Papers by Keyword: SHPB

Abstract: This article does some research on SiC-W composite material. Getting the material with SPS, the micro-structure was observed. The micro-structure of SiC is mainly lamellar structure and the Tungsten did not infiltrate the SiC. Via mechanics performance test of SiC-W, we found although both SiC and SiC-W show the characters of brittle material, but the Tungsten mixing can improve the toughness in certain level.

Abstract: Using the HJC dynamic constitutive model, the Split Hopkinson Pressure Bar (SHPB) impact test with confining pressure for concrete was simulated in the software ANSYS/LS-DYNA. The confining pressure was simulated by applying constant pressure around the specimen. The triangle velocity wave, which has less diffusion, is used as loader in the simulation. The confining pressures used were 0MPa, 2MPa, 4MPa, 8MPa and 16MPa and the stress-strain curves were presented. The influence of confining pressure on the dynamic properties was analyzed by comparing the stress-strain curves of concrete under different stress states. The strain rate decreases sensitively as long as the confining pressure increases. By debugging the impact velocity, the stress-strain curves under the similar strain rate were obtained, which indicate the toughening and reinforcing effect with the increase of confining pressure.

Abstract: The Split Hopkinson Pressure Bar (SHPB) testing technique has been used to derive the constitutive equations of engineering materials at high strain rate using the reflected and transmitted waves measured from the input and output bars. In this case, a precise measurement of the reflected and transmitted waves is important to determine a reliable stress-strain relation. In this study, to achieve the precise measurement of the reflected and transmitted waves in the SHPB experiment, a data acquisition scheme utilizing the LabVIEW software and a post processing program have been constructed. With the constructed system, an accurate data acquisition without a digital storage oscilloscope and a convenient post processing of the signals obtained through the SHPB test for identifying the mechanical properties have been possible. Therefore, a fast and simple generation of the strain rate - time curve and the nominal stress - nominal strain curve has been implemented by just selecting the specified regions on the reflected and transmitted wave profiles acquired. Also, the process to set the appropriate test configuration in the SHPB test for various kinds of materials has become easy with the constructed system.

Abstract: A new experimental technology based on the Split Hopkinson Pressure Bar (SHPB) is developed for conducting expanding ring tests. The technique is useful for the studies of the dynamic tensile deformation and the fracture (fragmentation) properties of ductile metallic materials. The loading fixture includes a hydraulic cylinder filled with the incompressible fluid, which is pushed by a piston connected to the input bar. As the liquid is driven, it transfers the pressure to the specimen, compressing and expanding the metallic ring specimen in the radial direction. The approximately incompressible property of the liquid makes it possible to transfer a relatively low piston-driving velocity to a very high radial-expansion velocity of the specimen, as the sectional area of the cylinder narrows significantly. Using this experimental technology the ring specimens made of LY12 aluminum alloy were dynamically expanded and fragmentized. Results show apparent increases of the fragment numbers and fracture strain of the specimen with the increase of the impact velocity. The recovered ring fragments were examined and measured to obtain the average fragment sizes (lengths) during each test. These fragment sizes were compared with the estimates from the classical fragmentation theory that was initiated by N.F. Mott and later developed by D.E. Grady. It was found that the Mott-Grady theory provides reasonably good predictions of the fragment sizes for ductile materials. This conclusion agrees with the recent findings of ours based on the numerical simulations and physical arguments.

Abstract: The strategic concrete structures are often required to resist impact loads arising from the projectile strike, falling weight, blast generated missile etc. The existing structures found deficient in resisting these loads are required to be retrofitted whereas the upcoming structures are required to be designed for expected impact loads. This paper explores the ways of strengthening existing reinforced concrete (RC) structures using externally bonded carbon fiber reinforced polymer (CFRP) sheets and improving the impact resistance of concrete by mixing hybrid fibers in its production. The impact response of concrete structures is assessed using experiments involving the impact of projectiles of different nose shapes on slab specimens. The material behavior at high strain rate is established using split Hopkinson pressure bar (SHPB) testing at varying strain rates. Analytical models are developed for predicting penetration depth, scabbing thickness, ballistic limit velocity and ejected mass. The experimental results were also validated through numerical modeling using LS-DYNA.

Abstract: As a model material, commercial pure titanium was rolled to plates with different dislocation boundaries. The dynamic mechanical response of Ti specimen was analyzed during impacted with Split Hopkinson Pressure Bar (SHPB) at different strain rates, and microstructure evolution was investigated using optical microscopy and transmission electron microscopy. It was found that adiabatic shear sensitivity was decreased with increasing strain rates for all as-annealed, 25% and 50% cold rolled states. To the contrary, for 70% cold rolled state the adiabatic shear sensitivity was increased with increasing strain rates. The microstructure of adiabatic shear bands (ASBs) were developed from elongation morphology to fine equiaxed grains in the specimens of 25% cold rolled state, and ASBs became broader with increasing strain rate.

Abstract: An experimental system is designed by combining the split Hopkinson pressure bar (SHPB) with microwave heating device, based on numerical simulation and 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: With the cylindrical concrete specimens of C30, C40 and C50 strength grades confined by basalt fiber-reinforced polymer, the strengths of confined concrete specimens at the strain rate of 100/s~200/s are obtained in test of impact by Φ100 mm SHPB based on quasi-static loading test. Analysis shows that the quasi-static strength ratio of basalt fiber confined concrete have a good linear relationship with restraint ratio. Under impact loading, the strengths of confined specimens increase with the increase of strain-rate. They are more sensitive to strain-rate than the plain specimens. The strain-rate effect is strengthened with the increase of basalt fiber layers, but it tends to decrease when the fiber is increased to three layers.

Abstract: This study derived the five parameters in Johnson-Cook equation of CP titanium Gr2. Quasi-static and dynamic compression tests were designed to measure mechanical properties at strain rates of 10^-3s^-1 and 6000s^-1. In order to secure the validity of tested data, a novel fixture was proposed to reduce the displacement measurement error in MTS testing system and the signal processing procedure of compressive split Hopkinson pressure bar for the present study was demonstrated. With the tested data and calculated adiabatic heating temperature rise, parameters A, B, n, m, C have been derived based on mathematical deduction and solve. It was found that the constructed constitutive model fit the tested data well and was able to restore the yield strength value at high strain rate.

Abstract: This paper chooses the remit foam aluminum by Shanghai co., LTD provides high pressure filtration method is used to make the opening of aluminum foam material. System research of relative density and strain rate changes on the relative density is high (> = 0.255) of aluminum foam materials shock stress - strain behavior, deformation failure mechanism and the influence law of energy absorption characteristics. These studies can not only expand the awareness of foam metal mechanical behavior, but also on the domestic industrial production of the performance of the foam aluminum material design, optimization and production preparation plays a guiding role.