Strain Rate Tension Research Articles

Deformation of thermosetting resins at impact rates of strain. Part I: Experimental study

Three thermosetting resins have been tested in compression at strain rates between 10 −3 and 5×10 3 s −1 . A smaller number of tests have been performed on the same resins at similar strain rates in tension. The testing technique is described and the results obtained are presented. Significant differences between the three materials were found over the whole range of strain rates. All three exhibited a pronounced strain rate sensitivity. Temperature measurements, performed in compression tests at the higher strain rates, showed evidence of adiabatic heating. This revealed the presence of energy storage mechanisms in both yield and strain–stiffening regimes.

An experimental method for dynamic tensile testing of concrete by spalling

A new application of the spalling phenomenon in long specimens is reported in this paper. The new experimental technique is based on an experimental setup which consists of an air launcher of cylindrical projectiles with a Hopkinson bar as a measuring tool and a relatively long concrete specimen in contact with the bar. The incident compression wave transmitted by the Hopkinson bar into the specimen is reflected as a tensile wave causing spalling. Although such configurations have been reported in the past, the main advantage of the present approach lies in the application of the detailed analysis, based on the wave mechanics with dispersion, to extract the specimen behaviour. Such an approach leads to an exact estimation of the local failure stress in tension at high strain rates, even above 100 s −1. This paper demonstrates, using two series of tests on concrete, that this experimental setup can cover one decimal order of strain rates, from ∼10 to ∼120 s −1. The tests performed at high strain rates on wet and dry concrete have indicated that the tensile strength is substantially influenced by the loading rate or strain rate. The absolute value of the failure stress for wet and dry concrete is almost the same for a particular strain rate, which does not occur when subject to low strain rates in tension or compression. A brief discussion is offered on a high rate sensitivity of concrete strength in tension at high strain rates.

Experimental and numerical study of concrete at high strain rates in tension

Test results for concrete loaded at high strain rates in tension, obtained with a new experimental technique, and numerical simulations of those experiments by discrete element method (DEM), are presented in this paper. The experimental method is based on the Hopkinson bar principle combined with the spalling phenomenon. The setup was equipped with a high-speed CCD camera (10 6 pictures/s) for the recording of the fracture process. This original technique allowed for determination of the tensile strength of wet concrete at high strain rates (higher than 20 s −1). Such data are unique in the literature, particularly in this range of strain rates, and they demonstrate a high rate sensitivity of tensile strength. A local cumulative criterion is proposed and implemented in the numerical analysis. The discrete element method, adapted for cohesive materials, approximates the concrete as an assembly of rigid particles connected by interaction laws. The experimental data and the numerical results of the test simulations are presented and compared.

High strain rate compression and tension response of high hard tool steel

The cores of armor piercing (APM2) bullets are generally made of high hard (Rc -60-62) 1070 steel. Tool steel of type AISI O1 is very similar in composition to 1070 steel and can be heat-treated to Rc 60-61. We are conducting a study to generate material model data to numerically simulate the penetration of.30 and.50 caliber M2AP bullets into a variety of ceramic/aluminum/steel ballistic targets. Compression and tension properties of heat-treated tool steel are to be presented. The compressive and tensile behavior of AISI O1 tool steel is studied through quasi-static tests, Hopkinson bar experiments and Taylor impact tests. Compressive strength of the heat-treated tool steel increases by a factor of 3 compared to untreated tool steel. Furthermore, experimental data suggest that hard tool steel is strain rate insensitive in tension as well as in compression. However, measured compressive strength (3.5 GPa) and tensile strength (2.5 GPa) at high strain rates (10 3 /s) are different, suggesting that the material behaves almost like a ceramic. A constitutive model for the material is developed based on the experimental data and is used to simulate ballistic penetration into 6061-T6 aluminum and alumina ceramic/aluminum targets.

Dynamic Bauschinger effect

An experimental investigation of the “Bauschinger effect” in materials under dynamic loading conditions is presented. In this study, a tension split Hopkinson bar with a momentum trap is used to subject a tensile specimen to a single high strain-rate tension pulse of known magnitude and duration. The uniformly deformed gauge length of the tension specimen is then sectioned and loaded in a compression split Hopkinson bar with a momentum trap, at essentially the same strain rate as that of the initial tension test. Comparison is made between these high strain rate Bauschinger experiments and similar tests carried out under quasi-static conditions. Two different material microstructures were examined: solid-solution strengthened and precipitation-strengthened alloys. The Bauschinger effect is found to be a function of the initial material microstructure as well as strain rate.

Computer Simulation of Early Stress Relaxation Behaviour

In a screw-driven machine, the transition from tension to stress relaxation occurs over a finite time that is required by the cross head to decelerate from a constant speed (tension) to a dead stop (relaxation). Computer simulation with a simple yet realistic model shows that several apparently anomalous features of early stress relaxation can be ascribed to this transition time. The extent to which transition time modifies the early relaxation is found to depend upon the strain rate sensitivity of the flow stress of the specimen, the machine stiffness and the strain rate in tension

Deformation kinetics by crazing in glassy polymers

In order to confirm the proposed theory of the plastic deformation caused by crazing, the theoretical deformation curves derived from the dislocation analogue were calculated using the data of craze behaviour measured under static tension and compared with the experimental results of creep and constant strain-rate tension in PMMA and PVC plates wetted by kerosene as a crazing agent. Favourable agreement between the theoretical and experimental results may provide evidence that the proposed method is valuable for estimating the amount of the plastic strain caused by crazing.

Plastic deformation by crazing in polycarbonate

On the basis of the data of craze behaviour under static tension, the deformation curves followed by continuous initiation and growth of crazes are plotted for a variety of testing conditions, such as constant stress, constant strain-rate and constant strain tensions applying the Johnston-Gilman theory for dislocations. Experimentally determined values of the density and growth rate of crazes, which are regulated in accordance with a simple rate theory, are used for the calculations. Comparison of the theory with the experimental results is favourable except for the results of high strain-rate tension and stress relaxation. The application of the dislocation analogue approach to the craze deformation kinetics was found to be valuable.

変態超塑性の粘弾性的挙動について

The transformation superplastic behavior in commercial pure iron, hypoeutectoid steel (SS 41) and eutectoid steel (SK 5) has been examined, using an originally desinged differential type apparatus for measuring dynamic superplasticity. Strain rates in tension and torsion are measured and analysed with special attention to the principal stresses.The main results obtained are as follows:(1) The transformation strain of all the materials mentioned above varies linearly accompanying an increase of the applied stress at the stage of the lower stress level, and a linear relation-ship between the applied stress and the maximum strain rate was observed.(2) For the materials under the transformation superplastic deformation, the three times-law of viscosity, λ=3η, could be applied to the relation between the normal viscosity λ and the coefficiency of viscosity η.(3) When defining the effective stress \barσ and strain rate \bar\dotε like \barσ=3τ and \bar\dotε=\dotγ⁄3 respectively, where τ is the shear stress and \dotγ is the shear strain rate, the experimental data for two different types of the strain of tension and torsion due to the transformation superplastic flow can be explained by a unified curve.

Dependence of mechanical characteristics of St. 35 steel on strain rate in tension at low temperatures

Dependence of mechanical characteristics of St. 35 steel on strain rate in tension at low temperatures