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There is a range of thresholds for the response of condensed matter under loading in compression, from the yield point to that at which the bond strength is overcome and warm dense matter is formed. Yield stress shows a correlation between the length scale swept by the rise of the pulse and the defect distribution within the target for a range of materials. Strain rate is also a useful term that reflects the evolution of the stress state within a target but must also be defined for a volume element containing a particular defect distribution to reflect continuum conditions acting within; it thus applies to a defined length scale within a target. Examples are shown using shock pulses that spall metal targets. Different stacking shows differing behaviour yet in each case momentum is conserved. This overview suggests simple observations must take account of mechanisms operating at different timescales and lengthscales in the development of damage in materials and structures. [ABSTRACT FROM AUTHOR]

The current study assesses the application of the Taylor Test to validate hydrocode modelling of composite materials. 0° in-plane and through-thickness rods were cut from a 25 mm thick composite panel, made from autoclave cured 0°, 90° uni-directional carbon/epoxy prepreg. The rods were fired against a semi-infinite steel anvil and high-speed video imaging was used to capture the difference in rod shape and damage patterns during the experiments. Results of simulation with a rate sensitive, transversely isotropic composite material model implemented in the CTH hydrocode were compared with the present experiments. The model showed good correlation with global deformation of the rods, and was used to qualitatively assess some of the asymmetric deformation features in the material. As the present model implementation did not account for damage at this stage, it did not predict inter-ply delamination normal to the impact face for the in-plane 0° rods and that parallel to the impact face in the through-thickness samples. [ABSTRACT FROM AUTHOR]

A series of uni-axial strain experiments have been undertaken to determine the spall response of 21-6-9 stainless steel under varied peak stress and tensile strain-rate loads. The material shows a positive dependency of spall strength on peak stress and strain-rate over the 7–18 GPa longitudinal stress regime. Structure is observed in the reload signal which is suggested to represent evidence for either secondary spall resistance or two concurrent fracture processes. [ABSTRACT FROM AUTHOR]

The response of the magnesium alloy, AZ61 to shock loading has been investigated in terms of it’s Hugoniot (Equation of State) and variation of shear strength with impact stress. Comparison of the Hugoniot with that of the similar magnesium alloy AZ31 shows very little difference, and hence gives us confidence in our results. Measurement of the lateral stress shows a decrease behind the shock front which suggests a degree of time dependent hardening. Similar results have been observed in fcc metals, corresponding to observed increases in dislocation density in recovered samples. [ABSTRACT FROM AUTHOR]

Shock-loading of a material in contact with a high explosive (HE) experiences a “Taylor wave” (triangular wave) loading profile in contrast to the square-wave loading profile imparted via the impact of a flyer plate. Detailed metallographic and microtextural analysis of the damage evolution in spalled Cu samples as a function of square/triangle and sweeping detonation-wave loading is presented. [ABSTRACT FROM AUTHOR]

A series of shock loading experiments have been performed on two heat-treated states of the aluminium alloy, 6061; T0, a solution treated condition, and T6, a solution treated and fully aged state. Lateral stress measurements indicate the T6 condition is stronger than T0, as would be expected. Results also indicate that the rate of hardening behind the shock front is somewhat greater in T0 than T6, indicating a shift in deformation from one based upon the generation of, and storage of, dislocations, to one where the presence of intermetallic precipitates appears to inhibit dislocation generation and storage processes. [ABSTRACT FROM AUTHOR]

Experimental stress and velocity profiles in a lead filled glass demonstrate a pronounced kinetic behaviour for failure waves in the material during shock loading. The present work summarises the experimental proofs of the kinetic behaviour obtained with stress and velocity gauges. The work describes a model for this behaviour employing a kinetic description used earlier for fracture waves in Pyrex glass. This model is part of a family of two-phase, strain-rate sensitive models describing the behaviour of damaged brittle materials. The modelling results describe well both the stress decay of the failure wave precursor in the stress profiles and main pulse attenuation in the velocity profiles. The influences of the kinetic mechanisms and wave interactions within the test assembly on the reduction of this behaviour are discussed. [ABSTRACT FROM AUTHOR]

It is difficult to obtain experimental data for the behaviour of material under shock loading due to the dynamic nature of this process and the finite time available during which measurements can be taken. As a result the shock recovery technique was been developed to allow recovery of material after a single shock-release loading. The main goal of this experimental technique is to examine material properties after a single, well-defined shock wave followed by a single release wave have been introduced. The process should be such that any change found in the sample after recovery can be attributed to the shock process alone, the geometry and design of the target and the fixture play an important role in achieving this. In this work a shock recovery experimental configuration is proposed from simulations performed using the Lagrangian hydrocode DYNA. The investigation of the shock wave in the simulation entails examining the time histories for a single element, or block of elements of interest. A new design is developed with improved performance. [ABSTRACT FROM AUTHOR]

Lateral stress gauges have been used to measure the variation of shear strength with longitudinal stress in shock loaded Ti-6Al-4V. Results show that lateral stress decreases slightly behind the shock front before reaching a constant level. We believe that this is due to the deformation microstructure not reaching its steady state immediately, but rather evolving over time. We have also observed that the Hugoniot and shear strength of our material is in close agreement to previous work. Recovered Taylor impact specimens show a circular foot print, and x-ray tomography examination shows no evidence of tensile damage immediately under the impact face. [ABSTRACT FROM AUTHOR]

There is a recent interest in the response of thermoplastics to shock. Previous work on three simple hydrocarbons has indicated that the shear strength increases with the complexity of the side group. Strength values have been calculated using lateral stress measurements with manganin gauges that have been recalibrated for use in the low stress regime. The present work aims to investigate the effect of the configuration of the thermoplastic's chain when side groups are added. Results show that whilst polyethylene has the lowest shear strength, polypropylene and polystyrene have similar values. In all cases the strength of polymer increases with time after the shock has past. As the applied stress increases, polystrene and polypropylene strengthen to a higher degree when compared with polyethylene. Explanations are offered in terms of microstructure and tacticity of the chain. [ABSTRACT FROM AUTHOR]

In a recent series of papers, we have made a study of the shock response of a number of polymers, whilst systematically changing their structure, for example pendent side group size (polyethylene, polypropylene and polystyrene) or degree of halogenation (polyethylene, polyvinylidene difluoride and polytetrafluoroethylene). In this study, we examine a single polymer, polyethylene in two structural forms—high density weight and cross-linked. Results show that overall, the shear strengths of these two variants of polyethylene are similar. However, we note that the rate of change of shear strength with applied shock stress is greater in the cross linked material. We have suggested that this be due to the crosslinking restricting the ability of the polymer chains to move relative to each other. [ABSTRACT FROM AUTHOR]

There is an ongoing interest in identifying inexpensive armour materials for use in the protection of personnel and vehicles. The response of AD995 under shock loading is one of the materials most extensively investigated. Over recent years, workers have reported failure occurring in various polycrystalline ceramics behind the shock front. This phenomenon has been investigated using embedded stress sensors and a recovery technique that has allowed observation of the microstructure above and below the Hugoniot Elastic Limit (HEL) and these results are brought together here to explain the observed behaviour. The failure front velocity is found to change with the applied stress, in particular it slows as the HEL is exceeded. The microstructure shows the response below the HEL is dominated by intergranular failure whilst above it, the grains exhibit plasticity (including twinning). The HEL is thus shown to be characteristic of alumina viewed as a composite with randomly oriented alumina grains. [ABSTRACT FROM AUTHOR]

The Taylor anvil test is widely used for the validation of constitutive models in non-linear continuum mechanics codes. Numerical simulations have been performed on two modified specimen geometries: a sleeved cylindrical projectile and a sleeved conical projectile. In this study the core material is aluminum and the sleeve material is tungsten alloy, providing a large difference in impedance. The objective is to develop concepts that allow the stress profile along the axis of the projectile to be controlled and varied, allowing a greater range of material behavior to be investigated through anvil tests. The simulations show that by altering the lateral stress relief waves the stress profiles are significantly altered. The sleeved conical projectile achieves significantly higher compressive pressure on the axis than achievable through uniaixal compression for a given velocity. [ABSTRACT FROM AUTHOR]

The measurement of shear strength via the use of lateral stress gauges has been shown to be a viable technique in a number of materials. An experimental investigation on the intermediate-rate behaviour and shock response of the aluminium alloy, 6082-T6, is reported here. Results obtained using the lateral stress gauge technique show that the shear strength increases with impact stress. The lateral stress behind the shock front is seen to be relatively flat, unlike many other face-centred cubic metals and alloys, where a decrease in lateral stress indicates an increase in shear strength. This unusal response may be a reflection of the high stacking fault energy of aluminium and its alloys resulting in a reduction of the work hardening (i.e. increases in dislocation and/or twin density). Further plate impact results show that the Hugoniot of 6082-T6 is in effect identical to that of the more widely known 6061-T6. Split Hopkinson pressure bar results are used to provide a fuller picture of the rate-dependant behaviour of 6082-T6 over a range of loading rates and conditions. [ABSTRACT FROM AUTHOR]

Interest in the behaviour of the common stainless steel grade 304 at high rates of strain is always high due to the materials regular use in industry. Longitudinal and lateral stresses during the shock loading of SS-304L have been measured using manganin stress gauges. The shear strength has been shown to increase with impact stress. Comparison with a pure fcc metal (nickel) shows a significant increase in strength. Strengths are similar to those of mild steel, but the rate of increase with impact stress is much greater in SS-304L. These results are discussed in terms of structure and degree of alloying. [ABSTRACT FROM AUTHOR]

The shock response of polyvinylchloride has been measured using manganin stress gauges, and compared to those of polyethylene. Results show that this polymer, with the replacement of a hydrogen atom with chlorine, has significantly lower shock velocities and release velocities. We have suggested that the presence of the highly electronegative chlorine atom may reduce the stiffness of the carbon-carbon backbone by drawing charge towards itself. [ABSTRACT FROM AUTHOR]

The response of a 2-D glass-fibre epoxy composite to one-dimensional shock loading has been investigated as a function of orientation of the fibres to the loading axis, to determine its equation of state. When the shock axis is parallel to a fibre direction, the shock front appears ramped at low stresses, steepening as the impact stress increases. Analysis of these traces suggests that a low stress amplitude wave is transmitted along the fibres at a high velocity, with a lower velocity wave is transmitted through the matrix between those fibres, taking the material to its final stress amplitude. [ABSTRACT FROM AUTHOR]

In the present paper we address the phenomenon by which embedded manganin gauges between soda-lime plates always fail to record the full stress history when the shock level is above 5.5 GPa. Our explanation for this early failure is related to the fracture wave generated in the backing glass plate which affects the gauge or its leads, in such a way as to disconnect them. 1D numerical simulations and several plate impact experiments were made in order to support our assumption. [ABSTRACT FROM AUTHOR]

A series of experiments have been performed which show that the response of manganin gauges in lateral orientation is dependent upon the gauge geometry. Below a lateral stress of ca. 3.5 GPa T-shaped gauges have a lower change in resistance than their more common grid shaped counterparts. However, above this level, T and grid gauges have a common response. A preliminary analysis indicates that the T-gauges are behaving more like an embedded wire gauge in this stress regime. Such behaviour must be accounted for when using these gauges, especially in low impedance materials shocked to low stress levels. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Longitudinal and lateral stresses during the shock loading of pure tungsten have been measured using manganin stress gauges. The Hugoniot has been compared to the previous work of others and shown to be in close agreement. Lateral stresses have been shown to increase behind the shock front, implying that the shear strength decreases. Whilst this is similar to results in tantalum, comparison with recovery experiments in the literature suggests that this may be due in part to a brittle failure process. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Previous work by a number of authors has shown that the spall strength of the engineering alloy, Ti 6Al - 4V increases markedly with pulse duration. In this paper, we have reproduced those results in a low oxygen variant of the alloy, over a range of impact stresses. The microstructure consisted of a mixture of primary α grains in a matrix of transformed β. Samples have also been shock loaded and recovered under conditions of one-dimensional strain, to compliment the results of the stress gauge experiments. In all the recovered samples, complete spallation occurred, but examination of damage at secondary sites showed that this occurred via nucleation and growth of pores. Ductile failure appears to be a mixture of void formation and coalescence within primary α grains and along primary α / transformed β boundaries. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The dynamic response of the shape memory alloy NiTi has been of interest to a number of investigators because it displays a shape memory effect. The dynamic tensile (spall) strength of this material is measured under one-dimensional shock loading. The loading stress pulse length and impact stress were varied to a peak stress of 15 GPa. The pull back stress (σpbs) was found to increase with the applied pulse length. This suggests that the dynamic tensile strength is dependent upon the generation of a deformation micro structure that evolves behind the shock front. In contrast, increasing stress levels result in a near-constant pull back stress, although at the lowest applied stress, spallation did not occur. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper investigates the influence of the impact stress on the magnitude of the shear stress under one-dimensional shock loading. The shear stress is calculated from the measured longitudinal and the lateral stresses. New data in terms of shock stress, particle velocity and shock velocity has been gathered. Results indicate that the lateral stress has a positive dependence on the impact stress. A general decrease of the lateral stress was also observed immediately after the impact, while the longitudinal stress remains constant for the duration of the pulse length. This suggests that the shear strength increases behind the shock front. This decrease had been found to reach a constant value for the specimens impacted at lower stress. A complex mechanism of deformation behind the shock front during loading was thus reveals. This limit, related to the inflexion point noted on the Hugoniot (Us-up), seems to be an effect of the martensitic phase transformation undergoes by the material. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The behaviour of the intermetallic compound, Ni3Al under shock loading conditions has been measured. The Hugoniot Elastic Limit occurs at ca. 530 MPa, which converts to a 1-D yield stress of 273 MPa, in agreement with quasi-static data. In contrast, the ductility at shock-induced strain-rates appears much reduced when compared to lower strain-rates. The Hugoniot in terms of shock velocity and particle velocity suggests that Ni3Al is more compressible than pure nickel. This is in agreement with the greater stiffnesses in nickel, measured using ultrasonic techniques. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The response to shock loading of a glass-fibre epoxy composite has been investigated in terms of stress, particle velocity, shock velocity, release velocity and reload signal due to spall. The shock velocity has a linear relationship with particle velocity, and shock stress lies a little above the corresponding hydrodynamic pressure. Results show that the likelihood of spallation increases with pulse duration, suggesting that damage in the material accumulates behind the shock front. This would seem confirmed by release wave speed measurements, that show the zero particle velocity intercept is lower than either c0 (for the shock velocity — particle velocity relationship) or the longitudinal sound speed (cL). © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The dynamic response of pure nickel (Ni), and its alloy, Ni-60Co (by weight %), has been investigated during one-dimensional shock loading. Few materials’ properties are different and the only significantly altered feature is the reduced stacking fault energy (SFE) for the Ni-60Co. This paper considers the effect of this reduced SFE on the shear strength. Data (in terms of shock stress, particle velocity and shock velocity) are also presented. The influence on the shear stress, τ of cobalt additions in nickel are then investigated and presented. Results indicate that the lateral stress is increasing in both materials with the increasing impact stress. The shear stress was found to be higher in the nickel than in the Ni-60Co. The progressive decrease of the lateral stress noted during loading indicates a complex mechanism of deformation behind the shock front. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The variation of shear strength with impact stress in an alumina-filled epoxy has been measured with lateral stress gauges. At lower stresses, a degree of hardening behind the shock front has been observed, which diminishes as shock stress increases. It is believed that this is due to a transition from a viscous response dominated by the epoxy matrix, to a more viscoplastic response. The measured shear strength has also been observed to reach a near constant level, as was suggested in a previous paper. We have also used these results to make an estimation of the HEL at ca. 2.0 GPa. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The behaviour of a carbon fibre — epoxy composite has been investigated as a function of specimen thickness. Results show that both the shock velocity and the shock stress are unaffected by transit distance. The relationship between Us and up over the range of measurements made in this investigation shows a higher value of c0 and lower value of S than that of a similar material within the literature. We believe that this is due to the slightly higher proportion of carbon fibres within the microstructure reducing the compressibility. Differences between the Hugoniot stress and the calculated hydrodynamic pressure suggests that the shear strength of this material increases with shock stress. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Manganin stress gauges have been used to determine the Hugoniots of two ferroelectric ceramics, lead zirconium titanate (PZT) and a similar material modified with tin (PSZT). Comparison with previously published data shows close agreement between our results for PZT and earlier work. The Hugoniot Elastic Limit has been determined, and also agrees with previous data. In the case of PSZT, the Hugoniot in terms of stress and particle velocity is similar to PZT. In terms of elastic wave velocity — particle velocity, results show an overall increase, in contrast to PZT, where wave speed was observed to decrease with increasing particle velocity. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Manganin stress gauges have been used to measure the lateral stress in a shock-loaded alumina. In combination with known longitudinal stresses, these have been used to determine the shear strength of this material, behind the shock front. The two-step nature of the lateral stress traces shows a slow moving front behind the main shock, behind which shear strength undergoes a significant decrease. Results also show that this front decreases markedly in velocity as the HEL is crossed, suggesting that limited plasticity occurs during inelastic deformation. Finally, comparison of measured shear strengths with other aluminas shows a high degree of agreement. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Transmission electron microscopy (TEM) has been used in an attempt to assess the nature and density of dislocations present in samples of a number of Ti alloys subjected to low and high strain rate deformation. It has been found that conventional defect analysis is straightforward in samples strained at low strain rates of 10-1 s-1 but it is not possible to carry out defect analysis in samples strained at 5 s-1. In samples strained at higher strain rates, such as 103 s-1 or as high as 108 s-1, similar difficulties can be encountered in some grains but in others defect analysis is possible. These results are interpreted in terms of the elastic anisotropy of the hexagonal phase in these alloys and in terms of the level of internal stress introduced by deformation in these two-phase alloys. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The shock Hugoniots of alumina-epoxy composite materials at two different alumina loadings have been investigated, using manganin stress gauges. These have been determined in terms of both the shock stress and the shock velocity with regard to particle velocity. Results show that the shock velocity has a linear relationship with particle velocity, in common with many other materials. These in turn have been used to determine the shock stress, and show a high degree of agreement with the measured shock stresses. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Samples of an aluminium-zinc-magnesium alloy, typical of high strength weldable aluminium alloys, have been heat treated to produce two different microstructural conditions, these being peak-aged and under-aged. Mechanical tests have been performed, both at quasi-static strain rates and under shock loading conditions to determine how the mechanical properties change with heat treatment. Results indicate that the material has its highest strength when peak aged. Properties are discussed in relation to observed features within the microstructure, as recorded by optical and scanning electron microscopy. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The shock response of poyether ether ketone (PEEK) has been investigated using manganin stress gauges mounted in longitudinal and lateral orientation to the impact axis. Measurements of the longitudinal stress with gauges at different positions within the shock assembly have determined the Hugoniot in terms of shock stress, shock velocity and particle velocity. It has been shown that the shock velocity has a simple linear response to particle velocity, in common with many but not all polymers. Measurements of lateral stress show a decrease behind the shock front, implying an increase in shear strength, possibly due to the viscoplastic nature of PEEK. Shear strength was also observed to increase with shock stress. A break in slope was observed at ca. 1.0 GPa, indicating a divergence between elastic and inelastic behaviour. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The dynamic behaviour of a transparent glass-ceramic material, Transarm, developed by Alstom UK for the UK MoD has been studied. Plate impact experiments have been used to measure the materials Hugoniot characteristics and failure behaviour. Longitudinal stresses have been measured using embedded and back surface mounted Manganin gauges. Above a threshold stress of ca. 4 GPa, the longitudinal stress histories exhibit a significant secondary rise, prior to attaining their Hugoniot stress. Lateral stresses were also measured by embedding Manganin gauges in longitudinal cuts. Significant secondary rises in stress were observed when the applied longitudinal stress exceeded the 4 GPa threshold, indicating the presence of a failure front. The dynamic shear strength of the glass has been measured using the longitudinal and lateral data. Even though significant strength drops have been measured before and behind the failure front, the material has a high post-failure strength compared to non- crystalline glasses. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

It is increasingly import to understand the high-strain rate response during impact of polymeric materials due to their widespread use in automotive and aerospace applications. There are three broad classes of polymer materials; elastomers, thermoplastics and thermosets. It is one of the first of these three classes that is investigated in this work. Research has been conducted to determine the Hugoniot of polychloroprene which was investigated using plate-impact experiments measuring the stress at varying positions whilst simultaneously probing the shock velocity in the material and the stress-particle velocity state. The shock-particle velocity data allows deduction of the constants co and S for the material whilst the other measurements made allow plotting of the measured stresses with the hydrodynamic curve to view the offset of the Hugoniot in a single series of experiments. For perfectly elastic/plastic materials, the shear strength of the material is given by the offset of the Hugoniot and hydrostat. In this material it is found to be either constant or to reduce slightly with increasing shock stress. The shear strength of polychloroprene is explored further using embedded lateral stress gauges. From these measurements, the shear strength has been determined as a direct experimental variable, and it's variation with shock stress deduced. [ABSTRACT FROM AUTHOR]

The Hugoniot of an epoxy resin has been measured using multiple, embedded manganin stress gauges. In this way, not only is stress measured as a function of particle velocity, but due to known spacings of the stress gauges, shock velocity has also been determined as an independent experimental parameter. In both cases, the results have been shown to be similar to those of previous investigations. However, it has been observed that stresses calculated from the shock velocity-particle velocity curve tend to be somewhat lower than the directly measured stresses, especially at the higher end of the stress range studied. It is believed that this may be a reflection of the variation in shear strength of this material under shock loading. [ABSTRACT FROM AUTHOR]

Longitudinal strain has been measured in DEDF (Type D, Extra Dense Flint), a high-density, lead-filled glass, over the stress range 2.0 GPa to 4.5 GPa (the supposed Hugoniot Elastic Limit -- HEL). Such glasses have been shown to fail in compression across a front which has been called the failure wave. Strain gauges have been mounted either near the impact face, such that the effect of failure may be observed, or near the rear (free) surface, such that the failure wave does not enter the gauge location. Below the stress at which the glass first supports a failure wave, measured strains agree well with values calculated from using elastic relations. Above this stress, the arrival of the failure wave results in an increase in compressive strain, and this has been correlated with the measurements of other variables such as lateral stress. Interestingly, only the measured values of strain behind the failure wave agree with calculated strains. [ABSTRACT FROM AUTHOR]

Plate impact experiments have been performed on two igneous rocks of differing grain size. Shock stresses have been measured by means of embedded manganin stress gauges, up to ca. 12 GPa. In the coarser grained material data was obtained from both copper impactors on rock and the reverse situation. Results are compared and contrasted to the existing data for other geological materials. [ABSTRACT FROM AUTHOR]

The B1/B2 phase transformation in potassium chloride (KC1) under shock loading conditions has been investigated using constantan strain gauges. These have been mounted in the samples in such an orientation so that they are sensitive to longitudinal strain. The samples themselves are made from pressed, polycrystalline potassium chloride. At the phase transformation stress of ca. 2 GPa, measured strains of ca. -0.1 are slightly higher than values calculated from knowledge of the particle and shock velocities at that stress level. Residual porosity in the microstructure has been suggested as a possible cause. Total strains over the stress range 2.5 GPa to 4.0 GPa show reasonable agreement with the work of others at lower stresses, but some disagreement at higher stress levels. We suggest that this might be due to the material being in a non-equilibrium state at the time of measurement. [ABSTRACT FROM AUTHOR]