High-speed Tensile Tests Research Articles

Fatigue life assessment of thermite welded rails based on laboratory tests and field measurement data

This in-depth study assesses the fatigue life of thermite-welded 60E1 rails by combining fatigue experimental tests with field measurement data. Material characterization, conducted using X-ray Diffraction (XRD), X-ray Fluorescence (XRF), and Scanning Electron Microscopy (SEM), aimed to understand the fatigue behavior of these materials. The research was particularly focused on high-speed rail lines in South Korea, targeting areas with influence of track condition to collect strain data. By combining dynamic modulus calculations from high-speed tensile tests with the rain flow counting method for determining wheel loads, and employing the Linear Cumulative Damage method for estimating rail fatigue life, this study provides novel insights into the maintenance and durability of thermite welded rails. The integration of detailed laboratory experiments with field stress data offers a significant contribution to the predictive maintenance and lifecycle management of high-speed railway infrastructure.

Effect of tensile speeds on mechanical properties of Young’s modulus and Poisson’s ratio of 3D-printed ABS-like specimens

Abstract Additive manufacturing (AM) is a well-known method of 3D printers. The AM method forms components by laminating thin layers. Therefore, this method can make prototypes of parts and does not involve any tooling or human interference. However, the mechanical parts made by the AM method have unique problems. In particular, the effect of the strain rate on the mechanical property of Young’s modulus and Poisson’s ratio has not been studied in detail. Therefore, we investigated the effect of strain rates on 3D-printed ABS-like specimens in this study. In order to investigate the effect of tensile speed on 3D-printed ABS-like specimens, tensile tests were conducted at 0.2 mm/min, 2 mm/min, 60 mm/min, 800 mm/min, and 1000 mm/min. We obtained the experimental results that Young’s modulus increased with increasing tensile speed. Also, the specimen broke at multiple points in high-speed tensile tests. Poisson’s ratio values for all tensile speeds were almost constant around 0.38.

Dynamic mechanical properties and constitutive model establishment of QSTE420 steel

The uniaxial tensile tests of QSTE420 steel under different strain rates were carried out using an electronic universal material testing machine, a high-speed tensile testing machine and a split Hopkinson tension bar (SHTB) device, the engineering stress-strain curves of steel within the range of 0.001– 1000 s−1 were obtained and the mechanical properties of steel at different strain rates were analyzed. The results show that in the static strain rate range of 10−3– 10−2 s−1, the yield strength and tensile strength of QSTE420 steel exhibit minimal variation, fluctuating between 430– 434 MPa and 507– 515 MPa, respectively; while the uniform elongation and elongation at break remain approximately at 12% and 35%, respectively. In the high strain rate range of 10−1– 103 s−1, both yield strength and tensile strength exhibit a consistent increase in direct correlation with the tensile rate. Specifically, the yield strength increases from 444 to 607 MPa and the tensile strength increases from 523 to 640 MPa as the strain rate escalates from 10−1 to 103 s−1. Moreover, the elongation at break demonstrates a general increasing trend and reaches its peak value of 45.65% at 100 s−1. The morphology of fracture surfaces under different strain rates are observed by Scanning Electron Microscopy (SEM). The fracture appearance analysis reveals numerous dimples in the fracture, indicating a ductile fracture. Furthermore, the comparison demonstrates that steel exhibits enhanced plasticity at a strain rate of 100 s−1. Based on the experimental results, the Johnson-Cook constitutive model was established and modified. The modified Johnson-Cook model exhibits a higher determination coefficient (R2) compared to the original version, signifying an improved fitting accuracy.

Dynamic tensile properties of carbon/glass hybrid fibre composites under intermediate strain rates via DIC and SEM technology

Carbon/glass hybrid fibre-reinforced plastic (C/GFRP) can effectively reduce product costs in manufacturing; however, its dynamic tensile properties remain unclear. In this study, the mechanical characteristics of C/GFRP and glass-fibre-reinforced plastic (GFRP) laminates were investigated using an HTM5020 high-speed tensile tester, digital image correlation (DIC), and scanning electron microscopy (SEM) at intermediate strain rates. Six strain rates (1, 10, 100, 250, 500 and 800 s−1) followed by three stacking sequences ([C2,G3,C2]s, [G3,C2,G3]s and [G8]s) were developed. The failure mechanism of C/GFRP under intermediate strain rates was identified using stress–strain curves, DIC sub-images, and macro/micro failure modes. Additionally, the variation laws for fracture strain, elastic modulus, and dynamic tensile strength of C/GFRP were examined. In response to an increase in strain rate, the strength and fracture strain of [C2,G3,C2]s increased by 36.6% and 142.9%. The elastic modulus [G3,C2,G3]s increased by 41.8%. Hybrid laminates are prone to interlaminar failure, resulting in lower strength and higher strain-rate sensitivity. Adding a carbon fibre-reinforced plastic layer effectively improves the stiffness of the laminates. A stiffness prediction formula for C/GFRP is proposed.

Mechanical properties and deformation behaviour of TWIP steel at different strain rates

The mechanical properties of TWIP at different strain rates ranging from 5 s−1 to 500 s−1 were investigated by a VHS 160/100-20 high-speed tensile testing machine. The Johnson-Cook (J-C) dynamic constitutive model of TWIP steel was established based on the test results and verified by numerical simulation. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to analyse the microstructures of TWIP steel before and after tensile deformation. The findings demonstrate that under the tested strain rate, both the tensile strength and yield strength of TWIP steel increase with increasing strain rate, whereas the elongation decreases first and then increases. The strain rate of 100 s−1 is the turning point of the mechanical properties. The stack fault energy (SFE) is 26 mJ m−2 at room temperature, and the microstructure of TWIP steel before and after deformation is composed of single austenite, which demonstrates that only TWIP effect occurs. Dislocations accumulate along grain boundaries, forming structures such as dislocation cells and dislocation walls, causing stress concentration and promoting the formation of microcracks. With increasing strain rate, the dislocation cells are more obvious, and the thickness of the deformation twins decreases, resulting in an increase in the stress required for dislocations to cross the twin boundaries and material strengthening. The formation of nanoscale twins can not only effectively hinder the dislocation motion, but also provide space for dislocation slip and change the grain orientation, so that the slip system which is not conducive to deformation has a new orientation, resulting in a synergistic effect on strength and plasticity of TWIP steel. This work elucidates the relationship between the microscopic deformation mechanism and the macroscopic mechanical properties of TWIP steel at a specific strain rate, and a dynamic constitutive model is established, which can provide a reference for the application of TWIP steel in the design of anti-explosion and anti-impact structures.

Multi-objective crashworthiness optimization of energy-absorbing box with gradient lattice structure

To improve the lightweight and crashworthiness of energy-absorbing box, an energy-absorbing box with spatial lattice structure and multi-objective optimization method are proposed. First, a novel single-cell structure is proposed, which is replicated and arranged to form the spatial lattice structure. Then, the mechanical properties of the material are tested by quasi-static and high-speed tensile tests. The finite element model of the spatial lattice structure is established, and the numerical results are verified by the drop weight impact test. Finally, four different types of approximate models are used to fit different responses, and the combination of approximate models with higher accuracy is obtained. And the multi-objective optimization of our model is carried out. The optimal design of our model is obtained based on the grey relational analysis coupling entropy weight method. Compared with the energy-absorbing box with initial lattice, the specific energy absorption of the optimal design of our model is increased from 6.23kJ/kg to 8.91kJ/kg, an increase of 43.0%, and the mass is reduced from 1.1kg to 0.798kg, a reduction of 27.4%. The results show that the optimal design of our model has the advantages of lightweight and energy absorption.

A high-accuracy dynamic constitutive relation of die-cast Alâ¿¿Si aluminium alloy

Die-cast Al–Si aluminium alloys are increasingly used in the lightweight design of automobiles; their mechanical properties under dynamic loading are crucial and thus must be investigated. The original Johnson–Cook (J–C) constitutive model does not accurately predict the mechanical properties of this alloy, which further affects the reliability of subsequent analysis and calculations. To improve the predictive accuracy of the constitutive model and investigate the dynamic mechanical properties of this alloy, high-speed tensile tests of die-casting aluminium alloy Al–10Si–yCu–xMn–zFe are conducted. The tests are executed at room temperature using a universal electrical testing machine and a high-velocity testing system in a wide strain rate range of 1–800 s−1. The tensile deformation behaviour of this alloy at various strain rates is investigated. The experiments show that the flow stress of the alloy gradually increases with strain and varies significantly with the strain rate. The J–C model is unsuitable for predicting the flow stress of this alloy owing to its unsatisfactory goodness-of-fit. To accurately predict the flow stress of die-cast Al–Si aluminium alloys, we propose a new model based on experiments. Unlike other models, the proposed model incorporates the critical strain and flow stress limit value, which allows the flow stress to be predicted more precisely at various strain rates over a wide strain range of 0–0.17. The experimental data of other die-cast Al–Si alloys validate our model. The goodness-of-fit of the proposed model for this alloy is higher than that of the J–C model, which demonstrates that our model outperforms existing models in terms of estimation accuracy.

Effects of low temperatures and high strain rates on the tensile properties of polyurethane polymers for adhesives

ABSTRACT The mechanical properties of polyurethane compounds were experimentally investigated by changing the composition of their components. Polyol components (polyoxypropylene glycol: PPG, polyoxytetramethylene glycol: PTMG, and polycarbonatediol: PCD) were mixed with monomeric methylene diphenyl diisocyanate to synthesize polyurethane pre-polymer, mixed with chain extenders (1,4’-butanediol: 1,4’-BD or dimethylthiotoluene diamine: DMTDA), and cured, to prepare four types of polyurethane resins. Tensile tests were conducted using a mechanical testing machine with a strain rate of approximately 0.3 s−1 and a hydraulic high-speed tensile testing machine with a strain rate of approximately 500 s−1. The temperature was controlled to be −40°C, −10°C, or 25°C. When PTMG was used as the polyol, the stress-strain relationship was less sensitive to temperatures and loading rates, and the material properties exhibited a relatively good balance between elongation and strength. Additionally, the use of 1,4’-BD as a chain extender resulted in higher elongation and lower strength than the use of DMTDA. Conversely, the stress-strain relationship was dramatically altered by the test conditions when PPG and PCD were used as the polyol and embrittlement under a combination of low temperature and high strain rate was confirmed. Furthermore, there were certain compositional combinations that exhibit necking at low temperatures.

Study on Defect Evolution of Steel Strip under High-speed Cold Rolling

In this paper the strain rate effect of the material was quantitatively tested by INSTRON tensile testing machine and Zwick/Roell HTM5020 high-speed tensile testing machine. The dimple size of the fracture surface of the tensile specimen was determined and analyzed by using the scanning electron microscope. Based on the Cowper-Symonds constitutive model, the parameters in the dynamic constitutive model and the true stress-strain curve under quasi-static condition were obtained by combining the results of quasi-static and dynamic tensile tests and the finite element numerical analyses. Considering the strain rate effect of the material the effects of cold rolling speed on the evolution of different types of defects were analyzed by the ANSYS/LS-DYNA dynamics code. The results show that with the increasing of crack length and decreasing of crack width, the critical rolling speed decreases. But if the crack length is less than 5 mm and the aspect ratio of crack length to crack width is larger than 5, the critical rolling speed of crack growth can be much large.

High-speed tensile tests on high-manganese steel at low temperatures

Abstract Particularly in the automotive industry and the sector of liquid–gas storage, austenitic steels with a high energy absorption capacity are used. The light metals frequently used do not meet all requirements. Therefore, especially for components involved in crash situations, the cost-effective alternative with outstanding properties is used. In this respect, the high-manganese TWIP steels are of great interest, specifically due to their strength and ductility. Also in other research areas, the high-strength steels are moving into the focus of attention. For example, the properties of welded high-manganese steels at low temperature applications, such as those encountered during storage and transport of liquefied gases, are to be investigated. For this purpose, high-speed tensile tests are used to experimentally determine how the material behaves at different low temperatures and high strain rates. The investigations carried out provide results that can be used to draw conclusions about the strain rate and temperature dependence of the mechanical characteristics. These dependencies are shown as well.

Determination of strain rate dependence at intermediate strain rates using acceleration information

Precise stress-strain characteristics of materials for intermediate strain rates need to be utilized for analyzing various events in industry such as metal forging, sheet metal forming in manufacturing processes and automotive crash tests. However, the accurate evaluation of the load is not easy at intermediate or high strain rates, owing to the inertial effect. The present study aims at characterizing the hardening behavior using acceleration data without utilizing the load information with an application to a dual-phase DP980 steel sheet sample. Virtual measurements were obtained from a finite element model to check for the minimum acceleration magnitude necessary for stable identification. The same identification procedure as that used for the experiments was adopted. Also, a high-speed tensile testing equipment for steel sheet specimens was modified to increase the acceleration magnitude to implement the proposed methodology experimentally. The virtual fields method was chosen as an inverse tool to determine the strain-rate dependence of the sheet metal specimens. The stress–strain curve of an advanced high-strength steel at intermediate strain rates obtained from the acceleration was compared with the curve from the load data, and promising results were obtained.

Research on Dynamic Nonlinearity of Materials Based on Tensile Test

The collision impact process of a structure is a complex nonlinear dynamic response process, and the key factor to ensure the accuracy of the calculation results when calculating the simulation collision problem is the definition of the dynamic nonlinear parameters of the material during the simulation analysis, and there is no uniform treatment for the collision impact problem. Based on Q235 steel, quasi-static tensile and high-speed tensile tests were carried out, and the material parameters were calibrated to meet the requirements of the collision simulation calculation based on the test data, considering the material strain rate sensitivity and material hardening properties. The research results can be used as a reference for the simulation of large structure impact problems.

Mechanical characteristics and ballistic behaviors of high strength and hardness armor steels

Armor steel has huge prospective applications in the design of military equipment against the high-speed impact of projectiles due to its high strength, hardness, ductility, etc. This study aims to assess the mechanical characteristics and ballistic behaviors of newly developed NP450 and NP510 armor steels with high strength and hardness based on systematic test and numerical simulations. Firstly, a series of basic mechanical tests, i.e., quasi-static tensile test under room (25 °C) and elevated temperatures (100-900 °C), quasi-static notched specimen tensile test (notched radii with 3 mm, 6 mm, and 9 mm), high-speed tensile test (strain rates of 10-600 s-1), and Split Hopkinson Pressure Bar compressive test (strain rates of 300-1900 s-1) were carried out. Secondly, all the parameters in the Johnson-Cook flow and fracture model for the present two armor steels were calibrated. By further conducting the Taylor impact test and the corresponding numerical simulations, these model parameters were validated by comparisons of the residual length, residual maximum diameter, and failure mode of impact specimens. Thirdly, total fifteen shots of deformable projectile (15 mm in diameter) perforation test with utilizing high-speed three-dimension digital image correlation technology was conducted to examine the ballistic behaviors of two armor steels. The effects of projectile impact velocity and target thickness on the damage modes, e.g., shear plugging, ductile tearing, ductile hole enlargement, were analyzed. The corresponding numerical simulations with the validated model parameters were performed, and the predicted residual velocity of projectile and out-of-plane displacement of target agree well with the test data.

Strain rate sensitivity and toughness behaviour of ductile iron under specific loading

An efficient assessment of the mechanical properties of ductile iron (DI) under dynamic loading is usually missing. To address this gap, a plasticity model for DI grade EN-GJS-500-14 was suggested. Fracture mechanics (FM) and Charpy impact (CI) tests, high-speed and impact tensile tests as well as tensile tests at variable temperature and stress states were carried out on DIs with silicon contents from 2.10 to 3.64 wt-%. Toughness-related results indicate a difference in the transition temperatures of 100–140 K between CI and FM tests. The reason for this is assumed to be a pronounced strain rate sensitivity, which could be confirmed in the study. The plasticity model was able to predict toughness properties in CI tests.

Functionality Study of an Optical Measurement Concept for Local Force Signal Determination in High Strain Rate Tensile Tests

Many mechanical material properties show a dependence on the strain rate, e.g. yield stress or elongation at fracture. The quantitative description of the material behavior under dynamic loading is of major importance for the evaluation of crash safety. This is carried out using numerical methods and requires characteristic values for the materials used. For the standardized determination of dynamic characteristic values in sheet metal materials, tensile tests performed according to the guideline from [1]. A particular challenge in dynamic tensile tests is the force measurement during the test. For this purpose, strain gauges are attached on each specimen, wired to the measuring equipment and calibrated. This is a common way to determine a force signal that is as low in vibration and as free of bending moments as possible. The preparation effort for the used strain gauges are enormous. For these reasons, an optical method to determine the force by strain measurement using DIC is presented. The experiments are carried out on a high speed tensile testing system. In combioantion with a 3D DIC high speed system for optical strain measurement. The elastic deformation of the specimen in the dynamometric section is measured using strain gauges and the optical method. The measured signals are then compared to validate the presented method. The investigations are conducted using the dual phase steel material HCT590X and the aluminum material EN AW-6014 T4. Strain rates of up to 240 s-1 are investigated.

Dynamic crushing of uniform and functionally graded origami-inspired cellular structure fabricated by SLM

This paper investigated the dynamic crushing of a novel periodic origami-inspired cellular structure. The large-scale multi-layer metallic specimens considered geometry, anisotropy and gradient design were fabricated by an SLM system. Mechanical properties and energy absorption characteristics under dynamic load were investigated through drop hammer impact test. The results show that this novel structure has obvious negative Poisson's ratio (NPR) effect and relatively balanced mechanical properties in the three orientations under impact load. Among them, the z-axis orientation was the best bearing orientation. Three gradient modes of this structure were designed and tested for the first time. Results showed the gradient design effectively improved the energy absorption performance of this structure. Besides, high-speed tensile tests on the additively manufactured metallic coupons showed the strain rate effect and anisotropy of AM stainless steel 304L were significant. Corresponding Cowper-Symonds models were fitted. The numerical simulation reproduction based on LS-DYNA was validated to be well-matched with the test results. Parametric analysis showed that the initial folding angle was the crucial factor for the initial peak force, and the gradient growth rate can significantly affect the energy absorption of the structure.

High-Speed Erichsen Testing of Grain-Refined 301LN Austenitic Stainless Steel Processed by Double-Reversion Annealing

Austenitic Cr–Ni stainless-type 301LN steel was subjected to a double-reversion annealing (DRA) treatment to develop bulk grain-refined microstructures. The tensile properties and formability of the DRA structures were determined by high-speed tensile and Erichsen cupping tests at a strain rate of 1.5 s−1 (50 mm s−1) and compared with those of coarse-grained steel. Detailed microstructural features of the DRA structures were characterized using the electron backscatter diffraction technique and X-ray diffraction analysis. The DRA structures achieved by annealing for 1 second at 800 °C and 900 °C exhibited a superior combination of yield (~ 950 and 770 MPa, respectively) and tensile (~ 1050 and 950 MPa, respectively) strengths and ductility (~ 35 and 40 pct, respectively, as well as reasonable Erichsen index values under high-speed biaxial strain. Due to adiabatic heating, the DRA structures had higher austenite stability during high-speed stretch forming, i.e., were less prone to strain-induced martensitic transformation. The finite-element method (FEM) was used to conduct coupled field thermomechanical analyses of the high-speed deformation processes for the coarse-grained and DRA structures. Comparison of the FEM analyses with the experimental results revealed a considerable influence (~ 20 pct) of martensitic transformation on the adiabatic temperature rise. The balance of the yield strength and Erichsen index value of the developed nanograined microstructure is comparable to that of coarse-grained commercial steel.

Dynamic deformation behavior and corresponding constitutive model of ultra-high strength DP1000 steel

The static and dynamic mechanical properties of DP1000 steel were tested using an electronic universal testing machine controlled by a microcomputer at the strain rates of 10−4–10−2 s−1 and a high speed tensile testing machine at the strain rates of 10−1–103 s−1. The effect of strain rates on the stress-strain curves and the work hardening rate were obtained and analyzed. The modified dynamic Johnson-Cook model was established to characterize the dynamic deformation behavior. The dynamic compression characteristics and energy absorption law of thin-walled beam of DP1000 steel were determined by testing and using the Abaqus finite element simulation on account of the modified dynamic Johnson-Cook model (shortly the J-C model) to verify that the predicted values are in good agreement with the experimental ones.

鋼材のひずみ速度依存性材料データ作成の検討

Preparation methods of the stress-strain curve with rate dependency for steels have been studied using two estimation formulas. One of the formulas can estimate yield point and tensile strength as a function of strain rate, and another formula can estimate stress – strain curve from the two values, yield point and tensile strength. Two kinds of methods are proposed. Simulation of high-speed tensile tests using the finite element method have been carried out to validate the two kindss of methods. It is found the method considering rate dependency of both yield point and tensile strength shows better repeatability of experiments than the method considering rate dependency of only yield points.

Highly Stretchable, Crack-Insensitive and Compressible Ceramic Aerogel.

Ceramic aerogels are attractive candidates for high-temperature thermal insulation, catalysis support, and ultrafiltration materials, but their practical applications are usually limited by brittleness. Recently, reversible compressibility has been realized in flexible nanostructures-based ceramic aerogels. However, these modified aerogels still show fast and brittle fracture under tension. Herein, we demonstrate achieving reversible stretch and crack insensitivity in a highly compressible ceramic aerogel through engineering its microstructure by using curly SiC-SiOx bicrystal nanowire as the building blocks. The aerogel exhibits large-strain reversible stretch (20%) and good resistance to high-speed tensile fatigue test. Even for a prenotched sample, a reversible stretch at 10% strain is achieved, indicating good crack resistance. The aerogel also displays reversible compressibility up to 80% strain, ultralow thermal conductivity of 28.4 mW m-1 K-1, and excellent thermal stability even at temperatures as high as 1200 °C in butane blow torch or as low as -196 °C in liquid nitrogen. Our findings show that the attractive tensile properties arise from the deformation, interaction, and reorientation of the curly nanowires which could reduce stress concentration and suppress crack initiation and growth during tension. This study not only expands the applicability of ceramic aerogels to conditions involving complex dynamic stress under extreme temperature conditions but also benefits the design of other highly stretchable and crack-resistant porous ceramic materials for various applications.