Impact Behavior Research Articles

Effects of Rubber Core on the Mechanical Behaviour of the Carbon-Aramid Composite Materials Subjected to Low-Velocity Impact Loading Considering Water Absorption.

The large-scale use of composite materials reinforced with carbon-aramid hybrid fabric in various outdoor applications, which ensures increased mechanical resistance including in impact loadings, led to the need to investigate the effects of aggressive environmental factors (moisture absorption, temperature, thermal cycles, ultra-violet rays) on the variation of their mechanical properties. Since the literature is still lacking in research on this topic, this article aims to compare the low-velocity impact behaviour of two carbon-aramid hybrid composite materials (with and without rubber core) and to investigate the effects of water absorption on impact properties. The main objectives of this research were as follows: (i) the investigation of the mechanical behavior in tests for two impact energies of 25 J and 50 J; (ii) comparison of the results obtained in terms of the force, displacement, velocity, and energy related to the time; (iii) analysis of the water absorption data; (iii) low-velocity impact testing of wet specimens after saturation; (iv) comparison between the impact behaviour of the wet specimens with that of the dried ones. One of the main findings was that for the wet specimens without rubber core, absorbed impact energy was 16% less than the one recorded for dried specimens at an impact energy of 50 J. The failure modes of the dried specimens without rubber core are breakage for both carbon and aramid fibres, matrix cracks, and delamination at matrix-fibre interfaces. The degradation for the wet specimens with rubber core is much more pronounced because the decrease in the absorbed impact energy was 53.26% after 10,513 h of immersion in water and all the layers were broken.

Quantitative evaluation on the cavitation damage energy of metals via multiscale approaches

In-situ experimental observation cannot be an effective method in the impact process of metal cavitation erosion, and the impact damage energy prediction theory has not been established based on a detailed mathematical and physical model. Research has shown that the metal material can be regarded as a sensor to reflect the impact parameters. Soft metal materials such as industrial pure copper with a single α-phase microstructure can be a suitable sensor to detect cavitation erosion effects, revealing the impact behaviors of the cavitation jet through the depth, width and spatial distribution of cavitation pits on the surface. In this scenario, volume loss of cavitation pits on a macro/mesoscale are obtained by three-dimensional surface measurement. A coupled fluid-solid simulation model calculating the impact damage energy on a macro/mesoscale is established based on the Smoothed Particle Hydrodynamics (SPH) and the Crystal Plasticity Finite Element Method (CPFEM). Python programming is used to set the trajectory of SPH particles to determine the macro cavitation flow field. IFEM methods were used to construct the prediction theory of cavitation impact energy in a relatively simple exponential equation, establishing the quantitative relationship between cavitation impact damage energy and measured volume of cavitation pits. Compared with conventional measurement and simulation, the present multiscale approaches are assumed as a further step advancement towards calculating the impact damage energy of cavitation water jet.

The low velocity impact properties of three- dimensional (3D) warp interlock woven composites according to the fabric architecture

Three-dimensional (3D) warp interlock woven composites (3DWIWC) are in demand in various industries due to their excellent delamination resistance, damage tolerance and fracture toughness properties. The 3D warp interlock woven fabric architecture can be defined by numerous fabric parameters such as: the binding and stuffer warp yarns, the woven pattern, the presence of yarn groups, etc. …. The effect of the fabric architecture on the impact behaviour of 3DWIWC made with carbon yarns has not been fully investigated. The binding warp yarns with the weave pattern play the main role in the arrangement of yarns within the final composite. In order to highlight their main influence, the 3D woven composites had been differentiated according to the main fabric architectural parameters, which are the angle and depth of binding warp yarn, presence of stuffer warp yarn and weave pattern of binding warp yarn. Afterward, their low velocity impact properties and damage mechanisms were examined. Thanks to the precise combination of these internal parameters of the fabric architecture, the contact force and absorbed energy values of 3DWIWC could be increased almost %50 and %15, respectively. Moreover, their damage mechanisms could be significantly improved.

Enhancement of the impact resistance of masonry walls using fiber-reinforced polymer composites

Many civilian structures are masonry ones. However, masonry walls are susceptible to impact loading. Despite the vulnerability, research on enhancing the impact resistance of masonry walls is substantially scarce, especially under high-velocity impact. Hence, in this study, the effect of fiber-reinforced polymer (FRP) composites on the impact resistance of masonry walls was numerically investigated, especially considering high-velocity impact loading. For this purpose, finite element analysis (FEA) was implemented deploying LS-DYNA. In modeling, the Add Erosion and the Smooth Particle Hydrodynamics options were employed to effectively represent impact behaviors of masonry walls subject high-velocity impact loading. Firstly, the developed masonry wall models were validated by comparing the numerical results with experimental ones. Using the verified numerical models, various parametric studies were performed. The main parameters were the directions and types of fiber, different velocities of an impactor, and the number of impactors. Based on the study, the near-surface-mounted (NSM) FRP method was found to be inefficient in improving the impact resistance of masonry walls. Although the externally-bonded (EB) FRP technique was more effective than the NSM FRP one, the impact behavior varied depending on the types and number of FRP. For instance, strengthening a masonry wall using one layer of high-modulus carbon FRP (HCFRP) EB sheet resulted in the perforation of the HCFRP sheet due to the low ultimate strain of HCFRP sheet. Although one layer of standard CFRP (SCFRP) EB sheet was effective to prevent a masonry wall from being perforated against one impactor, the strengthened masonry wall was penetrated by multiple impactors. It was found that two woven SCFRP EB sheets were optimum to evade the perforation of masonry walls subject to high-velocity impact loading. Furthermore, equations for correlations between the maximum impact force and impact energy are proposed.

Experimental study on the influence of turbulence on hail impacts

Hailstorms, characterized by their intensity, are often accompanied by strong winds and heavy rain, posing significant destructive potential. Data indicate that the economic losses caused by hail to buildings, particularly solar panels, have been increasing annually. However, research on the hail resistance of photovoltaic panels has predominantly focused on the isolated effects of hail impacts and wind loads, neglecting the coupling effects between wind and hail. In this study, a device was designed to couple both wind and hail. The effects of turbulence, hail size, and velocity on hail impact behavior were systematically studied and quantified. A predictive formula for the peak load of hail impact on structures was established. The results indicate that the impact of turbulence on hail is significant. When turbulence intensity varies with hail velocity, hail impact force increases as turbulence decreases and hail velocity increases. When both turbulence and hail diameter vary, the impact force of smaller hailstones shows less variation with increasing turbulence. According to variance analysis, hail velocity is the most significant factor affecting hail impact, followed by hail diameter and finally turbulence. The regression equation is given by F=-0.624Iu+5116.25D+7.85Vhail-259.709\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F = - 0.624I_{{\ ext{u}}} + 5116.25D + 7.85V_{hail} - 259.709$$\\end{document}, where F\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F$$\\end{document} represents the peak impact force in Newtons (N), Iu\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$I_{{\ ext{u}}}$$\\end{document} denotes the turbulence intensity, D\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D$$\\end{document} is the hail diameter in meters (m), and Vhail\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_{hail}$$\\end{document} is the hail velocity in meters per second (m/s).

Correlates of intention-to-attend and confirmed cervical screening attendance during the COVID-19 pandemic in Australia: Findings from Compass-PLUS, a prospective cohort study

ObjectiveThe coronavirus pandemic impacted health-seeking behaviour and access to primary care in Australia. We investigated factors associated with intention-to-attend and attendance of cervical screening during the pandemic, mainly in Victoria, Australia. MethodsWe used questionnaire and attendance data (Aug 2020-Nov 2022) from Compass-PLUS, a sub-study of the Compass randomized-controlled trial of Human Papillomavirus-based vs cytology-based screening. Data was restricted to the HPV-screening arm for comparability to the national program. We investigated associations overall and for younger (25–39 years) and older (≥40 years) cohorts, between intention-to-attend/attendance, and socio-demographics, anxiety-related scores, and agreement with beliefs about screening during the pandemic (e.g. importance of screening, increased workload, working from home, risk of infection). ResultsAmong 2,226 participants, positive intention to attend screening was more likely among those with a family history of cancer (p = 0.030) or living outside major cities (p = 0.024). Increased attendance was associated with increasing age (p < 0.001), prior regular cervical screening history [adjusted relative risk (aRR) for 2 screens in 6 years vs none: 1.23 (95 %CI 1.09,1.40); p < 0.001], and part-time employment or retirement compared to full-time employment [aRR:1.08 (1.02,1.14); aRR:1.12 (1.03, 1.22); respectively]. Lower attendance was related to increased agreement with statements indicating screening de-prioritisation (p-trend < 0.05) and higher recent anxiety, specifically in the older cohort (p-trend = 0.002). ConclusionsReduced priority of screening and heightened recent anxiety may partly explain indications of lower-than-expected cervical screening rates during the pandemic. It is important that catch-up of missed HPV screens is performed to prevent a possible increase in cancer diagnoses in the long term.

Effect of core densities on quasi‐static and low‐velocity impact behaviors of AFRP‐aluminum foam hybrid sandwich beams

AbstractThe hybrid sandwich structures possessing composite faces and an aluminum foam (ALF) core exhibit lightweight and superior impact resistance. However, limited studies pay attention to the mechanical behavior of hybrid sandwich beams with various ALF densities. The present article has focused on the influence of foam densities on the quasi‐static and low‐velocity impact (LVI) behaviors of hybrid sandwich beams with aramid‐fiber‐reinforced polymer (AFRP) faces and ALF core. The failure mode, loading response, and energy absorption of sandwich beams have been obtained experimentally and the failure map with a wide range of dimensional configurations has been established theoretically. Increasing core density significantly enhances the load‐carrying capacity of the sandwich beam, and the enhanced effect becomes more obvious for a thicker core. The medium‐density ALFs provide the maximum specific energy absorption, while the high‐density ALFs offer the highest energy absorption for hybrid sandwich beams. The applicability of core densities in hybrid sandwich structures is provided.Highlights Normal strain distribution under quasi‐static loading is analyzed using DIC. AFRP face microbuckling provides higher impact resistance than core failure. The applicability of core density in hybrid sandwich structures is given.

Experimental and Numerical Investigation of Impact Behaviour of Anchored CFRP-to-Concrete Bonding Interface

In the last 20 years, Carbon Fiber Reinforced Polymers (CFRP) have become a common alternative to strengthening and retrofitting. The performance of the strengthened specimens is closely related to the bond slip between the CFRP strips and the adhesion surface. Therefore, researchers have begun to concentrate on the various anchoring methods to delay the debonding of the CFRP from the surface of strengthened specimens. When the literature review of the adhesion behavior between the anchored CFRP strips and the concrete surface is examined, it has been shown that the investigations are mostly done under the effect of static or reversible cyclic loads. In the literature review, there is not any research related to the adhesion behavior between anchored CFRP strips and the concrete surface under the effect of sudden dynamic impulsive impact loading. Therefore, the variables examined in the experimental study are the anchor type used in the CFRP strips, CFRP strip adhesion length, and the number of anchors placed on the strip. As a result of the experiments, the acceleration-time, displacement–time curves of the beams, and the strain–time curves along the CFRP strips were interpreted. In addition, simulation models of the test specimens were created with ABAQUS software, and non-linear finite element analyzes were performed. Finally, by comparing numerical results with experimental ones, the effects of variables such as bond length, applied anchor types and numbers on the impact behavior of the beam and the strain distributions along the CFRP strips were interpreted.

Lattice Boltzmann study of droplet dynamic behaviors impinging on textured surfaces under an external electric field

Textured surfaces contribute to enhancing the cooling effectiveness of electrostatic spray, while the droplet impacting dynamics on such substrates under the influence of electric field are crucial for cooling efficiency. This study utilized a multiphase lattice Boltzmann method combined with the leaky dielectric model to systematically examine the dynamics of droplet impingement on textured surfaces when exposed to electric field. The impact of Weber number, microstructural surface parameters, and electric field strength on droplet impact behavior was discussed in detail. Simulation outcomes reveal that, without the presence of an electric field, the impingement of droplets on textured surfaces results in three distinct deposition states: the Cassie state, partial penetration state, and Wenzel state, primarily contingent upon the surface solid fraction and the droplet impingement velocity. In the Cassie impact regime influenced by an applied electric field, the droplet spreading behaviors exhibit minimal sensitivity to the electric field, with surface tension and inertia primarily governing the spreading dynamics. Throughout the retraction stage, the droplet elongated the direction of the electric field as a result of electric field forces, and eventually, as the electric field strength grows, it bounces off the surface. In the Wenzel impact regime, as the strength of the electric field escalates, the droplet undergoes upward stretching and splits into satellite droplets during the retraction phase, attributed to the dynamic pressure and electrostatic pressure at the apex exceeding the capillary pressure and gravity. These findings could aid in advancing electrostatic spray cooling technology.

On low-velocity impact behavior of flexible and stiff composites for better energy absorption

On low-velocity impact behavior of flexible and stiff composites for better energy absorption

Oxide precipitation strengthening in Cu alloy modified with trace amounts of Nd during dynamic impact

In this study, three kinds of Cu-Nd alloys were prepared. The effect of Nd content on the dynamic impact behavior of the Cu-Nd alloys and its strengthening mechanism were studied. The results show that during the dynamic impact process, nano-scale oxide particles are precipitated in the alloy matrix, and a large number of cracks are formed along the grain boundaries, and the formation of shear bands and thermal grooves are also observed in local areas. With the increase of Nd content, the compressive strength of the alloys increases significantly, the grain size is refined, the number of twins increases, the grooves are much deeper and the number of the precipitated nano-oxide particles also increase significantly. In addition, due to the refinement of the grain size, the crack length is reduced. The increase of the alloy strength is mainly attributed to the nano-scale oxide precipitation strengthening and grain refinement strengthening.

Modeling and Simulation of the Impact Behavior of a Sports Knee Joint Protector Using the Preparation Method of Ferroelectric Photovoltaic Thin Film

Modeling and Simulation of the Impact Behavior of a Sports Knee Joint Protector Using the Preparation Method of Ferroelectric Photovoltaic Thin Film

Water Impact Dynamics and Mechanism Analysis of Polypropylene and Polypropylene/poly(ethylene-co-octene) Replica Surfaces with Nanowires under Low Temperature Conditions.

In this work, polypropylene (PP) and PP/poly(ethylene-co-octene) (PP/POE) blend replica surfaces with densely arranged nanowires are fabricated using a molding process. Morphology analysis shows that the nanowires on these replica surfaces have sharp tips and high aspect ratios. The droplet impact behaviors on the surfaces of the PP/POE blend replicas and PP replicas are investigated before and after freezing at -20 °C for 4 h. The height of the nanowires on the PP/POE blend replica surfaces is higher than that on the PP surface before and after freezing. The static wettability and droplet impact tests on the surfaces of PP/POE blend replicas and PP replica show that adding POE into the PP matrix can significantly increase the toughness of the nanowires on the PP/POE blend replica surfaces during the droplet impact at low temperatures. These investigations are favorable to broaden the practical applications of superhydrophobic surfaces in some severe environments.

Dynamic behaviors of shear-thinning droplet impacting on a spherical particle surface

Non-Newtonian droplet impact is common in nature and industry. The viscosity of non-Newtonian liquids changes with shear stress, leading to different impact behaviors compared to Newtonian liquids. This study prepared shear-thinning solutions by adding HPMC polymer into deionized water and investigated its impact dynamics on hydrophobic spherical surface. The evolution patterns of droplet spreading factor, film thickness, and dynamic contact angle are investigated under different impact conditions. The results show that addition of polymers increases the energy dissipation during impact and suppresses droplet rebound from spherical surface compared to Newtonian droplet with similar viscosity. The droplet-impacting process is distinguished into three phases: (I) initial deformation, (II) inertia-dominated, and (III) viscosity-dominated phases. The temporal evolution of film thickness in Phases I and II is fitted by simple equations. In addition, an empirical formula that integrates Weber and Reynold numbers is proposed to predict the maximum spreading factor of HPMC droplets.

Comparative study on the impact behaviors of CFWST columns reinforced with steel spiral and tube

To obtain superior corrosion resistance and impact resistance, as well as good economic benefits, two new types of composite structure called as steel tube internally-reinforced concrete-filled weathering steel tube (STRCFWST) and steel spiral internally-reinforced concrete-filled weathering steel (SSRCFWST) columns are proposed and compared in terms of their impact resistance in this paper. Eleven impact tests were conducted and three parameters comprising steel spiral diameter, wall thicknesses of outer and inner steel tube were considered to evaluate their influences on the lateral impact behaviors. Results show the presence of inner steel tube and reinforcement cage significantly enhances the impact resistance while slightly decreases the energy absorption capacity. Increasing inner steel tube wall thickness helps to improve the impact resistance, however the contribution is not so good as that produced by increasing the outer steel tube wall thickness, whilst varying steel spiral diameter almost has no impact. Numerical models were developed by ABAQUS/Explicit and verified via the test, based on which the full-range behaviors of STRCFWST, SSRCFWST and unreinforced concrete-filled weathering steel tube (CFWST) columns under impact loading were compared and discussed. It is demonstrated that steel tube and reinforcement cage provide little confinement on concrete infill under impact. With the same internal steel ratio, inner steel tube makes a greater contribution to sectional bending moment resistance and energy absorption as compared to the reinforcement cage.

Influence of sand particle size on the erosion-corrosion resistance of Ni2FeCrMo0.2 HEA in seawater: Particle-surface-electrochemistry interaction

The erosion-corrosion mechanism in rotary flowing seawater is hugely complicated due to the multiscale coupling processes of particle-surface impact, ion mass transfer, and interface electrochemistry. Therefore, developing erosion-corrosion resistant material and exploring the synergistic mechanism between sand erosion and electrochemical corrosion is vital. This study conducted the erosion-corrosion test on Ni2FeCrMo0.2 high-entropy alloy under the particle-seawater flow. Based on a coupled analysis of multi-component weight loss, electrochemical behavior, and microscopic damage morphology, the multiscale coupling processes of sand transportation, particle-surface impact, ion mass transfer, and interface electrochemistry were revealed. The present study found that with the increase of sand size, the energy carried by the particles promoted impact erosion. Additionally, particle movement enhanced ion mass transfer through turbulent effects, and the impact behavior disrupted the passivation film to promote electrochemical processes by reducing the thickness of the passivation film, leading to an increase in the erosion-corrosion rate. However, when the particle size continued to increase to a certain extent, the impact frequency decreased, reducing the erosion-corrosion rate. As the sand size grew, the dominant damage mechanism transitioned from pure corrosion (100 μm) to synergistic effects (200 μm, 400 μm) and then to pure erosion (800 μm). This study provides an in-depth understanding of the erosion-corrosion mechanism in seawater from the perspective of particle-ion-fluid-surface interaction by multi-element characterization.

Employee social impact behavior scale: conceptualization, measure development and validation

Purpose While existing research in organizational behavior has explored such constructs as perceived social impact and extra-role behaviors, there remains a limited understanding of how employees can make positive changes inside and outside the organization within their professional roles. This study aims to bridge the existing research gap by introducing a novel construct, Employee Social Impact Behavior (ESIB), alongside developing and validating a corresponding scale, the Employee Social Impact Behavior Scale (ESIBS), to measure employees' contributions both within their organizations and toward broader societal welfare. Design/methodology/approach The authors used Hinkin’s (1998) psychometric methodology to develop and validate the ESIBS. The process encompassed initial item generation, item reduction with reliability estimation, confirmatory factor analysis and convergent and discriminant validity examination. The authors used data from diverse samples to find that the ESIBS had a consistent unidimensional structure. Findings The scale exhibits both convergent and discriminant validity, and criterion-related validity is demonstrated through the scale’s relation with related constructs such as perceived social impact and extra-role behaviors. Overall, the ESIB is found to be a reliable and valid measure. Originality/value This study unveils a validated ESIB construct, serving both researchers and practitioners to assess impactful employee behaviors within organizations and toward society. This marks a pivotal enhancement in measuring contributions that extend beyond traditional organizational roles to broader societal change.

Experimental study on impact behaviour of normal strength mortar at cryogenic temperatures and after freeze-thaw cycles

Concrete structures employed for the storage of Liquefied Natural Gases (LNG) currently undergo temperature as low as −170 °C. These critical engineering structures may also experience dynamic loads such as impact or explosion during service life. Therefore, it is crucial to explore the mechanical response of concrete at intermediate to high strain rates together with low temperatures or cryogenic freeze-thaw (FT) cycles. This study presents experimental research into the combined effects of low temperatures and strain rate on normal strength mortar, providing a preliminary analysis of the dynamic performance of concrete at low and cryogenic temperatures. A Split Hopkinson Pressure Bar (SHPB) device was used to investigate the characteristics of dynamic compression (at strain rates of 40, 80, 120 and 160 s−1) and dynamic split tension (at strain rates of 20, 40, 60 and 80 s−1) of Normal Strength Mortar (NSM) at different low temperatures. In addition, the dynamic compression (at strain rates of 80, 130 and 180 s−1) after cryogenic FT cycles was also explored. The findings revealed that the failure pattern of NSM samples exposed to coupled low temperature or cryogenic FT cycles and high strain rate loading notably varied from that observed under room temperature condition. Both the dynamic compressive and split tensile strengths of NSM increased with the strain rates at all temperatures. At −160 °C, the dynamic compressive and splitting tensile strengths of NSM specimens were greater than those at room temperature (by 10.94 % and 28.29 %, respectively) and −70 °C (by 3.13 % and 4.12 %, respectively). Cryogenic freeze-thaw cycles evidently impacted the material static and dynamic performance. An empirical model was developed to predict the dynamic increase factors (DIFs) for both dynamic compression and splitting tensile strengths of NSM at low/cryogenic temperatures and after freeze-thaw cycles. Scanning electron microscopy (SEM) technique was performed to study and comprehend the microscopic processes and microstructural changes after FT cycles.

Machine learning approach to evaluating impact behavior in fabric-laminated composite materials

Fabric-layered composites play a crucial role in safety and surveillance applications, making it imperative to accurately predict their impact behavior. This research focuses on creating a machine-learning model to predict the impact behavior of fabric-stacked composites, specifically carbon and Kevlar fabrics. Low-velocity impact tests were performed with varying parameters, and the impact energy and laminate thickness information were used to train machine-learning models to predict impact properties such as impact force, displacement, and absorbed energy. It was observed that the impact force increased by 118.5 % in carbon-laminated fibers and 175.8 % in Kevlar-laminated fibers, while the hybrid layer showed a 101.4 % increase upon impact from 16J. Displacement can affect the stability of the layered structure; thus, a similar stacking sequence is less stable than the hybrid laminated structure. In terms of absorbed energy, as the laminated layers increase, carbon fiber laminate absorbs 4.8 times more energy, and Kevlar fiber and hybrid laminated structures absorb 3 times more energy at higher impact energy. Furthermore, four machine learning models were used to investigate the impact behavior of identical and mixed-layered laminated composites. The impact force and displacement were predicted with higher accuracy using the polynomial regression model, achieving 80 % and 89 % accuracy, respectively. The support vector machine predicted the absorbed energy with approximately 96 % accuracy. In continuing, the experimental results closely matched the predictions made by the other machine learning models utilized in this study. Additionally, the importance of distinctive features and their influence on the performance of the machine learning-based model were interpreted using transposed features of importance and dependency plots. Various failure modes in fabric laminated composites were also identified, providing insights to enhance the performance of stacked fiber materials.

Water Impact: When a Sphere Becomes Flat.

A large hydrodynamic force accompanies the vertical impact of bodies on water. While added mass phenomena govern these forces for both spherical and flat impactors, the dynamics of a trapped gas layer critically alters the flat case, reducing the peak pressure below that predicted by water hammer theory. An impactor with a spherical nose cap looks increasingly flat as the nose curvature approaches zero. This causes one to ask at what curvature a spherical cap impactor transitions to flat impact behavior. We find this transition, relate limiting behaviors to theories, and dispel the long-held belief that the largest water impact forces occur for flat bodies.