A two scale damage concept applied to fatigue

The ductile type of damage is a phenomenon now well understood. Once the fully coupled set of constitutive equations is identified, Damage Mechanics is a powerful tool to predict failure. Brittle materials do not exhibit such a damageable macroscopic behavior. Nevertheless, they still fail. On the idea that damage is localized at the microscopic scale, a scale smaller than the mesoscopic one of the Representative Volume Element (RVE), we propose a three-dimensional failure modeling for monotonic as well as for fatigue loading. We develop a two scale model of what we shall call brittle damage: at the microscopic scale, micro-cracks or micro-voids exhibit a damageable plastic-like behavior with no effect on the global (mesoscopic) elastic behavior. Microscopic failure is assumed to coincide with the RVE failure. This model turns out to represent quite well physical phenomena related to high cycle fatigue such as the mean stress effect, the nonlinear accumulation of damage, initial strain hardening or damage effect and the nonproportional loading effect for bi-axial fatigue. The model has been implemented as a post-processor computer code. A simplified identification procedure for the determination of the material properties is given. This revised version was published online in July 2006 with corrections to the Cover Date.     

Surface modifications induced in 316L steel by laser peening and shot-peening. Influence on pitting corrosion resistance

The influence of laser peening (LP) on the electrochemical behavior of AISI type 316L stainless steel in a saline environment was evaluated. Surface modifications were investigated as they might have beneficial effects on the corrosion behaviour. Low residual stress and work hardening levels were found, when compared with a conventional shot-peening (SP) treatment, mainly because of the absence of martensite transformation in the case of LP. Surface changes were accompanied by small roughening effects and a global preservation of the surface chemistry after treatment. Therefore, electrochemical tests performed on samples after LP and SP treatments showed increases in rest potentials, reductions of passive current densities and anodic shifts of the pitting potentials evidenced by a stochastic approach of pitting. The better pitting resistance was observed after LP treatment, which seems to reflect a reduction or an elimination of active sites for pitting at lower potentials. Even though the deleterious surface state of shot peened surfaces possibly counterbalances the beneficial influence of residual stresses, a beneficial influence of mechanical surface treatments has been demonstrated regarding the localized corrosion properties.     

Epidemicity of cholera spread and the fate of infection control measures

The fate of ongoing infectious disease outbreaks is predicted through reproduction numbers, defining the long-term establishment of the infection, and epidemicity indices, tackling the reactivity of the infectious pool to new contagions. Prognostic metrics of unfolding outbreaks are of particular importance when designing adaptive emergency interventions facing real-time assimilation of epidemiological evidence. Our aim here is twofold. First, we propose a novel form of the epidemicity index for the characterization of cholera epidemics in spatial models of disease spread. Second, we examine in hindsight the survey of infections, treatments and containment measures carried out for the now extinct 2010–2019 Haiti cholera outbreak, to suggest that magnitude and timing of non-pharmaceutical and vaccination interventions imply epidemiological responses recapped by the evolution of epidemicity indices. Achieving negative epidemicity greatly accelerates fading of infections and thus proves a worthwhile target of containment measures. We also show that, in our model, effective reproduction numbers and epidemicity indices are explicitly related. Therefore, providing an upper bound to the effective reproduction number (significantly lower than the unit threshold) warrants negative epidemicity and, in turn, a rapidly fading outbreak preventing coalescence of sparse local sub-threshold flare-ups.     

Photochemistry of polymeric systems VII. Photo-cross-linking of liquid polysiloxanes including cinnamic groups

Cinnamoyloxymethyl dimethyl vinyl silane was synthesized and bound to a series of commercial polydimethylsiloxane-type copolymers bearing variable amounts of Si? H functions through a hydrosilylation reaction. This reaction was controlled in order to avoid side reactions between the photosensitive unsaturated moiety and the Si? H groups. The photosensitivity of polymeric films was studied by a photoresist test described in previous papers. The results emphasize the role of the molecular weight of the starting copolymer and the percentage of pendant photosensitive groups.     

Analysis and design of CMOS fuzzy logic controller in current mode

This paper presents a new definition of fuzzy numbers. Employing the new definition, the new approach to the design of a current mode fuzzy microchip controller was performed. The controller was constructed with CMOS current mirrors. The circuit allowed two premises, one conclusion, and nine rules; the latter were programmable with current sources. The chip consumed 2 mA at a 5 V power supply for a core area of 0.4 mm². Furthermore, the performance of the developed fuzzy architecture reached 10 M FLIPS (fuzzy inferences per second) for the standard 1.2 μm CMOS technology. We present a real-time application that successfully used the chip to control a metallic ball with an electromagnetic field. Finally, we discuss the silicon compiler, called SCOFIC, used for the automatic synthesis of the above circuit