One-dimensional Shock Loading Research Articles

The role of orientation on the shock response of single crystal tantalum

The response of single crystalline tantalum to one-dimensional shock loading has been investigated as a function of crystalline orientation to the loading axis. Results show that this has a significant effect, particularly on the Hugoniot elastic limit (HEL). [100] and [111] HELs are near identical with the [110] HEL having the lowest strength. This is contrary to predictions obtained by applying the Schmid factor analysis, where the ordering was expected to be (highest strength first) [111], [110], with the [100] orientation being the softest. Adopting a more appropriate model based on uniaxial strain conditions, as was previously done successfully for FCC aluminum and copper, did not rationalize our observations. We show that a non-Schmid effective stress model, incorporating twinning/anti-twinning asymmetry, has much greater success in reproducing the experimental relative HELs magnitudes. Using this model, we make a quantitative estimation of the magnitude of non-Schmid effects and compare these to equivalent low temperature, quasi-static estimates from the literature.

Spall Strength of Amorphous Carbon (Glassy Carbon) under Shock Loading in the Region of Its Anomalous Compressibility

The spall strength of SU-2000 amorphous glassy carbon has been studied in two series of shock experiments. The one-dimensional shock loading of samples has been performed by the impact of flat impactors. The primary experimental information includes velocity profiles of the rare surface of flat samples making contact with air or Plexiglas. The measurements have been performed in the range of anomalous compressibility of glassy carbon from ~−0.3 to +3 GPa. The spall strength of glassy carbon has been found to be −0.23(7) GPa. The theoretical estimate of the spall strength of SU-2000 glassy carbon is −2.4 GPa.

The variance on the shock response of a carbon fibre composite due to the orientation of the weave

Three different orientations of a tape-wrapped carbon fibre composite with phenolic resin matrix (abbreviated to TWCP) have been investigated under one-dimensional shock loading. This has been achieved via a single-stage gas gun, with manganin gauges as the diagnostic tool. The orientations of TWCP studied in this paper were 25°, 45° and 90°, with respect to the impact face. The shock response of these orientations, for this material, has been obtained (the Hugoniot equation of state). These results have been contrasted with previously reported literature data for the same material at different orientations (0° and 20°). It was found that orientation had minimal effect on the behaviour of this composite under shock. The exception to this was the 90° orientation which exhibited an elastic precursor at particle velocities of less than 0.65 mm µs−1; where the shock velocity was equivalent to the elastic sound speed of the material.

Tolerance of Artemia to static and shock pressure loading

Hydrostatic and hydrodynamic pressure loading has been applied to unicellular organisms for a number of years due to interest from food technology and extremophile communities. There is also an emerging interest in the response of multicellular organisms to high pressure conditions. Artemia salina is one such organism. Previous experiments have shown a marked difference in the hatching rate of these organisms after exposure to different magnitudes of pressure, with hydrostatic tests showing hatching rates at pressures up to several GPa, compared to dynamic loading that resulted in comparatively low survival rates at lower pressure magnitudes. In order to begin to investigate the origin of this difference, the work presented here has focussed on the response of Artemia salina to (quasi) one-dimensional shock loading. Such experiments were carried out using the plate-impact technique in order to create a planar shock front. Artemia cysts were investigated in this manner along with freshly hatched larvae (nauplii). The nauplii and cysts were observed post-shock using optical microscopy to detect motility or hatching, respectively. Hatching rates of 18% were recorded at pressures reaching 1.5 GPa, as determined with the aid of numerical models. Subjecting Artemia to quasi-one-dimensional shock loading offers a way to more thoroughly explore the shock pressure ranges these organisms can survive.

Spall strength and fracture behavior of Ti–10V–2Fe–3Al alloy during one-dimensional shock loading

The spall fracture behavior of a typical metastable β titanium alloy, Ti–10V–2Fe–3Al, is systemically investigated during one-dimensional shock loading. Shock pressures over 14 GPa are achieved through a series of plate impact experiments. The results show that the shock-induced β-to-α″ martensite (SIM) phase transformation strongly influences the spall fracture behavior of this alloy. The spall strength of Ti–10V–2Fe–3Al ranges from 2.5 to 3.1 GPa, and drops by nearly 20% as the shock pressure exceeds 9 GPa. The acicular SIM phases provide additional nucleation sites and propagation paths for micro-damage, leading to the reduction of spall strength of Ti–10V–2Fe–3Al. Microstructural analyses also suggest that Ti–10V–2Fe–3Al is likely to spall in a mixed fracture manner containing both brittle and ductile failure features. The spall fracture surface of this alloy is very rough and consists of facets covered by ductile dimples.

The Mechanical and Optical Response of Polychlorotrifluoroethylene to One-Dimensional Shock Loading

A series of plate impact experiments have been performed to probe the shock behavior of polychlorotrifluoroethylene (PCTFE), in terms of its optical and mechanical response. Interfacial velocity measurements using interferometric techniques have shown differences between measured and actual velocities, and been used to determine changes in refractive index due to shock-induced density increases. These have further been used to determine an optical correction factor, and allow the possibility of PCTFE being used as an optical window in future shock loading experiments. The shear strength of shock loaded PCTFE has also been shown to be near-constant behind the shock front, in common with other fluorinated polymers, although the strength variation with impact stress is greater than other similar materials. It has been suggested that the presence of a larger chlorine atom replacing a fluorine allows for a degree of tacticity between polymer chains, with local variations of charge density along the chain (due to the presence of the chlorine atom) also having an effect.

Effect of shock-induced martensite transformation on the postshock mechanical response of metastable β titanium alloys

Abstract Two metastable β titanium alloys, Ti–10V–2Fe–3Al (Alloy 1) and Ti–10Mo–8V–1Fe–3.5Al (Alloy 2), were subjected to one-dimensional shock loading and reloaded under a strain rate of 10 −3 s −1 and about 3 × 10 3 s −1 , respectively. The results show that the shock-induced β-to-α″martensite phase transformation dramatically influences the postshock mechanical properties of these alloys. The residual acicular martensite phases seriously worsen the ductility of the preshocked alloy, although they strengthen the material to some extent. Considering the severe deterioration in ductility of the postshocked alloy, this martensite transformation should be controlled in metastable β titanium alloys used as structural materials that need to withstand repeated shock loads. The shock Hugoniot for Alloy 2 was also determined in terms of shock wave velocity, particle velocity, and stress.

Shock-induced mechanical response and spall fracture behavior of an extra-low interstitial grade Ti–6Al–4V alloy

The mechanical response and spall fracture behavior of an extra-low interstitial (ELI) grade Ti–6Al–4V alloy are systemically investigated during one-dimensional shock loading. The effects of oxygen content on the shock response and dynamic failure characteristic of Ti–6Al–4V are also shown through the comparison of the obtained results with those for commercial Ti–6Al–4V. The measured Hugoniot elastic limit (HEL) of Ti–6Al–4V ELI is lower than that of commercial Ti–6Al–4V. While the fitted shock parameters and the measured Hugoniot in the stress-particle velocity space of Ti–6Al–4V ELI are found to be almost identical to those of commercial Ti–6Al–4V. These results indicate that the oxygen content can significantly affect the HEL of Ti–6Al–4V, but has little or no influence on the shock response of this alloy beyond the HEL. The postshock Ti–6Al–4V ELI does not display shock-induced strengthening during quasistatic and dynamic compression tests. Transmission electron microscopy (TEM) analyses reveal that the lack of high density dislocations or dislocation cells limits the shock-induced strengthening effect, although dislocation multiplication and tangles lead to increased yield strength and strain hardening rate of the reloaded material. Finally, Ti–6Al–4V ELI is demonstrated to spall in a ductile manner, and has similar spall strengths to those of commercial Ti–6Al–4V under different shock loading conditions. The oxygen content exerts no effect on the spall fracture manner of Ti–6Al–4V, although reducing the oxygen content enables this alloy to endure more micro-damages.

Mechanical response and effects of β-to-α" phase transformation on the strengthening of Ti–10 V–2 Fe–3 Al during one-dimensional shock loading

Plate impact experiments and quasistatic reload compression tests were conducted on a typical metastable β-titanium alloy, Ti–10V–2Fe–3Al, to investigate its mechanical response and strengthening behavior under one-dimensional shock-loading conditions. The Hugoniot elastic limit (HEL) for this alloy was measured to be 2.89GPa using a velocity interferometer (VISAR). The shock Hugoniot was also determined by measuring the stress, shock, and particle velocity as independent variables using manganin stress gauges. The fitted shock parameters (C0 and S) of Ti–10V–2Fe–3Al were found to be nearly identical to those of the α+β-titanium alloy Ti–6Al–4V. However, the measured Hugoniot in the stress-particle velocity space lied slightly above that of Ti–6Al–4V due to the higher density of Ti–10V–2Fe–3Al. The results of the quasistatic reload compression tests show that the postshock Ti–10V–2Fe–3Al is strengthened. The martensitic (β-to-α") phase transformation during shock wave loading may play a crucial role in the strengthening of this alloy. Finally, the inflection point corresponding to the phase transition was not observed in the VISAR trace even though the occurrence of the β-to-α" phase transformation was confirmed by microstructural analyses. The unobserved inflection point can be attributed to the difficulty in resolving the break of the wave fronts due to a very small or no change in the specific volume resulting from the martensite transformations.

The influence of microstructure on the shock and spall behaviour of the magnesium alloy, Elektron 675

Alloying elements such as aluminium, zinc and rare earth metals allow precipitation hardening of magnesium (Mg). The low densities of such strengthened Mg alloys have led to their adoption as aerospace materials and (more recently) they are being considered as armour materials. Consequently, understanding their response to high strain-rate loading is becoming increasingly important. Here, the plate-impact technique was employed to measure stress evolution in an armour-grade wrought Mg alloy (Elektron 675) under one-dimensional shock loading. The effects of sample orientation and heat treatment were examined. The spall behaviour was interrogated using a heterodyne velocimeter system, with an estimate made of the material’s spall strength and Hugoniot elastic limit (HEL) for both aged and unaged materials. In particular, it is shown that the HEL and spall strength values are higher along the extrusion direction. It is thought that this is caused by striations of relatively small grains that run along the extrusion direction.

The impact of structural composite materials. Part 1: ballistic impact

Composite materials are increasingly being used in the design of structures that will be subjected to high-velocity impact during their lifetime. In this review we will look at the recent advances in our understanding of how rigid composite materials behave under high-velocity impact. In particular, this review will focus on rigid structural composites such as carbon fibre reinforced plastic and glass fibre reinforced plastic laminates and what we have learned with regards to how they respond under ballistic-loading conditions. We will focus on a velocity regime that includes impacts from explosively-driven fragments, ice particles and bullets. The hypervelocity-impact response and how these materials behave under one-dimensional shock loading will be studied in an accompanying review (Part II).

Analytical and experimental study on the fluid structure interaction during air blast loading

A new fluid-structure interaction model that considers high gas compressibility is developed using the Rankine–Hugoniot relations. The impulse conservation between the gas and structure is utilized to determine the reflected pressure profile from the known incident pressure profile. The physical parameters of the gas such as the shock front velocity, gas density, local sound velocity, and gas particle velocity as well as the impulse transmitted onto the structure are also evaluated. A series of one-dimensional shock loading experiments on free standing monolithic aluminum plates were conducted using a shock tube to validate the proposed model. The momentum was evaluated using high speed digital imagery. The experimental peak reflected pressure, the reflected pressure profile, and the momentum transmitted onto the plate were compared with the predicted results. The comparisons show that the gas’s compressibility significantly affects the fluid structure interaction behavior, and the new model can predict more accurate results than existing models. The effect of factors, such as the areal density of a plate and the peak incident pressure on momentum transfer are also discussed using the present model. Moreover, the maximum achievable momentum and the fluid structure interaction time are defined and calculated.

On the response of ballistic soap to one-dimensional shock loading

The effects of projectile penetration into soft tissue are often studied using the tissue simulant ballistic soap. Consequently, a full understanding of the high strain-rate response of ballistic soap is desirable. Using the plate-impact technique, key shock parameters have been measured for impacts in the range 81–968 m/s, allowing derivation of the Hugoniot equation-of-state for soap in the U S– u P and σ X– u P planes. A polynomial Hugoniot relationship was found in the U S– u P plane, with the general form U S = 1.96 + 2.41u P − 0.72u P 2 ( ρ 0 = 1.107 g/cc). Further, embedded lateral manganin stress gauges were employed to interrogate the evolution of lateral stress within the soap. A gradient in lateral stress, whose magnitude increased incrementally with impact stress, was apparent behind the shock for σ X >1 GPa. It is proposed that at higher values of σ X, increased compression of hydrocarbon chains acts to increase the materials resistance to shear, a phenomenon consistent with steric hindrance.

On the behaviour of body-centred cubic metals to one-dimensional shock loading

The response of metallic materials to shock loading, like all loading regimes, is controlled largely by factors operating at the microscopic or atomic levels. Over the past few years, face-centred cubic (fcc) metals have received a level of attention where the role of features such as stacking fault energy and precipitation hardening have been investigated. We now turn our attention to body-centred cubic (bcc) metals. In the past, only tantalum, tungsten, and their alloys have received significant attention at high strain-rate conditions due to their use by the ordnance community. In particular, this investigation examines the shear strength of these materials at shock loading conditions. Previous results on tantalum, tungsten, and a tungsten heavy alloy are reviewed, and more recent experiments on niobium, molybdenum, and Ta–2.5 wt% W presented. Results are discussed in terms of known deformation mechanisms and variations of Peierl’s stress.

The role of aging on the mechanical and microstructural response of aluminum 6061 to one-dimensional shock loading

The shock response of the aluminum alloy 6061, and its variation according to heat treatment have been monitored via the placement of stress gauges in such orientations so as to be sensitive to the lateral component of stress, and hence the shear strength. To complement these measurements, the postshock microstructure and mechanical response have also been determined via full one-dimensional recovery techniques. Results have shown that the solution treated (T0) state, as a largely single phase material displays a fast rising shock pulse with a significant degree of hardening behind the shock front. This indicates that a high degree of dislocation generation is expected. Postshock analysis of recovered samples has confirmed this hypothesis, with dislocation cells being observed and a notable increase in the yield strength in comparison to the as-received material. In contrast, the aged (T6) experiments showed a much longer rise time with a lower degree of hardening behind the shock front. Microstructural analysis postshock shows a more randomized dislocation distribution, with little or no postshock hardening occurring once the shock induced strain has been accounted for. This has been attributed to the presence of fine Mg2Si precipitates inhibiting the motion and generation of dislocations. These measurements are in agreement with work previously carried out on this material. Comparison of the shear strengths of the two heat treatments also shows that although the T6 condition is a little higher than T0, the differences are somewhat lower than expected.

On the behaviour of the magnesium alloy, AZ61 to one-dimensional shock loading

The behaviour of the magnesium alloy AZ61 during one-dimensional shock loading has been investigated in terms of the Hugoniot (shock-induced equation of state) and the shear strength variation in terms of variation with impact stress and pulse duration. The Hugoniot has been shown to be near identical with the similar AZ31, as would be expected with related dilute alloy systems. The shear strength has been observed to increase with applied shock stress, in common with many other materials. The shear strength has also been observed to increase with time behind the shock front. It has been suggested that this be due to twinning early in the deformation process, followed by dislocation based at later stages.

Modeling nonlinear electromechanical behavior of shocked silicon carbide

A model is developed for anisotropic ceramic crystals undergoing potentially large deformations that can occur under significant pressures or high temperatures. The model is applied to describe silicon carbide (SiC), with a focus on α-SiC, specifically hexagonal polytype 6H. Incorporated in the description are nonlinear anisotropic thermoelasticity, electrostriction, and piezoelectricity. The response of single crystals of α-SiC of various orientations subjected to one-dimensional shock loading is modeled for open- and short-circuit boundary conditions. The influences of elastic and electromechanical nonlinearity and anisotropy on the response to impact are quantified. For elastic axial compressive strains less than 0.1, piezoelectricity, electrostriction, and thermal expansion have a negligible influence on the mechanical (stress) response, but the influences of nonlinear elasticity (third-order elastic constants) and anisotropy are not insignificant. The model is extended to incorporate inelastic deformation and lattice defects. Addressed are Shockley partial dislocations on the basal plane and edge dislocation loops on the prism plane, dilatation from point defects and elastic fields of dislocation lines, and cleavage fracture. The results suggest that electric current generated in shock-loaded α-SiC crystals of certain orientations could affect the dislocation mobility and hence the yield strength at high pressure.

The variation in lateral and longitudinal stress gauge response within an RTM 6 epoxy resin under one-dimensional shock loading

The dynamic response of a commercially important epoxy resin (RTM 6) has been studied using plate impact experiments in the impact velocity regime of 80–960 m/s. Both longitudinal and lateral manganin stress gauges were employed to study the development of orthogonal components of stress both during and after shock arrival. In light of recent work raising doubts about the interpretation of lateral gauge data, lateral response within the RTM 6 resin was also used to investigate the physical phenomena being measured by the embedded lateral gauges. US–uP and σX–uP Hugoniot relationships were in good agreement with data for similar polymer materials from the literature. Derivation of shear strength behaviour both during and after shock arrival showed evidence of strengthening behind the shock front, attributed to compression of the cross-linked epoxy resin polymer chains. Comparison of the change in lateral stress behind the shock to the behaviour of an epoxy resin possessing a similar US–uP Hugoniot from the literature showed a different response; likely attributable to enhanced cross-linking present in this second resin. This result suggests that the embedded lateral gauges were, at least in part, measuring a physical response behind the shock within the resin. A Hugoniot elastic limit of 0.88 ± 0.04 GPa was derived and found to be of the same order of magnitude as results found elsewhere for similar materials.

The Behavior of Ni, Ni-60Co, and Ni3Al during One-Dimensional Shock Loading

The response of pure nickel (Ni), a binary Ni-60 at. pct cobalt (Co) alloy exhibiting a low stacking fault energy (SFE), and the ordered face-centered-cubic (fcc) alloy Ni-24Al-0.01B to shock loading has been studied using the technique of plate impact. Changes in the variation of mechanical properties with shock amplitude and pulse duration have been explained in terms of a shift from dislocation dominated to twin dominated plasticity in the case of the Ni-Co alloy and the increasing effect of brittle failure in the case of Ni3Al.

The response of two ferroelectric ceramics to one-dimensional shock loading

The shock response of the ferroelectric ceramics PZT and PSZT is monitored using maganin stress gauges in longitudinal orientation. Comparison with previously published data shows good agreement between our PZT and similar compositions. A reduction in wave speed below the Hugoniot elastic limit (HEL) with increasing impact severity is explained in terms of the degree of phase transformation between the ferroelectric and antiferroelectric phases. In contrast, the PSZT wave speeds show the opposite trend, although we believe that a similar mechanism is operating. The HELs of both materials are determined. Although the PSZT has a significantly higher strength, comparison with established trends of the HELs of this class of material with density suggests that the strength of these materials is controlled by density rather than composition.