International audienceTwo different viscoelastic frameworks adapted to large strain rate-dependent response of elastomers are compared; for each approach, a simple model is derived. Within the Finite Linear Viscoelasticity theory, a time convolution integral model based on an extension to solid of the K-BKZ model is proposed. Considering the multiplicative split of the deformation gradient into elastic and inelastic parts, an internal variable model based on a large strain version of the Standard Linear Solid model is considered. In both cases, the strain energy functions involved are chosen neo-Hookean, and then each model possesses three material parameters: two stiffnesses and a viscosity parameter. These parameters are set to ensure the equivalence of the model responses for uniaxial large strain quasi-static and infinitely fast loading conditions, and for uniaxial rate-dependent small strain loading conditions. Considering their responses for different Eulerian strain rates, their differences are investigated with respect to the strain rate; more specifically, both stiffness and dissipative properties are studied. The comparison reveals that these two models differ significantly for intermediate strain rates, and a closing discussion highlights some issues about their foundations and numerical considerations

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a b s t r a c tThe present article is concerned with the resistance of a ship during a collision with another ship. The paper is directly related to the so called super-elements method developed to estimate the capability of a ship to withstand to an impact. This approach consists of dividing the structure into several elements (the socalled super-elements), whose resistance to collision is evaluated individually. At the recent stage of development, the superelements method is only able to treat the case of perpendicular collision scenarios. The purpose of this paper is to go one step further, by establishing analytical formulations giving the resistance of various super-elements to an oblique impact. As a first step, the paper gives a short description of the original super-elements method. After that, analytical calculations in oblique collision cases are performed for the different superelements involved in the procedure. Finally, the formulations are validated by comparison with results provided by classical nonlinear finite element method. As a conclusion, some perspectives on the future work are presented.

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This paper presents a user-friendly rapid prediction tool of damage to struck and striking vessels in a ship collision event. To do this, the so-called upper bound theorem is applied to calculate internal forces and energies of any substructure involved in the ships crushing process. At each increment of indentation, the total crushing force is transmitted to the external dynamics MCOL program, which calculates the global ship motion correction by solving the hydrodynamic force equilibrium equations. As a first step, the paper gives a brief description of the upper bound method originally developed for perpendicular collisions and recently enhanced for oblique ones. Then, the theory developed in MCOL program for large rotational ship movements is detailed. By comparing results obtained with and without MCOL, the importance of hydrodynamic effects is highlighted. Some simulation results are compared with results provided by classical nonlinear finite element calculations. Finally, by using the developed analytical tool, which mixes internal and external dynamics, different crushing scenarios including oblique collisions are investigated and the influence of some collision parameters like longitudinal and vertical impact location, impact angle, and struck ship velocity is studied.

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International audienceElastomers are widely used for damping components in various industrial contexts because of their remarkable dissipative properties: they can bear severe mechanical loading conditions, i.e., high strain rates and large strains. Depending on the strain rate, the mechanical response of these materials can vary from purely rubber-like to glassy. In the intermediate strain rate range (1-100/s), uniaxial extension experiments are classically conducted at constant nominal strain rate. We present here a new experimental methodology to investigate the mechanical response of soft materials at constant true strain rate in the intermediate strain rate range. For this purpose, the displacement imposed on the specimen by the tensile machine is an exponential function of time. A high speed servohydraulic machine is used to perform experiments at strain rates ranging from 0.01 to 100/s. A specific specimen is designed in order to achieve a uniform strain field (and thus a uniform stress field). Furthermore, an instrumented aluminium bar is used to measure the applied force; which overcomes the difficulties due to dynamic effects. Simultaneously, a high speed camera enables the measurement of strain in the sample using a point tracking technique. Finally, the method is applied to determine the stress-strain curve of an elastomer for both loading and unloading responses up to a stretch ratio $\lambda$ = 2.5; the influence of the true strain rate on both stiffness and dissipation of the material is then discussed

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