Papers by Keyword: Split Hopkinson Pressure Bar (SHPB)

Abstract: A split tensile test methodology has been established for the concrete spheriform specimens with the principal stress ratio of σ1:σ2:σ3=0.24:0.24:-1 in order to study the tensile-tensile-compressive tri-axial strength. Using a Universal Material Testing Machine and Split Hopkinson Pressure Bar, the quasi-static and dynamic spliting tensile tests have been conducted for the concrete spheriform specimens consisting of 1% steel fiber. In the quasi-static test, the average strain rate of the steel fiber reinforced concrete specimens was 8.3×10^-5s^-1 and the split tensile strength was found to be 0.77MPa, which is consistent with the existing literature. In the high strain rate tests, the average strain rate was 170s^-1 and the split tensile strength was found to be 1.01MPa. When compared with the quasi-static testing results, it is seen that the split tensile strength of the steel fiber reinforced concrete increases with increasing strain rate. The split tensile test methodology established in the present paper is simple and inexpensive, while the strength obtained located on the meridian plane of tension and compression, has practical significance.

Abstract: A high temperature split Hopkinson pressure bar (SHPB) test system is used to investigate the effects of temperature as well as those of strain and strain-rate. Effects of temperature for the vanadium alloy (V-5Cr-5Ti) are investigated by developing a high temperature SHPB test system. In this work, high temperatures greater than 1100°C are attained in the SHPB test specimens by using a synchronically assembled heating system .When testing with the high-temperature SHPB apparatus, care is required to prevent oxidation of the surface of the specimen, and to prevent an inhomogeneous temperature distribution from developing in the specimen. To determine the true flow stress–true strain relationship, specimens are tested from 15°C to 1100°C and at a strain-rate of about 3000 s-1: The parameters for a Johnson–Cook constitutive equation is determined from the test results. The Johnson–Cook constitutive equation is suitable for expressing the dynamic behavior of the V-5Cr-5Ti vanadium alloy.

Abstract: The purpose of this work is to assess the dynamic mechanical behaviour of a commercial glass similar to that of the laminated glass structures used for protection and security applications in buildings. In particular, the study has been focussed on the influence of the strain-rate on the compressive (standard compression test) and tensile (splitting tensile test) strength of this glass. Tests at different strain-rates have been performed in the range between 10^-3 to 10³ s^-1 using standard test equipment for quasi-static tests and a SHPB equipped with a high-speed camera for the dynamic ones. Test data for compression tend to show that there is no substantial sensitivity to the strain-rate concerning ultimate strength and Young modulus. An appreciable increase in the ultimate tensile strength is revealed at higher strain-rate.

Abstract: This paper presents a laboratory experimental study on the effect of high strain rate on compressive behavior of plain and fiber-reinforce high-strength concrete (FRHSC) with similar strength of 80-90 MPa. Steel fibers, polyethylene fibers, and a combination of these were used in the FRHSC. A split Hopkinson pressure bar equipment was used to determine the concrete behavior at strain rates from about 30 to 300 s^-1. The ratio of the strength at high strain rates to that at static loading condition, namely dynamic increase factor (DIF), of the concretes was determined and compared with that recommended by CEB-FIP code. Fracture patterns of the specimens at high strain rates are described and discussed as well. Results indicate that the CEB-FIP equation is applicable to the plain high strength concrete, but overestimates the DIF of the FRHSC at strain rates beyond a transition strain rate of 30 s^-1. Based on the experimental results, a modified equation on DIF is proposed for the FRHSC.

Abstract: An experimental system is designed by combining the split Hopkinson pressure bar (SHPB) with microwave heating device, based on stress wave theory, availability of the experiment technique is analyzed. Tests of concrete whose temperature changes from room temperature to 650°C and impact velocity from 5m/s to 12m/s are completed and for the first time high-temperature dynamical damaging phenomena of concrete are obtained. Based on data analysis, the dynamical mechanical behavior of concrete with high temperature is affected by not only the strain rate effect whose influence keeps on decreasing with temperature increasing, but also the high temperature weakening effect. And the strain rate hardening effect is coupled with high temperature weakening effect, but the latter has greater influence.

Abstract: The behaviour of geologic material such as granite under impact loading is involved in the study of safety requirements of structures in extreme simulations such as earthquakes, accidental impacts or explosions. Based on incident pulse shaping design of quasi-brittle material for dynamic tests, experiments on granite under uniaxial and active confinement conditions are conducted with the split Hopkinson pressure bar(SHPB). By adding the soft material mass as the pulse shaper, the stress uniformity in the specimens before fracture is ensured and the fluctuation of test data due to incident stress pulse is avoid. The experimental results show that the compressive strength is increasing with the strain rate and the confined pressure. The fragments size decreases with the strain rate. The research method and conclusion could be used to analyze the dynamic behavior of the other brittle materials.

Abstract: Three alloys of the magnesium AZ-series (AZ31, AZ61 and AZ91) were processed by multi-temperature equal channel angular pressing (ECAP) with five passes using route B_C. The ECAP temperature was decreased from 275 °C to 250 °C during the process for better grain refinement. The mechanical behaviour was investigated over a wide range of strain rates (10^-3 s^-1 up to 10³ s^-1) under compressive loading at room temperature. The investigations show that significant grain refinement takes place during the ECAP-process. The initial grain size of 12 μm, 9 μm and 5.8 μm for extruded AZ31, AZ61 and AZ91, respectively, could be refined to 2.5 μm. The grain refinement occurs by dynamic recrystallisation. Compared to extruded initial Mg-alloys, the yield stress increases slightly for all selected alloys after ECAP processing, while the amount of strain hardening decreases at the same time, due to reduced grain size and texture effects. Furthermore, the flow stress of extruded and ECAPed material is less affected by strain rates within a range of 10^-3 s^-1 to 10^-1 s^-1.

Abstract: In order to systematically study dynamic mechanics character of reactive powder concrete (RPC), impact compression experiments and impact flattened Brazilian disc specimens of RPC have been investigated with modified split Hopkinson pressure bar (SHPB) experimental facility using brass pulse shaper, curves about stress versus strain and other parameters at strain rates of 20.3/s~137.0/s were obtained from impact compression. The dynamic tensile strength and tensile failure strain at strain rates of 3.4/s~26.2/s were obtained from impact flattened Brazilian. For comparison, the quasi-static compress and split tension of RPC were obtained with an MTS 810 materials test system and CSS-88500 electron universal material testing machine.The experimental result show that dynamic compression strength , elastic modulus and failure strain,dynamic tensile strength and failure strain significantly increase comparing to quasi-static experiment, RPC have the character of impact harding and ductility enhancement. RPC exhibit excellent failure patterns at high strain rate. Whether impact compression or impact splitting under strain rate including this paper ’s experiments, the relationship between the DIFC or DIFT and the logarithm of strain rateis linear.

Abstract: Concrete might be subjected to impact or blast loading. To analyze the concrete behaviors under such loading cases, it is of interest to study the dynamic damage and failure behavior of concrete under high strain rate. In the present paper, a mesoscale model is developed to numerically analyze the dynamic damage process of concrete samples under high strain rate tension. In the mesoscale model, the concrete is regarded as a three-phase composite consisting of coarse aggregate, mortar matrix, and interfacial transition zone (ITZ) between the aggregate and the mortar matrix. Different coarse aggregate shapes, such as circular, oval, and polygon, are calculated and compared. It is found that the shapes of the coarse aggregates do affect the tensile strength and failure pattern.

Abstract: Dynamic impact experiments of man-made rock were carried out with the Split Hopkinson Pressure Bar (SHPB) apparatus in this paper. The impact process was analyzed and the influence of rock porosity on dynamic mechanical behavior was investigated. The stress-strain curves in rock were obtained by the one-dimensional stress wave theory. The curve lays foundation for numeric simulation of rock fracture under impact loading. The damage profiles of rock specimen under the impact loading show that the man-made rock exhibits obvious shear damage under the impact loading because it is a typical porous medium containing large quantities of defects such as pores, cracks and grain boundaries at the microscale. The experimental results also indicated that rock porosity plays an important role in dynamic mechanical behavior.