable gelatin/dextran at pH 5.0 unchanged after gelation. • Microstructure determined gel properties more than the macrophase separation. • GE A volume fraction in the mixed gel might explain the effect of microstructures. • The gel strength of gelatin/dextran decreased with decreasing GE A volume fraction.

The pH-dependent phase separation kinetics of type-A gelatin and dextran with different initial microstructures

The phase separation kinetics of type A gelatin and dextran (GE/DE) with different microstructures were investigated to get information on the relation between technofunctional properties and structures using static multiple light scattering (S-MLS), fluorescence microscopy, and macroscopic observations. GE/DE mixtures of 5.0 wt%/2.0 wt% and 5.0 wt%/3.0 wt% at pH = 5.50–9.00 were selected as the typical samples with the DE-in-GE and bicontinuous microstructures, respectively. Macrophase separation was found to occur in both the two mixtures at pH = 5.50–9.00 with the upper phase rich in GE and the lower phase rich in DE. However, the effect of pH on the phase separation rates of the two mixtures was different: pH-independent in DE-in-GE mixtures, while pH-dependent in bicontinuous mixtures. Specifically, the order of phase separation rates for the bicontinuous mixtures at pH = 5.50–9.00 was pH5.50 > pH6.00 > pH9.00 > pH7.00 ≈ pH8.00. Changes in the electrostatic interaction or steric exclusion effect among GE (DE) droplets at pH = 5.50–9.00 were used to explain the different phase separation kinetics of GE/DE mixtures with GE-in-DE, DE-in-GE, and bicontinuous microstructures. This work characterized the phase separation processes of GE/DE mixtures with three kinds of microstructure and provided the parameters for the phase separation kinetics at the macro-level.

Templating Polymer/Chromophore Crystallization in a Gyroid Matrix

Blending the small molecule nonlinear optical chromophore, 2-chloro-4-nitroanaline (CNA), with a semicrystalline block copolymer, polystyrene-poly(ethylene oxide) (PS-PEO), drives the formation of a bicontinuous cubic microstructure, known as gyroid (GYR), demonstrating Ia3̅d cubic space group symmetry. The morphology transition is due to the selective partitioning of CNA into the PEO domains, which happens to be the majority phase while PS forms the GYR network. Furthermore, PEO and CNA cocrystallize together, forming a single crystalline phase that exhibits a different crystal structure from the starting PEO and CNA materials. At room temperature, PEO crystals and PEO/CNA cocrystals coexist and display different melting temperatures, Tm,PEO = 45 °C and Tm,PEO/CNA = 78 °C, respectively. Interestingly, although the PEO domain is the matrix, the GYR network templates the crystallization of the PEO/CNA cocrystal by precisely controlling the cocrystal long period. Furthermore, circular dichroism (CD) measurements indicate that the crystallized sample contains a chiral component when the PEO/CNA cocrystal is present, and upon melting of the PEO/CNA cocrystal (Tm,PEO/CNA = 78 °C), the CD signal vanishes. The results shown here indicate that adding a small molecule to semicrystalline block copolymer in which one block will form a cocrystal with the small molecule opens the possibility of controlling hierarchical structure and material functionality.

Microstructural design via spinodal-mediated phase transformation pathways in high-entropy alloys (HEAs) using phase-field modelling

Even though the majority of the so-called high-entropy alloys (HEAs) are multi-phase rather than single-phase solid solutions at thermodynamic equilibrium, recent studies on HEAs do open up a massive compositional space for the exploration of novel microstructures with the potential of exhibiting greatly enhanced functional or mechanical properties. Understanding the phase transformation pathways (PTPs) and microstructural evolution in multi-phase HEAs will aid alloy and process designs to tailor the microstructures for specific engineering applications. In this work, we study microstructural evolution in two-phase HEAs where a disordered parent phase separates into a mixture of two phases: an ordered phase (β′) + a disordered phase (β) upon cooling via two different PTPs: (i) congruent ordering followed by spinodal decomposition in the ordered phase and then disordering of one of the ordered phases, i.e., β→β′→β1′+β2′→β+β2′ and (ii) spinodal decomposition in the disordered phase followed by ordering of one of the disordered phases, i.e., β→β1+β2→β1+β′. We systematically investigate the effects of equilibrium volume fractions of individual phases, free energy landscapes (in particular, the location of the critical point of the miscibility gap relative to the compositions of the final two equilibrium phases), and elastic modulus mismatch between the two equilibrium phases on the microstructural evolution of these HEAs. We focus on the following morphological characteristics: bi-continuous microstructures vs. precipitates + matrix microstructures, ordered matrix + disordered precipitates vs. disordered matrix + ordered precipitates, and the discreteness of the precipitate phase. This parametric study may aid in multi-phase HEA design for desired microstructures.

A carbon fiber lamina electrode based on macroporous epoxy with vertical ion channels for structural battery composites

Structural battery (SB) composites based on carbon fibers (CFs) are promising multifunctional composite materials to simultaneously realize load-bearing and electrical energy storage. Conventional structural battery electrolytes (SBEs) have bicontinuous phase microstructure characteristics, which makes a further considerable improvement in both mechanical and electrochemical performance of structural batteries rather challenging. Herein, a novel SBE with vertical ion channels in the form of patterned macropores was developed by photolithography based on the UV-initiated cationic polymerization, which was subsequently used in the fabrication of the CF half-cell lamina. The mechanical and electrochemical properties were characterized for both SBE and SB half-cells. The Young's modulus and ionic conductivity of the porous epoxy post-filled with liquid electrolyte were 1.2 GPa and 3.7 mS/cm, respectively, which exceeded the state-of-art multifunctional performances of bicontinuous SBEs. The specific capacity of the SB half-cell could reach 222 ± 10 mAh/g (2nd) at 0.17C, while the tensile modulus of the CF half-cell lamina was 66 ± 4 GPa (Vf = 22.5 %). This work could provide new insights into a microstructural design for structural batteries towards high multifunctional performances.

High strength and damage-tolerance in echinoderm stereom as a natural bicontinuous ceramic cellular solid

Due to their low damage tolerance, engineering ceramic foams are often limited to non-structural usages. In this work, we report that stereom, a bioceramic cellular solid (relative density, 0.2–0.4) commonly found in the mineralized skeletal elements of echinoderms (e.g., sea urchin spines), achieves simultaneous high relative strength which approaches the Suquet bound and remarkable energy absorption capability (ca. 17.7 kJ kg−1) through its unique bicontinuous open-cell foam-like microstructure. The high strength is due to the ultra-low stress concentrations within the stereom during loading, resulted from their defect-free cellular morphologies with near-constant surface mean curvatures and negative Gaussian curvatures. Furthermore, the combination of bending-induced microfracture of branches and subsequent local jamming of fractured fragments facilitated by small throat openings in stereom leads to the progressive formation and growth of damage bands with significant microscopic densification of fragments, and consequently, contributes to stereom’s exceptionally high damage tolerance.