2005 Fiscal Year Final Research Report Summary
Integrity assessment through dynamic behavior of advanced pre-stressed layered composites.
| Project/Area Number |
16560062
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Materials/Mechanics of materials
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
WIJEYEWICKREMA Anil C. Tokyo Institute of Technology, Graduate School of Science and Engineering, Associate Professor, 大学院・理工学研究科, 助教授 (10323776)
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| Co-Investigator(Kenkyū-buntansha) |
KISHIMOTO Kikuo Tokyo Institute of Technology, Graduate School of Science of Engineering, Professor, 大学院・理工学研究科, 教授 (30111652)
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| Project Period (FY) |
2004 – 2005
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| Keywords | compressible / dispersion / elastic waves / layered composite / pre-stress / decay rates |
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| Research Abstract |
Three areas related to pre-stressed composites have been studied.
Wave propagation in pre-stressed imperfectly bonded compressible elastic layered composites : The dispersive behavior of in-plane time-harmonic waves propagating in a pre-stressed imperfectly bonded compressible symmetric layered composite has been analyzed. The imperfect interface is simulated by a shear-spring type resistance model, which can also accommodate the extreme cases of perfectly bonded and fully slipping interfaces. The dispersion relation is obtained by formulating the incremental boundary-value problem and using the propagator matrix technique. The behavior of the dispersion curves for symmetric waves is for the most part similar to that of anti-symmetric waves at the low and high wavenumber limits. At the low wavenumber limit, depending on the pre-stress, for perfectly bonded and imperfect interface cases, a finite phase speed may exist only for the fundamental mode while other higher modes have an infinit
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e phase speed. However, for a fully slipping interface, at the low wavenumber limit it may be possible for both the fundamental mode and the next lowest mode to have finite phase speeds. For the higher modes which have infinite phase speeds in the low wavenumber region, an expression to determine the cut-off frequencies is obtained. At the high wavenumber limit, the phase speeds of the fundamental mode and the higher modes tend to the phase speeds of the surface wave or the interfacial wave or the limiting phase speed of the composite. For numerical examples, either a compressible two-parameter neo-Hookean material or a compressible two-parameter Varga material is assumed, and the effect of imperfect interfaces on both kinds of waves is clearly evident in the numerical results.
Scattering of plane SH-waves by a circular cavity in a pre-stressed medium : The effect of pre-stress on the scattering of plane SH-waves from a circular cylindrical cavity in a compressible isotropic elastic medium, is studied. The complex function method is employed to analyze the incremental boundary value problem. The spatial variables (x_1,x_2) are mapped onto two different complex planes so that the series solution of the incident waves and the scattered waves are expressed as functions of two different complex variables. The coefficient of each term in the series solution can be computed numerically from a set of linear simultaneous equations, which are constructed by satisfying the incremental traction-free boundary condition along the surface of the cavity. Varga material is assumed in the numerical examples. Varying the principal stretches, the effect of pre-stress on the dynamic stress concentration factor and the scattered energy is investigated.
Stress decay rates in pre-stressed compressible semi-infinite composite strips : Stress decay rates in pre-stressed, compressible, semi-infinite composite strips with traction free boundaries are studied. The characteristic equations for the decay rate are obtained for symmetric and anti-symmetric deformations using two methods. The limiting decay rates at low initial stretch for both deformations are determined by asymptotic analysis. Since the slowest decay is associated with smallest root, the analysis of decay rate relations is focused on the smallest root. Decay rate curves corresponding to various thickness ratios are determined for nearly incompressible and highly compressible materials. Less
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