Wave Propagation in Auxetic Tetrachiral Honeycombs

This paper describes a numerical and experimental investigation on the flexural wave propagation properties of a novel class of negative Poisson's ratio honeycombs with tetrachiral topology. Tetrachiral honeycombs are structures defined by cylinders connected by four tangent ligaments, leading to a negative Poisson's ratio (auxetic) behavior in the plane due to combined cylinder rotation and bending of the ribs. A Bloch wave approach is applied to the representative unit cell of the honeycomb to calculate the dispersion characteristics and phase constant surfaces varying the geometric parameters of the unit cell. The modal density of the tetrachiral lattice and of a sandwich panel having the tetrachiral as core is extracted from the integration of the phase constant surfaces, and compared with the experimental ones obtained from measurements using scanning laser vibrometers

A numerical and experimental study of woven composite pin-joints

A numerical and experimental study was carried out to determine the stiffness and the bearing strength of bolted woven composite joints. The main objective was to investigate the possibility of predicting the properties of the joint from the properties of the material measured with standard tests. A refined finite element model was developed in which the nonlinearities due to both the material and the contact angle between the pin and the hole were taken into account. Particular attention was paid to account for the influence of the clearance which has been shown to be very significant. In conclusion, good agreement between experimental results and numerical predictions has been obtained. <br/

The virtual fields method with piecewise virtual fields

This paper deals with the identification of constitutive parameters of materials from whole-field strain data. The inverse identification procedure used is the virtual fields method. It is based on the principle of virtual work written with particular virtual fields. A keypoint of the method is the determination of the virtual fields since they directly extract the unknown parameters from the measured fields. The main improvement of the present paper is to show the feasibility of piecewise virtual fields. These piecewise virtual fields are defined by virtual nodal displacements. The headlines of the virtual fields method are recalled in the first part of the paper. The procedure leading to the definition of piecewise virtual fields is then described. Numerical simulations finally illustrate the relevance of the approach and its sensitivity to noisy data.<br/

Investigation into the time-dependent behaviour of reinforced concrete specimens strengthened with externally bonded CFRP-plates

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Almost compatible microstructures in shape memory alloys

Coherent stress-free (CSF) microstructures with specific morphologies are favored in shape memory alloys (SMAs) when special relations are satisfied by the lattice parameters. Experimentally observed microstructures are, however, also formed at non-exact CSF conditions. Here we propose a framework for the investigation of almost compatible (i.e. non-perfectly CSF) twinned wedges in SMAs, and make a systematic study of these microstructures for two types of symmetry-breaking martensitic transformations. We determine the domains in lattice-parameter space wherein there exist, and coexist, different families of almost compatible wedges with low overall stress. We find these to be wide regions largely unrelated to the existence of special CSF relations, if any even exist, giving stress-free configurations. We propose SMA improvement can be obtained by targeting domains in lattice-parameter space wherein, besides satisfying other suitable properties, a maximum number of almost compatible microstructures can also form in the material. We develop this approach for wedges in SMAs undergoing the cubic-to-orthorhombic transformation