Mécanique et mécanisme de perforation des matériaux de protection
Nguyen, Chien Thang
Puncture resistance is among the major mechanical properties often required for protective clothing, especially in the medical sector. However the intrinsic material parameters controlling puncture resistance of protective materials are still unknown. Therefore, the purpose of this work is to study the mechanism and mechanical behaviors of puncture resistance of protective clothing materials to various probe types. A better understanding of puncture mechanics will be helpful to develop suitable methods to evaluate the puncture resistance and to predict the failure of protective clothing materials. The thesis includes 4 articles which expose two major phases in this study. Article I and II studied the mechanics and mechanisms of puncture by conical and cylindrical probes used in the standard test methods (ASTM F1342 and ISO 13996). The results show that the punctures of rubber membranes by conical and cylindrical probes are controlled by a maximum local deformation (or puncture failure strain) that is independent of the probe geometry. The puncture strengths of elastomer membranes are much lower than their tensile and biaxial strengths. In addition, a simpler cylindrical probe can be used in the place of the costly conical probe required by the ASTM standard and still provides a quantitative characterization of puncture. Actually, since 2005, an alternative method B had been added to F1342 ASTM with 0.5 mm-diameter rounded-tip cylindrical probe. Furthermore, the puncture probes used in the ASTM F1342 are very different to the actual pointed objects (medical needle, pointed tip of knife... ) and cannot accurately characterize the puncture resistance to real objects. Therefore, in the second step, the mechanics and mechanisms of puncture by medical needles were studied. Article III shows that the puncture by sharp-pointed objects like medical needles is very different from the puncture by conical probes used in the ASTM standard test. For medical needles, the puncture resistance involves cutting and fracture energy of material. Using the fracture mechanics, based on the change in strain energy with the change in fracture surface, the fracture energy in puncture was estimated. This calculation assumes that there is no friction between the needle tip and fracture surface. However, even with the application of a lubricant on the needle surface, the effect of friction on the puncture process cannot be totally eliminated, preventing the determination of the material fracture energy. Therefore, Article IV has described a method, similar to that of Lake and Yeoh for cutting to access the precise value of fracture energy in puncture of rubbers by sharp-pointed objects. The method allows substantially eliminating the effects of friction on the evaluation of the fracture energy involved in the puncture process.
- Génie – Thèses