Dynamic study of adhesively bonded double lap composite joints

Composite structures may be subjected to high loading rates in naval applications.Hence, the composite assembly’s dynamic behaviour needs investigation. This paperpresents an investigation on the structural rate dependent behaviour of adhesivelybounded double lap joints. High rate tests showed ringing in the force/displacementcurves. An attempt was made to determine the origins of this phenomenon

Generalized interfacial energy and size effects in composites

The objective of this contribution is to explain the size effect in composites due to the interfacial energy between the constituents of the underlying microstructure. The generalized interface energy accounts for both jumps of the deformation as well as the stress across the interface. The cohesive zone and elastic interface are only two limit cases of the general interface model. A closed form analytical solution is derived to compute the effective interface-enhanced material response. Our novel analytical solution is in excellent agreement with the numerical results obtained from the finite element method for a broad variety of parameters and dimensions. A remarkable observation is that the notion of size effect is theoretically bounded verified by numerical examples. Thus, the gain or loss via reducing the dimensions of the microstructure is limited to certain ultimate values, immediately relevant for designing nano-composites. © 2017 Elsevier Lt

Visualization of subsurface damage in woven carbon fiber-reinforced composites using polarization-sensitive terahertz imaging

Polarization-sensitive terahertz imaging is applied to characterize subsurface damage in woven carbon fiber-reinforced composite laminates in this study. Terahertz subsurface spectral imaging based on terahertz deconvolution is tailored and applied to detect, in a nondestructive fashion, the subsurface damage within the first ply of the laminate caused by a four-point bending test. Subsurface damage types, including matrix cracking, fiber distortion/fracture, as well as intra-ply delamination, are successfully characterized. Our results show that, although the conductivity of carbon fibers rapidly attenuates terahertz propagation with depth, the imaging capability of terahertz radiation on woven carbon fiber-reinforced composites can nonetheless be significantly enhanced by taking advantage of the terahertz polarization and terahertz deconvolution. The method demonstrated in this study is capable of extracting and visualizing a number of fine details of the subsurface damage in woven carbon fiber-reinforced composites, and the results achieved are confirmed by comparative studies with X-ray tomography.The authors gratefully acknowledge the financial support of the Conseil Régional du Grand Est of the Fonds Européen de Développement Régional (FEDER), and of the Institut Carnot ARTS

Identification of Model Parameter for the Simulation of SMA Structures Using Full Field Measurements

With the design of new devices with complex geometry and to take advantage of their large recoverable strains, shape memory alloys components (SMA) are increasingly subjected to multiaxial loadings. The development process of SMA devices requires the prediction of their thermomechanical response, where the calibration of the material parameters for the numerical model is an important step. In this work, the parameters of a phenomenological model are extracted from multiaxial and heterogeneous tests carried out on specimens with the same thermomechanical loading history. Finite element analysis enables the computation of numerical strain fields using a thermodynamical constitutive model for shape memory alloys previously implemented in a finite element code. The strain fields computed numerically are compared with experimental ones obtained by DIC to find the model parameters which best matches experimental measurements using a newly developed parallelized mixed genetic/gradient-based optimization algorithm. These numerical simulations are carried out in parallel in a supercomputer to reduce the time necessary to identify the set of identified parameters. The major features of this new algorithm is its ability to identify material parameters of the thermomechanical behavior of shape memory alloys from full-field measurements for various loading conditions (different temperatures, multiaxial behavior, heterogeneous test configurations). It is demonstrated that model parameters for the simulation of SMA structures are thus obtained based on a reduced number of heterogeneous tests at different temperatures.NSF International Institute of Multifunctional Materials for Energy Conversion (IIMEC), award #084108

Identification d'un critère d'endommagement anisotrope de composites SMC en sollicitations rapides : Machine virtuelle d'essais multiaxiaux fondée sur une modélisation multi-échelle

National audienc

Comparison of stiffness measurements and damage investigation techniques for a fatigued and post-impact fatigued GFRP composite obtained by RTM process

International audienc

Identification d'un critère d'endommagement anisotrope de composites SMC en sollicitations rapides : Machine virtuelle d'essais multiaxiaux fondée sur une modélisation multi-échelle

National audienc

Direct identification of the damage behaviour of composite materials using the virtual fields method

In the present work the virtual fields method (VFM) has been used to extract the whole set of material parameters governing a nonlinear behaviour law for composite materials. The nonlinearity considered here is due to the damage inherent to the in-plane shear response. The identification method is performed by applying the principle of virtual work knowing the whole strain field onto the surface of a tested specimen. The test chosen here is a shear bending test using a rectangular coupon loaded in a Iosipescu fixture. To illustrate the capabilities of the method, the identification is performed on data provided by finite element simulations. First, the nonlinear finite element model is described. Then, numerical aspects of the VFM are discussed, in particular the stability of the technique with respect to noise in the data. Finally, first elements of test optimisation are given by studying the effect of the length of the active area and the effect of the material anisotropy. This work contributes to the development of the VFM as a tool adapted to the processing of full-field measurement to identify parameters from general constitutive equations.<br/

Experimental identification of a nonlinear model for composites using the grid technique coupled to the virtual fields method

The present paper shows some experimental results of the identification of the full set of parameters driving a nonlinear model for the inplane behaviour of a unidirectional composite laminate. The strain field at the surface of a rectangular coupon submitted to a shear/bending loading is measured using the grid technique. The strain fields are then processed by the virtual fields method to retrieve the six constitutive parameters: the linear elastic orthotropic in-plane stiffnesses Qxx, Qyy, Qxy, Qss and softening parameters K and ?0s driving the shear nonlinearity. It is shown that the shear response is correctly identified, with coefficients of variation similar to the ones of standard tests. The other parameters are identified with larger errors and higher coefficients of variation because their identification is affected by the lower normal strain levels in the specimen. It is therefore necessary to design new tests providing balanced strain levels for improving the identification procedure