Series Of Plate Impact Experiments Research Articles

Shock-wave stability in quasi-mono-disperse granular materials

This study investigated the stability of shock-waves in brittle granular materials and thus determined whether materials, such as sand, could be represented by a Hugoniot equation to describe their shock response. A series of plate impact experiments on quasi-mono-disperse soda-lime glass microspheres was conducted with the aim of measuring the shock-wave profile to determine if there was any change over time/run distance. Granular bed thickness and input stress were varied to study the effects of dispersion on shock-wave velocity ( C sh ). It has been shown that it is possible to sustain steady shock-waves in brittle granular materials due to no measurable wave dispersion occurring in the samples tested. This study also highlighted an unsteady precursor wave that is present in the wave profiles at low stresses.

Shock compression behavior of a S2-glass fiber reinforced polymer composite

Synthetic heterogeneous material systems, e.g., layered composite materials with organic matrices reinforced by glass fibers (GRP), are attractive materials for a variety of lightweight armor applications. However, while the dynamic response of homogeneous materials, such as, metals and ceramics, has been well documented, the ballistic response of heterogeneous material systems is poorly understood. In the present study, in an attempt to better understand the shock-induced compression response of GRPs, a series of plate impact experiments were conducted on a S2-glas fiber reinforced polymer composite comprising S2-glass woven roving in a Cycom 4102 polyester resin matrix. The plate-impact experiments were conducted using an 82.5 mm bore single-stage gas-gun at the Case Western Reserve University. The history of the shock-induced free-surface particle velocity at the rear surface of the target plate was monitored using the multibeam VALYN™ VISAR system. The results of the experiments indicate the absence of an elastic front in the shock-induced free-surface particle velocity profile in the GRP. Moreover, in the low impact velocity range, relatively weak late-time oscillations are observed in the particle velocity profiles. Increasing the amplitude of the shock-induced compression resulted in a decrease in the rise-time of the shock wave front. The critical shock stress amplitude at which a clear shock-front is seen to develop during the shock loading was determined to be between 1.5 and 2.0 GPa. The results of the experiments are used to obtain the equation of state of the GRP in the stress range 0.04–20 GPa. Moreover, the Hugoniot curve (Hugoniot stress versus Hugoniot strain) was calculated using the Rankine–Hugoniot relationships; the departure of the Hugoniot stress versus the particle velocity curve from linearity allowed the estimation of the Hugoniot elastic limit of the GRP to be about 1.6 GPa.

Shock propagation in a cemented tungsten carbide

WC-based ceramic metal composites (cermets) are of great importance in both armor and munition design due to the combination of properties imparted by the presence of two different phases. WC–Co cermets are of interest in this area due to the hardness and strength imparted by the WC phase while the cementing Co matrix acts to increase plasticity and toughness. Here the dynamic response of G13 WC–Co manufactured by Kennametal Engineered Products B.V. was studied via a series of plate impact experiments involving both longitudinal and lateral gauges, which allowed determination of the Us−Up relationship, measurement of a Hugoniot elastic limit of 3.3±0.2 GPa, measurement of a spall strength of 4.38 GPa, and an investigation of the stress dependence of shear strength in such a strong material.

More on the behavior of soda lime glass under shock loading

A series of plate impact experiments with soda-lime glass specimens was performed in order to further investigate the complex behavior of this material in the 0–8 GPa range of shock loading. Using commercial manganin gauges we followed the stress histories and their different shapes as the stresses increase from 3.5 to about 8.0 GPa. In particular, we find that there are meaningful differences between the shapes of these signals at pressures below about 4.0 GPa, in between 4.0 and 6.0 GPa and above 6.0 GPa. We also gather more data on the fractured glass behind the fracture wave front, from our measured stress histories, and offer a new way to determine the Hugoniot elastic limit of this material, as well as other brittle solids.

Spall strength of glass fiber reinforced polymer composites

In the present paper results of a series of plate impact experiments designed to study spall strength in glass–fiber reinforced polymer composites (GRP) are presented. Two GRP architectures are investigated—S2 glass woven roving in Cycom 4102 polyester resin matrix and a balanced 5-harness satin weave E-glass in a Ciba epoxy (LY564) matrix. The GRP specimens were shock loaded using an 82.5 mm bore single-stage gas-gun. A velocity interferometer was used to measure the particle velocity profile at the rear (free) surface of the target plate. The spall strength of the GRP was obtained as a function of the normal component of the impact stress and the applied shear-strain by subjecting the GRP specimens to normal shock compression and combined shock compression and shear loading, respectively. The spall strengths of the two GRP composites were observed to decrease with increasing levels of normal shock compression. Moreover, superposition of shear-strain on the normal shock compression was found to be highly detrimental to the spall strength. The E-glass reinforced GRP composite was found to have a much higher level of spall strength under both normal shock compression and combined compression and shear loading when compared to the S2-glass GRP composite. The maximum spall strength of the E-glass GRP composite was found to be 119.5 MPa, while the maximum spall strength for the S2 glass GRP composite was only 53.7 MPa. These relatively low spall strength levels of the S2-glass and the E-glass fiber reinforced composites have important implications to the design and development of GRP-based light-weight integral armor.

Structure of shock waves in glass fiber reinforced polymer matrix composites

Glass fiber reinforced polymer (GRP) composites are attractive candidates for future combat vehicle armor systems. Due to their complex architecture, shock waves in GRP undergo geometric and material dispersion as well as attenuation with distance of shock wave propagation. In the present study a series of plate impact experiments is conducted to investigate the structure of shock waves in the GRP. The effects of material and geometric dispersion as well as the GRP’s hydrodynamic response on the attenuation of the shock waves are considered. It is observed that the hydrodynamic effects dictate the structure of shock waves in the GRP.

Characterization and evaluation of boron carbide for plate-impact conditions

This article addresses the response of boron carbide (B4C) to high-velocity impact. The authors previously characterized this material in 1999, using the Johnson-Holmquist [AIP Conf. Proc. 309, 981 (1994)] (JH-2) model. Since then, there have been additional experimental data presented in the literature that better describe the hydrostatic pressure (including a phase change). In addition, a series of plate-impact experiments (one-dimensional, uniaxial strain) that used configurations that produced either a shock, a shock release, or a shock reshock was performed. These experiments provide material behavior regarding the damage, failed strength, and hydrostat for which previously there has been little or no data. Constitutive model constants were obtained for the Johnson-Holmquist-Beissel [J. Appl. Phys. 94, 1639 (2003)] model using some of these plate-impact experiments. Computations of all the experiments were performed and analyzed to better understand the material response. The analysis provided the following findings: (1) The material fails and loses strength when the Hugoniot elastic limit (HEL) is exceeded. (2) The material has significant strength after failure and gradually increases as the pressure increases. (3) The shear modulus does not degrade when the material fails (as has been postulated), but rather increases. (4) When the material is reloaded from an initial shocked (failed) state, the loading appears to be elastic, indicating the material is not on the yield surface after failure. To provide more insight into the behavior of B4C, the strength versus pressure response was compared to that of silicon carbide (SiC). The strength of SiC increases as the pressure increases beyond the HEL, probably due to pressure hardening or strain hardening. It appears that B4C does not experience any hardening effects and fails at the HEL. Although the HEL for B4C is higher than that of SiC, the hardening ability of SiC produces a similar maximum strength with more ductility. Another important issue with B4C is that there are significant differences between plate-impact data reported by different researchers. These differences are due to one or more of the following possibilities: errors in obtaining the test data, errors in analyzing the test data, a high degree of scatter due to failure of the material, and/or the different manufactured forms of B4C simply behave as different materials. These differences also make it difficult to validate the model (constants) determined from one set of data by applying it to other data reported in the literature. Lastly, the model was used to simulate ballistic impact experiments over a large range of impact velocities (1500–4500m∕s). The computed results overpredict the penetration at low velocities and underpredict the penetration at high velocities. Future work will address this inconsistency, but until this issue is resolved, the current model and constants should be used with caution when applied to ballistic impact and penetration.

Analysis of the response of silicon carbide subjected to shock-reshock and shock-release plate-impact experiments

This paper presents computational results, and analyses, that investigate the dynamic response of silicon carbide to reshock and release plate-impact experiments. Recently, a series of plate-impact experiments was performed that used configurations that produced either a reshock (reloading) or release (unloading) from an initial shocked state. These experiments provide material behavior for damaged (permanently deformed) silicon carbide for which previously there has been little or no data. Computations of the experiments were performed using the recently developed JHB ceramic model. Generally, the computed results were in very good agreement with the experiments. The computed results were used to help analyze and understand the test data resulting in the following findings: 1) The release waves indicate the strength of the damaged material remains approximately constant, at about 13 GPa. up to a shock stress of 62.7 GPa, but then appears to decrease to approximately 6.5 GPa at a shock stress of 87.8 GPa. 2) The wave profiles produced from reshock are sensitive to changes in material strength and also indicate that the strength of silicon carbide remains constant when reshocked from 45.6 GPa to 62.7 GPa. 3) The shear modulus does not degrade as the material damages (as has been postulated), but rather increases slightly.

More on commercial carbon resistors as low pressure gauges

Commercial carbon resistors have been used for over 30 years as low pressure gauges in dynamic experiments. Their low-cost, robust performance and high piezoresistivity are some of their main advantages. On the other hand, there are large differences between the various calibration curves published by these workers. This is mainly due to the fact that different resistors were used under various loading conditions. In the work presented here, we focus on several issues concerning the use of commercial carbon resistors as well-calibrated dynamic pressure gauges. In particular, we explore the question of reproducibility of their response, its strain sensitivity, and the issue of hysteresis upon stress unloading. These issues are examined through a series of plate impact experiments. We also present our calibration results for 10 Ω resistors ( 1 8 W ), in the pressure range of 0–8.0 GPa, which were chosen as our pressure gauges for this range.

Dynamic behavior of selected ceramic powders

An experimental setup has been developed on the continuous recording of the stress profiles in ceramic powders subject to shock loading with manganin gauges. A series of plate impact experiments on highly porous ceramic powders such as Al 2O 3, SiC and B 4C were conducted at the laboratory's single stage powder gun facility. The relationship between shock wave velocity and particle velocity was measured to obtain the Hugoniot data. Plate impact onto powder sample experiments were conducted at loading stresses ranging from 1.6 to 4.2 GPa. The experimental results show that the shock wave speeds in various ceramic powders vary between 1 and 2 km/s. Linear Hugoniot relations between shock velocity ( D) and particle velocity ( u) are observed. The loading stress–specific volume form of Hugoniot relations ( P– V) was constructed using the data from quasistatic compression test results, Hopkinson bar dynamic compression test results and powder gun plate impact experiment results. The P–V diagram shows that the crush strength of ceramic powders is comparable to the loading stress level. The B 4C and SiC powders with bigger particle size more easily reach the solid state Hugoniot than the powders with smaller particle size at the same loading condition. In the case of Al 2O 3, the material shows less sensitivity to particle size difference at the same level of loading rate as compared to B 4C and SiC.

Dynamic behavior of boron carbide

Boron carbide displays a rich response to dynamic compression that is not well understood. To address poorly understood aspects of behavior, including dynamic strength and the possibility of phase transformations, a series of plate impact experiments was performed that also included reshock and release configurations. Hugoniot data were obtained from the elastic limit (15–18 GPa) to 70 GPa and were found to agree reasonably well with the somewhat limited data in the literature. Using the Hugoniot data, as well as the reshock and release data, the possibility of the existence of one or more phase transitions was examined. There is tantalizing evidence, but at this time no phase transition can be conclusively demonstrated. However, the experimental data are consistent with a phase transition at a shock stress of about 40 GPa, though the volume change associated with it would have to be small. The reshock and release experiments also provide estimates of the shear stress and strength in the shocked state as well as a dynamic mean stress curve for the material. The material supports only a small shear stress in the shocked (Hugoniot) state, but it can support a much larger shear stress when loaded or unloaded from the shocked state. This strength in the shocked state is initially lower than the strength at the elastic limit but increases with pressure to about the same level. Also, the dynamic mean–stress curve estimated from reshock and release differs significantly from the hydrostate constructed from low-pressure data. Finally, a spatially resolved interferometer was used to directly measure spatial variations in particle velocity during the shock event. These spatially resolved measurements are consistent with previous work and suggest a nonuniform failure mode occurring in the material.

Shock to detonation transition in a plastic bonded explosive

It is important to define a methodology to assess the safe handling conditions of explosive materials. Such a route must be simple enough to capture relevant mechanisms in order to construct a modeling capability. To this end, a series of plate impact experiments has been undertaken in order to characterize the unreacted Hugoniot of a research, castable, plastic-bonded explosive (PBX) RF-38-22. A second program, using embedded particle velocity sensors, has been undertaken to investigate the shock to detonation transition (SDT) in the PBX. The experimental facility is described, the techniques used are discussed, the material is introduced, and results obtained are reported. The data obtained have been used to calibrate a hydrocode model for SDT based on viscoplastic ignition and subsequent grain burning, with pressure-dependent kinetics. This model is described, and results of calculations are presented. This represents the program in the construction of the methodology. It is hoped that further work will increase its applicability.

Experimental characterization of the dynamic failure behavior of mortar under impact loading

The failure behavior of mortar under dynamic impact loading is characterized through a series of plate impact experiments. The analysis focuses on the spall strength and the shear stress carrying capacity in different regions of the specimen under normal impact loading. Special attention is paid to the possible existence of a failure wave phenomenon that has been widely recognized as an important failure mechanism for glasses during plate impact. The experiments are designed to allow the strengths of the medium at locations behind and ahead of a possible failure wave front to be analyzed. The diagnostics used include velocity interferometer system for any reflector (VISAR) recording of the free surface velocities of targets and monitoring of the internal stresses via polyvinylidene fluoride (PVDF) gauges embedded in the specimen. Experiments conducted do not provide evidence for the existence of a failure wave phenomenon for mortar under plate normal impact loading. While the study suggests that a threshold impact stress must be exceeded for failure to occur, a clearly defined failure wave that propagates behind the loading wave is not observed. Instead, a gradual failure process that initiates upon the arrival of the loading wave and progresses thereafter is observed. This gradual failure process in mortar is in contrast to the well-defined failure front and complete loss of tensile strength associated with the failure wave phenomenon reported for glasses. The study also indicates that, under impact involving high levels of input stresses, attenuation of the loading wave occurs as it propagates through the failed medium.

Influence of the load conditions on the failure wave in glasses

Previously, a series of plate impact experiments have provided evidence for the appearance of failure waves in glasses under uniaxial compression. Presented herein is a continuation of research, performed on K9 crown glass and ZF1 dense flint glass at varied shock stresses with a goal to uncover the failure wave source and to make clear whether or not the failure wave can be formed at stresses above the Hugoniot elastic limit (HEL). It has been found that, at peak stresses below the HEL, the failure wave can be initiated on both the impact surface and the internal surface inside the sample, indicating that the glass surface is a direct source for the failure wave nucleation. However, when the peak stress exceeds the HEL, brittle glasses become ductile as a result of irreversible densification, and the Failure wave disappears. The high spall strength revealed in the stress range above the HEL indicates that ductility is also preserved under the subsequent tension.

The shock wave response of a filled glass

The shock wave loading of brittle materials has been the subject of much recent interest. One of the outstanding questions concerning the compressive behaviour is the mechanism for failure at the Hugoniot elastic limit (HEL). While much work has centred around relatively open structure, low density glasses such as borosilicate (pyrex) and soda-lime (float, which is partially filled), relatively little has addressed the response of highly filled lead glasses. This work presents the results of a series of plate impact experiments carried out on the lead glass DEDF. This material was shocked in uniaxial strain and the longitudinal component of stress was measured. The material showed pronounced elastic precursor decay and response reminiscent of alumina ceramics.

Failure in a shocked high-density glass

One of the outstanding questions concerning the compressive behavior of brittle materials concerns the failure wave observed in glasses. While much work has centered around relatively open structure, low density glasses such as borosilicate (pyrex) and soda-lime (float, which is partially filled), none has addressed the response of highly filled lead glasses. This work presents the results of a series of plate impact experiments carried out on the lead glass DEDF.TM This material was shocked in uniaxial strain and the longitudinal and lateral components of stress and strain were measured. The failure wave, observed in lower density glasses, was observed in this material but its velocity reached that of the shock at less than twice the Hugoniot elastic limit (HEL).

Dynamic high-pressure properties of AlN ceramic as determined by flyer plate impact

The dynamic properties of hot-pressed aluminum nitride ceramics were determined in a series of plate impact experiments using longitudinal and transverse in-material manganin gauges. The Hugoniot curve for hot pressed specimens was determined in the range of 0–190 kbar with a value of 94±2 kbar for the Hugoniot elastic limit (HEL). Using both gauge orientations, the stress deviator in the specimens was determined as the difference between longitudinal and transverse stresses. It was found that the stress deviator remains relatively constant above the HEL, and is about 10% higher than the value at the HEL point. The inferred Hugoniot converges to the extrapolation of the hydrostat. Since the convergence is not due to loss of strength, it may be due to a phase change in the AlN from low-pressure (wurtzite) structure to high-pressure (rocksalt) structure.