Paul Hazell

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.

On the dynamic behavior of three readily available soft tissue simulants

Plate-impact experiments have been employed to investigate the dynamic response of three readily available tissue simulants for ballistic purposes: gelatin, ballistic soap (both subdermal tissue simulants), and lard (adipose layers). All three materials exhibited linear Hugoniot equations-of-state in the US-uP plane. While gelatin behaved hydrodynamically under shock, soap and lard appeared to strengthen under increased loading. Interestingly, the simulants under test appeared to strengthen in a material-independent manner on shock arrival (tentatively attributed to a rearrangement of the amorphous molecular chains under loading). However, material-specific behavior was apparent behind the shock. This behavior appeared to correlate with microstructural complexity, suggesting a steric hindrance effect.

In-fiber shock propagation in Dyneema®

In this work, the in-fiber shock propagation in Dyneema® has been studied such that the shock propagated along the axis of one of the fiber directions. A fast moving precursor wave was detected that corresponded to the elastic wave velocity of the fibers suggesting that the fibers themselves were acting as wave guides. Further, it was noticed that above a threshold shock stress of ca. 3.5 GPa, this wave was not discernable. This shock stress corresponded with the stress at which shock-induced melt would be expected to occur suggesting that melting inhibited the fibers’ ability to act as wave guides.

THE DYNAMIC BEHAVIOUR OF BALLISTIC GELATIN

In order to characterise the effect of projectiles it is necessary to understand the mechanism of both penetration and resultant wounding in biological systems. Porcine gelatin is commonly used as a tissue simulant in ballistic tests because it elastically deforms in a similar manner to muscular tissue. Bullet impacts typically occur in the 350–850 m/s range; thus knowledge of the high strain‐rate dynamic properties of both the projectile and target materials are desirable to simulate wounds. Unlike projectile materials, relatively little data exists on the dynamic response of flesh simulants. The Hugoniot for a 20 wt.% porcine gelatin, which exhibits a ballistic response similar to that of human tissues at room temperature, was determined using the plate‐impact technique at impact velocities of 75–860 m/s. This resulted in impact stresses around three times higher than investigated elsewhere. In US−uP space the Hugoniot had the form US = 1.57+1.77 uP, while in P−uP space it was essentially hydrodynamic. ...

The shock and spall response of three industrially important hexagonal close-packed metals: magnesium, titanium and zirconium

Magnesium, titanium and zirconium and their alloys are extensively used in industrial and military applications where they would be subjected to extreme environments of high stress and strain-rate loading. Their hexagonal close-packed (HCP) crystal lattice structures present interesting challenges for optimizing their mechanical response under such loading conditions. In this paper, we review how these materials respond to shock loading via plate-impact experiments. We also discuss the relationship between a heterogeneous and anisotropic microstructure, typical of HCP materials, and the directional dependency of the elastic limit and, in some cases, the strength prior to failure.

Impact, penetration, and perforation of a bonded carbon-fibre-reinforced plastic composite panel by a high-velocity steel sphere: An experimental study:

In this work, the response of a bonded carbon-fibre-reinforced plastic composite panel, which had been manufactured by bonding two laminates together, to impact, penetration, and perforation by a high-velocity steel sphere has been studied. The response of a relatively thick (about 12 mm) laminate has been compared with similar data from previous work by Hazell et al. where relatively thin monolithic laminates were impacted by the same type of projectile. It was found that the ballistic performance of the system was increased over the impact energy range of interest when compared with these similar, relatively thin composite laminates. Furthermore, both the energy absorbed per unit thickness of laminate and the level of damage as measured by a C-Scan system when the panels were perforated at normal incidence and oblique incidence were similar. This raises the prospect of reducing experimental testing at oblique angles, if the behaviour at normal incidence is known.

The high strain-rate behaviour of selected tissue analogues

The high strain-rate response of four readily available tissue simulants has been investigated via plate-impact experiments. Comparison of the shock response of gelatin, ballistic soap (both sub-dermal tissue simulants), lard (adipose layers) and Sylgard(®) (a potential brain simulant) allowed interrogation of the applicability of such monolithic tissue surrogates in the ballistic regime. The gelatin and lard exhibited classic linear Hugoniot equations-of-state in the US-uP plane; while for the ballistic soap and Sylgard(®) a polymer-like non-linear response was observed. In the P/σX-v/v0 plane there was evidence of separation of the simulant materials into distinct groups, suggesting that a single tissue simulant is inadequate to ensure a high-fidelity description of the high strain-rate response of complex mammalian tissue. Gelatin appeared to behave broadly hydrodynamically, while soap, lard and Sylgard(®) were observed to strengthen in a material-dependent manner under specific loading conditions at elevated shock loading pressures/stresses. This strengthening behaviour was tentatively attributed to a further polymeric-like response in the form of a re-arrangement of the molecular chains under loading (a steric effect). In addition, investigation of lateral stress data from the literature showed evidence of operation of a material-independent strengthening mechanism when these materials were stressed above 2.5-3.0GPa, tentatively linked to the generically polymeric-like underlying microstructure of the simulants under consideration.

A study on the strength of an armour-grade aluminum under high strain-rate loading

The aluminum alloy 5083 in tempers such as H32 and H131 is an established light-weight armour material. While its dynamic response under high strain-rates has been investigated elsewhere, little account of the effect of material orientation has been made. In addition, little information on its strength under such loadings is available in the literature. Here, both the longitudinal and lateral components of stress have been measured using embedded manganin stress gauges during plate-impact experiments on samples with the rolling direction aligned both orthogonal and parallel to the impact axis. The Hugoniot elastic limit, spall, and shear strengths were investigated for incident pressures in the range 1–8 GPa, providing an insight into the response of this alloy under shock loading. Further, the time dependence of lateral stress behind the shock front was investigated to give an indication of material response.

On the interpretation of lateral manganin gauge stress measurements in polymers

Encapsulated wire-element stress gauges enable changes in lateral stress during shock loading to be directly monitored. However, there is substantial debate with regards to interpretation of observed changes in stress behind the shock front; a phenomenon attributed both to changes in material strength and shock-dispersion within the gauge-encapsulation. Here, a pair of novel techniques which both modify or remove the embedding medium where such stress gauges are placed within target materials have been used to try and inform this debate. The behavior of three polymeric materials of differing complexity was considered, namely polystyrene, the commercially important resin transfer moulding (RTM) 6 resin and a commercially available fat (lard). Comparison to the response of embedded gauges has suggested a possible slight decrease in the absolute magnitude of stress. However, changing the encapsulation has no detectable effect on the gradient behind the shock in such polymeric systems.

The shock response of a rendered porcine fat

Characterization of the shock response of biological materials is required in order to develop an understanding of how such materials behave under high strain-rate loading. In this work, a predominately linear Us-up Hugoniot relationship for a rendered porcine fat has been established using the plate-impact technique. This has been shown to take the form Us=1.58+2.47up (ρ0=0.945 g/cc) and comparison has been made between the dynamic behavior of the adipose material and both 20 wt % ballistic gelatin and water. The adipose material has been shown to behave in likeness with simple polymers such as polyethylene and to strengthen under shock loading, unlike ballistic gelatin, which has been shown to behave hydrodynamically. An experimental design incorporating direct insertion of lateral stress gauges within the rendered fat has given insight into both the behavior of lateral gauges and the lateral stress response of the material under dynamic loading.