Pressure-shear Impact Research Articles

Plastic behavior of Zr51Ti5Ni10Cu25Al9 metallic glass under planar shock loading

Planar shock compression experiments are performed on a Zr-based bulk metallic glass (BMG), Zr51Ti5Ni10Cu25Al9 at peak shock stresses from 10 GPa to 27 GPa to investigate its plastic behavior under high pressure and high strain-rate. The particle velocity profiles measured at the free surface of the samples are analyzed to estimate longitudinal stresses of the Zr-based BMG in the shock loading process,and then shear stresses are obtained by comparing longitudinal stresses with a hydrostat. Though there is an obvious relaxation effect after elastic front, the Hugoniot elastic limit of the Zr-based BMG is found to increase with shock stress increasing. However, the shear stresses across the plastic shock front display stress hardening above the Hugoniot elastic limit followed by a stress relaxation (softening) to Hugoniot state, and the relaxation level also increases with shock stress increasing. The changes of shear stresses under planar shock compression are consistent with the results from molecular dynamic simulations, but obviously different from the pressure-shear impact experimental results or uniaxial stress impact experimental results.

Dynamic shearing resistance of molten metal films under high pressures and extremely high shearing rates

In the present study plate-impact pressureshear experiments have been conducted to study the dynamic shearing resistance of molten metal films at shearing rates of approximately 107 s−1. These molten films are generated by pressure-shear impact of relatively low melt-point metals such as 7075-T6 Al alloy with high hardness and high flow-strength tool-steel plates. By employing high impact speeds and relatively smooth impacting surfaces, normal interfacial pressures ranging from 1–3 GPa and slip speeds of over 100 m/s are generated during the pressure-shear loading. The resulting friction stress (∼100 to 400 MPa) combined with the high slip speeds generate conditions conductive to interfacial temperatures approaching the fully melt temperature regime of the lower melt-point metal (7075-T6 aluminum alloy) comprising the tribo-pair.

On pressure-shear plate impact for studying the kinetics of stress-induced phase transformations

Pressure-shear plate impact experiments are proposed for studying the kinetics of stress-induced phase transformations. The purpose of this paper is to determine loading conditions and specimen orientations which can be expected to activate a single habit plane variant parallel to the impact plane, thereby simplifying the study of the kinetics of the transformation through monitoring the wave profiles associated with the propagating phase boundary. The Wechsler-Lieberman-Read phenomenological theory was used to determine habit plane indices and directions of shape deformation for a CuAlNi shape memory alloy which undergoes a martensitic phase transformation under stress. Elastic waves generated by pressure-shear impact were analyzed for wave propagation in the direction of the normal to a habit plane. A critical resolved shear stress criterion was used to predict variants which are expected to be activated for a range of impact velocities and relative magnitudes of the normal and transverse components of the impact velocity.

Pressure-shear impact investigation of strain rate history effects in oxygen-free high-conductivity copper

A combined experimental and computational investigation of the behavior of oxygen-free high-conductivity copper under very high shear rates is presented. Pressure-shear plate impact is used for conducting constant strain rate tests and strain rate change texts in which the specimen is strained at shear rates up to 10 6s −1 for 1μs and then strained at substatially lower shear rates for another microsecond. The specimen is sandwiched between two hard elastic plates to impose conditions of simple shear at very high strain rates and constant hydrostatic pressure. Marked increases in flow stresses are observed at strain rates of 10 5s −1 and higher. Flow stresses decrease gradually after a sharp drop in strain rate in all strain rate change tests. Homogeneous equiaxed dislocation cells are found as the predominant substructure in the deformed specimens. Theoretical analyses of the nonlinear wave propagation within the specimen are carried out using a general internal variable formulation in which the hardening rate depends on the rate of deformation. The governing system of hyperbolic partial differential equations is solved using a finite-difference scheme; computational results are compared with the experimental results. Both small- and finite-deformation formulations are considered. Only the internal variable model which incorporates a strong rate sensitivity of strain hardening is successful in describing the observed response to the change in strain rate. The enhanced rate sensitivity at high strain rates is concluded to be related primarily to the rate sensitivity of strain hardening, not the rate sensitivity of the flow stress at constant dislocation structure. The generation and evolution of dislocation cells appears to be the dominant micromechanical process during the high- rate deformation of pure metals.

Pressure-shear impact and the dynamic viscoplastic response of metals

Pressure-shear plate impact experiments are used to investigate the viscoplastic response of metals at shear strain rates ranging from 10 5 s −1 to 10 7 s −1. Flat specimens with thicknesses between 300 μm and 3 μm are sandwiched between two hard, parallel plates that are inclined relative to their direction of approach. Nominal stresses and strains in the specimens are determined from elastic wave profiles monitored at the rear surface of one of the hard plates. Results are reviewed for two fcc metals: commercially pure aluminum and an aluminum alloy. New results are presented for bcc high purity iron, a high strength steel alloy and vapor deposited aluminum. For commercially pure aluminum the flow stress increases strongly with strain rate as strain rate increases from 10 4 s −1 to 10 5 s −1. At strain rates above 10 5 s −1 the flow stress, based on results for thin vapor-deposited aluminum specimens, increases strongly, but less than linearly, with increasing strain rate until it saturates at strain rates between 10 6 s −1 and 10 7 s −1. Preliminary results for high purity alpha-iron indicate that the flow stress increases smoothly over eleven decades of strain rate, and faster than logarithmically for strain rates from 10 2 s −1 to greater than 10 6 s −1. In contrast, for a high strength steel alloy the flow stress depends only weakly on the strain rate, even at strain rates at high as 10 5 s −1. Such contrasting behavior is attributed to differences in the relative importance of viscous glide and thermal activation as rate controlling mechanisms for dislocation motion in the various metals. Numerical studies indicate that experiments performed at the highest strain rates on the thinnest specimens are not adiabatic, thus requiring a full thermal-mechanical analysis in order to interpret the data.

Discussion of pressure-shear impact and the dynamic viscoplastic response of metals

Discussion of pressure-shear impact and the dynamic viscoplastic response of metals

On the dynamical response of particulate-loaded materials. I. Pressure-shear loading of alumina particles in an epoxy matrix

Results of a pressure-shear impact experiment conducted on alumina-filled epoxy are presented. In the pressure-shear experiment the coupled longitudinal and transverse motion generated by the normal impact of Y-cut quartz is transmitted into an alumina-filled epoxy sample. This provides data on the response of the sample material to more general loading conditions than those obtained in the uniaxial strain configuration and allows the development of more complete material models. Experimental results are presented in this paper, and a model for alumina-filled epoxy which incorporates the data is presented in the following paper [J. Appl. Phys. 53, xxxx (1982)].

Pressure-Shear Impact of 6061-T6 Aluminum

Experimental results are presented for impact of two parallel plates of 6061-T6 Aluminum, skewed at an angle of 26.6° from the axis of the projectile. A transverse displacement interferometer (TDI) [1] with a 200 lines/mm grating is used to monitor the transverse motion of the rear surface of the aluminum target plate. Two first-order diffracted laser beams are used for this TDI with a resulting sensitivity of 2.5 μm per fringe. In addition the normal motion of the rear surface is monitored simultaneously by means of a velocity interferometer [2] in which the zeroth-order diffracted beam is used as the beam reflected from a moving mirror. Comparison of the velocity-time profiles of the target rear surface with those predicted by the analysis given by Abou-Sayed and Clifton [17] indicates that the computed transverse velocity-time profiles have regions of steeper slope than observed in the experiments. This discrepancy appears to be mainly due to the inadequacy of the assumption of isotropic hardening and the Huber-Mises yield function in the analysis [17]. The sensitivity of the transverse velocity profiles to the plastic flow characteristics of the material suggests that the pressure-shear impact experiment, when used with a TDI, is a good technique for the study of material properties at very high strain rates (104 ∼ 105 sec−1) and under postshock conditions.