Papers by Keyword: Split Hopkinson Pressure Bar (SHPB)

Abstract: The solid-state process of friction stirring is increasingly applied to weld or process Aluminum alloy 5052, which is essential to various applications, such as marine, aerospace, and automotive. Friction stirring typically induces microstructural changes and grain refinement, affecting the processed material's constitutive response. Applications involving friction-stir processed aluminum alloy 5052 might be subjected to impact and high-strain-rate loadings. Accordingly, this work investigates the effect of friction stir processing on the high-strain-rate behavior of aluminum alloy 5052. A Split Hopkinson Pressure Bar (SHPB) system is used to experimentally measure the high-strain-rate compressive response of friction-stir processed aluminum alloy 5052 at strain rates ranging between 2700 s^-1 to 5000 s^-1. A high-speed imaging system and the digital image correlation technique were used to measure full-field strain fields. Results showed that friction stir processed samples exhibit lower yield strength (less by 20.8% at strain rate 5000/s) than their unprocessed counterparts at the same strain rate. However, friction stir processed samples exhibited a higher hardening rate.

Abstract: The present study investigates the dynamic compressive behavior of hybrid carbon/flax fiber-reinforced polymer composites in which epoxy resin is used as the matrix. The hybrid carbon/flax and non-hybrid flax polymer composite laminates were fabricated by hand lay-up followed by hot-compression molding. The Split-Hopkinson pressure bar test (SHPB) was utilized to evaluate the dynamic compressive mechanical properties of the fabricated composites. Compressive strength and failure strain were determined in the sample’s out-of-plane direction at strain rates ranging from 2638 s^-1 to 6716 s^-1. Macroscopic images were used to assess the progressive accumulated damage mechanisms due to the impact loading. Experimental results proved that non-hybrid flax and hybrid carbon/flax epoxy composites are high strain-rate-sensitive materials. For instance, the compressive strength of hybrid carbon/flax composites has increased from 327 MPa to 498 MPa as the strain rate increased from the lowest to the highest value in the considered range. At all impact pressures, hybrid carbon/flax composites have shown higher compressive strength than non-hybrid flax composites. The macroscopic inspection of post-tested composite specimens indicated that the accumulated damage becomes more severe with increasing the strain rate; and the main failure modes were shearing and splitting for both hybrid and non-hybrid composites. Overall, carbon/flax hybridization was found to be an effective technique for improving the load-bearing capacity of the polymer composites subjected to impact loading conditions.

Abstract: Glass fiber reinforced polymers (GFRPs) are becoming increasingly important in aerospace, construction, and automotive industries due to their potential for weight reduction, high strength, and excellent fatigue resistance. The failure mechanisms of GFRPs are influenced by factors such as strain-rate, frequency, stress state, and temperature. However, existing constitutive models have predominantly focused on characterizing the material's behavior under quasi-static conditions, potentially limiting their accuracy when applied to situations involving higher strain rates. This study employs explicit dynamics finite element analysis to examine the impact of high strain rates on the dynamic compressive behavior of glass fiber reinforced polymers (GFRPs) in an ABAQUS CAE environment using the Split Hopkinson Pressure Bar (SHPB) experimental setup. The mechanical response of the [0/90]₁₆ GFRP laminate system is characterized using the orthotropic elasticity material model and Hashin Damage Criteria is used to model the damage properties. Based on stability of total model energy, mesh convergence test was conducted across various mesh sizes to obtain the optimal mesh size for validating the developed FE-model. The simulation results highlight a notable increase in the compressive stress of the GFRP, rising from 200 MPa to 663 MPa as the strain rate increases from 596 s^-1 to 1743 s^-1. These results have shown the strain rate sensitivity of GFRPs and offer valuable insights for the prospective design and application of GFRP composites.

Abstract: This paper presents an experimental study on the high strain rate compressive behavior of micro-fibre reinforced ultrahigh performance cementitious composite, which is intended to be used as a matrix for slurry infiltrated fibre concrete (SIFCON). Cementitious composite specimens with 5 different types of microfibres, namely aramid, carbon, wollastonite, polypropylene and glass in amounts of 1.5-2.0% by volume were prepared and investigated. Split Hopkinson pressure bar (SHPB) equipment was used to determine the cementitious composite behavior at strain rates up to 1600 s^-1. Quasistatic tests were performed, as well and ratios of these properties at high strain rates to their counterparts at static loading were compared. The dynamic increase factors were calculated. Strain rate sensitivity was observed - compressive strength was found to be increased with strain rate for all tested specimens. Peak stress values, critical compressive strain and post peak behaviour varies for specimens with different micro-fibre reinforcement, which allows to find the optimal reinforcement for high strain rate impacted structures.

Abstract: Failure modes of jointed rock mass with different joint dip angle, joint center continuity degree, joint sets, load strain ratio and joint filling width under SHPB test are studied with model tests. The results show that failure modes and dynamic strength of jointed rock mass are much related to joint geometry. To rock mass with a single joint, its strength and failure mode are greatly controlled by the joint dip angle. The dynamic strength of the samples with joint dip angle 0° and 90°, whose failure modes are both tensile failure, is 90% and 71% of that of intact one, respectively. The dynamic strength of the samples with joint dip angle 60° is nearly zero. The dynamic strength of the samples with joint dip angle 30° and 45°, whose failure modes are mainly shear failure with partly tensile failure, is 50% and 18% of that of intact ones, respectively. The dynamic strength of the samples with 1/4, 1/2 and 4/5 joint center continuity degree is 95%, 74% and 28% of that of intact one, respectively. The dynamic strength of the samples with 1, 2 and 3 sets of joints is 54%, 23% and 10% of that of intact one, respectively. The dynamic strength of the intact and jointed samples both increases with load strain ratio, and the sensitivity to load strain ratio of the former is much higher than that of the latter, whose failure mode becomes more complicated accordingly. With increase of joint fillings width, the samples dynamic strength decreases gradually, but its failure mode does not change.

Abstract: The assumption of uniform stress in a test specimen is fundamental to SHPB test technique. In the present paper, a numerical simulation of wave propagation in SHPB is performed to validate the assumption. A one-dimensional model based on CSPM is firstly developed. Then the wave propagations in SHPB with various area ratios of bar/specimen are simulated. The results show that the condition of stress uniformity is not satisfied, especially at the beginning of wave propagation. For the large area specimen, the stress tends to be uniform. While for the small area specimen, the non-uniformity of stress is more apparent.

Abstract: Dynamic mechanical properties of silica fume concrete in a number of strain rate under the conditions of dynamic compression mechanical properties subjected to various strain rates were studied, and gained the stress versus strain curves, details of an experimental investigation using 74 mm-diameter split Hopkinson pressure bar(SHPB) apparatus were presented. The results showed that: The admixture of silica fume concrete impact resistance, especially under the impact of the performance of high-speed has a very important influence, with the impact velocity increased, the strain rate increase, and its impact more obvious.

Abstract: In order to study dynamic mechanical properties of float glass under blast and ballistic/fragmentation impacts, the curves of stress- strain are obtained in higher ranges by using the modified Split Hopkinson Pressure Bar (SHPB) techniques. Experimental results indicate that float glass is nonlinear elastic-brittle materials, and its dynamic curves of stress-strain are nonlinear and can be divided into three stages: elastic, nonlinear strengthening and stress drop. The dynamic Young’s modulus and the dynamic compressive strength of float glass increase with the increasing of strain rate. Finally, an explanation was given according to principle of energy equilibrium of Griffith.

Abstract: The specimen size has always been crucial in defining the materials behaviour and becomes more important when materials are subjected to high rates of loadings. In the current study, the effect of specimen size on the mechanical behaviour of AZ31B alloy has been investigated under dynamic compression using the Split Hopkinson Pressure Bar (SHPB) and results are presented. Specimens were made in different sizes with fixed slenderness ratio (l/d) of 0.5 and with bar to specimen diameter ratio varying between 0.47 and 0.79. When deformed at the same strain rate 1500±50s-1, the smaller specimens give higher stresses and smaller strains. The smaller size specimens give more uniform strain rate as compared to the larger size specimens. However, some spurious oscillations are observed in the stress-strain curves for smaller size specimens. The alloy shows higher hardening behavior for larger size specimen; the hardening exponent n is larger for larger size specimens.

Abstract: The dynamic response of the turbine blade materials is indispensable for analysis of erosions of turbine blades as a result of impulsive loading associated with gas flow. This paper is concerned with the dynamic hardening equation of the Nickel-based superalloy Inconel 718 which is widely used in the high speed turbine blade. Reported representative dynamic hardening equations have been constructed and evaluated using the dynamic hardening characteristics of the Inconel 718. Dynamic hardening characteristics of the Inconel 718 have been obtained by uniaxial tensile tests and SHPB tests. Uniaxial tensile tests have been performed with the variation of the strain rate from 0.001/sec to 100/sec and SHPB tests have been conducted at the strain rate ranging up to 4000/sec. Several existing models have been constructed and evaluated for Johnson-Cook model, Zerilli-Armstrong model, Preston-Tonks-Wallace model, modified Johnson-Cook model, and modified Khan-Huang model using test results at various strain rate conditions. The most applicable equation for the Inconel 718 has been suggested by comparison of constructed results.