by Nguyen, C. Thang; Vu-Khanh, Toan; Dolez, Patricia I.; Lara, Jaime

Resistance to puncture is a critical property for several applications, in particular for elastomer materials used in protective clothing. To evaluate the puncture resistance of membranes, some methods have been proposed as standard tests. However, the rounded puncture probes used in these tests are very different from real pointed objects like medical needles, and may not measure the level of material resistance that corresponds to them. In fact, puncture by medical needles is shown to proceed gradually as the needle cuts into the membrane. This behavior is highly different from puncture by rounded probes which occurs suddenly when the strain at the probe tip reaches the failure

by Nguyen, C. Thang; Vu-Khanh, Toan; Dolez, Patricia I.; Lara, Jaime

Resistance to puncture by medical needles is becoming one of the most critical mechanical properties of rubber membranes, which are heavily used in protective gloves. Yet the intrinsic material parameters controlling the process of puncture by medical needles are still unknown. In a first paper presenting this two-part study, it has been shown that puncture by medical needles proceeds gradually as the needle cuts through the rubber membrane. The phenomenon of puncture by medical needles was revealed to involve contributions both from friction and fracture energy, in a similar way as for cutting. The use of a lubricant was not successful for removing the friction contribution for

by Rupnowski, Przemyslaw; Sopori, Bhushan

This paper describes a model to predict mechanical strength distribution of silicon wafers. A generalized expression, based on a multimodal Weibull distribution, is proposed to describe the strength of a brittle material with surface, edge, and bulk flaws. The specific case of a cast, unpolished photovoltaic (PV) wafer is further analyzed. Assuming that surface microcracks constitute the dominant mechanism of wafer breakage, this model predicts the strength distribution of PV silicon that matches well the experimental results available in the literature.

DOI: 10.1007/s10704-009-9324-9
Online Date: 3/3/2009
Print publication date: 1/1/2009
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by Codrington, John

Plate thickness can have a profound effect on fatigue crack growth following theapplication of an overload cycle. A modified strip-yield model is presented for determining the effects of plate thickness based on the mechanism of plasticity-induced crack closure and first-order plate theory. This approach eliminates the need for any empirical or fitting parameters. Comparisons are made with experimental data for the case of a single tensile overload applied under otherwise constant. ΔK loading. The theoretical crack growthpredictions are found to be in good agreement with the experimental data.

DOI: 10.1007/s10704-009-9322-y
Online Date: 2/27/2009
Print publication date: 1/1/2009
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by Zemri, M.; Mazari, M.; Bouchouicha, B.; Benguediab, M.; Ranganathan, N.

The growth of crack is related to the existence of a plastic zone at the crack tip; whose formation and growth is accompanied by energy dissipation. The estimation of this energy is generally done by the so called global methods (hysterisis loops) or the micro-gages. In the present study, the micro-hardness measures in the plastic zone are used to evaluate the energy dissipated in the fracture process zone by plastic deformation. The obtained results on the aluminium alloy 7075 T7 and E460 steel are compared to those obtained by other methods.

DOI: 10.1007/s10704-009-9319-6
Online Date: 2/18/2009
Print publication date: 1/1/2009
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by Roux, Stéphane; Hild, François

Considering a semi-infinite planar crack propagating along a plane where the local toughness is a random field, the addressed problem is to compute the effective (or homogeneous and macroscopic) toughness. After a brief introduction to the two regimes—strong and weak pinning—that are expected depending on the system size, a self-consistent homogenization scheme is introduced. It is shown that this scheme allows one to predict not only the mean value but also the standard deviation and even the complete probability distribution function of the toughness. A discussion about the quality of this prediction as compared with direct numerical simulations is proposed.

DOI: 10.1007/s10704-008-9271-x
Online Date: 2/17/2009
Print publication date: 11/1/2008
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