High strain rate testing

Split Hopkinson bar (SHB) techniques are commonly used to experimentally characterise materials at high strain-rates. One important aspect of high-strain rate characterisation using SHBs is the necessity to tailor the input pulse to the needs of the material to be tested. Here, a new method to shape the input pulse, specifically developed for tensile SHBs (SHTB), is presented. The new method overcomes several challenges of existing designs, allows for a controlled adjustment of the pulse rising time, and significantly reduces wave dispersion effects.

A new test method to directly characterize fiber-matrix interface properties under high rate of loading has been developed. A tensile Hopkinson bar with a modified incident bar is used to load a microdroplet test specimen. Numerical simulations were carried out to design the test specimen geometry and validate data reduction procedures for the dynamic interface experiments. Stress wave propagation in an S-2 Glass/Epoxy microdroplet specimen was studied with different droplet sizes (100 mm - 200 mm) and fiber gage lengths (2 mm - 6 mm). Simulation results indicate that dynamic equilibrium can be maintained up to a displacement rate of 10 m/s. Dynamic microdroplet experiments were conducted at a displacement rate of 1 m/s on S-2 glass/epoxy interface. Experimental results and post-failure inspection of the fiber matrix interface showed that the new test method is effective in measuring high rate interface properties of composites.

Two noncrimp 3D woven carbon fibre composites (through thickness angle interlock) of binder volume fractions 3% and 6% were characterised for their response to applied deformation. Experiments were performed at quasi static, medium and high strain rates under a large variety of load cases (tension in warp/weft direction, interlaminar/intralaminar shear, through thickness tension/compression, 3-point bending and plate bending). During the study, novel experimental methods were developed in order to address several challenges specific to 3D composite materials. The results show that, while the different binder volume fractions of 3% and 6% have only a small effect on the in-plane stiffness (warp and weft direction), its effect on the delamination resistance in plate bending experiments is considerable. This is a very important result for the use of these materials in the future. The availability, in previous publications, of complementary data for the matrix and the interface between matrix pockets and fibre bundles makes the comprehensive data set a generically useful reference for hierarchical numerical modelling strategies.

This review paper is devoted to discussing the development and the present state of some key aspects of the mechanical behaviour of composite materials under impact loading. The experimental techniques employed for determining the behaviour of composite materials at high strain rate in tensile, compressive and shear loading are presented and discussed. The discussion includes their fundamental advantages and limitations. Directions for future research are also indicated.

Issues in simulation modeling, materials and high-energy explosives have been the three areas of research that have had the most impact on warhead technology. The present study focused on the materials issues and simulations and the relationship between the two in the case of Explosively Formed Penetrators (EFPs). Tantalum (Ta), Armco iron (Fe) and oxygen-free high conductivity copper (OFHC Cu)

Virtually all types of collagenous tissues have been transferred in and around the knee joint for intra-articular and extra-articular ligament reconstructions. However, the mechanical properties (in particular, strength) of such grafts have not been determined in tissues from young adult donors, where age and disuse-related effects have been excluded. To provide this information, we subjected ligament graft tissues to high-strain-rate failure tests to determine their strength and elongation properties. The results were compared with the mechanical properties of anterior cruciate ligaments from a similar young-adult donor population. The study indicated that some graft tissues used in ligament reconstructions are markedly weak and therefore are at risk for elongation and failure at low forces. Grafts utilizing prepatellar retinacular tissues (as in certain anterior-cruciate reconstructions) and others in which a somewhat narrow width of fascia lata or distal iliotibial tract is utili...

In this paper, the state-of-the-art progress in research on novel mechanical properties of nanocrystalline materials and carbon nanotubes is reviewed. There is evidence that the relation between the strength of nanocrystalline materials and grain size does not observe the classic Hall-Petch plot. Lowtemperature and high-strain rate superplasticity have been found in some nanocrystalline materials. Theoretical prediction and experimental data indicate

The changeover to lead-free solder and components metallization in conjunction with the market transition to portable products is expected to have a strong impact on the reliability of lead-free electronics. For handheld electronic products, particular concern has raised over solder joint fracture induced by drop impact. Existing test methods used to evaluate solder ball attachment, shear and pull test, thus

This report describes the major components and activities of EXPLOMET 90, an international conference on shock-wave and high-strain-rate effects held at UCSD August 12-17, 1990. The conference was attended by approximately 200 scientists and engineers from throughout the world and was enriched by invited/keynote lectures by a group of world-renowned scientists. Over 110 talks were presented and twenty posters were displayed. The proceedings are being published by M. Dekker and will appear in February 1992. Sessions were devoted to the following topics: (1) High Strain Rate Deformation; (2) Shock and Combustion Synthesis; (3) Dynamic Consolidation; (4) Shaped Charge Phenomena; (5) Shear Localization; (6) Dynamic Fracture; (7) Shock Phenomena and Superconductivity; (8) Shock Waves and Shock Loading; (9) Shock and Dynamic Phenomena in Ceramics; and (10) Explosive Welding and Metalworking.

This work presents an investigation on the effects of adiabatic heating and strain rate on the dynamic compressive response of titanium, iron, copper, and tin. The high strain rate tests were carried out with a Split Hopkinson Pressure Bar (SHPB) and the low strain rate tests with a servohydraulic testing machine. The temperature increase of the specimens during deformation was measured with high speed infrared thermography (IRT). The results show that all the investigated materials have positive strain rate sensitivity and temperature increases of up to 65 • C were observed in the high strain rate experiments (500-3100 s − 1). Adiabatic heating in all investigated materials increased with strain rate. The temperature increase at the strain rate of 1 s − 1 clearly diminished the strain hardening rate of iron and titanium but was seemingly insufficient to impact the mechanical behavior of copper and tin. The Taylor-Quinney coefficients (β int and β diff) were found to be strain and strain rate dependent. At higher strain rates (1200-3100 s − 1), the integral β int was smaller in the beginning of the test (0.2 to 0.7) and increased to approximately 0.8-0.9 at larger plastic strains. The differential β diff comprised gaussian curves as a function of strain whose maximum values were from 0.9 to 1.2 for the investigated materials. Tin had lower β int and β diff with higher strain hardening rates, while copper had a higher β int and β diff with a low strain hardening rate throughout the high strain rate tests. These results indicate that copper had a more stable microstructure during deformation and converted most of the applied plastic work into heat, while tin had a faster evolving microstructure which stored more plastic work in its microstructure during plastic deformation. Furthermore, this suggests that β int and β diff can be used as parameters to investigate the stability and the microstructural evolution of materials under high strain rate plastic deformation. β diff is more appropriate to describe the instantaneous thermomechanical behavior of a material and β int is more appropriate for applications which benefit from a single parameter to characterize how efficiently a material converts plastic work into heat up to a given strain level.

S-Glass Fibre Reinforced Epoxy (S-GFRP) extracted from GLARE® has been experimentally characterised at three distinct strain-rates (510-4 s-1, 10 s-1 and c.a. 2000 s-1) and in four loading directions (0°, 90° and 45° to the fibre direction and in the through thickness direction). A novel specimen clamping mechanism was developed and full-field optical strain measurement was applied. With the aid of these techniques a significant increase in failure-strength and apparent elastic modulus in all loading directions, particularly in fibre direction, was observed with increased strain-rate; strain to failure increased in the fibre direction and decreased in all other loading directions.

This work presents a comprehensive analysis of the effects of strain and strain rate on the adiabatic heating and the mechanical behavior of a CoCrFeMnNi high-entropy alloy (HEA). In this investigation, compression tests were carried out at quasi-static and dynamic strain rates. The temperature of the specimens was measured using high speed infrared thermography. The high strain rate tests were conducted with a Split Hopkinson Pressure Bar, and the tests at lower strain rates were performed using a universal testing machine. The material exhibited a positive strain rate sensitivity, as true stress-strain plots were shifted upwards with the increase in strain rate. With exception of the isothermal tests, temperature rise and the Taylor-Quinney coefficient (β) were noticeably similar for the investigated strain rates. This study shows that the common assumption that β can be considered 0.9 and constant is possibly not very accurate for the CoCrFeMnNi alloy. The β is influenced by at least strain and strain rate.