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Pyrometry is an established technique used in high strain rate experiments (such as plate impact experiments) whereby the temperature of a sample is determined from the measurement of collected thermal radiation. By applying Planck's Law, radiometry data can be used to determine temperature. A significant source of uncertainty in applying pyrometry to high strain rate experiments is due to possible changes in emissivity after a sample has been shocked; thus it is desirable to determine emissivity during the experiment. Kirchhoff's Law, which states emissivity is the complement of reflectivity, can be a pplied to determine emissivity in high strain rate experiments. Ideally the sample's reflectivity would be measured at the same wavelength and on the same experiment as the pyrometry measurement. A diagnostic has been developed which produces a modulated reflectivity signal that is insensitive to tilt and surface finish. Following characterisation of the system in the laboratory, dynamic tests were conducted. During the dynamic tests, the reflectivity signal was multiplexed onto the radiance signal allowing simultaneous measurement of radiance and reflectivity. A description of the diagnostic, results from laboratory t esting and r esults and analysis from dynamic experiments are presented. [ABSTRACT FROM AUTHOR]

We present a study on the dynamic fracture and fragmentation of Ti-6Al-4V cylinders at initial temperatures ranging from approximately 150 K to 750 K. Cylinders with an inner diameter of 50 mm and a wall thickness of 4 mm were driven into uniform axially-symmetric expansion at radial strain rates of 104 s-1 using the ogive-insert gas gun method. Diagnostics consisted of simultaneous high speed imaging and multiple points of laser velocimetry (PDV) along the length of the sample. The imaging and PDV provided a record of the expansion process, giving expansion velocity and the failure strain. Recovered fragments were examined with optical and scanning electron microscopy and electron backscatter diffraction techniques to determine the fracture mechanisms for each initial temperature. The failure strain (radial strain at first fracture) was observed to increase with temperature over the range tested, from 7:4 ± 5:2 percent at 158 K to 24:1 ± 2:4 percent at 724 K. In experiments from 158 K up to 609 K the fracture mechanism was found to be ductile tearing under mode II loading along the planes of maximum shear at 45° to the radius. At an initial cylinder temperature of 724 K the fracture mechanism transitioned to void nucleation and coalescence along adiabatic shear bands, again forming at 45° to the radial direction. The fragmentation toughness Kf was observed to also increase with temperature until the 724 K shot where there was a marked reduction, suggesting the formation of shear bands at high temperatures reduced the energy required to form fragments. The average value of Kf was 101 ± 13 MPa m1/2. [ABSTRACT FROM AUTHOR]

Calcite and sapphire were shock compressed along the <1 0 1 0> direction (a axis) in a plate impact configuration. Polarimetery and Photonic Doppler Velocimetery (PDV) were used to measure the change in birefringence with particle velocity in the shock direction. Results for sapphire agree well with linear photoelastic theory and current literature showing a linear relationship between birefringence and particle velocity up to 310 m s-1. A maximum change in birefringence of 5% was observed. Calcite however showed anomolous behaviour with no detectable change in birefringence (less than 0.1%) over the range of particle velocities studied (up to 75 m s-1). [ABSTRACT FROM AUTHOR]

Powders are well known for their dispersive properties, which derive from the many dissipative processes that occur during densification. While numerous studies have been devoted to understand these processes over a wide range of initial densities, the influence of particle morphology has been for the large part overlooked. In this paper, we discuss a new research campaign at the Institute of Shock Physics, to systematically investigate the role of starting configuration on the dynamic densification of metal powders. Multi-target gun loading experiments have been performed on both stainless steel and copper powders of equiaxed- and fiber-shaped morphology. Frequency-shifted PDV was employed to measure the structure and velocity of the dynamic densification wave, to yield the crush strength of the various powders. We find that while the crush strength for the stainless steel powders is reasonably described by a modified Wu-Jing model, this model underpredicts the densification stress for the copper powder. [ABSTRACT FROM AUTHOR]

Shock-induced intermetallic reactions have previously been shown to occur on a nanosecond timescale, with the role of mass mixing processes driven by inter-facial shear at material interfaces suggested as a possible explanation. Experimental setups allowing the role of friction on these mechanisms to be considered are presented. Simulations show that the use of an impedance mismatch, shock driven experimental setup should allow sliding velocities of 50 - 100 m s-1 to be attained with mechanical mixing the main reaction mechanism. A second setup utilising the oblique impact of small spherical projectiles upon a target plate is predicted to enable much higher sliding velocities of up to 2 Km s-1 to be attained with thermally driven diffusion reaction mechanisms becoming dominant. [ABSTRACT FROM AUTHOR]

High-velocity impacts on planetary surfaces are common events in the solar system. The consequences of such impacts depend, in part, on the properties of the target solar system body, such as surface strength, porosity and gravity. Bodies in the solar system exhibit a range of material properties, hence it is difficult to specify a general material model. Experimental investigations of impacts onto solar system surfaces often use sand as an analogue material and hydrocode simulations of impact often assume a sand-like equation of state (EoS) and strength model, which is valid only for a limited range of porosities. To simulate impact on smaller bodies in the solar system, such as asteroids, comets or smaller planetary satellites, requires a more appropriate material model. We compare iSALE-2D hydrocode simulations of impacts in porous granular materials with results from laboratory impact experiments made by [1] to test and refine a general-purpose material model applicable for a wide range of porous materials in the solar system. [ABSTRACT FROM AUTHOR]

Dyneema is a registered trademark of a self-reinforced polyethylene (manufactured by DSM) which is showing great promise as a replacement for brittle-fibre-reinforced epoxies in various dynamic applications. As part of an investigation of its high-rate mechanical properties, we have measured the response of Dyneema under the condition of uniaxial strain during shock-loading. Data on the principal-Hugoniot curve was obtained using in-material manganin stress gauges to measure both longitudinal stress and shock-wave velocity. Off-Hugoniot data was generated using a plate-impact reverberation technique, where a Dyneema sample was sandwiched between two higher impedance copper anvils. Manganin stress gauges mounted at the interface between the Dyneema sample and copper anvils monitored the ring-up of stress in the specimen. Finally, the release curve from a given principal-Hugoniot state was measured using a reverse ballistic impact technique where free-surface velocity was measured using VISAR. [ABSTRACT FROM AUTHOR]

Plate impact techniques were used to determine Equation of State data in liquids. A copper cell was constructed to confine a test liquid and facilitate the ring-up of stress in the sample. Copper flyer plates were impacted against the cell at a range of velocities inducing a number of stress states in the sample, both on and off the principal Hugoniot. It was assumed that a Mie-Grüneisen form of the Equation of State was applicable, where the stresses measured at each shocked state allow a best-fit value of the Gruneisen parameter to be determined. The volume-dependence of the Gruneisen parameter is also considered. [ABSTRACT FROM AUTHOR]

Piezoresistive gauges have been used extensively for many decades as in-material stress transducers during shock wave experiments. Manganin demonstrates a high piezoresistive response which is relatively temperature independent. As such manganin gauges have been widely calibrated by many authors for use during shock-wave experiments. The precise calibration has been demonstrated to depend on both the chemical composition and mechanical history of the manganin, and on the geometry of the gauge. The research presented in this paper refers to the calibration of a commercially available manganin gauge, Micro-measurements J2M-SS-580SF-025, generally referred to as the T-gauge owing to its geometry. The T-gauge has seen widespread use as a pressure transducer to measure lateral stress during plate-impact experiments. It has been previously proposed that T-gauges have a similar response to the grid foil-like manganin gauges extensively calibrated by Rosenberg et al. However, recently it has been suggested that they in fact behave in a wire-like manner. The results presented here demonstrate that the gauges’ behaviour is wire-like when mounted to measure longitudinal stress. A modified calibration can be applied successfully to convert the relative resistance change to the stress normal to the gauge element. These results have important ramifications for the reduction of lateral stress measurements previously made using the T-gauge. [ABSTRACT FROM AUTHOR]

Measurements of shock heating are important in determining Equations of State that incorporate entropic effects. The use of thin-foil nickel gauges to measure shock heating in material was proposed by Rosenberg et al. in the 1980s. This research investigates the use of such commercial thin-foil gauges at interfaces between materials of different thermal and shock properties. The technique requires analysis of the resistance changes of the gauge which is a function of both temperature and stress. The response of manganin gauges to shock loading is well understood, and was used to calibrate for the piezoresistive effect in nickel. Results are presented for a variety of well-characterised materials and the applicability of the proposed method discussed. [ABSTRACT FROM AUTHOR]

Concrete cylinders (170 mm×100 mm diameter) were impacted with half-inch steel spheres over a range of velocities (100–500 m s-1). Crater growth and debris cloud evolution were observed using high speed cameras aligned perpendicular and parallel to the impact direction. In-plane displacements of the impact face were tracked using Digital Speckle Photography (DSP). Radial cracking was seen to precede circumferential cracking on the high speed sequences and DSP showed bulk motion of fragments surrounding the impact zone. The profile images revealed no significant out-of-plane perturbations, and ejecta speed is seen to increase with impact speed. Final dimensions of craters were also seen to increase with increasing impact velocity. [ABSTRACT FROM AUTHOR]