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A material placed in direct contact with a high explosive experiences a Taylor wave (triangular-shaped) shock loading profile. While a large number of studies have probed the structure, properties, and tensile response of materials subjected to square-topped shock loading pulses histories, few studies have systematically quantified the influence of shock-wave profile shape on material response. Samples of 316L stainless steel were shock loaded to peak stresses of 6.6, 10.2, and 14.5 GPa to examine the influence of square-topped and triangular (Taylor wave)-shaped pulse loading on the dynamic tensile behavior (spallation). The 316L SS samples were loaded with a square-topped pulse to each peak shock stress, using a pulse duration of 0.9 μs. They displayed increasing incipient spallation damage with increasing peak stress. Samples loaded to the peak shock stresses of 6.6 and 10.2 GPa with a Taylor-wave loading pulse (which immediately unloads the sample after the peak Hugoniot stress is achieved) exhibited no damage. Only the 14.5 GPa Taylor pulse shocked sample exhibited both a pull-back signal and incipient damage following tensile loading. The damage evolution in the square-topped shocked samples was found to be a mixture of void and strain localization damage, the void fraction increasing with peak shock amplitude. With the Taylor-wave loading profile of amplitude 14.5 GPa, a high incidence of shear localization and low incidence of void formation was observed. Detailed analysis of the damage evolution as a function of shock pulse shape revealed that a nominally equivalent level of incipient damage was obtained using a Taylor-wave or square-topped loading pulse when a similar rear sample surface stress-time total impulse was applied. In order to induce equivalent damage with the two pulse shapes, the impulse applied needed to be nominally matched. For this to occur, the Taylor-wave profile required twice the amplitude of the square one and the durations of each pulse needed to be appropriately scaled. Detailed metallographic, microtextural, and void shape and size analyses of the damage evolution are presented as a function of the inferred loading pulse shape and the peak Hugoniot stress. [ABSTRACT FROM AUTHOR]

The behavior of a pure tungsten under conditions of one-dimensional shock loading has been monitored using Manganin stress gauges, in longitudinal and lateral orientations. The shock induced equation of state, in terms of stress and particle velocity (from the longitudinal gauges), shows that the Hugoniot of this pure material agrees with the results of previous workers, both in pure tungsten and tungsten alloys. Lateral stress traces show an increase in stress (and hence decrease in shear strength) behind the shock front, in a manner similar to that observed in a tungsten heavy alloy and pure tantalum. It has been proposed that this is due to the high Peierl’s stress initially restricting dislocation generation, followed by a later increased in dislocation density. However, the brittle manner in which tungsten fails under shock loading indicates that other mechanisms are in operation. It has been suggested that the shock front nucleates cracking, which progressively grows behind it, which in combination with the proposed dislocation mechanisms reduces shear strength. Finally, we show that the variation of shear strength with shock stress is in agreement with a number of other workers until a stress level of ∼10 GPa, where it is significantly higher. We have suggested that this is due to the higher strength of pure tungsten compared to the liquid phase sintered materials studied previously. [ABSTRACT FROM AUTHOR]

Polymers are increasingly being utilized as monolithic materials and composite matrices for structural applications historically reserved for metals. High strain-rate applications in aerospace, defense, and the automotive industries have lead to interest in the shock response of polytetrafluoroethylene (PTFE) and the ensuing changes in polymer structure due to shock prestraining. We present an experimental study of crystalline structure evolution due to pressure-induced phase transitions in a semicrystalline polymer using soft-recovery, shock loading techniques coupled with mechanical and chemical postshock analyses. Gas-launched, plate impact experiments have been performed on pedigreed PTFE 7C, mounted in momentum trapped, shock assemblies, with impact pressures above and below the phase II to phase III crystalline transition. Below the phase transition only subtle changes were observed in the crystallinity, microstructure, and mechanical response of PTFE. Shock loading of PTFE 7C above the phase II-III transition was seen to cause both an increase in crystallinity from 38% to ∼53% (by differential scanning calorimetry) and a finer crystalline microstructure, and changed the yield and flow stress behavior. [ABSTRACT FROM AUTHOR]

The shock response of the intermetallic compound Ni3Al (doped with boron to enhance ductility) has been investigated to determine equation of state and shock induced mechanical properties, and the response is compared to that of pure nickel. Examination of the Hugoniot data suggests that the Ni3Al has a higher compressibility than pure nickel. Elastic precursor decay has been observed, although due to the limited number of specimens available, we were not able to determine the point where the elastic amplitude became stable. Spall and shear strengths were observed to increase to a peak value (at a shock stress of between 6 and 7 GPa) before dropping again. We believe that this may be due to increasing amounts of damage behind the shock front as shocks of increased stress are applied. In a similar manner, spall strength was observed to decrease with pulse duration, again, most likely due to damage accumulating behind the shock front. Finally, it was observed that this material was brittle under all shock loading conditions studied in this investigation. We have proposed, due to the extremely high dislocation velocities imposed by the shock induced strain rates, that boron has effectively been removed from dislocations and hence cannot enhance ductility. [ABSTRACT FROM AUTHOR]

The equation of state and the mechanical response (dynamic tensile strength and dynamic shear strength) of the shape memory alloy NiTi have been investigated using plate impact. The Hugoniot has been extended with additional data and a nonlinear behavior of the Hugoniot (shock velocity-particle velocity) has been noted. A bilinear representation has been proposed for the trend. These two behaviors were attributed to the shock-induced phase transformation from B2 to monoclinic. However, this phase transformation seems to have no influence on the dynamic tensile strength. A minimum impact stress value was found necessary to create the spallation in NiTi but the pull back stress remains near constant above this value. A negative strain-rate dependency was also noted on the spallation. The shear strength (τ) of NiTi appears to increase continuously with the impact stress. The evolution of τ behind the shock front seems to be linked to the phase transformation observed in determination of the Hugoniot. Indeed, It was observed that there was no change of τ until an impact stress value corresponding to the inflection point on the Hugoniot, followed by increase behind the shock front above this value. [ABSTRACT FROM AUTHOR]

The shock response of 88% and 99.9% pure aluminas, chosen since they had been tested previously, was simulated at the mesoscale. Microstructures were investigated using electron microscopy and then digitized for use in simulation. These microstructural units were stacked to recover larger-scale structures generated randomly. These extended the length ranges in the simulations from the micrometer to the continuum scales. Modeling emphasized the inhomogeneity of the flow at this length scale and phenomena such as precursor decay were accentuated in the material with the greater impurities. The bulk composite behavior could be recovered from the properties of the individual phases by adopting simple expressions for the shock parameters. These behaviors include the profile of the stress histories and quantitative prediction of the Hugoniot elastic limits recovered using information derived purely on constituents. [ABSTRACT FROM AUTHOR]

It is important to understand the mechanical behavior of polymeric materials that have a range of industrial and defence applications. In particular, several are used as the binder phase in plastic bonded explosives and propellants. Binder materials used in energetics need to be understood first to ensure their long-term, high-temperature stability when cycled during service, and second to ensure that the accidental loading of such materials leaves the explosives crystals within safe to handle. This work presents experimental data on equation-of-state and shock-induced damage evolution of the polymers teflon, estane™ and Kel-F-800™. The tensile (spall) strength at high rate was quantified using real-time laser interferometric techniques on each polymer as a function of impact stress. Measurements were made of the lateral stress under impact using manganin gauges, which, when combined with longitudinal data, allowed investigation of the shear strength of each polymer. An increase of shear strength, determined in this manner, was noted for two polymers and comparisons are drawn with others investigated using the same technique. A discussion of the mechanical response of these polymers is presented. [ABSTRACT FROM AUTHOR]

Interfaces within glass targets give rise to variations in the mode of failure of material components. The wide use of such laminates merits further investigation of the failure mechanism. It is already known that when shocked above a threshold of 4 GPa, glass fails under compression behind a propagating front following the compression front. Work is presented which indicates how this failure process is altered by bonding together two plates to introduce an interface, rather than leaving a monolithic target. After crossing an internal interface, the failure wave propagates only after a delay in soda-lime glass and the failed strength of the material is increased at the inner interface compared with that at the impact face. Addition of a second interface illustrates these effects. Recent work has shown that failure of more than two plates bonded together during impact shapes the pulse transmitted through materials. Indeed it has been suggested that glass sheets bonded together show some of the features of polycrystalline brittle materials. In this work, the stress has been monitored at different stations in the laminate to ascertain the effect of varying the number of tiles within the laminate. It is found that the pulse rises to ca. 4 GPa quickly and then is ramped more gradually as the number of glass sheets is increased. [ABSTRACT FROM AUTHOR]

A previous work has reported that shock loading of ionic crystals produces an induced polarization and changes in electrical conductivity. However, previous measurements recorded an integrated electrical signal comprising the induced electrical field and that due to current flow. For this reason a differential system was designed to separate these effects that was adapted from that used in the investigation of the conductivity of hydrogen under shock. The measurement removes voltages produced in the shock-induced electrical field, allowing determination of those resulting from resistance changes. Although the mechanical response of potassium chloride to shock has been studied extensively, the electrical response is less studied. Here, experiments are reported in which it is shocked to various stresses in order to observe conductivity changes. The range of stresses induced includes several mechanical thresholds, including the elastic-plastic transition, the B1:B2 phase transformation, and the overdriving of the shock faster than the elastic wave. The behavior observed when single crystal and targets pressed from granular material (to close to full density) are shocked around each of these thresholds is presented. The effects of loading to a particular stress in a single step or in multiple steps are discussed. [ABSTRACT FROM AUTHOR]

The shock response of a silicon carbide has been investigated using the methods of plate impact, and monitored using manganin stress gauges mounted so as to be responsive to lateral stress. Close to the impact face, a two-step stress response is observed, indicating the presence of delayed failure at the impact face. As the shock front moves through the target, the failure wave appears to slow, before arresting between 4 and 6 mm from the impact face. Measured shear stresses (ahead of the failure front) are in good agreement with the calculated elastic response, and with similar measurements made by both ourselves in other grades of silicon carbide and other authors. In gauge traces where the failure wave was not observed, a slight decrease in lateral stress (and thus a corresponding increase in shear strength) has been noticed. A similar response in some metals (in combination with recovery work in other ceramics) has led us to suggest that a degree of plastic deformation, in combination with a more brittle response, has occurred. [ABSTRACT FROM AUTHOR]

The effect of particle size on the shock response of three soda-lime glass-hydroxyterminated polybutadiene composites has been investigated. While the shock velocity–particle velocity relationship has been shown to be nearly identical in all three materials, thus indicating that the hydrodynamic response is particle size independent, the shock stresses have been shown to be strongly dependent upon particle size. It has been proposed that this be due to the nature of the microstructure, with the larger particles restricting flow, and thus increasing shear strength, while the finer microstructure can flow as a whole. [ABSTRACT FROM AUTHOR]

The shear strength of a monolithic tungsten carbide has been measured as a function of impact stress. Results show that it increases with stress, in agreement with the work of others. Interestingly, it has also been shown that lateral stress increases, and thus shear strength decreases behind the shock front. Potential mechanisms are discussed, including cracking within the shock front itself, and stress relaxation due to high velocity dislocation motion within the shock front, followed by dislocation multiplication behind it. [ABSTRACT FROM AUTHOR]

Failure wave propagation in shocked soda-lime glass has been investigated as a function of internal strain. This has been varied by either examining the material in the as-received or a heat-treated state. Results show that while material strength does not seem to be significantly effected, failure wave velocity is reduced by an annealing treatment. Annealing has been shown to reduce the amount of internal strain, and thus the amount of available energy for crack propagation is likewise reduced. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Hydroxy-terminated polybutadiene (HTPB) is commonly used as a binder system in rocket propellants and plastic bonded explosives (PBXs). As such, the investigation of this material under high-strain-rate and shock-loading conditions is of importance if the response of propellants and PBXs is to be understood. Therefore, the Hugoniot of two different HTPB compositions has been investigated, using manganin stress gauges. Both materials have a linear Us–up relationship, with the material having a higher plasticizer content having a lower value of c0. It has been suggested that additions of plasticizer increase the compliance of the material. In addition, in one composition, shock recovery experiments have been performed. Results indicate that no changes in glass transition temperature, decomposition temperature, or molecular weight occur in the range of shock stresses investigated. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Porous materials may exhibit highly nonstationary behavior under shock-wave loading. The majority of existing experiments have measured the dependence between shock-wave velocity and particle velocity to define the Hugoniot for subsequent derivation of an equation of state. Such equations of state are nonconvex, which leads to significant thermodynamic and numerical problems. The present article suggests an experimental configuration and mathematical model, to overcome these difficulties. The experiment is based on a setup resulting in a continuous record of the stress profile with time using embedded manganin gauges. The model employs a homogenization approach enabling us to obtain a hyperbolic system of equations, which is completed with a convex equation of state so as to be suitable for implementation in commercial hydrocodes. Using available data for porous aluminum, an approach is elaborated for construction of constitutive equations. The model is tested with the present stress profiles in sand and demonstrates good agreement. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Lateral stresses generated by shock loading in tantalum have been determined using manganin stress gauges. These have been used in combination with the measured longitudinal impact stresses to determine the shear strength behind the shock. Results show that with an increase in impact stress, the shear strength in tantalum also increases. Analysis shows that during shock loading the lateral stress in tantalum increases behind the shock front. Since the longitudinal stress is nominally constant until arrival of the release, this implies that the shear strength is reducing behind the shock front. The shock-wave response of tantalum is discussed in the context of a previous weak-shock wave-profile analysis of tantalum, and in terms of the defect generation and storage response of pure face-centered- versus body-centered-cubic metals. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The present drive to make munitions as safe as is feasible and to develop predictive models describing their constitutive response, has led to the development and production of plastic bonded explosives and propellants. There is a range of elastomers used as binder materials with the energetic components. One of these is known as Kel-F-800™ (poly-chloro-trifluroethylene) whose structure is in some ways analogous to that of poly-tetrafluoroethylene (PTFE or Teflon). Thus, it is of interest to assess the mechanical behavior of Teflon and to compare the response of five different production Teflon materials, two of which were produced in pedigree form, one as-received product, and two from previous in-depth literature studies. The equations of state of these variants were quantified by conducting a series of shock impact experiments in which both pressure-particle velocity and shock velocity-particle velocity dependencies were measured. The compressive behavior of Teflon, based upon the results of this study, appears to be independent of the production route and additives introduced. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A fracture wave (FW) in a brittle material is a narrow transition region (border) of a continuous fracture zone, which may be associated with the damage accumulation process initiated by propagation of shock waves. In multidimensional structures the fracture wave may behave in an unusual way. The high-speed photography of penetration of a borosilicate (Pyrex) glass block [N. K. Bourne, L. Forde, and J. E. Field, Proc. SPIE 2869, 626 (1997)] shows a visible fracture zone with an apparent flat front although the projectile is a hemispherically nosed rod. A strain-rate-sensitive model is being developed and employed for analysis of the role of the complex stress state and kinetic description of the damage accumulation to describe the process of the impact. Numerical analysis is conducted with a one-dimensional wave propagation code employing the model and with the LS-DYNA2D hydrocode in which the model has been implemented. The analysis demonstrates that (i) the second (plastic) shock wave is superseded by quicker FW relaxing stress behind the elastic precursor, and (ii) the FW front flattening is apparently caused by the change in the acoustic directional properties. This change is associated with the phase-like transition due to the damage accumulation within the FW. In particular, the FW transition separates a highly anisotropic zone of material characterized acoustically by longitudinal and shear waves in front of the FW from a nearly isotropic region of the material characterized only by bulk waves behind the FW. [ABSTRACT FROM AUTHOR]

The response of an epoxy resin has been investigated using the methods of plate impact to generate planar shock waves. In particular, the Hugoniot, both in stress-particle velocity and shock velocityparticle velocity space, and the variation of shear strength with impact stress, have been investigated. Comparison of the results of this investigation with those of previous workers shows good agreement. Measurements of lateral stress, which have been used to determine the shear strength have indicated that shear strength increases with longitudinal stress in the range investigated. Further, lateral stresses have been shown to decrease behind the shock front, implying an increase of strength of this material during shock loading. It would seem possible that this is a manifestation of the viscoplastic nature of epoxy based resins. [ABSTRACT FROM AUTHOR]

The shock response of the aluminum alloy 7010-T6, induced by the technique of plate impact, has been investigated as a function of orientation to the loading axis to the rolling direction. Measurements of the Hugoniot elastic limit (HEL) and spall strength show that the material is stronger in the longitudinal orientation than the short transverse, in keeping with the mechanical properties measured at quasistatic strain rates. Furthermore, a comparison of the HELs to the 0.2% proof stresses suggests that there is a degree of strain-rate sensitivity in the longitudinal orientation, whilst the short transverse appears strain-rate insensitive. Thus, there exists the possibility that strain-rate sensitivity itself is orientation dependent in this alloy. Comparison of the ratios of spall strength according to orientation, to the equivalent quasistatic yield strengths provides further evidence of this hypothesis. A simulation using finite-element modeling has shown that while the model can reproduce the dependency of the HEL on orientation, the degree of success with the spall strength has not been so great. [ABSTRACT FROM AUTHOR]

The response of alloys based on the intermetallic compound NiTi to high-strain-rate and shock loading conditions has recently attracted attention. In particular, similarities between it, and other shape memory materials such as the alloy U-6%Nb in the propagation of the plastic wave in Taylor cylinders are of significant interest. In this article, the Hugoniot is measured using multiple manganin stress gauges, either embedded between plates of the NiTi alloy, or supported with blocks of polymethylmethacrylate. In this way, the shock stress, shock velocity, and details of the shock wave profile have been gathered. An inflection at lower stresses has been found in the Hugoniot curve (stress-particle velocity), and has been ascribed to the martensitic phase transformation that is characteristic of the shape memory effect in this alloy. In a similar way, the variation of shock velocity with particle velocity has been found to be nonlinear, contrary to other pure metal and alloy systems. Finally, a break in slope in the rising part of the shock profile has been identified as the Hugoniot elastic limit in NiTi. Conversion to the one-dimensional stress equivalent, and comparison to quasistatic data indicates that NiTi exhibits significant strain-rate sensitivity. [ABSTRACT FROM AUTHOR]

Plate-impact experiments have been performed upon a lead-filled glass to understand its shock response. Stress measurements have been made using manganin stress gauges in both longitudinal and lateral orientations. It has been observed that there is a pronounced decay in Hugoniot elastic limit with distance into the target. In the experiments conducted, a steady value for the precursor amplitude has not been reached. Failure waves were seen to sweep the entire thickness of the glass specimens until stopped by release waves from the rear of the target. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Plate impact experiments have been performed on samples of the γ-titanium alloy, Ti-48Al-2Cr-2Nb-1B to determine its mechanical response during shock loading. This alloy displays pronounced precursor decay. Comparison with the findings of a previous investigation on a similar material shows that the variation in the Hugoniot Elastic Limit can be explained in terms of the microstructure. The Hugoniot has also been determined, and stress, shock, and particle velocity have been measured as independent variables. The difference of these data from those of a similar intermetallic alloy have been explained in terms of the microstructure. It has been observed that the measured Hugoniot (in stress-particle velocity space) lies above that calculated from the measured shock velocities. We believe that this is due to the high degree of work hardening that this type of intermetallic alloy displays. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The high-strain rate response of polymers is becoming increasingly important to understand, given their widespread use in many industries. In particular, they are used as bonding agents in the production of materials such as polymer bonded explosives. In this case, their properties become especially important to understand since the safety of the energetic composition depends upon their response. There are three broad classes of polymer microstructure; elastomers, thermoplastics, and thermosets. The shock response of one of the first of these three classes is investigated in this work. Work is described in which the Hugoniot of the material is investigated using plate impact experiments, measuring the stress at varying positions to determine the shock and the stress-particle velocity state. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which used commercial strain gauges to measure the plate impact behavior of type D, extra dense flint, a high density, lead filled glass. Interest in the shock properties of silicate glasses under one-dimensional loading; Experimental procedure; Results and discussion; Conclusions.

Discusses a study which analyzed the shock-induced phase transformation in potassium chloride using constantan strain gauges. Details on plate impact experiments; Materials data; Results and discussion; Conclusions.