High Rate Compression Research Articles

Geometric effects on impact mitigation in architected auxetic metamaterials

Lightweight materials used for impact mitigation must be able to resist impact and absorb the maximum amount of energy from the impactor. Auxetic materials have the potential to achieve high resistance by drawing material into the impact zone and providing higher indentation and shear resistance. However, these materials must be artificially designed, and the large deformation dynamic effects of the created structures must be taken into consideration when deciding on a protection concept. Despite their promise, little attention has been given to understanding the working mechanisms of high-rate and finite deformation effects of architected auxetic lattice structures. This study compares the static and dynamic elastic properties of different auxetic structures with a honeycomb structure, a typical non-auxetic lattice, at equivalent mass and stiffness levels. In this study, we limit the investigation to elastic material behavior and do not consider contact between the beams of the lattices. It is demonstrated that the equivalent static and dynamic properties of individual lattices at an undeformed state are insufficient to explain the variations observed in impact situations. In particular, the initial Poisson’s ratio does not determine the ability of a structure to resist impact. To gain a thorough comprehension of the overall behavior of these structures during localized, high rate compression, the evolution of the elastic tangent properties under compression and shear deformation was monitored, leading to a more profound understanding. Observations made in one configuration of stiffness and mass are replicated and analyzed in related configurations.

Thermomechanical characterisation of a thermoplastic polymer and its short glass fibre reinforced composite: Influence of fibre, fibre orientation, strain rates and temperatures

Polycarbonate composites are widely used in products exposed to high strain rate deformation. This paper investigates the thermomechanical properties of polycarbonate and 20 wt% glass fibre reinforced polycarbonate to provide characterisation data and improved mechanistic understanding of the response to load, supported by Dynamic Mechanical Analysis and time–temperature superposition. Compressive behaviour is characterised from 0.001 to 5000 s−1 at room temperature and from −60 to 120 °C at 0.01 s−1; and a thermal imaging camera used to obtain temperature rise data. Quasi-static tensile experiments were also performed in different orientations relative to the injection flow direction. High-rate compression experiments are performed with X-ray imaging. As well as information about rate dependence of yield stresses and softening in the two materials, these data show how adiabatic shear band formation can cause significant softening in the composite. These data will enhance application of these polymers and facilitate development of advanced thermo-mechanical models.

Failure mechanical properties of lumbar intervertebral disc under high loading rate

BackgroundLumbar disc herniation (LDH) is the main clinical cause of low back pain. The pathogenesis of lumbar disc herniation is still uncertain, while it is often accompanied by disc rupture. In order to explore relationship between loading rate and failure mechanics that may lead to lumbar disc herniation, the failure mechanical properties of the intervertebral disc under high rates of loading were analyzed.MethodBend the lumbar motion segment of a healthy sheep by 5° and compress it to the ultimate strength point at a strain rate of 0.008/s, making a damaged sample. Within the normal strain range, the sample is subjected to quasi-static loading and high loading rate at different strain rates.ResultsFor healthy samples, the stress–strain curve appears collapsed only at high rates of compression; for damaged samples, the stress–strain curves collapse both at quasi-static and high-rate compression. For damaged samples, the strengthening stage becomes significantly shorter as the strain rate increases, indicating that its ability to prevent the destruction is significantly reduced. For damaged intervertebral disc, when subjected to quasi-static or high rates loading until failure, the phenomenon of nucleus pulposus (NP) prolapse occurs, indicating the occurrence of herniation. When subjected to quasi-static loading, the AF moves away from the NP, and inner AF has the greatest displacement; when subjected to high rates loading, the AF moves closer to the NP, and outer AF has the greatest displacement. The Zhu–Wang–Tang (ZWT) nonlinear viscoelastic constitutive model was used to describe the mechanical behavior of the intervertebral disc, and the fitting results were in good agreement with the experimental curve.ConclusionExperimental results show that, both damage and strain rate have a significant effect on the mechanical behavior of the disc fracture. The research work in this article has important theoretical guiding significance for preventing LDH in daily life.

An Efficient Heterogeneous Edge-Cloud Learning Framework for Spectrum Data Compression

Spectrum data compression with a high-rate compression and accurate reconstruction is of crucial importance for reducing the ultra-large data transmission from the edge sensors to the cloud for establishing high-quality spectrum maps. However, the current methods ignore the imbalanced edge-cloud computation resources and cannot tackle the outlier signals, resulting in significant challenges for achieving effective compression. Therefore, we develop an efficient heterogeneous edge-cloud learning framework. In the framework, paralleled methods compress normal data and outlier data distinctively based on their different structure information. Meanwhile, those methods are asymmetric for achieving low-cost compression at the edge and accurate reconstruction on the cloud. Based on the framework, we propose an outlier-processable attention-based asymmetric compression algorithm. A novel attention-based asymmetric convolutional neural network performs the normal data compression while a non-linear outlier compression algorithm realizes the outlier data compression. Compared with the state-of-the-art schemes in real-world settings, our proposed framework's convergence speed increases by 120\% . Meanwhile, our framework's reconstruction accuracy increases by 68.42\% under the interfered environments while maintaining superior compression speed and comprehensive performance. We also confirm our framework's generalization ability to transfer among different tasks by deploying it under various spectrum environments.

Response of Thoraco-Abdominal Tissue in High-Rate Compression.

Body armor is used to protect the human from penetrating injuries, however, in the process of defeating a projectile, the back face of the armor can deform into the wearer at extremely high rates. This deformation can cause a variety of soft and hard tissue injuries. Finite element modeling (FEM) represents one of the best tools to predict injuries from this high-rate compression mechanism. However, the validity of a model is reliant on accurate material properties for biological tissues. In this study, we measured the stress-strain response of thoraco-abdominal tissue during high-rate compression (1000 and 1900 s-1) using a split Hopkinson pressure bar (SHPB). High-rate material properties of porcine adipose, heart, spleen, and stomach tissue were characterized. At a strain rate of 1000 s-1, adipose (E = 4.7 MPa) had the most compliant stress-strain response, followed by spleen (E = 9.6 MPa), and then heart tissue (E = 13.6 MPa). At a strain rate of 1900 s-1, adipose (E = 7.3 MPa) had the most compliant stress-strain response, followed by spleen (E = 10.7 MPa), heart (E = 14.1 MPa), and stomach (E = 32.6 MPa) tissue. Only adipose tissue demonstrated a consistent rate dependence for these high strain rates, with a stiffer response at 1900 s-1 compared to 1000 s-1. However, comparison of all these tissues to previously published quasi-static and intermediate dynamic experiments revealed a strong rate dependence with increasing stress response from quasi-static to dynamic to high strain rates. Together, these findings can be used to develop a more accurate finite element model of high-rate compression injuries.

Scam Image Detection on Copy-Move by JPEG Features and Classical Block Matching with Improved Variant

Numerous methods have been developed to identify copy-move forgeries, which are among the most often used alteration strategies of digital photographs. The most widely used format of digital photographs is JPEG, which allows for high-rate compression without drastically altering the meaning of the picture. The objective of this work is to develop a system that can automatically identify the forgery type of the suspect image through in a single procedure, without requiring any kind of expert information. A preferable method is to run the same image through multiple algorithms, which saves time and prevents the needless evaluation of multiple detection results, from which it may be difficult to determine the correct output due to the presence of multiple confounding factors. Additionally, it has been shown that the established method is very effective in detecting expert forgeries when the duplicated region is picked in a non-rigid fashion, which is almost hard for the human eye to perform.

Effects of carbon black on epoxidized natural rubber composites: Rheological, abrasion, and mechanical study

A detailed analysis of the rubber composites is necessary for the designing and fabrication of advanced rubber products. In this study, composite materials are synthesized by adding different nanofillers of carbon black nanoparticles into epoxidized natural rubber (ENR). The specific characteristics of carbon black (CB) affect the crosslinking density between CB and polymeric chains in ENR. The effects of particle size, structure, thermal conductivity, and functionality of CB on rheology and mechanical properties of filled reinforced ENR are examined. The composite materials are thoroughly characterized for their abrasion, rheology, tensile, hardness, elongation, resilience, and compression behavior. The results revealed that various properties of composite materials depend on the characteristics of the reinforcing CB fillers. It was found that lower particle size and ordered structure provide good tensile strength, tear strength, abrasion, and aging resistance. In contrast, larger particle size and a lower ordered structure provide high flow rate, low hardness, excellent re-bounce, and good compression set characteristics.

Energy storage under high-rate compression of single crystal tantalum

When a material is plastically deformed the majority of mechanical work is dissipated as heat, and the fraction of plastic work converted into heat is known as the Taylor-Quinney coefficient (TQC). Large-scale molecular dynamics simulations were performed of high strain rate compression of single-crystal tantalum, and the resulting integral and differential TQC values are reported up to true strains of 1.0. A phenomenological model is proposed for the energy stored in the material as a function of plastic strain with an asymptotic limit for this energy defined by the deformation conditions. The model reasonably describes the convergence of TQC values to 1.0 with increasing plastic strain, but does not directly address the physical nature of thermo-mechanical conversion. This is instead developed in a second more detailed model that accurately accounts for energy storage with two distinct contributions, one being the growing dislocation network and the other the point defect debris left behind by moving dislocations. The contribution of the point defect debris is found to lag behind that of the dislocation network but to be substantial for the high-rate straining conditions considered here.

Piezoresistive Properties of 3D-Printed Polylactic Acid (PLA) Nanocomposites.

An increasing interest is focused on the application of 3D printing for sensor manufacturing. Using 3D printing technology offers a new approach to the fabrication of sensors that are both geometrically and functionally complex. This work presents the analysis of the 3D-printed thermoplastic nanocomposites compress under the applied force. The response for the corresponding resistance changes versus applied load is obtained to evaluate the effectiveness of the printed layer as a pressure/force sensor. Multi-walled carbon nanotubes (MWNT) and high-structured carbon black (Ketjenblack) (KB) in the polylactic acid (PLA) matrix were extruded to develop 3D-printable filaments. The electrical and piezoresistive behaviors of the created 3D-printed layers were investigated. The percolation threshold of MWNT and KB 3D-printed layers are 1 wt.% and 4 wt.%, respectively. The PLA/1 wt.% MWNT 3D-printed layers with 1 mm thickness exhibit a negative pressure coefficient (NPC) characterized by a decrease of about one decade in resistance with increasing compressive loadings up to 18 N with a maximum strain up to about 16%. In the cyclic mode with a 1 N/min force rate, the PLA/1 wt.% MWNT 3D-printed layers showed good performance with the piezoresistive coefficient or gauge factor (G) of 7.6 obtained with the amplitude of the piezoresistive response (Ar) of about -0.8. KB composites could not show stable piezoresistive responses in a cyclic mode. However, under high force rate compression, the PLA/4 wt.% KB 3D-printed layers led to responses of large sensitivity (Ar = −0.90) and were exempt from noise with a high value of G = 47.6 in the first cycle, which is a highly efficient piezoresistive behavior.

The direct impact method for studying dynamic behavior of viscoplastic materials

Equipping mathematical models of deformation of viscoplastic materials with the necessary parameters and constants requires comprehensive experimental data meeting the requirements of the problem being analyzed. For problems of evaluating strength of dynamically loaded structures, it is important to account for the strain rate effect on the yield surface radius. Experimental schemes for studying such an effect can be constructed based on the measuring rod technique. Such methods include, for instance, the well-known Kolsky method. The methodological limitations of the above experimental scheme necessitated the development of its alternative versions to widen the range of realized strain rates studied. The present paper gives the description and the results of numerical analysis of an experimental method implementing the socalled direct impact scheme that is also constructed based on the measuring bar technique. The method is used for determining deformation diagrams of viscoplastic structural materials loaded in high-rate compression with strain rates higher than those in the traditional Kolsky method. Using the Kolsky method and the direct impact method, deformation diagrams of copper S101 and aluminum alloy D16Т in the strain rate range of 1000 to 10000 s-1 have been obtained.

Time and temperature sensitivity of the hybrid III lumbar spine

Objective Researchers have found a variety of uses for the Hybrid III (HIII) dummy that fall beyond the scope of its original purpose as an automotive crash test dummy. Some of these expanded roles for the HIII introduce situations that were not envisioned in the dummy’s original design parameters, such as a relatively rapid succession of tests or outdoor testing scenarios where temperature is not easily controlled. This study investigates how the axial compressive stiffness of the HIII lumbar spine component is affected by the duration of the time interval between tests. Further, it measures the effect of temperature on the compressive stiffness of the lumbar spine through a range of temperatures relevant to indoor and outdoor testing. Methods High-rate axial compression tests were run on a 50th percentile male HIII lumbar component in a materials testing machine. To characterize the effects of tests recovery intervals, between-test recovery was varied from 2 hours to 1 minute. To quantify temperature effects, environmental temperature conditions of 12.5°, 25°, and 37.5 °C were tested. Results During repeated compressive loading, the force levels decreased consistently across long and short rest intervals. Even after 2 hours of rest between tests, full viscoelastic recovery was not observed. Temperature effects were pronounced, resulting in compressive force differences of 261% over the range of 12.5° to 37.5 °C. Compared to the stiffness of the lumbar at 25 °C, the stiffness at 37.5 °C fell by 40%; at 12.5 °C, the stiffness more than doubled, increasing by 115%. Conclusions A modest decrease in temperature can be sufficient to dramatically change the response and repeatability of the lumbar HIII component in compressive loading. The large magnitude of the temperature effect has severe implications in its ability to overwhelm the contributions of targeted test variables. These findings highlight the importance of controlling, monitoring and reporting temperature conditions during HIII testing, even in indoor laboratory environments.

The Taylor–Quinney coefficients and strain hardening of commercially pure titanium, iron, copper, and tin in high rate compression

This work presents an investigation on the effects of adiabatic heating and strain rate on the dynamic compressive response of titanium, iron, copper, and tin. The high strain rate tests were carried out with a Split Hopkinson Pressure Bar (SHPB) and the low strain rate tests with a servohydraulic testing machine. The temperature increase of the specimens during deformation was measured with high speed infrared thermography (IRT). The results show that all the investigated materials have positive strain rate sensitivity and temperature increases of up to 65 °C were observed in the high strain rate experiments (500–3100 s−1). Adiabatic heating in all investigated materials increased with strain rate. The temperature increase at the strain rate of 1 s−1 clearly diminished the strain hardening rate of iron and titanium but was seemingly insufficient to impact the mechanical behavior of copper and tin. The Taylor–Quinney coefficients (βint and βdiff) were found to be strain and strain rate dependent. At higher strain rates (1200–3100 s−1), the integral βint was smaller in the beginning of the test (0.2 to 0.7) and increased to approximately 0.8–0.9 at larger plastic strains. The differential βdiff comprised gaussian curves as a function of strain whose maximum values were from 0.9 to 1.2 for the investigated materials. Tin had lower βint and βdiff with higher strain hardening rates, while copper had a higher βint and βdiff with a low strain hardening rate throughout the high strain rate tests. These results indicate that copper had a more stable microstructure during deformation and converted most of the applied plastic work into heat, while tin had a faster evolving microstructure which stored more plastic work in its microstructure during plastic deformation. Furthermore, this suggests that βint and βdiff can be used as parameters to investigate the stability and the microstructural evolution of materials under high strain rate plastic deformation. βdiff is more appropriate to describe the instantaneous thermomechanical behavior of a material and βint is more appropriate for applications which benefit from a single parameter to characterize how efficiently a material converts plastic work into heat up to a given strain level.

Specimen-specific fracture risk curves of lumbar vertebrae under dynamic axial compression

Underbody blast attacks of military vehicles by improvised explosives have resulted in high incidence of lumbar spine fractures below the thorocolumbar junction in military combatants. Fracture risk curves related to vertical loading at individual lumbar spinal levels can be used to assess the protective ability of new injury mitigation equipment. The objectives of this study were to derive fracture risk curves for the lumbar spine under high rate compression and identify how specimen-specific attributes and lumbar spinal level may influence fracture risk. In this study, we tested a sample of three-vertebra specimens encompassing all spinal levels between T12 to S1 in high-rate axial compression. Each specimen was tested with a non-injurious load, followed by a compressive force sufficient to induce vertebral body fracture. During testing, bone fracture was identified using measurements from acoustic emission sensors and changes in load cell readings. Following testing, the fractures were assessed using computed tomographic (CT) imaging. The CT images showed isolated fractures of trabecular bone, or fractures involving both cortical and trabecular bone. Results from the compressive force measurements in conjunction with a survival analysis demonstrated that the compressive force corresponding to fracture increased inferiorly as a function of lumbar spinal level. The axial rigidity (EA) measured at the mid-plane of the centre vertebra or the volumetric bone mineral density (vBMD) of the vertebral body trabecular bone most greatly influenced fracture risk. By including these covariates in the fracture risk curves, no other variables significantly affected fracture risk, including the lumbar spinal level. The fracture risk curves presented in this study may be used to assess the risk of injury at individual lumbar vertebra when exposed to dynamic axial compression.

Compression-induced Phase Transition in Adsorbed Monolayers of Alkylgalactosides at the Air/Water Interface.

Compression-induced formation of condensed-phase domains in adsorbed monolayers of alkylgalactosides (AGs) at the air/water interface was observed. When an aqueous solution of AGs was poured into a Langmuir trough, the AG molecules were spontaneously adsorbed from the solution at the air/water interface to form the adsorbed or Gibbs monolayer in an expanded, liquid-like phase at equilibrium. The monolayer was subsequently laterally compressed by the barriers of the trough, while simultaneously observing the system using a Brewster angle microscope (BAM). The surface pressure-film area isotherm upon compression showed a kink at a surface pressure (πkink) comparable to or several mN・m-1 higher than the surface pressure at the critical micelle concentration (πCMC), followed by a plateau region. BAM observations revealed that condensed-phase domains were formed in the homogeneous expanded phase at the plateau. Hence, the plateau corresponds to a first-order phase transition from the expanded phase to the condensed phase. As expected, the compressed adsorbed monolayer was in a metastable state because the surface pressure decreased with time, and the condensed-phase domains disappeared when compression was discontinued. The transient formation of a quasi-stable condensed phase may originate from the combined effect of the lower solubility of AG molecules in water, moderately strong attractive intermolecular interactions between AG molecules at the air/water interface, and high-rate compression.

Beyond the physics and demonstration of ignition.

Fusion holds the promise of providing growing world energy demand with a carbon-free power source having a universally available fuel source and attractive safety and environmental characteristics. A significant global effort has been underway for over 50 years aimed at the achievement of fusion by inertial confinement. The effort to date has necessarily emphasized understanding the physics of compressing and heating a small amount of fusion fuel to the high densities and temperatures required for ignition and energy gain. Though steady progress has been and is still being made to achieve the required physics understanding and energy gain, those goals have not yet quite been met. It is timely to put progress toward fusion power by inertial confinement into perspective by developing an updated roadmap. Preparing a roadmap from present achievements to the ultimate goal of commercial fusion power requires formally identifying and implementing complementary efforts on a number of fronts. These include the choice, development and demonstration of high repetition rate compression drivers (e.g. lasers) to succeed present day single-pulse sources; design, fabrication and testing of high gain targets (gain of order 100); development of mass production, cost-effective, target fabrication and delivery systems capable of inserting targets into the reaction chamber several times per second, and demonstrating ability to accurately hit and efficiently compress those targets to reliably produce the required fusion yields; design and demonstration of reaction chambers capable of handling energy yields and target debris clearing at the levels required for achieving high power plant reliability with low induced radioactivity. A robust ongoing effort on competitive power plant conceptual design is necessary to guide the implementation of a roadmap, including the timing and level of effort on the 'beyond ignition' demonstrations. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

Phase and Structural Transformations in a VTI-4 (Ti–22Al–25Nb) Alloy during High-Rate Hot Compression

The behavior of a VTI-4 (Ti–22Al–25Nb) alloy during hot compression at a strain rate of ~2.5 s–1 is studied. Hot compression to a strain of 65% is carried out in the temperature range 850–1020°C, covering two phase regions β + Ο and β + α2. Hot compression results in the dissolution and spheroidization of lamellar O and α2 phases in the severe deformation zone. X-ray diffraction analysis does not reveal any qualitative changes in the phase composition after deformation. Energy dispersive X-ray spectroscopy (EDS) analysis conducted on a transmission electron microscope indicates niobium depletion of the O phase when the hot compression temperature increases or during compression. Niobium-depleted zones form near interphase boundaries during the dissolution and spheroidization of lamellar-shaped O and α2 phases. The dissolution and spheroidization process includes two stages. The first stage involves defect accumulation in the O-phase and α2-phase lattices, and it is accompanied by a simultaneous increase in the temperature due to deformation-induced heating. The second stage icludes niobium redistribution between the β matrix and the phase in defective sites, which leads to phase dissolution and spheroidization.

Dependence of microstructure and properties of polypropylene/bromo‐isobutylene‐isoprene rubber thermoplastic vulcanizates on the molding process

AbstractTo explore the dependence of the microstructure and properties of thermoplastic vulcanizates (TPVs) on the molding process. The polypropylene/bromo‐isobutylene‐isoprene rubber thermoplastic vulcanizates (PP/BIIR‐TPVs) are molded by high rate shear injection and compression molding, and the phase morphology and physical‐mechanical properties of PP/BIIR‐TPVs specimens are investigated. Detailed small‐angle X‐ray scattering, scanning electron microscopy and atomic force microscopy investigations demonstrate that the high rate shear of injection molding not only decreases the size of BIIR particles but also induces the orientation of the PP matrix and further increases its crystallinity. Subsequently, the PP/BIIR‐TPVs molded by injection molding have higher tensile strength and Young's modulus, while the compression molding benefits to higher elongation at break. The mechanism regarding the effects of high rate shear during injection molding on phase morphology development of PP/BIIR‐TPVs is discussed. This study guides the preparation of TPVs products with desired properties.

Heating-Induced Recrystallization in Copper Subjected to High-Rate Deformation during the Collapse of Massive Cylindrical Shells under Explosion Loading

The recrystallization process in copper subjected to high-rate compression deformation by collapsing a massive cylindrical shell into a cylinder has been studied in this work. Recrystallization occurs in two stages due to the peculiarities of the deformation structure. At the first low-temperature stage, regions with deformation-induced highly-misoriented (over 15 degrees) grains are recrystallized. At the second stage, regions containing deformation-induced cells with low angular boundaries are recrystallized. Recrystallization in copper after loading with a plane shock wave is investigated for comparison. The recrystallization occurs via migration of grain boundaries to form one step.

Distribution of mechanical strain in equine distal metacarpal subchondral bone: A microCT-based finite element model

Microdamage accumulation and adaptation of subchondral bone subjected to intensive cyclic loading are important processes associated with catastrophic bone failure, and joint degeneration in athletic humans and racehorses. At the tissue-level, they lead to a spatial variation in bone tissue mineral density (TMD) which affects the response of the bone to mechanical load. Quantifying the spatial distribution of mechanical load within the subchondral bone is critical for understanding the mechanism of the joint failure. Previously, a gradient of TMD and mechanical properties has been reported under unconfined compression in osteochondral plugs. In the present study, we used micro computed tomography (μCT)-based finite element (FE) models of cartilage-bone to investigate the gradient of strain in the subchondral bone (SCB) from the third metacarpal (MC3) condyle of racehorses under simulated in situ compression. Non-destructive mechanical testing of specimens under high-rate compression provided the apparent-level modulus of SCB. FE models were analysed using unconfined and confined boundary conditions. Unconfined FE-predicted apparent-level gradient of modulus across the SCB thickness correlated well with the experimental results (R2 ​= ​0.72, p ​< ​0.05). The highest strain occurred in the most superficial SCB (0.5–2.5 ​mm deep to the cartilage-bone interface) under the simulated in-situ compression through articular cartilage. The findings of this study provide an estimation for the spatial distribution of mechanical strain within SCB in-situ in the presence of heterogeneous bone tissue which is commonly observed in joints subjected to intensive cyclic loading.

ОСОБЕННОСТИ ФОРМИРОВАНИЯ ЗОН ЛОКАЛИЗОВАННОЙ ДЕФОРМАЦИИ ПРИ ГОРЯЧЕЙ ОСАДКЕ СПЛАВА ВТИ-4 И ПОСЛЕДУЮЩЕМ ОТЖИГЕ

Textural and macrostructural changes in the intermetallic titanium alloy VTI-4 based on the orthorhombic phase (Ti2AlNb) during hot high-rate compression and subsequent recrystallization annealing where studied. The main attention is paid to the formation features of localized deformation bands (LDB) in the central zone of the compressed sample, which are one of the signs of unstable and nonuniform deformation. It is shown that recrystallization annealing after hot compression does not eliminate the LDB and the compression texture. Reasons for this behavior of the material are studied applying the analysis of the solid solution state.