Theoretical and experimental issues of acquiring dispersion curves for bars of arbitrary cross-section are discussed. Since a guided wave can propagate over long distances in a structure, guided waves have great potential for being applied to the rapid non-destructive evaluation of large structures such as rails in the railroad industry. Such fundamental data as phase velocity, group velocity, and wave structure for each guided wave mode is presented for structures with complicated cross-sectional geometries as rail. Phase velocity and group velocity dispersion curves are obtained for bars with an arbitrary cross-section using a semi-analytical finite element method. Since a large number of propagating modes with close phase velocities exist, dispersion curves consisting of only dominant modes are obtained by calculating the displacement at a received point for each mode. These theoretical dispersion curves agree in characteristic parts with the experimental dispersion curves obtained by a two-dimensional Fourier transform technique.

In this paper, a technique for measuring a surface wave transmission coefficient across surface-breaking cracks and notches in a heterogeneous but globally isotropic material (concrete) is presented. Once the transmission coefficient across a surface discontinuity is known, its depth may be estimated. There are many difficulties in measuring the transmission coefficient experimentally owing to effects of wave path dependence, unknown characteristics of the receiver and the wave source, and the variation of impact event or receiver coupling. To eliminate the undesired effects, a self-calibrating measurement scheme is applied to obtain the surface wave transmission coefficient across notches and surface-breaking cracks in concrete. The obtained signal transmission coefficient is not affected by the experimental setup or the heterogeneous nature of the material. The testing scheme is described and experimental results obtained from concrete specimens with notches and surface-breaking cracks are presented. Repeatable and reliable measurements of surface wave transmission coefficient are obtained, which demonstrate a strong relation to normalized discontinuity depth. A numerical study using the boundary element method is presented, which verifies the experimental findings.

Although the luminous efficiency has been significantly improved in multilayered organic light-emitting diodes (OLEDs), understanding the major factors that influence degradation of OLEDs remains a major challenge due to their complex device structure. In this regard, we elucidate the crucial role of hole injection layer (HIL) in degradation of OLEDs by using systematically controlled hole injection interfaces. To analyze charge injection dependent degradation mechanism of OLEDs, we fabricate multilayered small-molecule OLEDs with molecularly controlled HILs. Although a reduced hole injection energy barrier greatly improves both a luminous efficiency and an operational lifetime (>10 times) of the OLEDs at the same time, large hole injection energy barrier increasingly aggravates its charge injection and transport during device operation. By using various kinds of nondestructive analyses at gradual stages of degradation, we demonstrate that accumulated charges at interfaces due to inefficient charge injection accelerates rate of device degradation.

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