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A simple method for characterizing synthetic graphite powders is presented in this paper. A thick glass cylinder contains a known weight of material, which is held between two conducting pistons. These allow the measurement of the electrical conductivity of the sample, and enable its compaction. The graphite powder is gently pressed, and its volume and conductivity variation are simultaneously measured. From these results, the relation between conductivity and the volume fraction of grains is derived: an equation based on the effective medium theory (EMT) is shown to fit the experimental data accurately. The adjustable parameters are directly linked with both the anisotropic conductivity and the morphology of the grains. On the one hand, conductivity measurements achieved on single particles give values of the same order of magnitude as those derived from the fits. On the other hand, the other parameters of the equation perfectly agree with the aspect ratios obtained from apparent density measurements. The percolation thresholds which would be expected from composites made of graphite powders imbedded in an insulating medium are also calculated via the EMT equation. Comparison with other theoretical and experimental values always leads to very good agreement, showing the accuracy of the EMT equation in supplying fair geometrical parameters for the particles.

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Two methods for evaluating the cut resistance of gloves were compared: one developed at ITF-Lyon (Institut Textile de France) and one developed at the IRSST (Institut de recherche en santé et en sécurité du travail du Québec) in Montreal, Canada. The ITF method uses a circular blade with a pressure of 5 N applied on the blade. The blade speed is sinusoidal with a maximum of 100 mm/s. The value to be measured is the number of cycles to cut the material and is compared with that of a reference material. The IRSST method uses a straight blade and the pressure is applied on the sample holder. Series of tests using at least two different weights must be performed at a constant blade speed. The cut resistance for the IRSST method is measured as the load required to cut the material at a 10-mm blade displacement. Eighteen glove materials of different levels of cut resistance were compared. With uniform materials such as neoprene, no variability is observed with the ITF method, while a coefficient of variation of approximately 10% is observed with the IRSST method. These results may be due to different sensitivities of the test methods. The ranking of cut resistance obtained with both methods can be considered as equivalent and the results are comparable with a correlation coefficient r of 0.89.

Among industrial injuries, those related to hands are most frequent. The mechanical aggressions essentially depend on the type of activity and most of them are easy to simulate. However, the objective and simple measurement of the cutting resistance of any protective material comes up against the reproducibility of the process, considering the delicate specifications and measurements of the sharpness of the blades used for this purpose. Moreover, we also have to distinguish between cutting by slicing (motion parallel to the surface) and cutting by impact (motion perpendicular to the surface). Whatever the case, the sharpness of the blade needs some sophisticated means of observation, which is expensive. In 1987, I T F - LYON (Institut Textile de France), at the request of I N R S (Institut National de Recherche et de Sécurité), developed a method to measure the cutting effects by slicing where blade sharpness supervision is not necessary with certain limits. This method consists of measuring the cutting effects on a given material against those measured on a defined control specimen.