High-strain Loading Research Articles

Mechanically robust, highly toughened, corrosion and impact resistant epoxy/silica nanocomposites by UV curing 3D printing technology

In this paper, a photosensitive resin was successfully synthesized using epoxy as a matrix and the effect of nanosilica on its properties was investigated. Micromorphology analyses show that the nanosilica has good dispersion and strong interaction with the matrix. Additionally, a finite element model was developed to predict the tensile performance of the nanocomposite under high-strain loads. Molecular dynamics simulations demonstrated a favorable binding energy between nanosilica and epoxy resin. The effects of nanosilica on the fracture toughness and energy release rate of photosensitive resins were investigated using load-enhanced tensile test method. The results showed that the addition of 1.0 wt.% nanosilica particles increased the toughness of the resin from 0.45 MPa m1/2 to 0.79 MPa m1/2, and the energy release rate from 248.3 J/m2 to 555.7 J/m2; compared with the neat photosensitive resins, the incorporation of nanosilica increased the tensile and impact strengths of the resins by 26.8% and 49.2%, respectively. The nanosilica was used to improve the tensile strength and impact strength of the resin by 26.8% and 49.2% respectively compared with the neat photosensitive resin. Electrochemical corrosion analysis showed that the photosensitive resin/nanosilica composites have excellent corrosion resistance. Under different corrosion environments of acid, alkali, and salt, the addition of 1 wt.% nanosilica in the photosensitive resin composite led to an increase in corrosion voltage by 0.023 V, 0.004 V, and 0.1 V respectively compared to neat photosensitive resin. Additionally, the corrosion current density decreased by 1.39 × 10−6 A/cm2, 0.525 × 10−4 A/cm2, and 2.57 × 10−6 A/cm2, respectively. On this basis, the independently synthesised photosensitive resin has excellent strength and 0.01 mm printing accuracy.

Elasto-Plastic Constitutive Behaviour Prediction and Uncertainty Quantification of Damaged Composite Structure under High-Strain Rate Loading

Abstract The current research assesses the consequences of various damages (crack and delamination) and high-strain loading conditions on the fibre-reinforced composite structure's elasto-plastic stress-strain (EPSS) characteristics. The constitutive responses are obtained numerically (finite element discretization) using higher-order polynomials (to count the deformation) with the help of the MATLAB platform. The EPSS responses are evaluated via the modified Ludwik equation and Cowper Symonds model under high strain rate loadings. The model accuracy has been tested through the comparison between the present numerical and the published experimental data available in open domain. Furthermore, various numerical examples present the effect of damages (debond and/or crack), forces and stress-strain characteristics for a wide range of strain rates (ranging from 0.001 s−1 to 50 s−1). The stochastic constitutive model is obtained to show the modelling importance and the corresponding analysis parameters including the uncertainty quantification. Finally, a detailed understanding of the damages and geometries on the polymeric composite structure are enumerated via the delve model for the futuristic design.

Effect of the temporal coordination and volume of cyclic mechanical loading on human Achilles tendon adaptation in men

Human tendons adapt to mechanical loading, yet there is little information on the effect of the temporal coordination of loading and recovery or the dose–response relationship. For this reason, we assigned adult men to either a control or intervention group. In the intervention group, the two legs were randomly assigned to one of five high-intensity Achilles tendon (AT) loading protocols (i.e., 90% maximum voluntary contraction and approximately 4.5 to 6.5% tendon strain) that were systematically modified in terms of loading frequency (i.e., sessions per week) and overall loading volume (i.e., total time under loading). Before, at mid-term (8 weeks) and after completion of the 16 weeks intervention, AT mechanical properties were determined using a combination of inverse dynamics and ultrasonography. The cross-sectional area (CSA) and length of the free AT were measured using magnetic resonance imaging pre- and post-intervention. The data analysis with a linear mixed model showed significant increases in muscle strength, rest length-normalized AT stiffness, and CSA of the free AT in the intervention group (p < 0.05), yet with no marked differences between protocols. No systematic effects were found considering the temporal coordination of loading and overall loading volume. In all protocols, the major changes in normalized AT stiffness occurred within the first 8 weeks and were mostly due to material rather than morphological changes. Our findings suggest that—in the range of 2.5–5 sessions per week and 180–300 s total high strain loading—the temporal coordination of loading and recovery and overall loading volume is rather secondary for tendon adaptation.

Study of effect of loading rate on mechanical properties of SS316LN and evaluation of parameters of Johnson-Cook model using parametric FE analysis and experimental data

Study of effect of loading rate on mechanical properties of SS316LN and evaluation of parameters of Johnson-Cook model using parametric FE analysis and experimental data

A novel algorithm to model concrete based on geometrical properties of aggregate and its application

A novel algorithm to model concrete based on geometrical properties of aggregate and its application

Terahertz characterization of combined pressure-shear shock loaded aromatic polyurea

Terahertz characterization of combined pressure-shear shock loaded aromatic polyurea

Effect of graphene oxide on cement mortar under quasi-static and dynamic loading

Cement composites are the most widely used construction material in the world; however, research on their resistance to high strain loads is lacking. This study investigated the effect of graphene oxide (GO) on the static and dynamic mechanical properties and microstructure of cement mortar. Dynamic tests were performed using a split Hopkinson pressure bar apparatus at strain rates up to approximately 290 s−1. The mechanical behaviors of mortar specimens infused with 0.005 and 0.01 wt% GO (weight% of GO to cement) were compared against control specimens made with ordinary Portland cement. Enhancement in the strength of cement composites was evident in both compression and split-tension when GO was added in specific doses, particularly at higher strain rates. Correlation between the dynamic increase factor and the applied strain rate is found based on the compressive and split-tensile experimental data of tested mortar specimens. The findings of this study highlight the great potential of GO for improving the performance of cement composites under high strain rate loading.

Comparison of 2D and 3D meso‐model of concrete under high strain loading rate

AbstractIn this paper, 2D and 3D meso‐models of concrete are developed numerically using different shapes of aggregate. For 2D model, circular and random polygon aggregate shapes are considered while for 3D model, spherical and convex hull aggregate shapes are adopted. Five different spatial distributions are employed in both circular and polygon shapes to get Circle1–Circle5 and Poly1–Poly5 geometrical model. Similarly, for 3D meso‐model, Spherical1–Spherical5 and one Convex hull geometrical models are developed. In all the numerical models, three different phases of concrete are considered, that is aggregate, mortar, and interfacial transition zone. Explicit analysis of the developed models has been performed using LS‐DYNA. All the developed models are verified by comparing the obtained results of stress–strain variations with the existing literature. The behavior of concrete is studied for both the loading conditions, that is quasi‐static and high strain loading rate. Added to this, the effect of spatial distribution of aggregates is also evaluated. Finally, the dynamic impact factors (DIF) are evaluated and compared for all the developed numerical models. Finally, cubic polynomial equations for DIF, for different shape aggregate 3D models, are obtained using regression analysis.

WITHDRAWN: Effect of geo-material on dynamic response of tunnel subjected to surface explosion

Prime materials involved in a problem such as underground structures are concrete, reinforcement steel and geo-material surrounding the tunnel. Among these three materials, concrete and steel are manufactured materials and their properties can be controlled up to a certain extent. However, geomaterial is a naturally occurring material whose constitutive properties vary from region to region making it highly unpredictable. Findings from one study cannot be applied to other geotechnical problems directly, especially, in the case of tunnels subjected to surface explosion. The blast wave generated has to travel through the geo-material before it interacts with the tunnel. As the shock wave propagates radially its characteristics are most likely to get altered by the geo-material. Limited study has been carried out considering this problem. In the present study, the effect of various types of geo-material on the blast response of tunnels subjected to surface explosion is investigated. Finite element analysis has been carried out using LS-DYNA® wherein the problem has been modelled using multi-material arbitrary Lagrangian Eulerian (MM-ALE) method. Materials with fluid behavior such as air, explosive and soil are modelled using ALE formulation. Other materials including tunnel lining, reinforcing steel and rock are modelled using Lagrangian formulation. Blast loading is simulated using Jones-Wilkins-Lee (JWL) equation of state. Geo-materials considered for the comparative study are sandy loam, sandstone, and granite. Vertical displacement measured at the crown of the tunnel is used to determine the response of tunnel. Sandy loam soil being a highly compressible soil, exhibits non-linear and fluid-like behavior under high strain loading such as explosion. Tunnel undergoes extreme deformation in the case of sandy loam soil as compared rock cases. Additionally, the effect of weathering of rock on the tunnel response is investigated in the case of sandstone and granite. It was observed that weathering rock led to more displacement of tunnel crown as compared to intact rock.

Anisotropic orientation dependent shock wave responses of monocrystalline molybdenum

Molybdenum (Mo) demonstrates excellent industrial application potentials in micro-nano devices, which are inevitably subjected to shock loads during their application under harsh service environments. This study employs molecular dynamics (MD) simulations to investigate the shock responses of Mo under high-strain loading conditions with respect to the effects of crystal orientations. The findings reveal that monocrystalline Mo, along the shock direction of [111], exhibits inhomogeneous microstructure features characterized by significantly high-density and high-temperature localized regions. Once the rarefaction wave is produced, the physical parameters, including density and lateral pressure, will gradually decrease while normal pressure retains a residual value. The us-up, Pzz-up, and Pzz-V/V0 relations along the shock loading direction of [111] show deviations from those of [001] and [110] directions, with this difference being more pronounced for Pzz-V/V0. The formation of dislocations and the magnitude of shear stress experienced within the post-shock region are strongly dependent on crystal orientations. Specifically, an elevated probability of dislocation formation was observed along the [110] direction. Moreover, the magnitude of shear stress induced by shock loading along the [001] and [110] directions can exceed that of the [111] direction when the shock velocity is 1.5 km/s. The MD simulation results can serve as a valuable supplement to the investigations of mechanical properties pertaining to Mo.

Development and prototyping of SMA-metamaterial biaxial composite actuators

Shape memory alloys (SMA) are excellent candidates for implementation in actuator systems due to their ability to recover their original shape after high-strain loading through a thermally-induced phase transition. In this work, we propose and develop a novel SMA-metamaterial actuator which is capable of exhibiting a reversible, global elongation in multiple directions induced by the unidirectional contraction upon heating of a single SMA component. This actuator consists of (a) an SMA component, (b) a bias component and (c) the metamaterial geometry, with each component having a distinct function: (a) actuation activation, (b) reversibility of actuation upon deactivation and (c) amplifying and re-directing the uni-directional SMA actuation globally throughout the actuator, respectively. A prototype actuator was designed and tested in various configurations over multiple activation/deactivation cycles in order to demonstrate the functionality and reusability of this system. Furthermore, a theoretical model which predicts the actuation stroke of the system on the basis of the material properties of the SMA and bias components as well as the geometry of the metamaterial system was developed and validated. The findings of this work demonstrate the considerable potential of SMA-metamaterial actuators for implementation in systems requiring a multi-axial actuation output.

Low-cycle fatigue behavior of Cu–Al–Mn superelastic alloys at different temperatures

Superelastic alloy (SEA) bars are widely used in structures subjected to moderate and strong earthquakes. Compared with conventional nickel-titanium (NiTi) SEAs, Cu–Al–Mn (CAM) SEAs has received increasing attention recently due to their cost-effectiveness and easier machinability. The authors’ previous research showed that despite their lower strength and limitations in the maximum length, the CAM SEAs have comparable superelastic strain recovery, a wider temperature range, and superior strain rate stability compared to NiTi SEAs. However, the previous research was limited to a few specimens and only conducted to a few hundred cycles without considering the full deterioration in the material properties. Besides, the existing research on CAM SEA was only limited to small sample sizes at room temperature, while the fatigue performance of large diameter CAM SEAs under low and high temperatures relevant for civil engineering structures has not been reported. To fill this knowledge gap, low-cycle fatigue performance of 20 mm diameter CAM SEAs was studied at room temperature 25 °C, low temperature, −40 °C, and high temperature, 50 °C. Both single crystal and polycrystal CAM SEAs were investigated to determine their feasibility as concrete reinforcement under repeated high strain loading cycles expected during an earthquake. Strain cycles up to 50 000 have been applied at a tensile strain amplitude of 5%. Variations in the superelastic properties were observed and analyzed, including the stress–strain curves, elastic modulus, transformation stresses, damping ratio and recovery strain. Stable hysteresis has been observed for cycles exceeding tens of thousands at all temperatures demonstrating the suitability of CAM SEAs for seismic applications in civil engineering structures.

Three-dimensional mapping of mineral in intact shark centra with energy dispersive x-ray diffraction

The centra of shark vertebrae consist of cartilage mineralized by a bioapatite similar to bone's carbonated hydroxyapatite, and, without a repair mechanism analogous to remodeling in bone, these structures still survive millions of cycles of high-strain loading. The main structures of the centrum are an hourglass-shaped double cone and the intermedialia which supports the cones. Little is known about the nanostructure of shark centra, specifically the relationship between bioapatite and cartilage fibers, and this study uses energy dispersive diffraction (EDD) with polychromatic synchrotron x-radiation to study the spatial organization of the mineral phase and its crystallographic texture. The unique energy-sensitive detector array at beamline 6-BM-B, the Advanced Photon Source, enables EDD to quantify the texture within each sampling volume with one exposure while constructing 3D maps via specimen translation across the sampling volume. This study maps a centrum from two shark orders, a carcharhiniform and a lamniform, with different intermedialia structures. In the blue shark (Prionace glauca, Carcharhiniformes), the bioapatite's c-axes are oriented laterally within the centrum's cone walls but axially within the wide wedges of the intermedialia; the former is interpreted to resist lateral deformation, the latter to support axial loads. In the shortfin mako (Isurus oxyrinchus, Lamniformes), there is some tendency for c-axis variation with position, but the situation is unclear because one dimension of the sampling volume is considerably larger than the thickness and spacing of the intermedialia's radially-oriented lamellae. Because elastic modulus in collagen plus bioapatite mineralized tissues varies significantly with both volume fraction of bioapatite and crystallographic texture, the present 3D EDD-derived maps should inform future 3D numerical models of shark centra under applied load.

Analyses of Damping Sustainability of Additively Manufactured Nickel Alloy Components Subjected to High Strain Loading Cycles

Abstract Integrally bladed rotors are more susceptible to vibration and high cycle fatigue failure. In response, damping treatments such as viscoelastic layers, hard coatings, and particle dampers have been utilized to reduce vibration of integrally bladed rotors and promote longer service life. In recent experiments, nickel-based alloy 718 structural beams representative of turbine blades were manufactured via laser powder bed fusion (LPBF) with internal geometries containing unfused powder. Compared to fully fused beams, these beams with internal particle dampers have demonstrated a significant improvement in damping performance, suppressing vibrations by as much as 95%. However, the inherent damping of the particle dampers decreases as the strain amplitude increases when some of the unfused powder fuses to the walls of the pockets. This study investigates the effect of the location of the particle dampers within the beam on the sustainability of its damping performance. The LPBF nickel-based alloy 718 beams are subjected to successive resonance dwells with increasing strain amplitude. After each dwell, the damping performance is assessed via the half-power bandwidth method of the frequency response function. Results from this study indicate that while the location of the particle dampers within the specimen does influence when the damping begins to degrade, it is not the optimal parameter for damping sustainability. The aim of this and future work is to improve the long-term damping performance and viability of the internal particle damper so that it can be more effectively utilized to extend the lifetime of turbomachinery components.

Effect of Geo-Material on Dynamic Response of Tunnel Subjected to Surface Explosion

Prime materials involved in a problem such as underground structures are concrete, reinforcement steel, and geo-material surrounding the tunnel. Among these three materials, concrete and steel are manufactured materials and their properties can be controlled up to a certain extent. However, geo-material is a naturally occurring material whose constitutive properties vary from region to region, making it highly unpredictable. Findings from one study cannot be applied to other geotechnical problems directly, especially in the case of tunnels subjected to surface explosions. The blast wave generated has to travel through the geo-material before it interacts with the tunnel. As the shock wave propagates radially, its characteristics are likely to be altered by the geo-material. Limited study has been carried out considering this problem. In the present study, the effect of various types of geo-material on the blast response of tunnels subjected to surface explosions is investigated. Finite element analysis has been carried out using LS-DYNA®, wherein the problem has been modeled using the multi-material arbitrary Lagrangian–Eulerian (MM-ALE) method. Materials with fluid behavior such as air, explosives, and soil are modeled using ALE formulation. Other materials including tunnel lining, reinforcement steel, and rock are modeled using Lagrangian formulation. Blast loading is simulated using the Jones–Wilkins–Lee (JWL) equation of state. Geo-materials considered for the comparative study are sandy loam, saturated clayey soil, sandstone, and granite. Vertical displacement measured at the crown of the tunnel is used to determine the response of the tunnel. Sandy loam soil, being a highly compressible soil, exhibits non-linear and fluid-like behavior under high-strain loading such as explosions. Tunnels undergo extreme deformation in the case of sandy loam soil and clayey soil compared to rock cases. Further, the effect of saturation in sandy loam on tunnel stability is studied. It is observed that with the increase in saturation of soil, more blast energy is transmitted to the structure, which results in higher deformation. Lastly, the effect of the weathering of rock on the tunnel’s response is investigated in the case of sandstone and granite. It was observed that weathering in rock led to more displacement of tunnel crown when compared to intact rock.

Static and Impact Response of a Single-Span Stone Masonry Arch

Unreinforced masonry structures are susceptible to man-made hazards such as impact and blast loading. However, the literature on this subject mainly focuses on masonry wall behavior, and there is a knowledge gap about the behavior of masonry arches under high-strain loading. In this context, this research aims to investigate both quasistatic and impact response of a dry-joint stone masonry arch using the discrete element method. Rigid blocks with noncohesive joint models are adopted to simulate dry-joint assemblages. First, the employed modeling strategy is validated utilizing the available experimental findings, and then sensitivity analyses are performed for both static and impact loading, considering the effect of joint friction angle, contact stiffness, and damping parameters. The outcomes of this research strengthen the existing knowledge in the literature regarding the computational modeling of masonry structures that are subjected to usual and extreme loading conditions. The results highlight that applied discontinuum-based numerical models are more sensitive to stiffness parameters in high-strain loading than static analysis.

Evaluation of a low-cost approach to 2-D digital image correlation vs. a commercial stereo-DIC system in Brazilian testing of soil specimens

Due to their cost, high-end commercial 3D-DIC (digital image correlation) systems are still inaccessible for many laboratories or small factories interested in lab testing materials. These professional systems can provide reliable and rapid full-field measurements that are essential in some laboratory tests with high-strain rate events or high dynamic loading. However, in many stress-controlled experiments, such as the Brazilian tensile strength (BTS) test of compacted soils, samples are usually large and fail within a timeframe of several minutes. In those cases, alternative low-cost methods could be successfully used instead of commercial systems. This paper proposes a methodology to apply 2D-DIC techniques using consumer-grade cameras and the open-source image processing software DICe (Sandia National Lab) for monitoring the standardized BTS test. Unlike most previous studies that theoretically estimate systematic errors or use local measures from strain gauges for accuracy assessment, we propose a contrast methodology with independent full-field measures. The displacement fields obtained with the low-cost system are benchmarked with the professional stereo-DIC system Aramis-3D (GOM GmbH) in four BTS experiments using compacted soil specimens. Both approaches proved to be valid tools for obtaining full-field measurements and showing the sequence of crack initiation, propagation and termination in the BTS, constituting reliable alternatives to traditional strain gauges. Mean deviations obtained between the low-cost 2D-DIC approach and Aramis-3D in measuring in-plane components were 0.08 mm in the perpendicular direction of loading (ΔX) and 0.06 mm in the loading direction (ΔY). The proposed low-cost approach implies considerable savings compared to commercial systems.

Effect of Weather Aging on Viscoelasticity and Fatigue Performance of Asphalt Mastic.

The long-term effect of climate factors, such as sunlight, oxygen, and water, leads to the performance degradation of the asphalt mastic, which is the binding part in the asphalt mixture. It is not conducive to satisfy the long-term performance requirements of long-life asphalt pavement. In this study, five kinds of base asphalt mastic and styrene-butadiene-styrene (SBS) modified asphalt mastic were prepared with the filler-asphalt ratio of 0.6, 0.8, 1.0, 1.2, and 1.4. The indoor simulated weather aging tests were carried out considering multi-factors including sunlight, oxygen, and water. The master curves of the complex shear modulus and phase angle of the asphalt mastic with different aging degrees were obtained by the frequency sweep test. The curves of fatigue damage characteristics and fatigue life were fitted based on the viscoelastic continuum damage (VECD) model. The influence of weather aging on the viscoelasticity and fatigue performance of asphalt mastic were analyzed. Results indicated that the effect of weather aging increases the elastic component and decreases the viscous component. The fatigue performance of SBS modified asphalt mastic was better than that of base asphalt mastic. As the aging degree deepens, the brittle failure characteristics of asphalt mastic with a higher filler–asphalt ratio were more obvious. The base asphalt mastic becomes more sensitive to the strain level due to weather aging, and its fatigue life increased under the low strain loading and decreased under the high strain loading. The fatigue performance of SBS modified asphalt mastic was less sensitive to the strain level. The fatigue life reduced after aging under low and high strain load. Taking the impact of weather aging on the fatigue performance into consideration, the optimal filler–asphalt ratios of the base asphalt mastic SBS modified asphalt mastic are 1.0 and 1.2, respectively.

Shear driven deformation and damage mechanisms in High-performance carbon Fibre-reinforced thermoplastic and toughened thermoset composites subjected to high strain loading

High strain loading response of high-performance aerospace grade polyether-ether-ketone (PEEK) and toughened epoxy carbon fibre-reinforced composites has been investigated in pre-impregnated laminates having identical carbon fibre volume fraction, i.e. nearly 65%. Tensile cyclic loading tests have been carried out on the laminates with [±45°]8S stacking sequence, in order to characterise inelastic (plasticity) parameters for the two laminates progressively up to high strains (up to 11% strains), in correlation with the fibre and matrix micro-scale deformation and damage characteristics. The most suitable processes to achieve ultimate mechanical performance were used for manufacturing of the laminates. It has been observed that the PEEK composite exhibits higher mechanical performance at high strains under cyclic loads compared to epoxy composites (150% ultimate failure strain, 380% strain hardening and 200% ultimate failure stress) due to having superior micro-scale shear deformation in PEEK attributed to interfacial strength of fibre–matrix prior to the ultimate failure, as opposed to extensive micro-cracking, coalescence and fibre–matrix debonding in the epoxy composite.

Damage mechanics based failure prediction for structures under seismic action

Abstract In this paper, a damage mechanics based failure criterion for seismic resistant structures is presented. The utilised innovative damage model serves to predict ductile material failure in terms of crack initiation and is suitable for cyclic high strain loading scenarios with all kind of stress states e.g. normal, shear or combined. An extensive testing program served to validate the new approach by conducting detailed 3D numerical simulations of experimental tests using solid elements. Reference moment resisting frame buildings have been designed and analysed dynamically to derive deformation time histories of the dissipative elements in the structure. The most critical elements of the reference structures have been identified by a fatigue analysis based on numerically established φ-N-curves. Finally, exemplary upper shelf toughness requirements of the most crucial structural parts have been determined depending on behaviour factor and seismic intensity. These toughness requirements refer to common C harpy impact toughness values.