No abstract

In this paper the fully nonlinear theory of finite deformations of an elastic solid is used to study the elastostatic field near the tip of a crack. The special elastic materials considered are such that the differential equations governing the equilibrium fields may lose ellipticity in the presence of sufficiently severe strains.The first problem considered involves finite anti-plane shear (Mode III) deformations of a cracked incompressible solid. The analysis is based on a direct asymptotic method, in contrast to earlier approaches which have depended on hodograph procedures.The second problem treated is that of plane strain of a compressible solid containing a crack under tensile (Mode I) loading conditions. The materials is characterized by the so-called Blatz-Ko elastic potential. Again, the analysis involves only direct local considerations.For both the Mode III and Mode I problems, the loss of equilibrium elliptieity results in the appearance of curves ("elastostatic shocks") issuing from the crack-tip across which displacement gradients and stresses are discontinuous.

No abstract

To prevent wheel lockup (and possible loss-of-control and capsize) during hard braking, motorcycle manufacturers have equipped motorcycles with antilock brake systems (ABS) either as an option or as standard equipment. Several studies utilizing real-world crash data have been published, which estimate the effectiveness of motorcycle ABS in reducing the risk of a crash based on varying assumptions. These investigations have reported mixed results. The present investigation relies upon the fatality analysis reporting system (FARS) and the Florida police-reported crash databases to further investigate the effectiveness of motorcycle ABS by expanding upon and refining previous approaches. Notably, a case-control approach is used, whereby crashes involving ABS- and non-ABS-equipped motorcycles are divided into five groups with a varying likelihood that ABS will affect the risk of crashes in that group. The group of crashes with the least likelihood of being influenced by ABS is considered the control group and used as a measure of exposure to crashes. This methodology attempts to reduce any selection biases that might exist in the two motorcycle classes. The results support the hypothesis that ABS is effective in reducing the crash risk in some crash types. However, it was found that the case-control approach does not incorporate all factors that might influence the overall effectiveness of ABS, e.g., motorcycle class and operator age. Accounting for these additional factors would likely require the use of regression analyses and would benefit significantly from additional data.

Analysis of accident data for consumer products can be used to identify accident modes and to aid in decisions about the feasibility of safety interventions for reducing risk. Decisions based upon a large accident data set, rather than upon a single accident, are much more likely to address important problems and to avoid creating negative consequences (e.g., increases in other kinds of accidents, loss in product utility). This paper describes the application of accident report analysis to a proposed safety intervention for all-terrain vehicles (ATVs). In order to evaluate the suggested use of conspicuity flags as standard equipment on all ATVs to prevent collision-related accidents, we reviewed 287 operating-ATV-associated “In-Depth Investigations” (conducted by the Consumer Product Safety Commission for ATV-associated injuries reported by the National Electronic Injury Surveillance System during a 2.5 month period in 1985). It was found that flags could have influenced only a very small portion of ATV injuries at best, and might even have a null or negative net impact when problems are considered. Thus, required usage of flags would be inappropriate for most riding environments.