Split Hopkinson Tensile Bar Apparatus Research Articles

Redesign of Split-Hopkinson Tensile bar to eliminate spurious wave and verification of strain signal using FEM

To get the reliable dynamic material properties, the optimization of measuring apparatus such as SHTB (Split-Hopkinson Tensile Bar) is essential. SHTB apparatus is a machine that can acquire the material properties of a specimen for given high-speed situation in [Formula: see text] strain rate region. In this study, a new model improved the waveform is proposed by redesigning and optimizing the initial SHTB equipment. Complete reflected pulse was not obtained, and a spurious wave was measured in original model. To obtain reliable material properties, the spurious wave must be removed or avoided. Factors affecting spurious wave were determined as length of striker bar, length of incident bar, and diameter of striker bar & flange, and verified using LS-DYNA, one of the FEM (Finite-Element Method) software. The modified model was redesigned and manufactured based on FEM results. In FEM results, the incident and reflected pulse were completely improved. Also, overlapping with spurious wave was avoided in redesigned experiment results. Redesigned model was confirmed the residual wave after the incident pulse by a pneumatic launcher and various mechanical components. However, the residual wave didn’t affect the reflected pulse and the waveform was improved than the original model.

Effect of high strain rate on tensile response and failure analysis of titanium/glass fiber reinforced polymer composites

The high strain rate tensile response of titanium-based fiber metal laminates (FMLs), consisting of layers of titanium Ti-6Al-4V alloy sheet and glass fiber reinforced composites, is examined. A hand layup method is used to fabricate four different layups of FMLs, exhibiting the same thickness of the total metal layer. A split Hopkinson tensile bar apparatus is used to load titanium and composite under a high strain rate to obtain baseline data. High-speed digital image correlation is used to measure the strain directly on the specimen gage region. The elastic-plastic response of FMLs up to maximum stress is predicted by the classical laminated plate model and orthotropic plasticity model. This is followed by a behavior considering the mechanics of delamination. The results show that the layup sequence of titanium-based FMLs considerably affects the failure behavior of composites following ultimate strength. This strength increases at high strain rates and seems higher for titanium-based FMLs than aluminium-based FMLs. This is primarily caused by the rate-dependent response of the titanium and composite. The failure strain of glass fiber reinforced epoxy (GFRP) constituent, failure strain, and toughness of FMLs are affected by isolating composite layers by metallic layers within FMLs and are found to be rate sensitive. Isolation of composite layers from one another by metallic layers results in more progressive failure of FMLs. The proposed models are validated with experiments of aluminium-based FMLs available in the literature.

Tensile and compressive behaviour of S355 mild steel in a wide range of strain rates

This paper presents a comparison between mechanical compressive and tensile properties of S355 structural (mild) steel in a wide range of strain rates. A split Hopkinson pressure bar apparatus is used to investigate the dynamic compressive behaviour at high strain rates (740–5880 s−1). A hydro-pneumatic machine (5–25 s−1) and a modified split Hopkinson tensile bar apparatus (300–850 s−1) are used to study the strain rate sensitivity under dynamic tension. Quasi-static tensile and compressive tests are conducted on a universal electromechanical testing machine. The model parameters of two commonly used constitutive equations (Johnson–Cook and Cowper–Symonds) are also compared, separately for each model during compression and tension deformations.

Experimental studies on mixed‐mode dynamic fracture behaviour of aluminium alloy plates with narrow U‐notch

AbstractMixed‐mode dynamic fracture behaviour of cast aluminium alloy ZL205A thin plates with narrow U‐notch was studied by split Hopkinson tensile bar apparatus. Specimens with different loading angles were designed to realize different fracture modes. The same loading condition was maintained during the tests. Recovery specimens show that crack propagates along the notch direction. Force–elongation relations show that with the loading angle increasing, the fracture force increases while the final elongation decreases. Deformation and fracture process was observed by a high‐speed camera. Displacement distribution around the crack was calculated through digital image correlation technique. Based on the photos and displacement results, initiation time of the crack was derived. Besides, two stress components (normal stress and shear stress) applied on the fracture surface were investigated. Results show that crack initiation stresses at different loading angles satisfy the ellipse equation. Pure mode I and II fracture stresses are 425.3 and 236.7 MPa, respectively. Furthermore, specific fracture energy of different specimens was calculated. The energy data vary with loading angle and located on an approximate upward parabolic curve. From the curve, the minimum specific fracture energy of the thin plate specimen is 42.0 kJ/m2 under loading angle of 76.3°.

Simulation on SHTB Apparatus Design Based on ANSYS/LS-DYNA

Split Hopkinson Tensile Bar (SHTB) apparatus is widely used in experimentally investigating the mechanical properties of materials. The experimental results are significantly depended on the amplitude, the shape and the wave length of incident wave. However, theres no research on the effect of incident wave especially the influence of parts of the SHTB equipment has been put forward. The mechanism of the overlying and the amplitude of incident wave by FEM has been analyzed, which can give much help for the theory basis of SHTB apparatus design.

Simulation on the Issue of One-Dimension Elastic Stress Pulse in SHTB Bar

Split Hopkinson Tensile Bar (SHTB) apparatus is widely used in experimentally investigating the mechanical properties of materials. The experimental results are significantly depended on the amplitude, the shape and the wave length of incident wave. However, theres no research on the effect of incident wave especially the influence of parts of the SHTB equipment has been put forward. The solid Hopkinson bar has faced many problems. The hollow Hopkinson Bar has more advantages than the solid Hopkinson bar. The mechanism of the overlying and the amplitude of incident wave by FEM has been analyzed, which can give much help for the theory basis of SHTB apparatus development and design to some extend.

Strain rate sensitivity and mechanical anisotropy of selective laser melted 17-4 PH stainless steel

Quasi-static and dynamic tensile testing was performed upon machined tensile specimens fabricated from bulk primitives produced by the consolidation of water atomized, 17-4 precipitation hardened stainless steel powder by layer-based, selective laser melting. Such mechanical evaluation was performed by a screw-driven uniaxial tension testing machine and a split-Hopkinson tensile bar apparatus. Strain rates evaluated include 10-3, 10-1 and 103 s-1. Prior to tensile testing, specimens underwent additional thermal processing in accordance with industry standards. Evaluations of the solution heat treatment and peak-age conditions were made alongside similarly prepared, but traditionally processed specimens meeting the same material standard for chemistry (drawn rod). Tensile strength across all strain rates is higher for these selective laser melted (SLM) specimens as a result of microstructure refinement through rapid melt, solidification and cooling during processing. Ultimate tensile and yield strengths increase with increasing strain rate and show no preferential direction relative to the building direction. Elongation anisotropy is observed as a consequence of directional porosity stemming from pores limited to within individual layers. Specimens loaded normal to the SLM building plane commonly rupture at small elongation because of this mechanical fibering from the selective laser melting process.

Mechanical behaviour of dual-phase high-strength steel under high strain rate tensile loading

The effects of strain rate on the tensile properties of two commercial steels (DP700 and DP500) were investigated. Quasi-static tests (0.001s−1) were performed using an electromechanical universal testing machine, whereas a split Hopkinson tensile bar apparatus was used for testing at high strain rates (~1100s−1, ~1800s−1, and ~3200s−1). The two high-strength steels show significant strain rate sensitivity. The material parameters of the existing Johnson–Cook model were determined from experimental results. This model fits the experimental data well in the plastic zone. Digital image correlation was used together with high-speed photography to study the strain localisation in the tensile specimens at high strain rates. By using digital image correlation, the in-plane strain field and local fracture strain of the specimen were obtained. The contours of the strain field indicate an early localisation even before the peak load is attained. Numerical simulations of the dynamic tensile tests were performed using the non-linear explicit finite element code LS-DYNA with the Johnson–Cook model. Good correlation between the experiments and numerical predictions is achieved, in terms of the strain gauge signals, deformed geometry, and strain field.

On the Dynamic Mechanical Characteristics of LIGA Nickel

The dynamic mechanical characteristics of LIGA nickel material are investigated by using a small split Hopkinson tensile bar apparatus (SSHTB). The strain rate related stress-strain curves of LIGA nickel are obtained and with which the dynamic mechanical characteristic parameters of LIGA nickel material under different strain rate are acquired. Meanwhile, the paper draws the conclusion that the dynamic mechanical characteristic parameters of LIGA nickel material increase with the increasing of strain rate by the experiment, which provides a theoretical basis for better application of LIGA nickel material under dynamic load conditions in Micro-electromechanical Systems (MEMS).

Effect of Loading Rate on Tensile Properties of Automotive Steel Sheet

Results of uni-axial tensile loading of three automotive steels at different strain rates (0.0011–3200s-1) are reported here. Quasi-static tensile tests were performed under the strain rate of 1.1×10-3 s-1 using an electromechanical universal testing machine, whereas dynamic tests were carried out under the strain rate in the range of 1100 to 3200 s-1 using a Split Hopkinson Tensile Bar apparatus. Based on the experimental results, the material parameters of widely used Johnson–Cook model which described the strain rate and temperature-dependent of mechanical behaviour were determined. The experiments show that strain-rate hardening is superior to thermal softening: yield stresses, tensile strength, deformation, and energy dissipation increase with the strain rate from quasi-static tests to dynamic tests. The Johnson–Cook model can describe the behaviour of these steels and provides the opportunity to study the material and structural response.

Strain rate effects on mechanical properties in tension of aluminium alloys used in armour applications

The mechanical properties in tension of two aluminium alloys (AA5059-H131 and AA7039-T651) used in armour applications were determined from tests carried out over a wide range of strain-rates on round specimens. The experimental research was developed in the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. The target strain rates were set at the following four levels: 10 −3 , 30, 300 and 1000s −1 . The quasi-static tests were performed with a universal electromechanical machine, whereas a hydro-pneumatic machine and a Split Hopkinson Tensile Bar apparatus were used for medium and high strain-rates respectively. The required parameters by the Johnson-Cook constitutive law were also determined.

Dynamic Tensile Properties of TiCp/Ti Composite

The tensile properties of a titanium alloy reinforced with 3% by volume fraction of TiC particles and of an unreinforced titanium alloy are studied over a range of strain rates from 0.0001s-1 to 1300s-1 using quasi-static material testing system (MTS810) and split Hopkinson tensile bar apparatus. The experimental results show that both the TiCp/Ti composite and its matrix alloy exhibit an obvious strain-rate hardening property. But the high strain-rate sensitivity of the TiCp/Ti composite is significantly higher than that of the matrix. The high strain-rate sensitivity of the TiCp/Ti composite is considered to be originated from the high dislocation accumulation rate during dynamic deformation and the constraint of TiC particles on the surrounding matrix, which dramatically enhances rate of the matrix. Finally, a phenomenological dynamic constitutive relation is established considering the composite is elastic-perfectly plastic material.