Mechanical characterization of rubber from one heterogeneous test

International audienceThe present study deals with the mechanical characterization of elastomeric materials. Classically, three homogeneous tests are considered to identify constitutive parameters, namely Uniaxial Tensile (UT), Pure Shear (PS) and Equibiaxial Tensile (ET) tests. Here, a new method is proposed: it consists in inducing the three previous homogeneous tests from only one heterogeneous mechanical test. For this purpose, a conventional tensile machine is used and a new apparatus is designed to be adapted on the machine. The test-induced heterogeneity is discussed related to two criteria based on the existence of UT, PS and ET and on the distribution of the maximal principal elongation at each material points of the sample surface. Experimentally, kinematic fields are provided on the sample surface by an image correlation code suitable for large deformations. Finally, an inverse technique, so-called Virtual Field Method, is used to identify the material parameters in the framework of the Mooney hyperelasticity

A new characterisation method for rubber

International audienceThis paper deals with the mechanical characterisation of elastomeric materials. An original method is proposed to identity the material parameters. It consists of performing only one heterogeneous mechanical test, measuring the displacement/strain field using suitable Digital Image Correlation software and applying an inverse method, namely the Virtual Fields Method, to process the resulting displacement/strain maps. For this purpose, a new apparatus is designed to be adapted to a conventional tensile machine. This apparatus enables us to obtain simultaneously uniaxial tension, pure shear and equibiaxial tension, using only one sample. The heterogeneity of the kinematic fields induced by the test is first discussed in relation to two criteria. The main features of the identification method are then presented, and results provided by a test performed on an elastomeric material are discussed in the context of hyperelasticity

Advances in biofilm mechanics

A knowledge of the mechanical properties of bacterial biofilms is required to more fully understand how a biofilm will physically respond, and adapt, to the physical forces, such as those caused by fluid flow or particle or bubble impingement, acting upon it. This is particularly important since biofilms are problematic in a wide diversity of scenarios and spatial and temporal scales and many control strategies designed to remove biofilms include a mechanical component such as fluid flow, particle or bubble impingement or a physical contact with the surface generated by scraping or brushing. Knowing when, and how, a biofilm might fail (through adhesive or cohesive failure) will allow better prediction of accumulation and biomass detachment, key processes required in the understanding of the structure and function of biofilm systems. However, the measurements of mechanical properties are challenging. Biofilms are living systems and they readily desiccate if removed from the liquid medium, it is not clear how quickly their mechanical properties might change when removed from their indigenous environment into a testing environment. They are also very thin and are inherently attached to a surface. They cannot be formed into standard test coupons such as plastics or solids, and cannot readily be poured or placed into conventional viscometers or rheometers, such as liquids and gels. Measured parameters such as the elastic and shear modulus, adhesive strength or tensile strength are sparse but are increasingly appearing in the literature. There is a large range of reported values for these properties, although there is general agreement that biofilms are viscoelastic. Biofilms have been assessed with various experimental methods depending on the desired characteristic and available equipment. The aforementioned challenges and lack of standard methods or equipment for testing attached biofilms have led to the development of many creative methods to tease out aspects of biofilm mechanical properties. In this paper, we review some of the more common techniques and highlight some recent result

Alcohol Consumption for People Admitted in French Emergency Departments: A Protocol for a Multi-Center Cluster Trial

International audienceBackground: According to a 2014 report by the World Health Organization, the highest alcohol consumption levels per capita continue to be found in the developed world, particularly in the European region. Drinking alcohol does not only lead to alcohol dependence; it also be linked to a higher risk for acute medical and surgical events. In France, recent data show that alcohol consumption levels in the general population are important and have remained relatively stable since 2010. In the Emergency Department population, few French data are available, while studies conducted across the Atlantic show that patients admitted into emergency rooms are reported to have high levels of alcohol consumption. Emergency Departments are an important location for the identification and early intervention of issues related to alcohol consumption. Therefore, the aim of this study is to carry out an epidemiological picture of alcohol consumption and search for indicators of harmful alcohol use in patients in the French emergency rooms of the Rhône-Alpes-Auvergne interregion. Methods and Analysis: This observational, and descriptive and randomized clinical study on human beings will consists of a collection of clinical variables on all patients that will be admitted to the Emergency Departments of the RAA Rhône-Alpes-Auvergne interregion aged of (16 years or older) and who will be agree to participate to the study. It will include one visit where the patient will respond to three auto-administrating screening tests on his or her alcohol consumption: Alcohol Use Disorders Identification Test – C (AUDIT C), Cut-down, Annoyed, Guilty, Eye-opener test (CAGE) and the Rapid Alcohol Problems Screen – Quantity Frequency test (RAPS4 – QF). Similarly, they will answer two self-administering questionnaires on socio-demographic and emergency data