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The core structures of dislocations are crucial for understanding the plastic deformation mechanisms and the functional properties of materials. Here, we use the scanning transmission electron microscopy imaging techniques of high-resolution high angle annular dark field and integrated differential phase contrast to investigate the atomic structure of a pair of climb-dissociated 1 2 a [ 01 1 ¯ ] dislocations in a bending-deformed relaxor ferroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb1/3)O3–PbTiO3 single crystal. Cations at one dislocation core are found to arrange in the same way as the climb-dissociated 1 2 a [ 01 1 ¯ ] dislocation core in SrTiO3, while the other one is different. Oxygen depletion was observed at both dislocation cores. Geometric phase analysis of the lattice rotation shows opposite signs at both sides of the dislocations, demonstrating the strain gradient, which is known to give rise to flexoelectric polarization. Using the peak finding method, the polarization (a combination of ferroelectric and flexoelectric) around dislocations was mapped at the unit-cell scale. The polarization direction obtained is consistent with that predicted based on the flexoelectric effect in a perovskite oxide with [011] geometry. Head-to-head positively charged and tail-to-tail negatively charged domain walls were revealed based on the polarization map, suggesting a new way to stabilize charged domain walls via dislocations. A distinct dislocation core configuration has been observed, and a unit-cell scale polarization map helps understand the flexoelectric effects (coupling between strain gradient and polarization) around dislocations in a relaxor ferroelectric. [ABSTRACT FROM AUTHOR]

Abstract: The reliability of the bonding between propellant and insulation plays an important role in estimating Solid Rocket Motor (SRM) structural integrity. In this paper we use experimental and numerical methods to analyze the Mode II fracture properties of the interface debonding between propellant and insulation. An adhesive-adherend sandwich of Hydroxyl-Terminated Polybutadiene (HTPB) propellant and HTPB based insulation is bonded by the HTPB adhesive, providing Single-Lap Joints with revised supports to analyze the shear behavior of the interface debonding. A bilinear model is used to construct the Finite-Element (FE) model and simulation. The estimated Cohesive Zone Model (CZM) parameters calibrated from experiments are optimized by an inverse analysis based on the Hooke-Jeeves optimization algorithm. Good agreement is found which indicates that the estimated CZM values were precise. The study presents a simplified way to test the shear behavior of the adhesive layer between propellant and insulation with ductile properties. The result may offer a contribution to optimizing the interface structure in SRM, to analyzing the structural integrity of SRM, and for conducting numerical analyses of SRM. [Copyright &y& Elsevier]

Interface debonding is one of the major failure modes for the adhesive joints of polymer–matrix composites. The interfacial fracture properties of adhesive interfaces involving large-scale yielding is difficult to determine. A hybrid method that combines modified data reduction and inverse analysis was used to determine the fracture energy of the composite propellant/insulation interface at different loading rates. The modified data reduction adopts effective crack length to account for the effect of the fracture progress zone and avoid monitoring the crack length. These estimated values of the fracture energy were then calibrated by inverse analysis based on the Hooke–Jeeves algorithm in which the interface layer is characterized by a cohesive zone model. The whole process of inverse analysis is conducted automatically without any intervention by procedures. Experimental and numerical results indicate that the proposed data reduction provided fracture energy sufficiently similar to those obtained by the inverse analysis. Moreover, the fracture energy of the propellant/insulation interface was found to rely heavily on the loading rate with a non-monotonic trend. [ABSTRACT FROM AUTHOR]