Elastic waves in structurally chiral composites
Abstract
Elastic wave propagation through structurally chiral (handed) media was studied. The primary objectives are to construct structurally chiral composites and to characterize their properties. Structurally chiral composites are constructed by stacking identical uniaxial plates, whose consecutive symmetric axes describe either a right or a lefthanded spiral. A matrix representation method is used to solve the elastic wave propagation in such layered composites. Numerical computation of the plane wave reflection and transmission characteristics for chiral arrangements are compared with those for the nonchiral one. It is concluded that the copolarized characteristics are unaffected by the structural chirality, while the crosspolarized reflected and transmitted fields are greatly influenced by it. Numerical modeling is also applied for the real samples. The polarization ellipse of the transmitted field of each sample is calculated. To verify the form chirality, four glassreinforced chiral and nonchiral composite samples are made from helix tape, molded, debulked, and cured individually under identical temperature and pressure histories. The spiral composites are characterized using shear and longitudinal wave transducers in ultrasonic experiments. Both the material properties and the polarization ellipse of the transmitted field of each sample are measured. It is proved conclusively that left and right handedness in the microstructuresmore »
 Authors:
 Publication Date:
 Research Org.:
 Pennsylvania State Univ., University Park, PA (USA). Davey Lab.
 OSTI Identifier:
 5853561
 Resource Type:
 Miscellaneous
 Resource Relation:
 Other Information: Ph.D. Thesis
 Country of Publication:
 United States
 Language:
 English
 Subject:
 36 MATERIALS SCIENCE; COMPOSITE MATERIALS; WAVE PROPAGATION; MATHEMATICAL MODELS; MATRICES; MICROSTRUCTURE; POLARIZATION; S WAVES; SYMMETRY; CRYSTAL STRUCTURE; MATERIALS; PARTIAL WAVES 360603*  Materials Properties
Citation Formats
Yang, Shiuhkuang. Elastic waves in structurally chiral composites. United States: N. p., 1990.
Web.
Yang, Shiuhkuang. Elastic waves in structurally chiral composites. United States.
Yang, Shiuhkuang. 1990.
"Elastic waves in structurally chiral composites". United States.
doi:.
@article{osti_5853561,
title = {Elastic waves in structurally chiral composites},
author = {Yang, Shiuhkuang.},
abstractNote = {Elastic wave propagation through structurally chiral (handed) media was studied. The primary objectives are to construct structurally chiral composites and to characterize their properties. Structurally chiral composites are constructed by stacking identical uniaxial plates, whose consecutive symmetric axes describe either a right or a lefthanded spiral. A matrix representation method is used to solve the elastic wave propagation in such layered composites. Numerical computation of the plane wave reflection and transmission characteristics for chiral arrangements are compared with those for the nonchiral one. It is concluded that the copolarized characteristics are unaffected by the structural chirality, while the crosspolarized reflected and transmitted fields are greatly influenced by it. Numerical modeling is also applied for the real samples. The polarization ellipse of the transmitted field of each sample is calculated. To verify the form chirality, four glassreinforced chiral and nonchiral composite samples are made from helix tape, molded, debulked, and cured individually under identical temperature and pressure histories. The spiral composites are characterized using shear and longitudinal wave transducers in ultrasonic experiments. Both the material properties and the polarization ellipse of the transmitted field of each sample are measured. It is proved conclusively that left and right handedness in the microstructures of a material rotates the plane of polarization of a propagating shear wave in the opposite directions. Thus it is now possible to say that by reducing the length scale of the handed microstructures tone more appropriate to its propagating wavelength, a medium is obtained that gives rise to effects similar to optical radar and optical dichroism.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1990,
month = 1
}

The experimental results reveal that AS4/PEEK thermoplastic composites exhibit cyclic softening and loading range effect under symmetric cycles of strain or stress, and show ratcheting effects under unsymmetric cycles of stress and mean stress relaxation under unsymmetric cycles of strain. The cyclic softening, loadingrange effect, ratcheting and mean stress relaxation are anisotropic. Based on the essential features of the material behavior, an elasticplastic constitutive model is proposed to describe the material response under cyclic loadings. Cyclic softening is achieved by the evolution of a generalized plastic modulus. The ratcheting effect is modeled in the frame of timeindependent cyclic plasticity bymore »

Elasticplastic behavior of thermoplastic composites under cyclic loadings
The experimental results reveal that AS4/PEEK thermoplastic composite exhibits cyclic softening and loading range effect under symmetric cycles of strain or stress, and shows ratchetting effect under unsymmetric cycles of strain. The cyclic softening, loading range effect, ratchetting, and mean stress relaxation are anisotropic. Based on the essential features of the material behavior, an elasticplastic constitutive model is proposed to describe the material response under cyclic loadings. A oneparameter yield surface is used. A oneparameter memory surface is introduced to characterize the loading range effect and to distinguish the deformation process during subsequent loading from the deformation process during initialmore » 
The effect of sliding interfaces and inhomogeneous interphases on thermal and elastic properties of composites
In the first problem, a composite containing either aligned or randomly oriented short fibers of spheroidal shape is studied. The interface between matrix and fiber allows sliding such that shear tractions are specified to vanish. Thermal stresses and thermal expansion coefficients of composites are determined by taking the matrix and the fiber to be isotropic in stiffness and transversely isotropic in thermal expansion coefficients. The effect of interface on thermal stresses and properties is investigated by comparing results for the sliding case with results for the perfectly bonded case. In the second problem, a composite containing aligned long fibers ofmore » 
A study of lasergenerated Rayleigh and Lamb waves in graphite/epoxy composites
This study explores the potential for application of laser generated Rayleigh and Lamb waves in graphite/epoxy composites. Numerical results are obtained by the solution of the wave equations using assumed solutions, and enforcing the boundary conditions. Experimentally, Rayleigh and Lamb waves were generated by a Qswitched ruby laser in the ablation regime and detected by piezoelectric pinducers which permitted accurate phasevelocity measurements. The Rayleigh wave velocity was measured at various directions relative to the fiber direction and results were found to agree closely with numerical predictions. The increase of surface wave velocity using thin plates could be useful for themore » 
Threedimensional random percolating composites: Electrical and mechanical properties of metal/high temperature superconductor composites and 1/F noise in metal/insulator composites
The physical properties of two types of threedimensional random percolating composites were studied. The first of these composites is a random mixture of normal metal (Ag, Au) and the ceramic oxide superconductor YBa{sub 2}Cu{sub 3}O{sub 7{delta}} (YBCO). Measurements were made of the resistance of Au/YBCO and Ag/YBCO composites as a function of temperature, and the currentvoltage characteristics of the AG/YBCO composites. Some preliminary work on the mechanical properties of the AG/YBCO composites was performed. The AG/YBCO composite exhibits a sharp superconducting transitions at temperatures above 77K. The currentvoltage characteristics of this composite have been measured as a function of superconductormore »