The mixed regime of lubrication is most frequently encountered in cold strip rolling processes. A model is presented hereafter. The lubrication at the interface is closely coupled with the mechanics of the rolling process. Therefore, the proposed model combines a macroscopic model of rolling (elastic-plastic slab method) with a microscopic mixed lubrication model, consisting of a Reynolds equation for rough surfaces (describing the formation of the lubricant film) and an equation for the evolution of roughness, describing the conformation of the strip surface to the roll. The bases of the model are presented and compared to models in the literature; its hypotheses and results are discussed, a few applications are given.

A model of lubricated cold strip rolling is extended to the thin foil case. The model considers the evolution of asperity geometry and lubricant pressure through the bite. Friction between the roll and the asperities on the strip is modelled using the Coulomb and Tresca friction factor approaches. The shear stress in the Coulomb friction model is limited to the shear yield stress of the strip. A novel modification to these standard friction laws is used to mimic slipping friction in the reduction regions and sticking friction in a central neutral zone. The variation of rolling load, lubricant film thickness and asperity contact area with rolling speed is examined, for conditions typical of rolling aluminium foil from a thickness of 50 to 25 μm.

Recent studies have shown that in certain situations, usually described by mixed lubrication models, a continuous ultra-thin film could separate two solids, even at the scale of asperities. In this paper, the consequences of this assumption are examined in the case of cold rolling geometries. The tribological behaviour is derived from the resolution of the Reynolds equation. The influence of the rheological parameters of the lubricant and of the existence of a cavitation zone is discussed.

The flow between rough surfaces in sliding motion with contacts has been analyzed through the volume averaging method for different geometries of surfaces, including the self-affine geometry encountered in cold rolling. In this paper, we simply give an overview of main results. An average flow model is derived, in which the influence of roughness is taken into account through effective transport tensors called "flow factors" . The flow factors have been determined for various deterministic (sinusoidal) and random roughness distributions.

The works described previously, and summarized here, have already been applied under various forms, to be described hereafter: explanation of industrial observations, knowledge models, new ideas for lubricant formulation, which now have to be tested. Of course, not all the needs of industry have been fulfilled, so that perspectives for further research are highlighted.

The hardness and wear resistance of 304 stainless steel have been increased by electric arc charging with two hyppereutectic alloy coatings. Oxidation tests have shown that, thanks to the presence of silicon in the coating, a protecting layer of Cr2O3 can develop, which leads to an oxidation rate similar to that of the substrate.

C-Mn steels and associated welds are susceptible to Dynamic Strain Ageing (DSA). In this case, fracture toughness shows a minimum when the temperature increases from 20°C to 300°C. After a literature review, the results of J - R tearing resistance tests, characterized by crack initiation resistance J$_{0,2}$ and tearing modulus dJ/da relative to a base metal (A48 French standard steel) and Manual Metal Arc deposited metals are presented and discussed. The decrease of both crack initiation resistance J$_{0,2}$ and tearing modulus dJ/da is related to the DSA sensitivity of the material. A simplified engineering method based on the evolution of the Ultimate Tensile Strength versus temperature and a method of J$_{0,2}$ determination according to a local approach model of ductile fracture are proposed to predict the maximal drop in tearing resistance exhibited by the materials around 200°C as a function of ageing sensitivity of the product.

It is economically important for manufacturers of high-temperature machines to be able to measure creep damage so they can predict residual service life more accurately. This paper describes and refines an image analysis method for evaluating creep damage in laboratory test pieces. It is a preliminary study of how to extract relevant information for damage measurement by cavities counting. Grain boundary extraction, which is directional information, is the major question to be overcome before measurement can be automated. The search for a crest-line extraction filter by the Canny method has led to the development of a directional wavelet transform filter. The results of this innovative filtering method are applied here.

The recent unexpected discovery of a degassing flow from the metal to the hydrogen charging environment, which operates simultaneously with the crude charging flow, has given new interest to the former concepts of internal and external hydrogen, coupled with a new type of cathode protonic reaction. This affects considerably the way permeation experiments are conducted and their results interpreted. This paper proposes a new approach allowing, among other things, to explain what appeared formerly as anomalies, especially in the area of thin membranes.