Piezospectroscopie RQN : jauge de contrainte pour les matériaux composites

Abstract : The determination of stress and strain distributions in opaque materials is a key issue to evaluate their mechanical behavior. However, most of the methods used today to measure stress are either extremely invasive or ineffective for opaque materials. Within this context, we propose to use the Nuclear Quadrupolar Resonance (NQR) signal of small crystals, embedded within non, or poorly, conductive materials. Stresses transferred by the matrix to the crystal induce a deformation of its lattice which in turn results in a modification of the Electric Field Gradient (EFG) at the nucleus of interest. NQR is, as a consequence, sensitive to deformations induced by external mechanical stress and the crystals act as local stress gauges at the micron-scale. We call this method NQR piezospectroscopy.The objective of this study is to prove that NQR piezospectroscopy can be used to measure stress within opaque materials and more precisely within elastomer. The fundamental link between the NQR frequency variation and the stress tensor applied to the crystal has been studied. For that purpose, 63Cu in cuprite has been selected as a NQR probe. The stress dependence of its NQR frequency is investigated experimentally using different mechanical loadings generated within an original integrated NQR – stress device and discussed in the light of DFT ab-initio calculations.In addition, as proof-of-concept of NQR piezospectroscopy, additional experiments were carried out using loading conditions proving, without hypothesis on cuprite’s mechanical properties, that its NQR frequency shift is representative of the hydrostatic component of the elastomer inner stress field. We then investigated the ability of this method to map an heterogeneous stress field.
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Romain Dubourget. Piezospectroscopie RQN : jauge de contrainte pour les matériaux composites. Chimie-Physique [physics.chem-ph]. PSL Research University, 2017. Français. ⟨NNT : 2017PSLET019⟩. ⟨tel-02313821⟩

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