High Strain Rate Effects Research Articles

Experimental study on bond behaviour between recycled aggregate concrete and basalt fibre-reinforced polymer bars under different strain rates

Concrete structures are constantly subjected to both static and dynamic loads. Hence, this study mainly focused on the strain rate effect on the bond behaviour between reinforced recycled aggregate concrete (RAC) and basalt fibre-reinforced polymer (BFRP) bars. Pull-out tests were conducted to investigate the bond performance between RAC and BFRP bars. The strain rates which indicate the static, earthquake, and impact loads were considered to investigate the strain rate effect on the bond behaviour. The bond mechanism was analysed according to the bond interface damage and bond stress–slip relationship. Furthermore, the bond stiffness, bond strength, and bond slip were examined. It is found that BFRP bars with different surface shapes induced different bond mechanisms. Although the high strain rate effect improved the bond behaviour, it changed the bond mechanism. Dynamic influence factors reflecting the strain rate effect were developed, and the corresponding formulae were proposed. It was confirmed that the proposed formulae can accurately predict the bond behaviour under different strain rates. Finally, a theoretical model that can simulate the dynamic bond behaviour between concrete and BFRP bars was proposed. The achievements of this study can provide reference for the dynamic bond design of BFRP bar-reinforced RAC structures.

A review on the influences of high speed impact surface treatments on mechanical properties and microstructures of metallic materials

The strain rate during the process of high speed impact surface treatments has a significant effect on the mechanical properties as well as the microstructures of metallic materials. In this paper, the effects of strain rate during the process of high speed impact surface treatments on the variation of both strength and ductility of metallic materials are reviewed from macroscopic and microscopic prospective based on the current research achievements. The emphases are concentrated on the microstructural evolution under various strain rates, including grain structures, adiabatic shear bands, phases, dislocation structures, precipitates and deformation twins. At relatively low strain rates, grains tend to be elongated with respect to the loading direction, and they may be refined when the strain increases to a certain extent. In comparison, with the increment of strain rates, the free path of dislocation motion is remarkably reduced so that grains can be further refined to consume the impact energy and dislocations are multiplied significantly. However, the relatively high strain rates may also bring about adiabatic temperature rise and frictional heat, which may give rise to dynamic recovery and recrystallization in some materials so that the dislocation density would in turn be reduced. Moreover, precipitates can be formed and they may interact with dislocations owing to the combined effects of high strain rates and temperature rise. When the strain rates increase to the extremely high level, the movement of dislocations may be inhibited and deformation twins can be triggered to coordinate the deformation. As a result, the strain rate effects are complicated phenomena which comprehensively affect the microstructural strengthening and softening effects. Based on these, the influences of both microstructural evolution and the transition of microscopic deformation mechanisms with strain rates on the enhancement and deterioration of mechanical properties are analyzed. Finally, the characteristics of deformation mechanisms of the gradient microstructures derived from high velocity impact surface treatments are concluded. Furthermore, a comprehensive model embodying the influences of different microstructures is proposed, which can provide a foundation for the further researches of strain rate effects.

Crushing response of Composite Metallic Foams: Density and High Strain Rate effects

The emerging demand for lightweight materials has had an impact in several industries, including biomedical, marine, and space forum applications wherein weight-reduction, impact energy, vibration and noise absorption are mandatory. In this paper, the crushing response of newly developed composite metallic foams (CMFs) with different relative densities (0.289, 0.293, 0.307 and 0.312) were experimentally investigated. As reinforcement, 10 wt% silicon carbide (SiC) particles (size: 20–40 µm) were used, while the foam behavior consisted of microstructure characterization, uniaxial compression tests and statistical analysis. The compressive properties of CMFs were determined using a Split Hopkinson Pressure Bar apparatus over a strain-rates range of 520–1560 s−1. It was found that the strength properties and energy absorption performance of the manufactured foams are strongly affected by the above-mentioned factors. However, the Analysis of Variance technique showed that the most contributing factor is the strain rate (89.10%), followed in order by the relative density (5.90%) and microstructure (3.10%).

Probabilistic framework for failure investigation of reinforced concrete wall panel under dynamic blast loads

Over the last decade, excessive devastations caused by extreme events, such as blast loading have raised significant concern on the performance of civil structural systems. Despite realizing the importance of inherent risk associated with this phenomenon, most of the studies neglected the effects of uncertainties associated with the system, wherein the design approaches have been entirely on deterministic scale. Hence, it is deemed important to identify the complexities in the system, and in this regard, a probabilistic framework is proposed which utilizes the effects of uncertainties in the system to compute the failure probabilities of a reinforced concrete (RC) structural member under extreme blast loading. The structural member adopted here is a three-dimensional (3-D) RC wall panel, which is modeled considering material and geometric nonlinearity, and the subsequent analysis is carried out under surface-burst and free airburst scenarios. High strain rate effect induced in the RC wall is modeled using available standard dynamic increase factors (DIFs) for concrete and steel. Uncertainty in the system is assumed in material capacity (strength), mechanical loads, and dynamic blast loads considering a certain mean and standard deviation. Responses are obtained in terms of deflection, stresses, and strains at center of the wall. Limit state of failure and the respective threshold limiting values are obtained from the United States Department of Defense manual, PDC-TR 06-08 (2008). Finally, first-order sensitivity analysis is conducted to show the extent of uncertainties in input parameters affecting the output response quantities. It is concluded that the uncertainty induced in the system has significant influence in the response of the wall panels under blast loading scenarios. Moreover, based on the sensitivity analysis performed, charge weight, standoff distance, and strength of concrete material are suggested to be crucial parameters for design of blast-resistant structures. To conclude, based on the currently considered scenario of intensity of blast, exposure type, and performance level required by the user, it is recommended to use wall panels of sizes more than 100 mm in civil structures, especially 125 mm to counter the effects of extreme blast loadings.

Dynamic mechanical response and a constitutive model of 42CrMo steel that incorporates the effects of high strain rates

<p indent=0mm>To study the dynamic mechanical properties and constitutive relationship of 42CrMo steel, which is primarily used in high-speed train axles, a dynamic compression test and a metallographic observation were conducted. The material exhibited strong strain-rate dependence, and the adiabatic shear behavior under dynamic loadings was found to be the dominant cause of the different mechanical properties resulting from different strain rates. The thermal activation theory, which separately considers the thermal and athermal stresses to explain the deformation mechanism, was employed to obtain the descriptions of the strain-rate effects. Accordingly, a physically based constitutive model was proposed that incorporated the effects of the high strain rates. A criterion for adiabatic shear, which was coupled to the model, was proposed to determine the onset of instability. The model was confirmed to sufficiently describe the quasi-static and dynamic mechanical behavior of the 42CrMo steel, especially the effects of strain hardening and strain rates on the yield stress.

Numerical study of the ultrasonic impact on additive manufactured parts

A hybrid fabrication method combining additive manufacturing (AM) and ultrasonic impact treatment (UIT) techniques was developed to improve the microstructure and mechanical properties of additive manufactured metal parts. Experimental and numerical methods were conducted to analyze the stress and strain fields of ultrasonic impact on additive manufactured parts. Laser metal deposition (LMD) technique was applied to prepare the 304 stainless steel (SS) samples and then the samples were post-treated by UIT. Considering high strain rate effect of metallic materials in the UIT process, the dynamic hardening properties of the as-deposited 304 SS sample were experimentally measured using a split Hopkinson pressure bar (SHPB) technique. The strain rate controlling factors and stress-strain relationship of the as-deposited sample in the SHPB tests were theoretically analyzed. The dynamic and high transient impact-rebound-impact process of UIT including the pin velocity, stress field and plastic strain field were investigated numerically via a three-dimensional finite element model. The impact stress field parameters such as the magnitudes and directions of principal stress and principal shear stress were investigated to further analyze the plastic deformation behavior of the deposited sample. The experimental results of plastic deformation zone obtained from optical microscopy, electron backscatter diffraction (EBSD) and microhardness testing are in good agreement with the numerical results. Both the experimental and numerical results confirm that UIT can effectively improve the performance of additive manufactured metal parts.

High Strain Rate Effect on Tensile and Compressive Property of Carbon Fiber Reinforced Composites

With high strength and stiffness-to-weight ratios, Carbon-Fiber-Reinforced Polymer (CFRP) composite has been applied to the separation device of the rocket by shaped charge jet. But dynamic tensile and compressive properties of CFRP under high rate strain are still unclear. In the article, tensile testing along transverse direction are conducted. The quasi-static tests (10-3 s-1) use a universal testing machine and high dynamic loadings of 800 s-1 and 1600 s-1 tests adopt a high-speed tensile testing machine. Meanwhile, dynamic compressive tests of unidirectional and cross-ply laminated specimen under the thickness direction loading are implemented by a Split Hopkinson Pressure Bar (SHPB) from dynamic loading 500 s-1 to 2500 s-1. Test results show that compared with static tests data, both transverse tensile modulus and strength of CFRP composites materials at dynamic loadings are sensitive to tensile tests. The compressive peak stress and stiffness of specimens also have an increasing tendency with the increases of the strain rate. Furthermore, for failure mode of tensile specimens, the crack propagation of the specimen fracture is along the interface of the fiber/matrix under all loading conditions. The failure modes of compressive specimens are different as the strain rate changes. The higher the strain rate, the more severe the crushing.

Activated slip and twin systems in electron beam melted Ti-6Al-4V subjected to elevated and high strain rate dynamic deformations

This study presents an investigation on the effect of elevated (700 s−1) and high strain rate (2100 s−1) on the dynamic mechanical properties and deformation mechanisms of electron beam melted (EBM) Ti-6Al-4V cylindrical rod printed in the horizontal orientation. Optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques were utilized to characterize the microstructural and texture evolution. The typical microstructure consists of transformed α+β phase, grain boundary-α (αGB) along prior β-grain boundaries that are near-parallel to the build direction. Dynamic impact tests were conducted at room temperature using a Split-Hopkinson pressure bar (SHPB) apparatus, where the build direction is perpendicular to the impact loading. The dynamic mechanical properties of the sample deformed at the strain rate of 2100 s−1 exhibited higher compressive strength (~250 MPa) and total strain (~13%) that of the sample deformed at the strain rate of 700 s−1. Compared to the as-built sample, deformed samples exhibited finer microstructure, lesser α-interlamellar spacing, and higher α-lamella's fragmentation with the increase in the strain rate. EBSD Schmid factor distribution maps were used to discuss the effect of the initial texture and the strain rate on the deformation mechanisms' possible changes.

Composites in extreme environments: Effects of high strain rate, humidity and temperature

Multifunctionality, lightweight and resistance to corrosion are some of the several advantages that fibre composites display with respect to other materials across a wide range of applications. In aerospace and marine industry, however, we can encounter challenges arising from certain working conditions that can significantly affect the mechanical response and integrity of composite structures. First, humidity or water exposure can induce reduction of the material strength and stiffness. Second, hot or cold temperatures that change the level of ductility in the composite. Finally, dynamics loads that may appear during service require strain rate sensitive properties to be considered. In this work, we show experimental capabilities and methodologies developed to account for all those three effects: rapidly applied loads (impact), humidity and temperatures from -55°C to 93°C. This understanding sets the basis for the development of advanced models to design better structures.

Numerical Methodology for Aerostructures Hail Impact Damage Prediction

The two numerical approaches for modelling of soft-body impact in Abaqus/Explicit have been applied in this work for prediction of high-velocity hail impact damage in aeronautical structures. The applied methods are the CEL (Coupled Eulerian Lagrangian) and SPH (Smoothed Particle Hydrodynamics), while the impacted structure is a metallic slat structure. Comparison of the CEL and SPH methods has been performed by impact simulations at a rigid plate, aimed to validate the applied material model, and by simulation of the slat structure impact. Two material models have been applied to study the effect of high strain-rates at the damage process in the metallic structure. The first is the standard isotropic plasticity model that defines material failure based on the value of equivalent plastic strain. The second constitutive model in the analyses is the Johnson-Cook model that includes the effects of strain rate and temperature on the material failure process. The simulations have been stable, illustrating the robustness of Abaqus/Explicit in these highly nonlinear impact cases. Compared to the CEL, the SPH method is computationally more efficient.

High strain-rate effects from blast loads on laminated glass: An experimental investigation of the post-fracture bending moment capacity based on time–temperature mapping of interlayer yield stress

To enhance the resilience of buildings, laminated glass panels are increasingly used in glazed façades. These ductile panels provide a superior blast resistance to that provided by monolithic glass panels, due to the improved residual capacity offered by the polymer interlayer following the fracture of the glass layers. The complex interaction between the attached glass fragments and the interlayer is still only partially understood. To help address this, this paper investigates experimentally the post-fracture bending moment capacity of laminated glass. Three-point bending tests are performed at low temperature on specimens pre-fractured before testing, to ensure controlled and repeatable fracture patterns. The low temperature simulates the effects of the high strain-rates that result from short-duration blast loads by taking advantage of the time–temperature dependency of the viscoelastic interlayer. In these experiments, polyvinyl butyral is considered as the interlayer, this being the most common interlayer for laminated glass used in building facades. A new time–temperature mapping equation is derived from experimental results available in the literature, to relate the temperatures and strain-rates that result in the same interlayer yield stress. The results of the low-temperature tests demonstrate an enhancement of the ultimate load capacity of the fractured glass by two orders of magnitude, compared to that at room temperature. This suggests an improved post-fracture bending moment capacity associated with the now stiffer interlayer working in tension and the glass fragments working in compression. Due to the time–temperature dependency of the interlayer, a similar enhancement is therefore anticipated at the high strain-rates associated with typical blast loading. Finally, the assumed composite bending action is further supported by the results from additional specimens with thicker PVB and glass layers, which result in enhanced capacity consistent with the bending theory of existing analytical models.

Effect of high strain rate on shear properties of carbon fiber reinforced composites

With the Carbon Fiber Reinforced Polymer (CFRP) composites widely applied in the aerospace engineering field, it is necessary to get proper understanding of shear mechanical properties under dynamic loading. Taking the experimental method, this paper studied the in-plane and interlaminar shear properties of composites using a high-speed tensile test machine at high strain rate loading. Meanwhile, quasi-static tests were carried out with a universal test machine as contrast. Digital Image Correlation (DIC) method and high-speed camera were adopted to obtain the strains and the failure process of the specimen. This paper also designed a new method on interlaminar shear tests, with the experimental design, data processing and result analysis presented. The test results show that the strain rate sensitivity of the in-plane shear properties is greater than that of the interlaminar shear properties. The empirical formulas of high strain rate effects of CFRP materials were also derived for strength and modulus prediction and furtherly instruct the development of constitutive equations at various strain rates. In addition, this paper analyzed and discussed the failure mode of specimens, and the multiple-ply cracking, fiber pulling out and delamination in the V-shaped fracture has been shown in the in-plane shear tests while the typical mode II shear failure occurred in the interlaminar tests from strain rate range of 0.001–1500 s−1.

Optimization on the Johnson-Cook parameters of Ti-6Al-4V used for high speed cutting simulation

The Johnson-Cook (J-C) parameters obtained from the conventional mechanical tests are usually adopted directly for the high-speed cutting simulations. However, the conventional J-C parameters can not describe the exact plastic deformation under the coupling effect of large strain and high strain rate occurred in high speed cutting. In this paper, the response surface approximation method was used to optimize the Ti-6Al-4V’s J-C parameters for high speed cutting simulation, and the experimental results obtained from our previous work were further adopted to validate the optimized parameters. The simulated chip size error obtained at the cutting speed of 15 m/s could reduce from 16% with using the conventional J-C parameters to 8% with using the optimized J-C parameters. Furthermore, the simulated chip morphologies achieved based on the optimized J-C parameters were compared with the experimental results with cutting speed ranging from 0.05 m/s to 86.5 m/s. The results show that the simulated chip morphologies could give good agreements with the experimental results, and the chip morphology transitions can be well predicted with using the optimized J-C parameters.

Piecewise strength model for three types of ultra-soft fine-grained soils

Problems of ultra-soft soils, with the characteristics of high water content and very low strength, have been gradually distinguished from those of typical soft soils in recent years to address the new requirements of ocean geotechnical engineering, such as the improvement of dredged fills and hazard assessment of submarine landslides. Focusing on effects of high water content and different shear strain rates on the undrained shear strength of ultra-soft soils, a series of experimental investigations were conducted, using a combination test method, on three types of fine-grained soils with different grain size distributions: kaolin soil, Bohai Sea soil, and South China Sea soil. After preparing ultra-soft soil samples with high water content two to three times the liquid limit, the relationship between the strength and the water content of the soil was analyzed. Then, the changing trend of strength with shear strain rates in a broader range of 0.001–20 s−1 was discussed. Based on the test results and theory of shear thinning behavior, a piecewise model for the ultra-soft soil strength was proposed. The piecewise strength model can adequately reflect the strength characteristics of ultra-soft soils at different shear strain rate ranges, and the parameters in the model can be measured, or simply estimated.

Crustal Thermal Structure and Exhumation Rates in the Southern Alps Near the Central Alpine Fault, New Zealand

AbstractWe investigate orogenic uplift rates and the thermal structure of the crust in the hanging wall of the Alpine Fault, New Zealand, using the hypocenters of 7,719 earthquakes that occurred in the central Southern Alps between late 2008 and early 2017, and previously published thermochronological data. We assume that the base of the seismogenic zone corresponds to a brittle‐ductile transition at some fixed temperature, which we estimate by fitting the combined thermochronological data and distribution of seismicity using a multi‐1‐D approach. We find that exhumation rates vary from 1 to 8 mm/yr, with maximum values observed in the area of highest topography near Aoraki/Mount Cook, a finding consistent with previous geologic and geodetic analyses. We estimate the temperature of the brittle‐ductile transition beneath the Southern Alps to be 410–430°C, which is higher than expected for Alpine Fault rocks whose bulk lithology is likely dominated by quartz. The high estimated temperatures at the base of the seismogenic zone likely reflect the unmodeled effects of high fluid pressures or strain rates.

Coupling effect of strain rate and temperature on tensile damage mechanism of polyphenylene sulfide reinforced by glass fiber (PPS/GF30)

Influence of loading temperature on the damage mechanism of polyphenylene sulfide (PPS) reinforced by glass fiber (PPS/GF30) under tension was experimentally studied from quasi-static (QS) to high strain rates. Two kinds of PPS/GF30 samples were prepared: PPS-0° and PPS-90° (correspond to fibers oriented parallel and perpendicular to the injection direction, respectively). After microscopic observation and thermomechanical characterizations by dynamic mechanical analysis, tensile tests up to failure with strain rates varying from 10−3 s−1 to 100 s−1 have been carried out at 25°C and 120°C with regard to PPS/GF30 glass transition temperature. To achieve the coupling effect of high strain rate and high temperature, a special chamber was designed to install on the servo-hydraulic machine. The results of QS tensile tests confirm the significant effect of fiber orientation and temperature on the Young’s modulus, the ultimate stress, and strain. High strain tensile test results showed that the PPS/GF30 composite is strain rate dependent at both temperatures. The results indicated that Young’s modulus remains constant by strain rate increasing at both temperatures while ultimate stress and strain are increased. No significant damage has been observed at 25°C in QS loading, whereas the macroscopic damage variable is increased to 20% at 120°C. Debonding at the fiber–matrix interface is the main damage mechanism at 120°C.

Effect of high strain rates and temperature on the micromechanical properties of 3D-printed polymer structures made by two-photon lithography

Two-photon lithography (TPL) enables the fabrication of metamaterials exhibiting unprecedented mechanical performance. Such lattice structures consist of micron-scale geometric features and are designed to achieve their envisioned properties through stretching and bending of individual trusses. Here, we present for the first time a comprehensive study of the effect of temperature and strain rate on the mechanical properties of micron-sized 3D printed polymers made by TPL using Nanoscribe’s negative tone photoresist IP-Dip. A strong strain rate dependency was identified for the yield strength, which increased fourfold in compression from 68 MPa to 230 MPa as the strain rate was raised from 7e−4 s−1 to 600 s−1. This trend was also seen in tension. The elastic modulus was found to increase with strain rate in the quasistatic regime but was constant at 3.2 GPa for strain rates of 0.7 s−1 and above. Even slightly elevated temperatures of 80°C led to a significant drop in the yield strength and elastic modulus, though the observed reduction was less severe at higher strain rates. Further, a model based on the strain rate-temperature superposition principle is reported that allows the extrapolation of the mechanical properties even beyond the conditions tested here.

Water saturation effects on dynamic behavior and microstructure damage of sandstone: Phenomena and mechanisms

Underground rock structures are frequently subjected to water erosion and dynamic disturbance simultaneously. Herein, in order to study the coupled effects of water and high strain rate on the mechanical behavior and microstructures of sandstone, we conducted a series of dynamic unconfined compressive tests on oven-dried and water-saturated sandstone core samples using a split Hopkinson pressure bar. Test results revealed that, three macroscopic final patterns, namely unbroken, axial split and pulverization, were observed. At given strain rates, the presence of water weakens the dynamic peak stress and the dissipated energy density (the ratio of energy dissipation to residual axial strain) of rock sample but enhances the elastic modulus regardless of the failure pattern. Additionally, the saturated sample owns a higher rate dependence of dynamic strength compared to the dry one under the explored range of strain rate (43.9–156.7 s−1), which indicates that water-weakening on rock strength gradually attenuates with the increase of strain rate. Interestingly, thin sections analysis microscopically showed that the failure of dry samples is characterized by the intra-granular fracturing in larger quartz grains while that of saturated samples by the inter-granular fracturing. The underlying mechanisms were interpreted with two micro-mechanical damage models.

High strain rate and low temperature effects on the compressive behaviour of concrete

Temperature and strain rate are important factors when considering the mechanical properties of engineering materials, as they can greatly influence the material behaviour. The research presented here is an experimental investigation to determine the effects of low temperatures and high strain rates on the compressive behaviour of concrete. The primary purpose of the research is the development of experimental stress–strain relationships under these conditions, as this is a largely unexplored research topic. Thirty-five 101.6 mm × 203.2 mm concrete cylinders were tested in uniaxial compression at the University of New Brunswick. The specimens were loaded either under static conditions or dynamically with an average strain rate of approximately 1 s−1, while being exposed to temperatures from 20°C to −70°C to simulate extreme climatic temperature and those attainable within industrial storage facilities. The compression strain of the specimens was obtained using digital image correlation. The mechanical properties studied were the compressive strength, strain associated with the peak stress and general stress–strain behaviour due to the increased strain rate and temperature variations.

On the importance of the bullet jacket during the penetration process: Reversed-ballistic experimental and numerical study

The behaviour of exposed and copper-jacketed 12.7 mm En8 steel cores impacting against 5 and 9 mm Armox Advance plates was investigated to determine the significance of the jacket during the penetration. The target plates were accelerated into stationary projectiles (a reversed-ballistic configuration) and the impact was monitored using a multichannel flash X-ray system to gain insight into the interaction of the core target. Numerical simulations were also carried out to compare result with the experimental testing. Explicit numerical software LS-DYNA was used to model the behaviour of the target and the projectile during the impact collision. Fragments of the core and target plate were collected post-shot for analysis. A similar penetration behaviour was observed for both plates, although the post-shot core was shorter after impacting against the 9 mm plate, consistent with enhanced erosion behaviour. The copper jacket protected the core, resulting in greater surface defeat and dwell compared to the unjacketed core. Numerical studies agreed on the cases of projectile impacting the 5 mm and 9 mm target. However, the target fracture cannot be captured. This could be caused by the input of material data and strain rate parameter modelling in LS-DYNA was limited, while the impact phenomenon was high velocity impact that the material exhibits a highstrain rate effect. Overall, the ductile jacket appeared to serve two functions: (1) Absorbing reflected energy during impact, hence cushioning the impact and thereby preserving the core, and (2) constraining or confining the core. In this study, the steel core design and copper jacket has a more complex geometry compared to the simplified steel core designs often applied in several earlier ballistic studies. The captured flash X-rays revealed significantly less erosion in the jacketed cores, agreeing with the post-impact core length measurements.