Research On Ultrasonic Guided Wave Characteristics In Quasi-crystal Structures

As a novel kind of solid material,quasi-crystal(QC)is of long-range quasi-periodic translational and long-range orientational orders.Owing to its quasi-periodic atomic arrangement,QC possesses many superior properties,such as low surface energy,andfriction coefficient,in addition to high abrasion resistance,hardness,temperature plasticity,thermal resistance and corrosion resistance resistivity.Thus,it has promising applications in the aerospace,machinery,energy,composite materials,chemical industry and other fields.Owing to its high brittleness,there are a lot of new challenges to the nondestructive testing with the rapid development and application of QC structures.Ultrasonic guided waves are of long propagation distance and wide coverag scope,and can quickly identify the defects,such as micro-crack and corrosion.Therefore,it also has a promising application in the nondestructive testing of QC structures.However,the prerequisite for utilizing this technique is to understand guided wave characteristics in detail.The coupled phonon and phason fields make it very difficult to analyze QC structures in theory.Along with the main research line that the QC waveguides are from simpleness to complexity,the Legendre orthogonal polynomial method is utilized to investigate the phonon-phason coupling effect on guided waves in QC structures.The detailed work is as follows:Firstly,guided wave characteristics in a 1-D hexagonal QC plate are investigated in the context of the Bak's model and elastohydrodynamic model,respectively.The phonon-phason coupling effect on wave characteristics is illustrated.Subsequently,guided waves in the functionally graded and multi-layered 1-D hexagonal QC plates are investigated in the context of Bak's model.The gradient field effect,layer thickness and stacking sequence on wave characteristics are illustrated.Results demonstrate that,for the bak's model,the phonon-phason coupling effect on phonon modes is extremely weak,and significant for phason modes;for the elastohydrodynamic model,the phonon-phason coupling effect has a significant influence on the phason modes which aren't propagative,without affecting phonon modes.Secondly,according to the linear electric-elastic theory of QC,guided waves in1-D hexagonal piezoelectric QC,functionally graded and multilayered plates are investigated,respectively.The phonon-phason coupling effect,piezoelectric effect on wave characteristics are analyzed.Results demonstrate that the variation in the polarization direction has more significant influence on phonon modes,and the variation in the quasi-periodic direction has more significant influence on phase mode.Thirdly,guided waves in 2-D hexagonal QC plates and 2-D piezoelectric QC plates with 10 fold are investigated,respectively.The influences of phonon-phason coupling effect,piezoelectric effect,gradient field effect and variation in the quasi-periodic direction on wave characteristics are analyzed.Results demonstrate that variation in the quasi-periodic direction has considerable influence on Lamb waves in 2-D QC plates,and weak influence on SH waves;phonon displacement components have the consistent symmetry with phonon displacement components in the quasi-periodic direction.Subsequently,by introducing the Legendre polynomial method into the cylindrical-coordinate system,circumferential and axial guided waves in the functionally graded 1-D hexagonal hollow cylinders and piezoelectric hollow cylinders are investigated,respectively.Results demonstrate that cut-off frequencies of phonon and phason modes for circumferential and axial guided waves decrease as the radius-thickness ratio increase;however,its influence on phonon modes is more considerable.In addition to some common 1-D waveguided structures including plates and cylinders,there are also a lot of 2-D waveguided structures in engineering,such as rectangular bars,cylindrical structures with sectorial cross-section.Consequently,to understand guided wave propagation in 2-D cylindrical structures with sectorial cross-section,the double Legendre orthogonal polynomial method is utilized to investigate guided waves in the functionally graded piezoelectric-piezomagnetic and multi-layered crystal cylindrical structures with a sectorial cross-section under axial initial stress.The influence of magneto-electric effect,initial stress,angular measure and radius-thickness ratio on wave characteristics are illustrated.Subsequently,the method is extended to investigate guided waves in 1-D hexagonal QC cylindrical structures with a sectorial cross-section.The phonon-phason coupling effect on wave characteristics is illustrated.At last,owing to its dispersion and multi-mode characteristics,a mapping relationship between group velocity of phason modes and elastic parameters in the phason field is established,and an inversion method in the context of the artificial neural network model is proposed to determine elastic parameters in the phason field.The elastic parameters in the phason field of 1-D hexagonal QC plates and hollow cylinders are simulated numerically.