This study aims ultimately to quantify the force needed to penetrate human tissue. The results will reduce the subjectivity of expert opinion in stabbing incidents. They will also aid clinicians in assessing the severity of injury and help prevent the unnecessary deaths which can occur when this is not fully appreciated. Tensile tests were performed to identify suitable skin simulants with synthetic chamois and pigskin as candidate materials. Quasi-static penetration experiments were also performed in which a knife blade penetrated a skin simulant target. Pigskin was found to be much stronger than chamois under tensile load yet the puncture resistance was almost identical for the two materials.

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Accurate, 3-D analyses of running impact require a constitutive model of the running surface that includes the material nonlinearity shown by many modern surfaces. This paper describes a hyperelastic continuum that mimics the experimentally measured response of a particular treadmill surface. The material model sacri®ces a little accuracy to admit a robust, low-order hyperelastic strain-energy functional. This helps prevent the premature termination of ®nite element simulations, due to numerical or material instabilities, that can occur with higher-order functionals. With only two free constants, it is also a more practical design tool. The best ®t to the quasi-static response of the treadmill was achieved with an initial shear modulus l 2 MPa and a power-stiffening index a )25. The paper outlines the method used to derive the material constants for the treadmill, a device that is not amenable to the usual materials laboratory tests and must be reverse-engineered. Finite element analyses were then performed to ensure that the treadmill model interacts with the other components of the multibody running system in a numerically stable and physically realistic manner. The model surface was struck by a rigid heel, cushioned by a hyperfoam material that represents a shoe midsole. The results show that, while the ground reaction force is similar to that obtained with a rigid surface, the maximum principal stress in the shoe is reduced by 15%. Such a reduction, particularly when endured over many load cycles, may have a signi®cant effect on comfort and damage to nearby tissue.

There is an abundance of experimental data on the ballistic performance of sporting shotguns. However the successful development of computational models, that will help to reduce the commercial and environmental costs of extensive test programs, has been elusive. This paper describes the development and evaluation of a 3-D model that uses a commercial implementation of the distinct element method. The simulation gives realistic results for the effect of muzzle chokes on the spread of shot and provides evidence to support the well-known belief of practical shooters that a tapered constriction of 0.040" (1.02 mm) in barrel diameter, the so-called`full-choke', produces the optimum shot pattern. Detailed investigation of the internal ballistics of the shotgun shows that the reduction in diameter at the choke serves to compress the shot laterally as it exits the gun barrel. This affects the severity of interparticle collisions, creating a tighter, more uniform pattern. The accuracy of the computational results in the absence of air resistance tends to imply that the internal ballistics, rather than aerodynamic drag, dominates the shot pattern, although not the penetration power, over short ranges. Useful predictions of shotgun performance might then be obtained without resorting to full computational¯uid dynamics simulation or to extensive ®eld trials.Units: Obsolescent British`Imperial' units such as inches (") and ounces (oz.) and pounds (lb.) are still in widespread use for some of the critical dimensions and weights relating to ®rearms and ammunition, especially in legal de®nitions and in everyday speech. These units are retained in the text when appropriate. Equivalent ISO units are given.