W. G. Proud

Mechanical properties of SnPb and lead-free solders at high rates of strain

The mechanical properties of 63% Sn–37% Pb and lead-free solders have been measured at high strain rates (500–3000 s−1) using a split Hopkinson pressure bar. The solders were produced by quenching in water from the melt, to give the phase structure associated with rapid cooling. Measurements were made at −40 °C, room temperature and +60 °C. The Sn–Pb solder was strongly strain rate and temperature dependent, whereas the lead-free solders showed only a weak dependence on these parameters. All of the materials behaved elasto-plastically until a plateau stress of circa 200 MPa. An unexpected, and possibly important, feature of the lead-free solders was the division of the specimens into two groups with different strengths at low temperatures.

High-strain rate Brazilian testing of an explosive simulant using speckle metrology

The application of high-speed photography and image correlation has allowed dynamic Brazilian tests to be carried out using the split Hopkinson pressure bar (SHPB) on PBS9501, an explosive simulant. The essential features of low-rate Brazilian tests are found to occur in the high-rate experiments, with the samples reaching equilibrium quickly and remaining in equilibrium throughout the experiment. The advantage of the approach described here is the ability to make tensile stress/strain measurements in the high-strain rate regime using a compression Hopkinson bar. This allows smaller sample sizes, making testing of expensive or dangerous materials easier, while expanding the capabilities of the compression bar.

Behaviour of ammonium perchlorate-based propellants and a polymer-bonded explosive under impact loading

The response of a range of ammonium perchlorate–based propellants and a polymer–bonded explosive to drop–weight impact loading has been studied using high–speed photography. This technique allows the generation of ‘hot spots’ and the subsequent growth of reaction to be recorded. In separate experiments, the mechanical properties of these materials were measured over the range of strain rates 0.01−8×103 s–1 using an Instron 1122 and a split Hopkinson pressure bar. In addition, the effect of temperature on their high–strain–rate properties was examined over the range −60 to +60 °C. Scanning electron microscopy studies were performed, on both as–received specimens and material which had been recovered from interrupted drop–weight experiments, to investigate the connection between microstructure and ignition sources. A close link was established between the mechanical properties at the appropriate strain rates and the ignition response to impact.

High-resolution optical study of the impact of carbon-fibre reinforced polymers with different lay-ups

The impact deformation of carbon-fibre reinforced polymer samples with different lay-ups was studied using high-speed optical techniques. The in-plane deformation of the sample was measured using time-resolved fine-grid analysis. The residual velocities of the projectiles were determined using streak photography and hence the energy dissipated during the penetration was obtained. Both microscopic damage and macroscopic damage to the plates were studied. The deformation, energy dissipation and damage all had a strong dependence on the composite lay-up. Unidirectional composites exhibited anisotropic behaviour and were significantly weaker than the other lay-ups. Though this is intuitively reasonable, this paper gives quantitative measures of this effect. Composite samples examined using the fine-grid technique exhibited cracking in the rear ply suprisingly early in the impact with wide-reaching delamination of this ply. Comparative measurements are presented for polymethylmethacrylate which deformed more isotropically until fragmentation.

Dynamic compaction of porous silica powder

The dynamic compaction characteristics of a porous silicon dioxide (SiO2) powder are reported. The initial specific volumes of the samples were either V00=1.30, 4.0, or 10.0cm3∕g whereas the silicon dioxide has a matrix specific volume of V0=0.455cm3∕g. The impact velocity ranges from 0.25to1.0km∕s and the shock incident pressure on the silica ranges from 0.77to2.25GPa. The shock velocity–particle velocity exhibited a linear relationship within this range. Although these tests represent the low end of dynamic compaction, the dynamic tests compare favorably to extrapolated data available in the open literature. Theoretical pressure–particle velocity and shock velocity–particle velocity curves were generated using a P-α compaction curve. The P-α compaction curve accurately represented the pressure–particle velocity and shock velocity–particle velocity Hugoniot curves for the low specific volume powder, specifically V00=1.30cm3∕g. However, the P-α compaction curve did not accurately represent the pressure–pa...

Fracture Studies of PBX Simulant Materials

Fracture studies have been performed on three inert PBX simulants; PBS 9501 which consists of sugar bound in Estane and is a PBX 9501 simulant. EDC1037 and EDC1032 which consist of barium sulphate and melamine bound in NC/K10 and Viton‐A respectively, and are simulants for EDC37 and EDC32. The effect of microstructure, geometry and testing rate are investigated, and through the application of elastic‐plastic fracture mechanics, energy release rates have been calculated. Such data are required for the development and validation of accurate failure models.

Adhesion Studies between HMX and EDC37 Binder System

EDC37 is a PBX which is composed of 91 % HMX and 9 % NC/K10 by weight. Previous studies have shown that damage under quasi‐static conditions occurs preferentially via the adhesive failure of the HMX/ binder interface. Single crystals of HMX have been grown for use in an idealised experiment in which HMX/ binder joints are broken in a simple tension geometry instrumented with a loadcell of millinewton sensitivity. This to quantitatively determine the parameters involved in this important failure mode. Such data are required for the development and validation of accurate microstructural models of PBXs. This paper outlines the current state of research and details the important observations to date.

SHOCK HUGONIOT DATA FOR LOW DENSITY SILICA POWDER

A series of plate impact experiments on low‐density silica powder have been conducted at the Cavendish Laboratory’s single stage gas gun facility. The experiments were conducted at impact velocities ranging from 600 to 1200 m s−1 to determine the powder’s low‐pressure shock response. Density of powder was 0.1 g cm−3 on average. Attempts to model the compaction features of the powder were conducted with the P‐α model for porous materials using the shock physics analysis package CTH with some success.

Hugoniot Properties of Dry Yorkshire Sandstone up to 8 GPA

A series of plate impact experiments has been performed to assess the dynamic behaviour of dry Yorkshire sandstone up to 8 GPa. Standard manganin gauges were inserted between samples in order to determine the principal Hugoniot curve. A VISAR system was used to measure the free surface velocity of the target. This work is in part of a research programme to understand the survivability of microbial life under impact and the creation of new habitats for microbial life as a function of shock processing of sandstone.

The Dynamic Behavior of Micro‐Concrete

A series of plate impact experiments has been performed to assess the dynamic behaviour of micro‐concrete (70% fine‐grain dolerite powder and 30% cement paste by weight) in both longitudinal and lateral directions. Information was obtained for the Hugoniot curve and dynamic shear stress properties. Hugoniot results are compared with published data on cement paste, mortar and concrete from the UK, Germany, France and the US. When the shear strength of micro‐concrete is compared to the cement paste very small differences are observed. Therefore, the shear strength of this system appears to be independent of the aggregates and mainly depends on the matrix material.