High-speed Tensile Tests Research Articles

Distributed cracking mechanisms in textile-reinforced concrete under high speed tensile tests

Distributed cracking mechanisms in textile reinforced concrete (TRC) subjected to high speed loads and temperature variations were studied using digital image correlation (DIC) analysis and finite difference modelling. Three different TRC composites made of laminated AR glass, warp-knitted AR glass and polypropylene were used. Both plain textile and TRC specimens were tested at a nominal strain rate of 100 s−1 at the temperature range of −30–80 °C. The non-uniform distribution of longitudinal strain in TRC systems was divided into three distinct zones of localization, shear lag, and uniform strain and the strain distribution in each zone was quantitatively measured. Tensile strength and postcrack stiffness decreased in various TRCs as the temperature increased with the highest tensile strength of 38.1 MPa, work-to-fracture of 46.6 J, and postcrack stiffness of 459.7 MPa recorded for the warp-knitted AR glass TRC specimens at −30 °C. A finite difference model was used to simulate the experimental crack spacing and stress–strain behaviors as well as the degradation in postcrack stiffness as a function of interfacial bond strength. The experimentally observed crack patterns and failure modes in TRC systems agreed with the numerical simulations and the measurements of slip zone size using DIC.

High strain rate visco-damageable behavior of Advanced Sheet Molding Compound (A-SMC) under tension

Advanced Sheet Molding Compound (A-SMC) is a serious composite material candidate for structural automotive parts. It has a thermoset matrix and consists of high weight content of glass fibers (50% in mass) compared to standard SMC with less than 30% weight fiber content. During crash events, structural parts are heavily exposed to high rates of loading and straining. This work is concerned with the development of an advanced experimental approach devoted to the micro and macroscopic characterization of A-SMC mechanical behavior under high-speed tension. High speed tensile tests are achieved using servo-hydraulic test equipment in order to get required high strain rates up to 100 s−1. Local deformation is measured through a contactless technique using a high speed camera. Numerical computations have led to an optimal design of the specimen geometry and the experimental damping systems have been optimized in terms of thickness and material properties. These simulations were achieved using ABAQUS explicit finite element code. The developed experimental methodology is applied for two types of A-SMC: Randomly Oriented (RO) and Highly Oriented (HO) plates. In the case of HO samples, two tensile directions were chosen: HO-0° (parallel to the Mold Flow Direction (MFD)) and HO-90° (perpendicular to the MFD). High speed tensile tests results show that A-SMC behavior is strongly strain-rate dependent although the Young's modulus remains constant with increasing strain rate. In the case of HO-0°, the stress damage threshold is shown an increase of 63%, when the strain rate varies from quasi-static (0.001 s−1) to 100 s−1. The experimental methodology was coupled to microscopic observations using SEM. Damage mechanisms investigation of HO and RO specimens showed a competition between two mechanisms: fiber-matrix interface debonding and pseudo-delamination between neighboring bundles of fibers. It is shown that pseudo-delamination cannot be neglected. In fact, this mechanism can greatly participate to energy absorption during crash. Moreover, the influence of fiber orientation and imposed velocity is studied. It is shown that high strain rate and oriented fiber in the tensile direction favor the pseudo-delamination.

The mechanical properties of Polyvinyl Butyral (PVB) at high strain rates

Polyvinyl Butyral (PVB) has been largely used as an interlayer material for laminated glass to mitigate the hazard from shattered glass fragments, due to its excellent ductility and adhesive property with glass pane. With increasing threats from terrorist bombing and debris impact, the application of PVB laminated safety glass has been extended from quasi-static loading to impact and blast loading regimes, which has led to the requirement for a better understanding of PVB material properties at high strain rates. In this study, the mechanical properties of PVB are investigated experimentally over a wide range of strain rates. Firstly, quasi-static tensile tests is performed using conventional hydraulic machine at strain rates of 0.008–0.317s−1. Then high-speed tensile test is carried out using a high-speed servo-hydraulic testing machine at strain rates from 8.7s−1 to 1360s−1. It is found that under quasi-static tensile loading, PVB behaves as a hyperelastic material and material property is influenced by loading rate. Under dynamic loading the response of PVB is characterized by a time-dependent nonlinear elastic behavior. The ductility of PVB reduces as strain rate increases. The testing results are consistent with available testing data on PVB material at various strain rates. Analysis is made on the testing data to form strain-rate dependent stress–strain curves of PVB under tension.

Dynamic tensile properties of reduced-activation ferritic steel F82H

The dynamic tensile properties of reduced-activation ferritic steel F82H was characterized by high-speed tensile tests over a strain-rate range of 0.01–1400s−1 at temperatures of 296 and 423K. As a result, the tensile strength of the F82H steel appears to be sensitive to strain-rate. This is explained by the activation volume of gliding dislocation. The uniform elongation is also sensitive to strain-rate but true fracture strain is considered to be less sensitive. Zerilli–Armstrong bcc model is found adequate to describe the dependence of yield stress of F82H on temperature and strain-rate tested in the present study.

Joining Al 5052 alloy to aluminized steel sheet using cold metal transfer process

The arc braze welding process for Al/Fe dissimilar metal joints was investigated to meet the needs for multi-material mixed structures in the automotive industry. In this study, the Al 5052 alloy was joined to hot-dip aluminized steel sheets using low-heat-input cold metal transfer (CMT) arc welding. Four kinds of filler wires (Al 4043, 4047, 5356, 5183) were examined in the dissimilar metal joint. Using aluminized steel sheets, although the wettability was relatively poor compared with galvanized steel, a lower intermetallic compound (IMC) layer thickness was observed between the dissimilar metals, which resulted in a higher joint strength. The Si content in the filler metal restricted the growth of IMC layer, namely, the growth of the trapezoidal Fe2Al5 IMC layer into the steel base metal. When AlMg filler wires were used, a thinner IMC layer was observed, but a relatively low tensile shear strength was measured due to micro cracks and porosities formed along the interface between braze welds and steel sheet. The joint strength of the combination of Al 5052/aluminized steel/AlMg filler wire was equal or higher than that of the heat-affected zone in the Al 5052 alloy. The integrity of the Al 5052/aluminized steel/AlMg filler dissimilar metal joint was guaranteed using both a high-speed tensile test and salt spray corrosion test.

Effects of Strain Rates on Mechanical Properties and Fracture Mechanism of DP780 Dual Phase Steel

The mechanical properties of DP780 dual phase steel were measured by quasi-static and high-speed tensile tests at strain rates between 0.001 and 1000 s−1 at room temperature. The deformation and fracture mechanisms were analyzed by observation of the tensile fracture and microstructure near the fracture. Dynamic factor and feret ratio quantitative methods were applied to study the effect of strain rate on the microstructure and properties of DP780 steel. The constitutive relation was described by a modified Johnson-Cook and Zerilli-Armstrong model. The results showed that the strain rate sensitivity of yield strength is bigger than that of ultimate tensile strength; as strain rate increased, the formation of microcracks and voids at the ferrite/martensite interface can be alleviated; the strain rate effect is unevenly distributed in the plastic deformation region. Moreover, both models can effectively describe the experimental results, while the modified Zerilli-Armstrong model is more accurate because the strain-hardening rate of this model is independent of strain rate.

Experimental and numerical analysis of laterally impacted stiffened plates considering the effect of strain rate

A proper numerical simulation method is developed to simulate structure impact problems that consider the effect of strain rate. High-speed tensile tests were carried out to obtain the stress–strain relationships at different strain rates, and these results were used as material inputs to analyze the dynamic response of laterally impacted stiffened plates. The simulation results are compared with falling weight impact experiments, and good agreement was obtained. The stress–strain relationships obtained from high-speed tensile tests and the Cowper–Symonds constitutive (CS) model were compared. Part of the results shows that the curve obtained from the CS model is higher than that obtained from the high-speed tensile test and that with increasing strain rate, the distance will become more pronounced. The numerical simulation is verified and fits the experimental result well. The failure strain is affected by the mesh size in finite element simulation and will decrease with decreasing mesh size. Different mesh sizes for the model can be simulated accurately, once an appropriate material input is obtained. These conclusions can be very useful for studying large-scale impact problems, such as ship collisions and groundings, and can guide engineering applications.

중변형률 속도 유동응력 확보를 위한 고속 인장 실험기 설계

중변형률 속도 유동응력 확보를 위한 고속 인장 실험기 설계

Strain rate dependent deformation and failure behavior of laser welded DP780 steel joint under dynamic tensile loading

Laser welded DP steel joints are used widely in the automotive industry for weight reduction. Understanding the deformation and fracture behavior of the base metal (BM) and its welded joint (WJ), especially at high strain rates, is critical for the design of vehicle structures. This paper is concerned with the effects of strain rate on the tensile properties, deformation and fracture behavior of the laser welded DP780 steel joint. Quasi-static and dynamic tensile tests were performed on the WJ and BM of the DP780 steel using an electromechanical universal testing machine and a high-speed tensile testing machine over a wide range of strain rate (0.0001–1142s−1). The microstructure change and microhardness distribution of the DP780 steel after laser welding were examined. Digital image correlation (DIC) and high-speed photography were employed for the strain measurement of the DP780 WJ during dynamic tensile tests. The DP780 WJ is a heterogeneous structure with hardening in fusion zone (FZ) and inner heat-affected zone (HAZ), and softening in outer HAZ. The DP780 BM and WJ exhibit positive strain rate dependence on the YS and UTS, which is smaller at lower strain rates and becomes larger with increasing strain rate, while ductility in terms of total elongation (TE) tends to increase under dynamic loading. Laser welding leads to an overall reduction in the ductility of the DP780 steel. However, the WJ exhibits a similar changing trend of the ductility to that of the BM with respect to the strain rate over the whole strain rate range. As for the DP780 WJ, the distance of tensile failure location from the weld centerline decreases with increasing strain rate. The typical ductile failure characteristics of the DP780 BM and WJ do not change with increasing strain rate. DIC measurements reveal that the strain localization starts even before the maximum load is attained in the DP780 WJ and gradual transition from uniform strains to severely localized strains occurs at high strain rates. The diffuse necking of the DP780 WJ occurs earlier during the tensile deformation process at higher strain rates under dynamic loadings.

Material Behaviour of Armco-Iron and AISI 4140 at High Speed Deformation during Machining

During machining of metals high temperatures and deformations occur at the surface layers leading to changing component states. Depending on the thermal and mechanical set of stress microstructural changes like residual stresses and grain refinement can be found. Grain refinement is influenced by the amount of deformation. In the present investigations high deformations of the surface layers are realized by using the cutting tool in opposed direction resulting in high negative rake angles. This test setup is used to investigate the material behaviour of Armco-Iron and AISI 4140 at different cutting velocities during machining. Furthermore the flow stresses at different strain rates and temperatures were determined by means of high speed tensile tests. The flow behaviour of the investigated materials is used to explain the results of the machining experiments.

Laser welding for hot-stamped tailor-welded blanks with high-strength steel/high-energy absorption steel

In this research, the laser weldability for tailor-welded blanks (TWBs) made of dissimilar hot-stamping steels was examined. Usibor and Ductibor from ArcelorMittal were combined, since they are steels that possess a high-strength and high-energy absorption, respectively. Additionally, combination of Usibor and SPRC440 was investigated for comparison. After laser butt welding, the specimens were heat-treated at high temperatures, and the subsequent quenching conditions were similar to those in the hot-stamping process. The mechanical and metallurgical characteristics of the welds were then analyzed. The TWBs with Usibor and Ductibor exhibited a high degree of elongation after hot-stamping but those with Usibor and SPRC440 showed a relatively low elongation. The AlSi coating on the base metal was included in the fusion zone, and it led to ferrite formation. However, in the static and high-speed tensile tests, the AlSi coating did not affect the tensile strength of the TWBs, and all tensile specimens were fractured at the base metal of Ductibor.

Study of Material Modeling of Polymers for Impact Analysis

High-speed tensile tests were carried out to investigate strain rate effect on both yield stress and failure strain using ASTM D1822 Type-S specimens made of polycarbonate. Based on test results, parameters for a material model suitable for polymers are determined, and numerical analysis is carried out to simulate test results. The material model is used to simulate tensile test using a dog-bone specimen and Charpy test other than the tensile test of Type-S specimens. It is found that good predictions can be obtained when rate dependent material parameters are used. Further, the high-speed tensile test considered in the present study is suitable for selection of parameters for material modeling of polymers for impact analysis.

Standard Uncertainty Evaluation for Dynamic Tensile Properties of Auto-Body Steel-Sheets

This paper is concerned with the standard uncertainty of the true stress–true strain curve as the tensile properties of auto-body steel sheets at intermediate strain rates ranged from 1 to 100 s−1. A procedure to obtain true stress–true strain data is properly designed for the experiment and data acquisition. An analytic model is then established to evaluate the standard uncertainty of the measurand. The measurand in this case is the true stress which is a function of the input quantities: the tensile load; the initial length, the thickness and the width of a specimen; and the deformed length of a specimen. Sources of uncertainties of the input quantities are evaluated for the high speed tensile test with their associated sensitivity coefficients. Uncertainty of the stress data acquired is also considered in the procedure of the fast Fourier transform (FFT) smoothing process used to remove unnecessary signals acquired from experiments. Image analysis using a high speed camera is carried out to measure deformation of the specimen during high speed tensile tests with proper uncertainty evaluation. A combined standard uncertainty is evaluated from the uncertainties of the input quantities as well as the influence factor for the true stress of auto-body steel sheets at intermediate strain rates. Consequently, the true stress–true strain data are obtained with proper standard uncertainty evaluation.

211 高速引張試験によるひずみ速度を考慮した材料特性の構築(OS7 オーガナイズドセッション《材料強度と構造設計》)

We provide a modeling method of strain rate dependent material which derived from force-displacement relationships for strain rates measured by high speed tensile tests. The strain dependent material model consists of a stress-strain rate relationship in low strain rate, a stress-strain rate elationship in high strain rate and a stress-strain relationship in large strain. To evaluate the modeling method, high speed tensile tests, the material modeling with test result and simulations of high speed tensile test with the material model were carried out. Then it found that the force-displacement relationships of analysis match to those of tests.

OS1402 混合ガス燃焼時の配管強度に関する研究 : 配管破断ひずみの推定

Carbon steel pipe specimens ruptured by internal H_2-O_2 detonation pressure were analyzed by FEM. The detonation pressure was estimated by computational fluid dynamics. The estimated pressure was loaded to an FEM model of the pipe specimen. We applied the obtained stress-strain relationship by high speed tensile material tests in the analysis. By these analyses, we estimated the strain at the pipe rupture was 20 - 22%. The analytical results were compared with the theories of fracture strain under multi-axial stress conditions. The difference between the elongation in the material test and rupture strain of the pipe specimen was explained by McClintock and ASME B&PV Sec III formulae. We took into account other factors for reducing fracture strain, for example, machining of piping, welded material, and scattering of material strength. We propose a limiting strain of 8%, which is one third of the minimum elongation in material tests. We suggest that estimating the strain of a pipe by FEM and comparing it with the proposed limiting strain is feasible as an assessment of integrity of piping subjected to detonation pressure.

Analysis of Dynamic Stress Concentration and Strain Rate Concentration for Notched Specimens Used for High Speed Tensile Test

Analysis of Dynamic Stress Concentration and Strain Rate Concentration for Notched Specimens Used for High Speed Tensile Test

A Comparative Study of Computer Simulation using High-Speed Tensile Test Results with Actual Crash Test Results of DP Steels

A Comparative Study of Computer Simulation using High-Speed Tensile Test Results with Actual Crash Test Results of DP Steels

Enhanced ALE data transfer strategy for explicit and implicit thermomechanical simulations of high-speed processes

The Arbitrary Lagrangian Eulerian (ALE) formalism, which allows the computational grid to move regardless of the material deformation, is a convenient way to avoid distorted meshes in finite element simulations. One crucial step of the ALE algorithm is the data transfer between the Lagrangian and the Eulerian meshes. In this paper, an enhanced transfer method is presented. It can handle complex finite elements which are integrated with more than one Gauss point. This method can thus be used either with an explicit or with an implicit time integration scheme. Choosing the adequate order of accuracy and the most appropriate number of physical fields to be transferred is always a compromise between the speed and the precision of the model. For example, some variables may be sometimes ignored during the transfer in order to decrease the CPU time. Therefore, the most effective way to use such an algorithm is demonstrated in this work by revisiting a classical ALE benchmark, the Taylor impact. An implicit thermomechanical ALE simulation of a high-speed tensile test is also presented and is compared to experimental results from the literature.

열가소성 폴리올레핀으로 구성된 범퍼 후방 보 개발에 관한 연구

Recently, the application of the plastic material to automotive components and structures has steadily increased to satisfy demands on the saving of overall weight and the improvement of energy efficiency. The objective of this paper is to investigate the development of a bumper backbeam using a thermoplastic olefin (TPO). The bumper back-beam was designed to be manufactured from the injection molding process. In order to obtain a proper design of the bumper back-beam, three-dimensional finite element analyses were performed for various design alternatives. Stress-strain curves for different strain rates were measured by high speed tensile tests of the TPO to consider strain rate effects in the FEA. The influence of the sectional shape and the rib formation on the contact force-intrusion curves, the deflection and the energy absorption rate of the bumper back-beam was examined. From the results of the examination, a proper design of the bumper back-beam was acquired. The bumper back-beam consisting of TPO was fabricated from the injection moulding process and the vibration welding. Pendulum crash tests were carried out using the fabricated bumper back-beam. The results of the tests showed that the designed bumper back-beam can satisfy requirements of the federal motor vehicle safety standard (FMVSS). Through the comparison of the previously designed bumper back-beam with the newly designed bumper back beam, it was noted that the weight of the designed bumper back-beam is lighter than that of the previously designed bumper back beam by nearly 16 %. In addition, it was considered that the newly designed bumper back beam can improve recycling of the bumper back-beam.

Effect of the matrix behavior on the damage of ethylene–propylene glass fiber reinforced composite subjected to high strain rate tension

This study investigates the origin of the strain rate effect on the mechanical behavior of a discontinuous glass fiber reinforced ethylene–propylene copolymer (EPC) matrix composite. This kind of composite materials are commonly used for automotive functional and structural applications. To this aim, a multi-scale experimental approach is developed. The deformation processes and the damage mechanisms observed at the microscopic scale are related to the material mechanical properties at the macroscopic scale. Tensile tests up to failure and specific interrupted tensile tests have been optimized and performed for high strain rates up to 200s−1 to quantify the strain rate effect at different scales. High speed tensile tests have also been performed on the pure copolymer matrix. The threshold and the kinetic of damage have been quantified at both microscopic and macroscopic scales. Experimental results show that the composite behavior is strongly strain-rate dependent. The multi-scale analysis leads to the conclusion that the strain rate effect on the damage behavior of the EPC matrix composite is mainly due to the viscous behavior of the EPC matrix. SEM observations and analysis show that a localized deformation in the interface zone around fibers occurs at high strain rates and directly affects the visco-damage behavior. It is established that when the strain rate increases, the local deformation zone around the fibers behaves like a dissipation zone. Consequently, the damage initiation is delayed and the related kinetic is reduced with respect to the quasi-static loading case.