Computational Homogenization of Architectured Materials

Architectured materials involve geometrically engineered distributions of microstructural phases at a scale comparable to the scale of the component, thus calling for new models in order to determine the effective properties of materials. The present chapter aims at providing such models, in the case of mechanical properties. As a matter of fact, one engineering challenge is to predict the effective properties of such materials; computational homogenization using finite element analysis is a powerful tool to do so. Homogenized behavior of architectured materials can thus be used in large structural computations, hence enabling the dissemination of architectured materials in the industry. Furthermore, computational homogenization is the basis for computational topology optimization which will give rise to the next generation of architectured materials. This chapter covers the computational homogenization of periodic architectured materials in elasticity and plasticity, as well as the homogenization and representativity of random architectured materials

Identification of heterogeneous elastoplastic behaviors using constitutive equation gap method

Cohesive zones models are commonly used in numerical simulations to take into account the onset and the propagation of microcracks leading to the fracture of materials. Their numerical implementation in finite element schemes is based on embedding surface traction-separation law between two adjacent bulk elements. The traction between two neighboring elements is linked to the corresponding opening by a cohesive relationship. The objective of the work reported here is to extend the approach developed in [1, 2] to identify the shape and parameters of the cohesive zone models in metal matrix composites with brittle inclusions and adapt this method to the study of initially heterogeneous material (e.g. graded metals or ceramics). To treat these applications where mechanical fields are heterogeneous, local stress fields are to be estimated in addition to conventional kinematic fields to build the energy balance associated with the transformation. Here we propose to estimate these fields by an identification method using kinematic and thermal data from imaging. The proposed method is based on the minimization of a functional associated with the error in constitutive relation (Constitutive equation gap method) [3]. In its classical (mechanical) formulation, this functional depends on two sets of parameters: the stress field and the mechanical material properties (elasticity, plasticity, damage). We show here that the identification procedure is capable to estimate the stress fields and material properties for elastic and elastoplastic behavior. The method was applied on noisy measured displacement fields to assess its robustness in the case of elastic behavior. The method is now being extended to damageable plasticity. The introduction of a second (calorimetric) term in the functional, related to the heat sources is also examined

Radiated susceptibility test procedure and setup exploiting crosstalk

In this work, basic principles of an alternative test procedure exploiting crosstalk to reproduce in the terminal loads of a wiring structure the same disturbances that would be induced by traditional radiated susceptibility (RS) tests are presented. Equivalence with radiation is achieved by the use of a generator circuit properly fed with two synchronized RF generators, and holds for whatever loads (even not linear) connected to the terminations of the cable harness. The proposed procedure is here tailored to the specific conditions of incidence foreseen by aerospace Standards on RS. Its effectiveness is validated by measurements carried out in an ad hoc test setup

Conducted-susceptibility testing as an alternative approach to unit-level radiated-susceptibility verifications

This work presents a theoretical rationale for the substitution of radiated-susceptibility (RS) verifications defined in current aerospace standards with an equivalent conducted-susceptibility (CS) test procedure based on bulk current injection (BCI) up to 500 MHz. Statistics is used to overcome the lack of knowledge about uncontrolled or uncertain setup parameters, with particular reference to the common-mode impedance of equipment. The BCI test level is properly investigated so to ensure correlation of currents injected in the equipment under test via CS and RS. In particular, an over-testing probability quantifies the severity of the BCI test with respect to the RS test

Nanostructured polymer microcomposites: A distinct class of insulating materials

International audienceExperimental evidence was produced and gathered to demonstrate the distinct nature of nanostructured polymer microcomposites. The case of a polymer composite consisting of a high-content of micrometric quartz with a small adjunct of nanoclay is discussed. Emphasis is put on dielectric behavior studies while some results on thermal characteristics are presented. Overall results strongly support the potential of this class of insulating material for electrotechnical application

Polymer Nanocomposites - Fundamental and Possible Applications to Power sectors

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