Impact Resistance Of Materials Research Articles

Bidirectional impact protective performance of bioinspired polyvinyl chloride/thermoplastic polyurethane foam composite with anti-sandwich structures

Polymer foams are widely used in human body protection but require combination with impact-resistant materials for adequate performance. Inspired by walnut shells, this study developed a novel bidirectional protective anti-sandwich structure (BPAS) for bidirectional protection. The nonlinear hyperelastic and viscoelastic behaviors of TPU foam were simulated using the compressible Hyperfoam model with Rayleigh damping, and the accuracy of the finite element model was verified by falling ball impact tests. By comparing with pure foam structure (PFS) and traditional sandwich structure (TSS), the BPAS showed more uniform and moderate stress distribution, transfer, and deformation under impact demonstrating a special bidirectional protection property, which is attributed to the energy dispersion of its upper foam, lateral stress redistribution, and energy dissipation effects of its rigid core. The developed model is effective in assisting structural design and performance prediction of BPAS, and the BPAS also exhibited excellent bidirectional protection capability in boxing.

Impact penetration response of fiber metal laminates padded with 3D continuous fiber-reinforced polyurethane foam

Novel composite combinations are needed to meet the broad mechanical requirements for lightweight structures by integrating various properties within a single structure. This includes high structural rigidity and impact resistance with low overall density. Fiber metal laminates (FMLs) are advanced composite materials composed of an alternating stacking sequence of metal alloys layers and fiber-reinforced polymers. However, FMLs exhibit lower puncture deformation potential compared to fiber-reinforced thermoplastics (FRTPs). To address this limitation, polyurethane (PUR) foam with 3D continuous fiber-reinforcement, is investigated as padding. The FML, manufactured via thermoforming, is based on basalt fiber-reinforced polyamide 6 and two layers of aluminum alloy. The PUR foam is fabricated through structural reaction injection molding and reinforced with a spacer fabric. Subsequently, low velocity impact tests are conducted for this novel composite and its single components. The results unveil significant insights into the impact behavior of the materials. The highest perforation resistance of 81 J is achieved by the FML padded with 3D continues fiber-reinforced polyurethane foam while offering equal deformation capability as without reinforced PUR foam. These findings underscore the superior impact performance of the fiber metal laminate padded with 3D continues fiber-reinforced polyurethane foam, offering valuable insights for the advancement of impact-resistant materials in various engineering applications.

Preparation and Application of Nature-inspired High-performance Mechanical Materials.

Natural materials are valued for their lightweight properties, high strength, impact resistance, and fracture toughness, often outperforming human-made materials. This paper reviews recent research on biomimetic composites, focusing on how composition, microstructure, and interfacial characteristics affect mechanical properties like strength, stiffness, and toughness. It explores biological structures such as mollusk shells, bones, and insect exoskeletons that inspire lightweight designs, including honeycomb structures for weight reduction and impact resistance. The paper also discusses the flexibility and durability of fibrous materials like arachnid proteins and evaluates traditional and modern fabrication techniques, including machine learning. The development of superior, multifunctional, and eco-friendly materials will benefit transportation, mechanical engineering, architecture, and biomedicine, promoting sustainable materials science. STATEMENT OF SIGNIFICANCE: Natural materials excel in strength, lightweight, impact resistance, and fracture toughness. This review focuses on biomimetic composites inspired by nature, examining how composition, microstructure, and interfacial characteristics affect mechanical properties like strength, stiffness, and toughness. It analyzes biological structures such as shells, bones, and exoskeletons, emphasizing honeycomb strength and lightness. The review also explores the flexibility and durability of fibrous materials like arachnid proteins and discusses fabrication techniques for biomaterials. It highlights impact-resistant materials that combine soft and hard components for enhanced strength and toughness, as well as lightweight, wear-resistant biomimetic materials that respond uniquely to cyclic stress. The article aims to advance sustainable materials science by exploring innovations in multifunctional and eco-friendly materials for various applications.

Tunable impact resistant materials: Synergistic enhancement of paraffin/MRP/re-entrant structures

In the realm of safety protection, there is a critical demand for materials capable of superior energy absorption and adaptability across diverse application scenarios. Here, this study presents integrated two-phase negative Poisson’s ratio (NPR) composites with adjustable mechanical properties sensitive to magnetic field, temperature and impact load. It is achieved by substituting the vacancy of re-entrant structures (frame phase) with soft paraffin/magnetorheological plastomer (MRP) fillers (matrix phase). The paraffin/MRP exhibits temperature-sensitive properties, enhanced magnetorheological (MR) effect (up to 4178%) and shear thickening (ST) effect (up to 2365%). Through quasi-static compression and dynamic impact tests, the composites demonstrate remarkable adaptability in impact resistance. Specifically, the first peak force exhibits responsiveness to changes in magnetic flux density, temperature, and impact velocity, with respective variations of 80.6%, 68.2%, and 30.3%. The design strategy paves the way for tunable impact resistant materials with potential for extreme environment buffering applications.

A novel composites of laser 3D printed CoCrFeNiMn/Ti6Al4V lattice structure with B4C/AlSi10Mg interpenetrating phases

Impact-resistant materials frequently encounter inherent trade-offs among damping, toughness, light weighting and strength. This study employed laser 3D printing combined with spark plasma sintering techniques to fabricate a novel biomimetic composites of CoCrFeNiMn/Ti6Al4V lattice structure with B4C/AlSi10Mg interpenetrating phase, showing the potential application of this composite as a novel impact-resistant material. Experimental results demonstrated that the composites exhibited outstanding compressive strength and strain energy absorption, attributed to their intricate interpenetrating dual-phase structure and interface bonding mechanism. The interpenetrating phase structure and the formation of interface nano-Ti3AlSi5 phases promote effective stress transfer within the composite material, resisting the propagation of local damage. During mechanical loading, cracks originating in the CoCrFeNiMn/Ti6Al4V lattice were mechanically interlocked by B4C/AlSi10Mg infiltration, thereby conferring heightened strengthening efficacy and exceptional damage tolerance. Effects of strain rate (10−3/s to 1/s) and temperature (from room temperature to 300 °C) on dynamic impact performance of the composites indicated a very competitive strain rate hardening and thermal softening performance.

Emergent Research Trends on the Structural Relaxation Dynamics of Molecular Clusters: From Structure-Property Relationship to New Function Prediction.

ConspectusMolecular clusters (MCs) are monodispersed, precisely defined ensembles of atom collections featured with shape-persistent architectures that can deliver certain functions independently. Their molecular compositions and surface functionalities can be tailored feasibly in a predefined manner, and they can be applied as basic structural units to be engineered into materials with desirable hierarchical structures and enriched functions. The chemical systems also offer great opportunities for the design and fabrication of soft structural materials without the chain topologies of polymers. The bulks of MC assemblies demonstrate viscoelasticity that is used to be considered as the unique feature of polymers, while the MC systems are distinct from polymers since their elasticities are resilient even at temperatures 100 K above their glass transition temperatures. The understanding of their anomalous viscoelasticity and the extended studies of general structure-property relationships are desired for the development of new chemical systems for emergent functions and the possibilities to resolve the intrinsic trade-offs of traditional materials.Meanwhile, general macroscopic functions or properties of materials are related to the transportation of mass, momentum, and/or energy, and they are basically realized or directed by the motions of structural units at different length scales. Structural relaxation dynamics research is critical in quantifying motions ranging from fast bond deformation, bond break/formation, and diffusion of ions and particles to the cooperative motions of structure units. Due to the advancement of measurement technology for relaxation dynamics (e.g., quasi-elastic scattering and broadband dielectric spectroscopy), the structural relaxation dynamics of MC materials have been probed for the first time, and their multiple relaxation modes across several temporal scales were systematically studied to bridge the correlation between molecular structures and macroscopic functions. The fingerprint information from dynamics studies, e.g., the temperature dependence of relaxation time and certain property, e.g., ion conductivity, was proposed to quantify the structure-property relationship, and the microscopic mechanism on the mechanical properties, ion conduction, and gas absorption and separation of MC materials can be fully understood.In this Account, to elucidate the uniqueness of MC materials, especially in comparison with polymers, four topics are mainly summarized: structural features, relaxation dynamics characterization techniques, relaxation dynamics characteristics, and quantified understanding of the structure-property relationship. The capability for new function prediction from relaxation dynamics studies is also introduced, and the typical example in impact resistant materials is provided. The Account aims to prove the significance of relaxation dynamics characterization for material innovation, while it also confirms the potential of MCs for functional material fabrications.

Bioinspired Bouligand-Structured Cellulose Nanocrystals/Poly(vinyl alcohol) Composite Hydrogel for Enhanced Impact Resistance.

Impact-protective materials are gaining importance because of the widespread occurrence of impact damage. Hydrogels have emerged as promising candidates owing to their lightweight and flexible nature. However, achieving soft impact-resistant hydrogels with exceptional stiffness, strength, and toughness remains a challenge. Inspired by the Bouligand structure found in the smasher dactyl club of stomatopods, we propose a straightforward multiscale hierarchical structural design strategy. This strategy integrates self-assembly and salting-out techniques to enhance the impact resistance of soft hydrogels. Rigid cellulose nanocrystals (CNCs) self-assemble into Bouligand-like structures within soft poly(vinyl alcohol) (PVA) matrix via supramolecular interactions. This rational structural design combines the CNC Bouligand structure with a cross-linked network of soft PVA crystalline domains, resulting in a composite hydrogel with impressive mechanical properties: high tensile fracture strength (30.2 MPa), elastic modulus (62.7 MPa), and fracture energy (75.6 kJ m-2), surpassing those of other tough hydrogels. Moreover, the multiscale hierarchical structure facilitates various energy dissipation mechanisms, including crack twisting, tortuous crack paths, and PVA chain orientation, resulting in notable force attenuation (80.4%) in the composite hydrogel. This biomimetic design strategy opens new avenues for developing soft and lightweight impact-resistant materials.

Mussel-inspired tough ionogel with robust adhesion and mechanical adaptivity for impact resistance

Intrinsic adhesiveness and mechanical adaptivity allowing spontaneous anchoring and impact-stiffening, which facilitate safer impact protection, remain challenges for the design and synthesis of advanced tough impact-resistant materials. Herein, a novel biomimetic mechanically robust impact-resistant ionogel with the mussel-inspired diphasic structure was elaborately developed. The salt-bridge hydrogen bonds between carboxyl and imidazole groups inside rigid clusters serve as reversible crosslinking sites and prime energy-dissipation motifs, leading to strong noncovalent cohesion. Furthermore, the hydrophobic ionic liquid enriches surface interactions, providing extensive adhesive performance for in-situ attachment under external impact. Benefitting from the dynamic nature of the salt-bridge hydrogen bonds, the ionogel possesses impressive energy dissipation, self-healing, and recyclable properties. Notably, the prepared ionogel exhibits rate-dependent mechanical adaptivity and outstanding impact-stiffening performance with extraordinary initial modulus (∼6.3 GPa), impact strength (∼178.5 MPa), and impact toughness (∼89.6 MJ m−3) under high-speed impact (∼5200 s−1). This work offers promising biomimetic design inspirations for the future development of advanced, flexible, sustainable, and protective materials.

Hierarchical Supramolecular Aggregation of Molecular Nanoparticles for Granular Materials with Ultra High-Speed Impact-Resistance.

The high-speed impact-resistanct materials are of great significance while their development is hindered by the intrinsic tradeoff between mechanical strength and energy dissipation capability. Herein, the new chemical system of molecular granular material (MGM) is developed for the design of impact-resistant materials from the supramolecular complexation of sub-nm molecular clusters (MCs) and hyper-branched polyelectrolytes. Their hierarchical aggregation provides the origin of the decoupling of mechanical strengths and structural relaxation dynamics. The MCs' intrinsic fast dynamics afford excellent high-speed impact-resistance, up to 5600 s-1 impact in a typical split-Hopkinson pressure bar test while only tiny boundary cracks can be observed even under 7200 s-1 impact. The high loadings of MCs and their hierarchical aggregates provide high-density sacrificial bonding for the effective dissipation of the impact energy, enabling the protection of fragile devices from the direct impact of over 200 ms-1 bullet. Moreover, the MGMs can be conveniently processed into protective coatings or films with promising recyclability due to the supramolecular interaction feature. The research not only reveals the unique relaxation dynamics and mechanical properties of MGMs in comparison with polymers and colloids, but also develops new chemical systems for the fabrication of high-speed impact-resistant materials.

Bioinspired stiff–soft gradient network structure for high-performance impact-resistant elastomers

Traditional impact-resistance materials relying on the combination of supporting materials and energy-dissipation elastomers can effectively reduce shock load, yet the sharp interface between two types of materials causes discontinuous stress transfer and cracking. Here, inspired by the squid beak, we report a type of high impact-resistance gradient elastomers with large-scale modulus gradient with about three orders of magnitude (modulus range of 7 × 103 ∼ 7 × 106 Pa) and high energy dissipation (loss factor > 0.6) over a wide temperature range by diffusively introducing stiff polymers in a highly damping elastomer with controlled mechanical properties. Under the action of an external force, our gradient elastomers exhibit soft-while-stiff attributes, combining cushioning and support. In drop hammer impact tests, our gradient materials can reduce impact strength by 80 %, significantly better than commercial protective gear. It is worth mentioning that the modulus of the bottom layer matches that of the tissues for better protection.

Viscoelastic properties of the equine hoof wall

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 significanceThe 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.

Optimizing shear-thickening fluid microencapsulation with high-temperature pickering emulsion for enhanced impact-resistant materials

Combining shear-thickening fluid (STF) with matrix material enables the creation of high-performance materials with enhanced impact resistance. However, effectively preventing STF leakage and avoiding potential reactions between the fluid and the matrix material remain notable challenges. Encapsulating STF through emulsion templating offers a viable solution to these issues. Traditional emulsion templating methods require adding extra solvents to STF to counteract the hindrance of shear-thickening on emulsification, accompanied with increased costs and environmental pollution, and difficulties in maintaining the integrity of core components. In this study, we developed STF microcapsules using a novel high-temperature Pickering double emulsion technique. Our investigation into the rheological properties of molecular sieve/diols suspensions demonstrates that the shear thickening effect could be controlled by particle concentration, surface charge of particles and solvent viscosity. Octadecyltrimethoxysilane-modified fumed silica and fumed silica were utilized as stabilizers for STF-in-paraffin primary emulsions and STF-in-paraffin-in-propylene glycol secondary emulsions, respectively. As temperature increased, droplet sizes of the primary emulsion were significantly reduced. The Pickering emulsion approach effectively preserves the STF composition by forming robust barriers at the emulsion interface with silica particles. Typical STF microcapsules were incorporated into a silicone rubber matrix, the composites exhibited a significant decrease in resilience and an enhanced impact resistance with a 20.9% reduction in maximum impact force. This study is the first to suggest the application of the high-temperature Pickering double emulsion technique for the microencapsulation of STF, offering a practical and scalable method without diluting the STF, thereby ensuring the controllability of the core components.

A Bioinspired Design of Protective Al2O3/Polyurethane Hierarchical Composite Film Through Layer-By-Layer Deposition.

Structural materials such as ceramics, metals, and carbon fiber-reinforced plastics (CFRP) are frequently threatened by large compressive and impact forces. Energy absorption layers, i.e., polyurethane and silicone foams with excellent damping properties, are applied on the surfaces of different substrates to absorb energy. However, the amount of energy dissipation and penetration resistance are limited in commercial polyurethane foams. Herein, a distinctive nacre-like architecture design strategy is proposed by integrating hard porous ceramic frameworks and flexible polyurethane buffers to improve energy absorption and impact resistance. Experimental investigations reveal the bioinspired designs exhibit optimized hardness, strength, and modulus compared to that of polyurethane. Due to the multiscale energy dissipation mechanisms, the resulting normalized absorbed energy (≈8.557MJ m-3) is ≈20 times higher than polyurethane foams under 50% quasi-static compression. The bioinspired composites provide superior protection for structural materials (CFRP, glass, and steel), surpassing polyurethane films under impact loadings. It is shown CFRP coated with the designed materials can withstand more than ten impact loadings (in energy of 10 J) without obvious damage, which otherwise delaminates after a single impact. This biomimetic design strategy holds the potential to offer valuable insights for the development of lightweight, energy-absorbent, and impact-resistant materials.

Integrating intrinsic and configural superiority into advanced impact-resistant organohydrogels via cryo-assisted direct ink writing

The growing safety consciousness towards life and engineering poses demand for efficient anti-impact materials. Decent advances have been made in material development and structure design, whereas the superiority synergism of materials and structures remains challenging. This work develops an advanced impact-resistant shear stiffening gel-polyvinyl alcohol-chitosan (SSG-PVA-CS) organohydrogel by integrating 3D printed customized architectures with strain rate enhanced matrix materials. Following rheological optimization of components, the precursor ink presents shear thinning and yield stress fluid behaviors enabling the direct ink writing (DIW) printing techinique. The printability is systemically explored through finite element modeling assisted flow dynamics analysis and experimental validating, and a quantitative phase diagram is constructed which determines the dependence of parameters on the printing mode and quality. The organohydrogel presents favorable mechanical strength, cyclic durability and rate enhancement effect, which imparts basis of impact resistance to the matrix. The rational structure design effectively reduces the volume density within 0.60 to 0.71 g/cm3 while maintaining considerable attenuation ratios of 73.09 % to 83.55 %, with structure-dependent dynamic mechanical behaviors clarified via finite element analysis. This study provides a reliable approach to fabricate impact-resistance materials with tailored architectures and mechanically functional matrix materials, unlocking paths to break through the performance bottleneck.

Ballistic resistance of 7XXX laminate aluminum alloy plates and base alloys subjected to different projectiles

The ballistic impact of two 7XXX aluminum alloys, 7A52-T6 and 7A62-T6, as well as their combination in a 7B52 laminate plate, was simulated and experimentally tested. Three types of projectiles were utilized hard ogival nosed, hard blunt nosed, and 304 steel core projectiles to investigate the ballistic resistance and failure mechanisms of the aluminum alloy targets. Additionally, an existing modified Gurson-Tvergaard-Needleman (GTN) model incorporating shear, void growth, and spalling failure mechanisms, was employed to simulate the ballistic impact process, utilized to analyze energy dissipation during impact. The results reveal that the 7A52 alloy only experiences ductile hole expansion failure, whereas the 7A62 high-strength aluminum alloy undergoes spalling and fragmentation subsequent to penetration, leading to potential impact hazards. Due to its backing layer being the highly ductile 7A52 alloy, the laminate plate will not produce fragments after penetration. The improved GTN model provided better predictions of the impact failure modes of the aluminum alloys. Concerning impact performance, when subjected to hard ogival projectiles, the laminate alloy did not enhance material impact resistance. However, when impacted by blunt-nosed projectiles, the laminate alloy exhibited a 27 % improvement over the 7A52 plate and an 11.9 % increase over the 7A62 plate. Furthermore, when impacted by 304 steel core ogival projectiles, the laminate alloy demonstrated over a 41.3 % improvement compared to the 7A52 plate and over a 15.5 % increase compared to the 7A62 plate. The laminate plate's high ballistic performance was attributed to the increased plastic deformation energy after spalling failure, while ensuring high energy absorption during ductile hole expansion penetration.

A comparative study on ballistic performance of 3D woven fabrics under different boundary conditions

The potential of 3D woven fabrics as impact resistant material is increasingly recognized. Clarifying their ballistic response under varying boundary conditions is essential prior to deployment. This study aims to investigate the influence of various boundary conditions on the ballistic performance of 3D woven fabrics. Three aramid interlock woven fabrics, each with the same layer count, were designed and fabricated. A verified finite element model of ballistic impact at the yarn level was constructed for a comprehensive analysis. The influence of various boundary conditions on ballistic performance, including ballistic curve, stress distribution, back deformation, and energy absorption, is analyzed. It indicates that boundary conditions significantly affect the impact resistance and response mechanism of the fabrics. Among the different conditions, the fabric under Warp-sides held exhibits greater sensitivity. In the study, the fabric with vertical through-thickness warp yarn structure has smaller out-of-plane displacement, while the fabric with a multi-layer warp yarn structure exhibits better stability in energy absorption performance. The study investigates the response and performance of fabric configurations subject to various boundary conditions, and findings are valuable for the creation of 3D woven fabric designs that leverage boundary effects.

Mechanically Adaptive Polymers Constructed from Dynamic Coordination Equilibria.

Designing materials capable of adapting their mechanical properties in response to external stimuli is the key to preventing failure and extending their service life. However, existing mechanically adaptive polymers are hindered by limitations such as inadequate load-bearing capacity, difficulty in achieving reversible changes, high cost, and a lack of multiple responsiveness. Herein, we address these challenges using dynamic coordination bonds. A new type of mechanically adaptive material with both rate- and temperature-responsiveness was developed. Owing to the stimuli-responsiveness of the coordination equilibria, the prepared polymers, PBMBD-Fe and PBMBD-Co, exhibit mechanically adaptive properties, including temperature-sensitive strength modulation and rate-dependent impact hardening. Benefitting from the dynamic nature of the coordination bonds, the polymers exhibited impressive energy dissipation, damping capacity (loss factors of 1.15 and 2.09 at 1.0 Hz), self-healing, and 3D printing abilities, offering durable and customizable impact resistance and protective performance. The development of impact-resistant materials with comprehensive properties has potential applications in the sustainable and intelligent protection fields.

Entropy-Driven Design of Highly Impact-Stiffening Supramolecular Polymer Networks with Salt-Bridge Hydrogen Bonds.

Impact-stiffening materials that undergo a strain rate-induced soft-to-rigid transition hold great promise as soft armors in the protection of the human body and equipment. However, current impact-stiffening materials, such as polyborosiloxanes and shear-thickening fluids, often exhibit a limited impact-stiffening response. Herein, we propose a design strategy for fabricating highly impact-stiffening supramolecular polymer networks by leveraging high-entropy-penalty physical interactions. We synthesized a fully biobased supramolecular polymer comprising poly(α-thioctic acid) and arginine clusters, whose chain dynamics are governed by highly specific guanidinium-carboxylate salt-bridge hydrogen bonds. The resulting material exhibits an exceptional impact-stiffening response of ∼2100 times, transitioning from a soft dissipating state (21 kPa, 0.1 Hz) to a highly stiffened glassy state (45.3 MPa, 100 Hz) with increasing strain rates. Moreover, the material's high energy-dissipating and hot-melting properties bring excellent damping performance and easy hybridization with other scaffolds. This entropy-driven approach paves the way for the development of next-generation soft, sustainable, and impact-resistant materials.

Evaluation of the low-velocity impact response of high-performance multi-axial warp-knitted flexible composites

This article aims to investigate the dynamic behavior of high-performance multi-axial warp-knitted flexible composite materials under low-velocity impact tests through experiments and numerical simulations. In this paper, high-performance multi-axial warp-knitted flexible composites were prepared. Three different preparation processes, 175°C-5 min, 185°C-10 min, and 195°C-15 min, were designed for the multi-axial warp-knitted flexible composites. Studied the impact response of different preparation processes, initial impact energy, and punch shapes and diameters on materials. The results showed that the flexible composites prepared by various processes exhibit the same impact response curves in the impact resistance process, while the damage morphology and failure modes of the samples are different. Different initial impact energies caused multiple failure modes in the samples. The material showed penetration damage at high energy impacts and permanent depression damage at low energies. For different punch shapes, the impact resistance of materials to hemispherical punches is better than that of cylindrical punches. Numerical simulations were carried out using the finite element software ABAQUS. The custom material subroutine (VUMAT) based on the Hashin damage criterion model was implemented in the finite element program. The experimental and numerical simulation results agree regarding impact response characteristics. This paper analyzes the composite damage shapes, crack extensions caused by low-velocity impact tests and finite element simulation on multi-axial warp-knitted flexible composites. It provides a valuable reference for failure and structural optimization of multi-axial warp-knitted flexible composites for architectural applications.

Robust anti-impact, energy absorption and thermal properties of polyurethane nanocomposites modified by phenol-amine chemistry

It is still a considerable challenge for polyurethane elastomers (PUE) to possess outstanding mechanical and thermal performance simultaneously against harsh dynamic impact environment due to their heat accumulation, thermal stress softening and mechanical failure. Thus, this article innovatively prepared binary nanofibers composed of carbon nanofiber (CNFs) and aramid nanofibers (ANFs) to reinforce PUE, where catechol (CC) and polyethyleneimine (PEI) were served as interfacial modifier between nanofibers and polymer matrix. PUE with 1.5 wt% binary nanofibers achieve 31.62 % increase in crosslinking density, 146.8 °C improvement in thermal decomposition temperature compared to Neat PUE. Besides, the absorption energy and dynamic compression strength of composites were increased by 40.36 % and 38.26 %, respectively. Because reinforced nanofibers with crosslinking network structures improve the interface interaction between fillers and matrix, facilitate stress transfer and increase the energy threshold of thermal decomposition. The paper supplements the impact resistance analysis of PUE-based protective materials under impact loads, providing a systematic and scientific reference for the design and manufacture of impact resistant materials.