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Based on the modeling method of 3D meso‐scale finite element model of plain concrete, a 3D meso‐scale finite element model of reinforced concrete is established considering the interface transition zone between reinforcement frame and mortar, and the reliability of the established meso‐scale finite element model is verified by split Hopkinson pressure bar (SHPB) test results. The failure process of reinforced concrete specimens under typical impact velocity and the influence of interface effect on specimen strength are analyzed by numerical simulation. The research results show that the 3D meso‐scale model of reinforced concrete considers the meso‐scale structure of reinforced concrete more realistically, and can better reflect the damage change process inside the material in the dynamic loading process. The weak interface effect caused by reinforcement can lead to the slight weakening of the dynamic strength of the material, but at the same time the weak interface effect of the reinforcement is also the main reason why the residual form of reinforced concrete remains well aligned with the shape of the reinforcement frame after the failure. [ABSTRACT FROM AUTHOR]

The escalating use of fiber-reinforced composites (FRCs) in aerospace, defense, automotive, and renewable energy industries underscores the need for a comprehensive understanding of their impact resistance and damage tolerance. This review meticulously examines low-velocity impact (LVI) on FRCs, covering impact mechanics, velocity classification, energy absorption, fiber architecture, and hybridization. Emphasizing the critical importance of damage assessment, the study analyzes intricate failure mechanisms and damages induced by LVI, addressing their potential impact on composite structural attributes. The paper critically reviews parameters influencing impact resistance and damage mechanics, evaluating performance through instrumented drop-weight impact testing. Additionally, the review explores nondestructive testing methods crucial for ensuring the reliability of composite structures. The aerospace sector and other applications requiring enhanced dynamic loading characteristics stand to benefit from a deeper understanding of composite behavior under transient impact loading. Specifically focusing on woven textile-reinforced composites, which offer specific material properties and a cost-effective manufacturing route. However, their susceptibility to out-of-plane impact loading leads to various failures, including delamination and spalling, limiting their applicability in advanced scenarios where structural integrity is paramount. It discusses advanced technology like 3D weaving as reliable methods to enhance impact resistance, damage tolerance, and delamination resistance. Notably, 3D woven composites demonstrate superior through-thickness fracture toughness, eliminating delamination as a failure mode. The findings offer valuable insights for designing structures with enhanced compression after impact and through-thickness tension characteristics. Overall, this review consolidates key advancements, challenges, and future prospects in the realm of woven composite materials and their behavior under impact loading, providing a valuable resource for academics and industry professionals alike. [ABSTRACT FROM AUTHOR]

An ultrasonic-wave system was developed to measure the rheological properties of non-Newtonian materials based on their responses to shear and pressure waves. This system was composed of a commercial shear wave transducer and various homemade devices, including a signal generator, a signal conditioner, and a transmission/receiving switch. The shear wave reflections at the interface between the delay line and the unknown test materials can be interpreted by the signals measured with calibration materials (e.g. air, water, olive oil and honey) that have well-known rheological properties. If the Voigt viscoelastic model is used to describe the dynamic behaviour of these test materials, the interpreted data can be used to determine the acoustic impedances, and thus solve for their shear moduli (G), kinematic viscosities (ν) and bulk densities (ρ). After the calibration procedures, the proposed system was used to test a consolidating kaolinite slurry with zero salinity and an initial suspended sediment concentration of 420 g l–1. The measurements showed that the shear modulus G is developed until consolidation for approximately 100 h. Afterward, the G gradually approached a value on the order of 500 N m–2 after approximately 200 h. This corresponded to an initial viscosity of approximately 7 × 10−5 m2 s–1, which decreased slowly over time to approximately 4 × 10−6 m2 s–1 after 300 h. With minor modification to capture pressure waves from the shear wave transducer, the bulk density can also be measured. The integrated system offers a non-invasive and efficient method for characterizing non-Newtonian fluids, providing valuable insights into their rheological properties, which are crucial for a wide range of industrial and scientific applications. [ABSTRACT FROM AUTHOR]

Assessing the dynamic properties of rocks remains a foundational pursuit in the field of rock engineering, providing crucial insights into their mechanical behaviors across a spectrum of loading conditions, including static, cyclic, and dynamic scenarios. This paper expounds upon the utilization of the nonresonance (NR) torsional shear test and its implications for understanding rock responses, particularly in the context of low and medium loading rates. The NR method serves as a pivotal tool for investigating model rock materials subjected to loading conditions characterized by low frequencies and amplitudes. Renowned for its efficacy, this method allows the simultaneous determination of two critical dynamic parameters: shear modulus (G) and damping ratio (D), all at a specific loading frequency. It has been ascertained that the loading rate increased as the loading frequency and applied amplitude of loading increased. With increasing loading rate, the shear modulus consequently increased while the damping ratio decreased. It is observed that the dynamic responses of both ramp and sinusoidal loading waveforms increase concurrently with the amplitudes of the applied torque and loading frequencies. The sinusoidal waveform exhibits greater dynamicity than the ramp waveform at a certain loading rate. Furthermore, this study delves into the intricate analysis of the nonlinear viscoelastic dynamic response exhibited by rocks, utilizing the modified hyperbolic (MH) model and the Ramberg–Osgood (RO) model as analytical tools. The findings derived from curve fitting exercises unequivocally underscore the superior applicability of the Ramberg–Osgood model, particularly in characterizing modulus reduction behavior. Conversely, the modified hyperbolic model emerges as the preferred choice for comprehensive damping ratio analyses. This study enhances the comprehension of rock dynamics and responses under diverse loading conditions, contributing valuable understanding to rock engineering. Insights into loading and strain rate effects aid informed decisions and preventive measures for rock deformation and collapse risks. Practical Applications: This research suggests vital findings regarding the response of intact model materials to various dynamic loading conditions, providing significant insights for comprehending the mechanical response of rock structures exposed to cyclic loading conditions, which have the potential to create weaknesses in rocks resulting in untimely failures. The research can be utilized to assess the response of rocks in the context of seismic incidents, specifically those characterized by shear waves at particular frequencies. This study evaluates the response of rocks during earthquakes by establishing a correlation between the amplitude of torsional shear loading and the peak ground displacement linked to seismic events. In addition to its seismic implications, this research aids in advancing accurate predictive models and instruments that assess the stability and integrity of rock formations under different loading rates—a consequence of the symbiosis between frequency and amplitude. Professionals may ensure efficient risk mitigation, make well-informed decisions, and execute preventative measures concerning rock collapse and deformation by virtue of their comprehensive awareness of the delicate relationship between loading rate and dynamic rock properties. Incorporating the findings into engineering design standards and codes can bring about substantial improvements, augmenting the overall reliability and protection of rock structures. [ABSTRACT FROM AUTHOR]

The softening effect has been widely accepted as the fundamental mechanical property of the granular materials, which underlies some specific phenomena such as fluidization during vibration. In this paper, a series of resonance column experiments are performed to observe the modulus softening of granular materials. A statistical softening model is subsequently proposed and its applicability is verified through a quantitative analysis of the variation of the normalized modulus by changing the external confining pressure. The average potential energy in grain contact has been found to be a power-law scaling with grain size. An evolution model is further implemented to account for the experimental findings on the evolution of modulus of the granular system subjected to different confining pressures. The modulus evolution, including softening and recovery, can be captured by the unified evolution model. [ABSTRACT FROM AUTHOR]

The mechanical behaviors of shales with transversely isotropic characteristics under dynamic loading have great significance for structural instability in geotechnical engineering. To understand the effect of transverse isotropy on the deformability and tensile strength of shales subjected to dynamic loading, a group of impact Brazilian tests were carried out on shale specimens via a split Hopkinson pressure bar (SHPB) testing system. High-speed digital image correlation technology was applied to monitor the fracture process. The experimental results demonstrate that the failure strength has considerable anisotropy as the bedding angle of the embedded layers changes. Moreover, the tensile strength of shales with vertical bedding is usually higher than that of shales with parallel bedding. The observed failure mode is mainly the interaction between tensile and/or shear fractures, and with increasing loading rate, layer-activated fractures tend to occur. Furthermore, five typical failure patterns of transversely isotropic shales characterized by different mechanisms under dynamic Brazilian testing were found. The shales were sensitive to the strain rate when the deformation and fracture response under dynamic loading were assessed. In addition, the modified Nova‒Zaninetti criterion that considers the strain rate effect was proposed according to the Brazilian splitting data and dynamic coordinate system. The established criterion not only properly represents the law of dynamic strength but also provides a new understanding of the effect of strain rate on strength. It has proven to be effective for predicting the dynamic strength characteristics of shales. Highlights: With increasing loading rate, the layer-activated fractures tend to occur. Under high strain rates, cracks generally develop along diversified directions inclined to the bedding planes. Five typical failure patterns of transversely isotropic shales under dynamic Brazilian splitting were concluded. The modified Nova‒Zaninetti criterion considering strain rate effect was proposed. [ABSTRACT FROM AUTHOR]

This paper demonstrates the application of the Johnson–Holmquist II (JH-2) model with correlated and validated parameters to simulate the behavior of a sandstone. The JH-2 model is used to simulate various tests, including single-element tests, structural quasi-static uniaxial and triaxial compression tests, and the split Hopkinson pressure bar test. Additionally, the model is used to simulate drop-weight impact test using a ball bearing and two loading scenarios involving small-scale blasting and projectile impacts. Quantitative and qualitative comparisons demonstrate that the JH-2 model agrees well with both experimental and analytical results. Limitations of the model are also highlighted, particularly for quasi-static problems, as the model was originally developed for high-strain-rate simulations. Ultimately, this study demonstrates that the JH-2 rock constitutive model can obtain reasonable results for a material other than the material for which the model was originally correlated and validated. This paper provides valuable guidance for modeling and simulating sandstone and other rock materials subjected to dynamic loadings. [ABSTRACT FROM AUTHOR]

Underground rocks in coal mining and oil exploration are usually subjected to in-situ stress and dynamic loading. In this paper, the tensile fracture behaviors of brittle rocks under coupled in-situ stress and dynamic loading are investigated numerically via the simulation of Brazilian disc (BD) tests of the modified split Hopkinson pressure bar (SHPB). To achieve this purpose, a cohesive zone model in the framework of the finite element method is used to model the cracking of the rock Brazilian disc under confining pressure. The pressure-dependent property of the rock is considered using the recently proposed bi-linear constitutive law. Dynamic Brazilian disc tests of the SHPB with two impact velocities of a striker are simulated for the rock. Comparisons between the simulated results and the reported experimental ones show a good agreement, demonstrating the accuracy and validity of the simulation models and the numerical approach. Due to the existence of holes in the rock in underground rock engineering practices, a pre-hole is inserted in the BD rock specimen in the modified SHPB tests to more realistically consider the rock fracture. The effects of the in-situ stress, the pre-hole size, and the pre-hole position on the dynamic fracture characteristics of the rock are numerically investigated using the modified SHPB test for BD rock specimen. [ABSTRACT FROM AUTHOR]

Among the failure forms of fiber reinforced materials, interface failure caused by fiber debonding is the most common but complex failure mode. This research proposed a fiber layering modeling method based on the different mechanical properties of the outer and inner parts of fiber yarn, then investigated the mechanical behavior of fiber reinforced materials under dynamic loads with different loading speeds. Two pullout models were established, considering the layering feature of fiber caused by the matrix penetration. The simulated results were compared with the existing experimental data to determine reliable parameters values of the fiber-matrix interface. Based on the values, another pullout model and tensile model were built. Distribution and development of stress in the loading process were discussed. Results show that fiber modeling with inner and outer parts, as well as the cohesive property with reliable parameters, could effectively represent the interface characteristics of fiber reinforced materials under dynamic load. [ABSTRACT FROM AUTHOR]

The shear modulus and damping ratio are arguably the two most crucial soil parameters to be used in seismic site-response analyses and a wide variety of other geotechnical engineering applications involving soil materials subjected to dynamic loading. The dependency of these parameters on the level of load-induced shear strains in the field has been investigated rather extensively for different types of soils. Most experimental studies, however, have relied on a limited set of controlled environmental factors and stress variables, mainly soil moisture and confinement. The present work is an attempt to gain further insights into the possible impact of an additional critical factor: soil temperature. A resonant column apparatus was upgraded to assess the dynamic response of three types of cohesive–frictional soils as they transitioned from linear to nonlinear behavior under thermo-controlled cyclic torsional loading. Emphasis was placed on shear modulus degradation, and hence variation in damping ratio, with increasing shear strain amplitude (cyclic torque magnitude). Results showed a mostly detrimental effect of increasing soil temperature on the normalized shear modulus, damping ratio, and threshold shear strain of clayey, silty, and sandy soils when subject to small to medium shear strain levels. [ABSTRACT FROM AUTHOR]

This document is an editorial for a special issue of the journal "Materials" focused on the topic of "Materials under High Pressure." It emphasizes the interdisciplinary nature of studying materials under extreme high pressure and mentions various scientific disciplines involved in this field. The special issue includes fourteen peer-reviewed research articles covering topics such as processing technology, characterization, testing, theoretical modeling, and simulation. The document provides a brief summary of some of the research findings presented in the special issue, including investigations on the dynamic mechanical properties of materials, dispersion characteristics driven by explosion, detonation-driven deformation and jet formation, and shock-induced chemical reactions in reactive materials. The document also discusses various studies on materials under high pressure, including the strain-softening effect of THV-based reactive materials and the strain-strengthening effect of PTFE-based reactive materials. It explores the control of shock-induced energy release characteristics in PTFE/Al-based energetic materials through experimentation and theoretical analysis. The mechanical properties, constitutive behaviors, and failure criteria of aluminum-polytetrafluoroethylene-tungsten reactive materials are investigated. Additionally, an impact-initiated chemical reaction model is proposed to describe the ignition and energy release behavior of Al/PTFE reactive materials. The document also includes studies on structural damage and material failure caused by high-velocity impact, such as the vibration features and fault mechanism of electronic components under shock load and the dynamics of a space harpoon impacting a target plate. The authors hope that this collection of case studies [Extracted from the article]

This paper presents a new polycrystalline model and Lagrangian computational framework for describing the large-scale thermo-mechanical response of energetic materials under dynamic loadings. In our multi-scale computational polycrystalline framework, at the grain level, the elastic response is modeled using an anisotropic Hooke's law, while the plastic behavior is described with a recently developed quadratic anisotropic single-crystal model that accounts for the intrinsic symmetries associated with the lattice of the constituent crystals. The orientation, plastic strains, and stresses in the individual grains are continuously updated, so the predicted macroscopic scale response takes into account the evolution of the thermo-mechanical state at the meso-scale. First, we illustrate the polycrystalline model capabilities by simulating the response of a pentaerythritol tetranitrate (PETN) polycrystalline high energetic system when subjected to dynamic compression. It is shown that there are strong differences in temperature and stresses between the constituent grains, depending on their relative orientation with respect to the wave direction. Moreover, it is shown that the rise in temperature in certain grains may be well in excess of the macroscopic value. We also present 3D finite element simulations of the impact of a penetrator made of a high-strength steel containing the same polycrystalline PETN system. Insights into the complex interactions between the energetic system and the metallic casing material are provided. Furthermore, it is shown that if the crystallinity is neglected, the predicted temperature rise and the extent of the zone of maximum heating in the energetic system during the impact event differ noticeably from those obtained with our polycrystalline model, which accounts for the crystallinity of the PETN material and the anisotropy in the plastic flow of its constituent crystals. [ABSTRACT FROM AUTHOR]

This paper presents the mechanical behavior of thermally sprayed coatings produced using an arc wire coating material. The produced coatings were cut and subjected to strength resistance tests in static and in dynamic loading. The compressive behavior for the strain rates between 0.001 1/s and 2612 1/s was examined. The strain rate sensitivity of the material was recognized in the material during dynamic loading using the SHPB technique. Microstructural observations were made, and properties such as changes in porosity and the microhardness of the coatings tested were examined. A significant reduction in coating porosity was demonstrated after static loading (90%) and dynamic loading (86%). The result of porosity reduction is the strengthening of the coatings through an increase in the microhardness of these coatings after loading in the static test (160 HV 0.3/8) and the dynamic test (278 HV 0.3/8). As a result of the tests, the coatings retain their cohesion and remain consistent. At the same time, they can absorb a significant amount of mechanical energy due to plastic deformation and porosity reduction. The presented results concern a completely new coating material created from a core wire. [ABSTRACT FROM AUTHOR]

The AA7075-T6 material is widely used in aerospace applications due to its favourable strength-to-weight ratio and cost-effectiveness. The material undergoes a process of cold rolling and subsequent stretching to form metal sheets. This process generates residual compressive stresses on the surface of the material. Surface changes in the material are observed at low stress levels, resulting in variations in residual stresses and surface roughness. This article presents an approach to monitor the surface state changes of AA7075-T6 material during dynamic loading using Fiber Bragg Grating (FBG) sensor. Numerical Finite Element Method (FEM) simulations analyse the transfer of deformations from the damaged surface through the adhesive layer to FBG with different cladding thicknesses. Loading induces microcrack-related intensity changes in the FBG optical spectrum and deformation response. The magnitude of the response is greater, when the cladding thickness of the optical fibre is thinner. Experimental results show that the FBG optical spectrum response varies with cumulative number of dynamic cycles. [ABSTRACT FROM AUTHOR]

The authors studied the influence of metro loads on the destruction of nearby buildings and construction structures with the help of BIM technologies in order to eliminate the human factor at the design stage. In the study, numerical modeling was carried out using the LIRA-SAPR software package, and dynamic loadings were set by the time integration technique. The suggested technique involved a nonlinear dynamic analysis conducted considering the time factor; the parameters of the stress-strain state (displacement, force, stress) were determined at each moment of exposure, changing the rigid characteristics of the building structures. The authors conducted a structural assessment of an unfinished construction facility, considering the vibrodynamic loads of the metro. Numerous models were adopted as the structural designs of buildings that consider various impact factors, such as nonlinear soil behavior and permanent action and the nature of dynamic loads. The comparison with experimental data confirmed the theoretical and computational parts of the developed technique. The study determined the vibrodynamic impact of the metro on the construction structures. Verification of the developed methodology based on BIM technologies was carried out by comparing the results of numerical experiments with the results of subsequent full-scale vibration tests. [ABSTRACT FROM AUTHOR]

Characterized by light weight and high strength, composites are widely used as protective materials in dynamic impact loading under extreme conditions, such as high strain rates. Therefore, based on the excellent tensile properties of continuous fiber and the good flexibility and toughness of the bionic spiral structure, this study uses a multi-material 3D printer to incorporate continuous fiber, and then modifies the G-CODE file to control the printing path to achieve the production of a continuous fiber-reinforced Polylactic Acid composite helicoidal (spiral angle 60°) structure (COF-HP). Dynamic behavior under high-strain-rate impact experiments have been conducted using the Split Hopkinson Pressure Bar (SHPB). Stress–strain curves, impact energy curves and high-speed camera photographs with different strain rates at 680 s − 1 and 890 s − 1 have been analyzed to explore the dynamic process and illustrate the damage evolution. In addition, some detailed simulation models considering the incorporation of continuous optical fiber (COF) and different strain rates have been established and verified for deeper investigations. The results show that the COF does enhance the impact resistance of the laminates. When the porosity is reduced, the maximum stress of the continuous fiber-reinforced composite material is 4~7% higher than that of the pure PLA material. Our findings here expand the application of COF and provide a new method for designing protective materials, which have broad application prospects in the aerospace and automotive industries. [ABSTRACT FROM AUTHOR]

A brief review of known digital speckle pattern interferometry methods for retrieving the surface displacement and deformation fields under dynamic loads is presented. A new nondestructive test method of three-step phase-shifting correlation speckle pattern interferometry to study the dynamic loads of structural materials is proposed. In this method three speckle interferograms (SIs) of the specimen surface, differing only by arbitrary unknown phase shifts, are recorded before the loading and one SI is recorded under the dynamic load. The surface displacement field under dynamic loading is determined using the obtained SIs. Two algorithms for the implementation of the method are proposed. They use an integrating bucket technique to record SIs and make it possible to determine the phase maps of the surface displacement fields at any moment of applying the dynamic load. We can use this method to produce a temporal sequence of surface displacement fields during loading. [ABSTRACT FROM AUTHOR]

The goal of this paper is to probe the effect of strain gage instrumentation bandwidth (BW) on the measured and calculated mechanical response of a brittle material under dynamic loading using a mini-Kolsky bar. If the BW on the strain gage instrumentation is too low, relative to the loading time, there will be a filtering effect whereby the "true" signals are not measured. As researchers miniaturize the Kolsky bar to increase the strain rate, anomalous data may be recorded, especially when testing brittle materials. The filtering effect was systematically studied by compressing a representative brittle material with progressively shorter loading times, while simultaneously recording the strain gage signals at two different bandwidths, 500/800 kHz (no filtering) and 100 kHz (possible filtering), to determine when deviations occur. The results show that there is only a small filtering effect but that it occurs at rise times that are greater than what would be expected based on the typically used BW-rise time relationship or from the frequency components of the measured waves. Concerningly, there is no obvious way to know if the signals are being inadvertently filtered, and the calculated stress–strain curves are only slightly affected. The filtering effect is discussed further in relation to Kolsky bar testing in general. [ABSTRACT FROM AUTHOR]

Fracture development and its possible relation with wave motion in a brittle rectangular solid material with sets of preexisting small-scale parallel cracks are investigated. Experimental observations using high-speed cameras under external quasi-static tensile or dynamic impact loading conditions indicate that depending on the inclination angle, length and distribution pattern of cracks, fractures evolve considerably differently. Quasi-static load generally produces dynamic or quasi-static primary fracture with ensuing dynamic secondary retrograde fractures that are initiated at distant positions. Fractures can be arrested and jump easily, often resulting in clusters. Impact-related waves can induce primary fracture moving in both prograde and retrograde directions. [ABSTRACT FROM AUTHOR]

The mechanical properties and failure characteristics of columnar jointed rock mass (CJRM) are significantly influenced by its irregular structure. Current research on CJRMs is mainly under static loading, which cannot meet the actual needs of engineering. This paper adopts the finite element method (FEM) to carry out numerical simulation tests on irregular CJRMs with different dip angles under different dynamic stress wave loadings. The dynamic failure modes of irregular CJRMs and the influence law of related stress wave parameters are obtained. The results show that when the column dip angle α is 0°, the tensile-compressive-shear failure occurs in the CJRMs; when α is 30°, the CJRMs undergo tensile failure and a small amount of compressive shear failure, and an obvious crack-free area appears in the middle of the rock mass; when α is 60°, tensile failure is dominant and compressive shear failure is minimal and no crack area disappears; and when α is 90°, the rock mass undergoes complete tensile failure. In addition, in terms of the change law of stress wave parameters, the increase in peak amplitude will increase the number of cracks, promote the development of cracks, and increase the proportion of compression-shear failure units for low-angle rock mass. The changes in the loading and decay rate only affect the degree of crack development in the CJRMs, but do not increase the number of cracks. Meanwhile, the simulation results show that the crack expansion velocity of the CJRMs increases with the increase in dip angle, and the CJRMs with dip angle α = 60° are the most vulnerable to failure. The influence of the loading and decay rate on the rock mass failure is different with the change in dip angle. The results of the study provide references for related rock engineering. [ABSTRACT FROM AUTHOR]

This study aims to analyze strength properties and low-cycle dynamic tests of composite materials modified with glass and basalt fibers. Biopolyamide 4.10 was used as the matrix, and the fiber contents were 15, 30, and 50% by weight. Static tensile tests, impact tests, and determination of mechanical hysteresis loops were carried out as strength tests. The length of the fibers in the produced composites and their processing properties were determined. The composite materials were compared with commercially available glass fiber-reinforced composites with 30 and 50% fiber contents. The results showed that such composites can successfully replace composite materials based on petroleum-based polymeric materials, providing high strength properties and reducing the negative environmental impact by using renewable sources. Composites with 30% basalt fiber composition were characterized by higher tensile strength by about 60% compared to commercially available composites with 30% glass fiber composition and an almost doubly increased Young's modulus. Increasing the content of basalt fibers to 50% results in a further increase in strength properties. Despite the lower tensile strength compared to polyamide 6 with 50% glass fiber content, basalt fibers provided an approximately 10% higher modulus of elasticity. [ABSTRACT FROM AUTHOR]

Puncture is a vital mechanism for survival in a wide range of organisms across phyla, serving biological functions such as prey capture, defense, and reproduction. Understanding how the shape of the puncture tool affects its functional performance is crucial to uncovering the mechanics underlying the diversity and evolution of puncture-based systems. However, such form-function relationships are often complicated by the dynamic nature of living systems. Puncture systems in particular operate over a wide range of speeds to penetrate biological tissues. Current studies on puncture biomechanics lack systematic characterization of the complex, rate-mediated, interaction between tool and material across this dynamic range. To fill this knowledge gap, we establish a highly controlled experimental framework for dynamic puncture to investigate the relationship between the puncture performance (characterized by the depth of puncture) and the tool sharpness (characterized by the cusp angle) across a wide range of bio-relevant puncture speeds (from quasi-static to ∼ 50 m/s). Our results show that the sensitivity of puncture performance to variations in tool sharpness reduces at higher puncture speeds. This trend is likely due to rate-based viscoelastic and inertial effects arising from how materials respond to dynamic loads. The rate-dependent form-function relationship has important biological implications: While passive/low-speed puncture organisms likely rely heavily on sharp puncture tools to successfully penetrate and maintain functionalities, higher-speed puncture systems may allow for greater variability in puncture tool shape due to the relatively geometric-insensitive puncture performance, allowing for higher adaptability during the evolutionary process to other mechanical factors. [ABSTRACT FROM AUTHOR]

Composite double-arrow auxetic structures were designed and fabricated. The local impact experiments were carried out on the auxetic structures to explore the dynamic responses and failure modes. The effects of relative density and impulse level on the impact properties were analyzed and discussed. As the relative density increased, the local deformation of the auxetic structures and the damage of the core layer decreased, and the overall response of the auxetic structure increased. The finite element model was used to simulate the impact responses of the auxetic structures, and the numerical simulation results were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

This paper focuses on stereolithography (an additive manufacturing technology working on the principle of curing liquid resins layer by layer using ultraviolet radiation) and the effect of aging on the mechanical properties of the material and printed samples. The aging of the material could be a problem for its subsequent use as the stability of the mechanical properties would not be maintained and unwanted deterioration of the material could occur. As part of the research, sets of samples were printed and subjected to different aging methods and subsequently subjected to quasi-static and dynamic uni-axial load tests. From the data obtained, the basic mechanical properties of the material were calculated and compared with each other. The aim of this paper was to investigate whether aging process causes significant changes in the mechanical properties of the materials used, which could have a consequential impact on their use in different industries. [ABSTRACT FROM AUTHOR]

Studies reveal that the most prominent cause of bearing failure is a crack on any of its mating surfaces. When the crack is initiated, the bearing can still be used for some duration, but this is majorly depending upon the loading conditions. This work primarily focuses on the effects of different levels of static loading on the crack propagation after crack initiation. To analyze the effect of static loading, an axial groove defect was seeded on the outer race of a taper roller bearing randomly and bearing run continuously under five different static loading conditions. Initially, the bearing was made to run under loading conditions to initiate the crack naturally but the crack was not initiated even after 800 h of running. Therefore, crack was initiated artificially for the purpose of studying crack propagation. It was observed from the experimentation that in the case of maximum static load of 20 kg, the crack propagates rapidly in terms of area after 109 h of continuous running, whereas in the case of no load, it started propagating quickly after 267.5 h of running. Statistical analysis was also carried out for the recorded signals at different intervals of times, and it was observed that the Shannon entropy value was showing a sudden rise with the edge breakage (visually verified) while the crack was propagating. However, in the statistical analysis, none of the parameters showed a correlation with crack propagation. To develop the correlation of crack propagation, Shannon entropy of high, medium and low frequency bands of continuous wavelet-based (CWT) was carried out using different wavelets. Shannon entropy for high frequency band of CWT using Daubechies 10 as mother wavelet has responded well to the crack propagation as the value showed a sudden rise and an overall increase for edge breakage and crack propagation, respectively. A high frequency band of CWT using Daubechies 10 was found suitable for detecting edge breakage and crack growth at the same time because of its capability to respond to transient characteristics for a large duration of time. [ABSTRACT FROM AUTHOR]

The performance of energetic materials subjected to dynamic loading significantly depends on their micro- and meso-scale structural morphology. The geometric versatility offered by additive manufacturing opens new pathways to tailor the performance of these materials. Additively manufactured energetic materials (AMEMs) have a wide range of structural characteristics with a hierarchy of length scales and process-inherent heterogeneities, which are hitherto difficult to precisely control. It is important to understand how these features affect AMEMs' response under dynamic/shock loading. Therefore, temporally and spatially resolved measurements of both macroscopic behavior and micro- and meso-level processes influencing macroscopic behavior are required. In this paper, we analyze the shock compression response of an AMEM simulant loaded under several impact conditions and orientations. X-ray phase contrast imaging (PCI) is used to track features across the observed shock front and determine the linear shock velocity vs particle velocity equation of state, as well as to quantify the interior deformation fields via digital image correlation (DIC) analyses. Photon Doppler velocimetry is simultaneously used to measure the particle velocities of the specimens, which are consistent with those obtained from x-ray PCI. The DIC analyses provide an assessment of the average strain fields inside the material, showing that the average axial strain depends on the loading intensity and reaches as high as 0.23 for impact velocities up to 1.5 km/s. The overall results demonstrate the utility of x-ray PCI for probing "in-material" equation of state and interior strains associated with dynamic shock compression behavior of the AMEM simulant. [ABSTRACT FROM AUTHOR]

Machine learning has the potential to enhance damage detection and prediction in materials science. Machine learning also has the ability to produce highly reliable and accurate representations, which can improve the detection and prediction of damage compared to the traditional knowledge-based approaches. These approaches can be used for a wide range of applications, including material design; predicting material properties; identifying hidden relationships; and classifying microstructures, defects, and damage. However, researchers must carefully consider the appropriateness of various machine learning algorithms, based on the available data, material being studied, and desired knowledge outcomes. In addition, the interpretability of certain machine learning models can be a limitation in materials science, as it may be difficult to understand the reasoning behind predictions. This paper aims to make novel contributions to the field of material engineering by analyzing the compatibility of dynamic response data from various material structures with prominent machine learning approaches. The purpose of this is to help researchers choose models that are both effective and understandable, while also enhancing their understanding of the model's predictions. To achieve this, this paper analyzed the requirements and characteristics of commonly used machine learning algorithms for crack propagation in materials. This analysis assisted the authors in selecting machine learning algorithms (K nearest neighbor, Ridge, and Lasso regression) to evaluate the dynamic response of aluminum and ABS materials, using experimental data from previous studies to train the models. The results showed that natural frequency was the most significant predictor for ABS material, while temperature, natural frequency, and amplitude were the most important predictors for aluminum. Crack location along samples had no significant impact on either material. Future work could involve applying the discussed techniques to a wider range of materials under dynamic loading conditions. [ABSTRACT FROM AUTHOR]

Carpet resiliency was better for carpets manufactured from engineered yarns. Keywords: Hand-made carpet; compression; contour plots; optimization; resilience EN Hand-made carpet compression contour plots optimization resilience 7382 7390 9 11/21/22 20221220 NES 221220 Introduction Carpets, since BC 5-6th centuries, have been produced due to the demand for a comfortable and warm floor and have an important place in home decoration. Contour plots show that the most preferment carpet are those made with a higher pile yarn linear density (>900 tex) and have a lower pile height (<7 mm). From these plots, we concluded that using pile yarns coarser than 900 tex and a low pile height could be a good compromise to obtain woolen hand-made carpet with a good resilience and an important useful life. [Extracted from the article]

This paper demonstrates the validity of the Naess–Gadai method for extrapolating extreme value statistics of second-order Volterra series processes through application on a representative model of a deep water small size tension leg platform (TLP), with specific focus on wave sum frequency effects affecting restrained modes: heave, roll and pitch. The wave loading was estimated from a second order diffraction code WAMIT, and the stochastic TLP structural response in a random sea state was calculated exactly using Volterra series representation of the TLP corner vertical displacement, chosen as a response process. Although the wave loading was assumed to be a second order (non-linear) process, the dynamic system was modelled as a linear damped mass-spring system. Next, the mean up-crossing rate based extrapolation method (Naess–Gaidai method) was applied to calculate response levels at low probability levels. Since exact solution was available via Volterra series representation, both predictions were compared in this study, namely the exact Volterra and the approximate one. The latter gave a consistent way to estimate efficiency and accuracy of Naess–Gaidai extrapolation method. Therefore the main goal of this study was to validate Naess–Gaidai extrapolation method by available analytical-based exact solution. Moreover, this paper highlights limitations of mean up-crossing rate based extrapolation methods for the case of narrow band effects, such as clustering, typically included in the springing type of response. [ABSTRACT FROM AUTHOR]

The dynamic fracture toughness of rock materials under blast load is the basis for studying the stability of rock blasting engineering. To study the dynamic fracture characteristics of sandstone with an explosive load, the initiation and propagation times of pre-crack samples with different lengths were obtained through physical experiments. The experimental–numerical method was used to obtain the stress intensity factor (SIF) curve and the crack initiation toughness of the specimens with different pre-crack lengths. By comparing and analyzing the dynamic SIF and explosion load curves at different pre-crack lengths, the following results and conclusions were obtained: (1) a polyvinylidene fluoride pressure gauge effectively measured the blast pressure curves at the blast hole wall and the blast hole with a diameter of 40 mm in the presence of a coupling water medium that could effectively avoid the formation of crushed zones and reduce the attenuation of the blast energy. (2) The crack-tip SIF curves were well correlated to the blast pressure curves with a minimal SIF lagging of 0.3–2.9 μs after the peak of the blast pressure curve and a maximum SIF lagging of 0.1–22.9 μs after the time when the peak blast pressure decayed to zero, and the lagging time increased with the pre-crack length. (3) The crack was affected by the reflected wave during the propagation process, and the reflected wave did not affect the crack propagation within 0–109.8 μs. The longer the pre-crack length was, the longer the reflected wave influence time was. (4) The SIF at the pre-crack tip was controlled to a degree such that the first wave was superposed on the surface wave of the crack surface. Both the peak value of the stress intensity factor curve and the crack initiation toughness value decreased with the increase of the pre-crack length, and an obvious separation inflection point appeared on the stress intensity factor curve with the increase of the pre-crack length. (5) The implications of these findings particularly regarding the test method for dynamic fracture of materials tested by explosion method are discussed. Highlights: The water coupling technology for loading hole effectively avoids the formation of crushing circle in loading hole. The pressure time range of the loading hole is accurately measured by a PVDF pressure sensor. The stress intensity factor curves of internal single-cracked square plate specimens under blast loading are significantly influenced by the superposition of the first wave and the surface wave on the crack surface. The degree of superposition between the first wave and the surface wave on the crack surface is significantly affected by the length of the prefabricated crack. The average loading rate of the stress intensity factor curve varies from 1036 GPa·m1/2·s−1 to 2198GPa·m1/2·s−1 with the change of pre-crack length. [ABSTRACT FROM AUTHOR]

The high rate of cassava vinasse (CV) generation from distilleries and its anti-environmental characteristics threaten the sustainable production of bioethanol. In this study, the production of biomethane via anaerobic digestion (AD) of CV was modelled and optimized with response surface methodology (RSM). The D-Optimal experimental designs produced 27 digestion experiments randomly executed to investigate the effects of CV (55–100%), poultry dropping, PD (0–45%), organic loading rates, OLR (2–10 gVS/l.d), inoculum to substrate percentage, ISP (10–30%) and hydraulic residence time, HRT (20–30 days) on methane yield (MY). Experimental data were fitted to a quadratic model and its significance was assessed using the analysis of variance (ANOVA), and lack of fit test. Model efficiency was experimentally validated in the laboratory. Results showed that the CV had a high carbon-to-nitrogen ratio (C/N) of 43.5:1 and a biochemical methane potential (BMP) of 247.1 Nml/gVS demonstrates the potential for biogas production. The optimum conditions established for biomethane production were 55% CV, 10% OLR, 30% ISP and 20 days HRT with a MY of 254.4 ml/g VS. For the developed model, a coefficient of determination (R2), standard deviation (SDev.) and p-value of 0.9925, 4.91, <0.0001 respectively indicate high predictive accuracy. The study provided vital information for the bioethanol industry and the environmental agencies, on alternative treatment and utilization options for CV. [Display omitted] • Methane yield from vinasse was optimized using D-optimal mixture design and CCD. • Simultaneous substrate/input variables optimization for maximum methane production. • Codigestion of vinasse and poultry droppings yielded more methane than vinasse only. • The anaerobic digestion of vinasse was modelled with RSM accurately with R2 = 0.9925 • Methane yield of 242.13 ml/gVS was obtained at the established optimal condition. [ABSTRACT FROM AUTHOR]

This research focuses on the load characteristics of piezoelectric transducers in the process of longitudinal vibration ultrasonic welding. We are primarily interested in the impedance characteristics of the piezoelectric transducer during loading, which is studied by leveraging the equivalent circuit theory of piezoelectric transducers. Specifically, we propose a cross-value mapping method. This method can well map the load change in ultrasonic welding to the impedance change, aiming to obtain an equivalent model of impedance and load. The least-squares strategy is used for parameter identification during data fitting. Extensive simulations and physical experiments are conducted to verify the proposed model. As a result, we can empirically find that the result from our model agrees with the impedance characteristics from the real-life data measured by the impedance meter, indicating its potential for real practice in controller research and transducer design. [ABSTRACT FROM AUTHOR]

Forming simulation requires a constitutive model whose parameters are typically determined with tensile tests assumed static. However, this conventional approach is impractical for high-speed forming simulation characterized by high strain rates inducing transient effects. To identify constitutive parameters in relation to high-speed forming simulation, we formulated the problem of constitutive modeling as inverse parameter estimation addressed by regularized nonlinear least squares. Regarding the proposed inverse constitutive modeling, we adopted the L-curve method for proper regularization and model order reduction for rapid simulation. For demonstration, we corroborated the proposed strategy by identifying the modified Johnson–Cook model in the context of a free bulge test with electromagnetic metal forming simulation. The L-curve method allowed us to systematically choose a regularization parameter, and model order reduction brought enormous computational savings. After identifying constitutive parameters, we successfully verified and validated the reduced and original simulation models, respectively, with a manufactured workpiece. In addition, we validated the numerically identified constitutive model with a dynamic material test using a split Hopkinson pressure bar. Overall, we showed that inverse constitutive modeling for high-speed forming simulation can be effectively tackled by regularized nonlinear least squares with the help of an L-curve and a reduced-order model. [ABSTRACT FROM AUTHOR]

Existing research on PTFE-based reactive materials (RMs) mostly focuses on Al/PTFE RMs. To explore further possibilities of formulation, the reactive metal components in the RMs can be replaced. In this paper, Zr/PTFE and Ti/PTFE RMs were prepared by cold isostatic pressing and vacuum sintering. The static and dynamic compressive mechanical properties of Zr/PTFE and Ti/PTFE RMs were investigated at different strain rates. The results show that the introduction of zirconium powder and titanium powder can increase the strength of the material under dynamic loading. Meanwhile, a modified J-C model considering strain and strain rate coupling was proposed. The parameters of the modified J-C model of Zr/PTFE and Ti/PTFE RMs were determined, which can describe and predict plastic flow stress. To characterize the impact-induced reaction behavior of Zr/PTFE and Ti/PTFE RMs, a quasi-sealed test chamber was used to measure the over-pressure induced by the exothermic reaction. The energy release characteristics of both materials were more intense under the higher impact. [ABSTRACT FROM AUTHOR]

The experiments were conducted in the artificial climate chamber from September to November 2021, using "Hongyan" strawberry(Fragaria×ananassa Duch "Benihope") as the test material for dynamic hightemperature environmental control experiments at the seedling stage (9-12 true leaves, leaf length ≥ 5 cm), with a daily maximum temperature of 32°C as the starting point and four levels of daily maximum/daily minimum temperatures of 32°C/22°C, 35°C/25°C, 38°C/28°C, and 41°C/31°C for 2d, 5d, 8d, and 11d, respectively, and 28°C/18°C as the control (CK). The relative air humidity is 60%-70%, the photoperiod is 12h/12h (6:00-18:00), and the light intensity is 800μmol·m-2·s-1. The chlorophyll content and hyperspectral reflectance of leaves under different treatments were measured, and the original spectrum was changed to refine the spectral characteristic information. Based on the correlation analysis, the original and first-order sensitive band vegetation indices were established, and then the spectral characteristic parameters that characterize chlorophyll content were screened, in order to build the best estimation model of chlorophyll content. The results showed that: (1) the chlorophyll a, chlorophyll b and total chlorophyll (a+b) contents of strawberry leaves tended to decrease as the temperature increased and the duration of high temperature increased. (2) The original spectra of strawberry leaves had green peaks and red valleys in the visible region, except for the green peaks and red valleys, which did not differ significantly among treatments, and the reflectance in the NIR region under high temperature conditions showed different degrees of increase compared with CK. Compared with the original spectra, the first-order derivative spectral curves oscillated more strongly and were able to highlight the red edge parameters significantly. The red edge position λr of each treatment was stable at 716nm, and the difference between the red edge amplitude Dr and the red edge area Sr was significant; while the green peak (near 550 nm) and red valley (near 675nm) of each treatment were completely highlighted in the continuous uniform removal spectra. (3) Based on the correlation analysis between spectral reflectance and chlorophyll content, R747, R800 and R'716, R'906, which have the strongest correlation between the original and first derivative spectra in the visible and near-infrared bands, were selected as the combination of sensitive bands to construct the vegetation index. (4) PVI, MSAVI, TSAVI, TSAVI', DVI', MSAVI', PVI', SAVI', Dr and Sr indices correlated with chlorophyll content at highly significant levels and can be used as hyperspectral characteristic parameters to characterize the chlorophyll content of greenhouse strawberry leaves in response to high temperature stress at seedling stage. The stepwise regression model with TSAVI, DVI' and PVI' vegetation indices was the best estimation model for chlorophyll content, with a coefficient of determination (R2) of 0.843, root mean square error (RMSE) of 0.379 and relative error (RE) of 12.65%. [ABSTRACT FROM AUTHOR]

Mesoscale imperfections, such as pores and voids, can strongly modify the properties and the mechanical response of materials under extreme conditions. Tracking the material response and microstructure evolution during void collapse is crucial for understanding its performance. In particular, imperfections in the ablator materials, such as voids, can limit the efficiency of the fusion reaction and ultimately hinder ignition. To characterize how voids influence the response of materials during dynamic loading and seed hydrodynamic instabilities, we have developed a tailored fabrication procedure for designer targets with voids at specific locations. Our procedure uses SU-8 as a proxy for the ablator materials and hollow silica microspheres as a proxy for voids and pores. By using photolithography to design the targets' geometry, we demonstrate precise and highly reproducible placement of a single void within the sample, which is key for a detailed understanding of its behavior under shock compression. This fabrication technique will benefit high-repetition rate experiments at x-ray and laser facilities. Insight from shock compression experiments will provide benchmarks for the next generation of microphysics modeling. [ABSTRACT FROM AUTHOR]

Natural rubber (NR)–based vulcanizates have been used as base isolation materials for many years. Combining good damping properties, low cost, and availability with acceptable mechanical and aging performance, these materials have always been the first choice for base isolation applications. In this research, we try to formulate a natural rubber base recipe with increased damping properties, which can fulfill mechanical and aging requirements of base isolation systems. For this purpose, a series of blends have been formulated by incorporating chloroprene (CR) or butadiene (BR) and acrylonitrile butadiene rubber (NBR) into the natural rubber base. Filler content accelerator type and vulcanization system have been chosen to optimize damping while maintaining a reference point. All vulcanizates have been tested for their mechanical properties. Moving die rheometer (MDR) and rubber process analyzer (RPA) have been used to obtain general cure data as well as storage (G′) and loss modulus and loss angle (η). Crosslink densities have been calculated using RPA and Lee and Pawlowsky's Coran approach. Dynamic material tests have been performed to obtain dynamic shear properties, equivalent damping ratio, and shear modulus. The results indicated that NR/NBR and NR/CR compounds with viscous damping values of 10.4% and 8.9% at frequency of.5 Hz can lay bases for formulating high-damping rubber (HDR) materials for base isolation systems due to their increased damping and rather good mechanical and relaxation performance. [ABSTRACT FROM AUTHOR]

A model of the deformation of 12Kh18N9 steel used in fuel assemblies is verified based on the results of experimental investigations. The characteristics of the investigated steel under dynamic loading are determined by the Kolsky method using Nicholas scheme. The values of the ultimate strength and their dependence on the strain rate and temperature are found based on the actual strain diagrams obtained under different loading conditions. The parameters of the Johnson–Cook model were determined from the experimental results on deformation of 12Kh18N9 steel under static and dynamic loading. The verification process showed that the selected mathematical model gives a very accurate description of the behavior of the material under dynamic loading conditions. [ABSTRACT FROM AUTHOR]

Void evolution at the microscopic scale is an important part of the shock response of porous metallic glasses (MGs). Here, large-scale molecular dynamics simulations are used to investigate the shock loading of Cu50Zr50 MG, including thermodynamic quantities, shock-induced void collapse, and spall behavior. The results show that the shear transformation zone nucleation and growth around the void is the main plastic deformation mechanism for the shock-induced void collapse in MGs. The stress around the void is analyzed to reveal the evolution of the void shape and the relationship between the critical stress for the void collapse and the Hugoniot elastic limit stress. A model is proposed to predict the void collapse time in MGs. Softening occurs at around the location of the void after the void collapse due to a local temperature increase. Consequently, spallation is colocated with the high temperature region, rather than at the position associated with maximum tensile stress. Void growth and nucleation of tension transformation zones compete with each other as the shock intensity increases. At a high strain rate, the Cu50Zr50 MG shows more brittle fracture behavior with a larger number of voids and smaller average void size. [ABSTRACT FROM AUTHOR]

We present a novel method for optimizing parameters of the Ignition and Growth (I&G) reactive flow model for high explosives. The I&G model predicts the shock initiation response of explosives subjected to dynamic loading. However, calibrating the model is a time-consuming process because it has several parameters, typically requires multiple data sets, and there are no direct correlations between parameters and data. In this study, we couple a scalable optimization algorithm to simulations of shock initiation experiments in the multi-physics code ALE3D. We develop four I&G model parameter sets for the HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane)-based explosive LX-07 [90 wt. % HMX, 10 wt. % Viton A] based on minimizing the difference between calculations and measurements at the embedded pressure gauges in 1D gun shock experiments. Our study shows that a cost function based on both shock time of arrival and pressure pulse shape demonstrates the best agreement with experimental data. [ABSTRACT FROM AUTHOR]

With the power system operating close to its stability margin, the increased penetration of renewable resources and loads with diverse characteristics, appropriate stability studies, and control decisions have become crucial. Due to the importance of accurate representation of aggregate loads in such studies, research interests for load modeling have increased. This paper puts forward a novel measurement-based load modeling approach that adapts itself based on the complex dynamics exhibited by the installed aggregate loads. The proposed approach primarily utilizes the collected measurements to gain insight regarding the dynamic trend in the measurements and subsequently determines the optimal order of an equivalent system or load model capable of effectively representing the aggregate load dynamics. An advanced signal pre-processing technique is employed, which effectively suppresses the noise and also preserves the transients present in the measurements. Afterward, an adaptive dynamic load model (ADLM) accurately represents the installed aggregate load. Lastly, the Refined Instrumental Variable (RIV) approach estimates the equivalent dynamic load model parameters. The results on a 2 bus and the IEEE 118 bus networks in DIgSILENT Powerfactory and a 7 bus network in Real-Time Digital Simulator (RTDS) reveal the efficacy of the proposed approach. [ABSTRACT FROM AUTHOR]

• Reporting the prevalence of multisite musculoskeletal symptoms (MSS) among electronic workers. • Using latent class analysis to determine the derived patterns of MSS among electronic workers. • The association of derived patterns of MSS with personal and work-related factors were analyzed. Introduction: Multi-site musculoskeletal symptoms (MSS) are considered to be more common and have more serious consequences than single-site MSS. This study aimed to determine whether derived patterns of MSS may be identified in electronic assembly workers and if extracted MSS classes are associated with personal and work-related factors. Method: A cross-sectional questionnaire study was performed with 700 participating electronic assembly workers. The questionnaire included individual factors, psychosocial and physical exposures, and MSS. The derived patterns of MSS and their relationships with ergonomic factors were analyzed using latent class analysis (LCA) and multinomial logistic regression models (MLRM). Results: The 1-year prevalence of MSS affecting only one body site or two or more body sites was 14.9% and 32.7%, respectively. The results of LCA showed three distinct classes of MSS patterns, which were labelled 'MSS in most sites' (5.0%), 'MSS in neck and shoulder' (27.0%), and 'MSS in one or no site' (68.0%). The results of MLRM showed that the 'MSS in neck and shoulder' was associated with job tenure (OR 5.579, 95% CI 2.488–12.511), excessive dynamic and static loads (OR 3.868, 95% CI 1.702–8.793 and OR 5.270, 95% CI 2.020–13.747, respectively); while the 'MSS in most sites' was associated with high job demands (OR 4.528, 95% CI 1.647–12.445) and excessive dynamic loads (OR 111.554, 95% CI 4.996–2490.793). Conclusions: The results showed unique patterns of MSS among electronic assembly workers that were associated with personal and work-related factors. Practical applications: The findings highlight that the high prevalence of multi-site MSS in this group should be a focus. It also provides further evidence that LCA considering the number and location of anatomical sites involving MSS can be used to determine distinct classes of MSS patterns, which is of great significance for the epidemiological study and management of MSS in the future. [ABSTRACT FROM AUTHOR]

In this paper, four types of truss lattices are designed by combining octet truss (FCC) unit cells with other elementary unit cells, including Simple Cubic (SC), Body-centered Cubic (BCC), Body-centered Block (BCB), and Z-pinned (Z). The elastic properties (uniaxial, shear, and bulk moduli, Zener's anisotropy index, and Poisson's ratio), yield strength, deformation modes, and energy absorption under quasi-static loading, and impact resistance under dynamic loading of these lattices were investigated through finite elements. The initial peak stress and subsequent plateau stress are elevated under dynamic loading. The stress waves velocity of the lattices is calculated by the dynamic enhancement term. Results indicate that the mechanical properties of the designed lattices are better than the reported FCC and BCC lattices. FCCBCB (which is combined with FCC and BCB elementary unit cell) remains stable for uniaxial compression at a relative density of about 0.2 and exhibits the highest energy absorption capacity at the relative density considered; the Zener index of FCCSC (which is combined with FCC and SC elementary unit cell) does not vary greatly with the increase of relative density (1.18 to 1.11 at the relative density considered), and the Zener index approaches unity indicating elastic isotropy; and FCCZ (which is combined with FCC and Z elementary unit cell) features the highest yield strength and Young' modulus among all lattices considered. The computational results are confirmed through uniaxial compression experiments on three-dimensional (3D)-printed specimens. [ABSTRACT FROM AUTHOR]

A simplified three-dimensional mathematical model for electronic packaging cabinets was derived from physical laws. Tridimensionality resulted from the domain division in volume elements (VEs) with uniform properties, each with one temperature, and empirical and theoretical correlations allowed for modeling their energetic interaction, thus producing ordinary differential equations (ODEs) temperatures versus time system. The cabinet (2048 mm × 1974 mm × 850 mm) thermal response with one heat source was measured. Data set 1 with a 1.6-kW power source was used for model adjustment by solving an inverse problem of parameter estimation (IPPE) having the cabinet internal average air velocities as adjustment parameters. Data set 2 obtained with a 3-kW power source validated model results. The converged mesh had a total of 7500 VE. The steady-state solution took between 16 and 19 s of CPU time to reach convergence and less than 3 min to obtain the 6500-s cabinet dynamic response under variable loading conditions, in an Intel CORE i7 computer. After validation, the model was used to study the impact of heat source height on system thermal response. Fundamentally, a sharp minimum junction temperature Tjct,min = 98.5 °C was obtained in the system hot spot at an optimal heat source height, which was 25.7 °C less than the highest calculated value within the investigated range (0.1 m < zjct < 1.66 m) for the 1.6-kW power setting, which characterizes the novelty of the research, and is worth to be pursued, no matter how complex the actual cabinet design may be. [ABSTRACT FROM AUTHOR]

The dynamic component of bridge traffic loading is commonly taken into account with a Dynamic Amplification Factor (DAF)—the ratio between the dynamic and static load effects on a bridge. In the design codes, this factor is generally more conservative than in reality. Recently a new method of calculation of this factor had been developed. Data from 15 different bridges have been analysed since then and this paper presents the results of the analyses. The background for Bridge Weigh-in-Motion is given, and the most recent method for DAF calculation is described. The sites from which the data originated are presented, and the selection of data discussed. The results of the analyses are presented and discussed and some examples of DAF calculations are shown. Data from the considered sites have invariably demonstrated a DAF decrease with increasing axle load. This is a significant result, especially for assessment of existing structures, since it is beneficial to use measured structural parameters to optimise structural analysis. [ABSTRACT FROM AUTHOR]

The aim of this research is to develop and validate an experimental model testing method of the erhu instrument. The model analysis is applied to investigate the dynamic behavior of materials, which results in the relationships between excited shape and its structure. There are three major factors which would directly affect the performance of erhu vibroacoustics: (1) the string, (2) the vibrating membrane, and (3) the wooden soundbox. However, the transducer mass effect is the significant impact factor in the membrane vibration measurement. Attention is focused on the erhu membrane vibration modes by using the scanning laser method. The method for experimental mode shapes of the erhu membrane was notable in that the equipment assembled a loudspeaker, a signal point laser, and a scanning laser vibrometer. Depending on the white noise, the mode shapes can be excited with plane acoustic waves to push on the membrane surface. The scanning laser method consists in two types of laser doppler vibrometer for various purposes. The single point laser measured the driving point vibration as the reference in the center of the membrane surface. The responses were measured by the scanning laser vibrometer with 276 measuring points on the surface. The results showed the vibroacoustics of the erhu membrane and the various mode shapes that are dependent on the frequency diversifications. The mode shapes of the erhu membrane can be classified into five vibroacoustic patterns according to various frequency ranges (20 to 5,000 Hz). Obviously, the scanning laser method is a convenient and readily reproducible setup to evaluate erhu vibroacoustic properties. As an engineering application, the proposed method can serve as a fundamental tool when predicting or even suppressing the possible excitations associated with vibration modes in the mechanical designs of instruments. [ABSTRACT FROM AUTHOR]

This research paper presents the analysis of vibration generated due to the race waviness of rolling element bearing which is under external dynamic load. The waviness on races is modeled either by sinusoidal function or superposition of sinusoidal functions of different orders. The mathematical model developed to analyze elastic deformations at race-rollers contacts and nonlinear contact forces for a defect free bearing under static external loading is modified and extended to take dynamic load into account. The radial waviness on races at these contacts is introduced in order to determine un-balanced excitations causing the bearing to vibrate. The set of equations that represent the dynamics of system have been obtained by inputting the excitations to linear vibratory model of bearing system. The vibration response of bearing has been obtained by numerical simulation of state space model representing dynamics of bearing system. The spectra of vibration response are analyzed for different amplitude contribution of dynamic component of external load. The numerical results have been obtained for NJ204 bearing with known values of order and amplitude of waviness. For harmonic loading, the additional spectral components have been observed for each order of waviness on both outer and inner race. The additional spectral components have also been observed for outer race waviness modeled as superposition of different order waviness models, whereas for inner race, there is some amplitude variation in spectral components. The vibration frequencies resulting from various orders of waviness on races have been validated with those of prior researchers. [ABSTRACT FROM AUTHOR]