Key Engineering Materials Vols. 321-323

Abstract: The purpose of this study was to investigate the contribution of the microstructural properties of trabecular bone in predicting its elastic modulus in the intertrochanteric region. A total of 15 trabecular bone core specimens were obtained from the proximal femurs of patients undergoing total hip arthroplasty. The micro-computed tomography (micro-CT) was used to scan each specimen to obtain micro-morphology. Microstructural parameters were directly calculated using software. Micro-CT images were converted to micro-finite element model using meshing technique, and then micro-finite element analysis (FEA) was performed to assess the mechanical property (Young’s modulus) of trabecular bone. The results showed that the ability to explain this variance of Young’s modulus is improved by combining the structural indices with each other. It suggested that assessment of bone microarchitecture should be added as regards detection of osteoporosis and evaluation of the efficacy of drug treatments for osteoporosis.

Abstract: The integrity assessment method for beam-like structures using continuous wavelet transform (CWT) is proposed. CWT is applied to the response acceleration of a structure to decompose the response acceleration correspond to each scale. The curvature difference of the normalized energy for each member caused by structural degradation clearly indicated the location of damaged members in the structure. It is shown that the proposed method can identify damaged members without performing complicated dynamic analyses which usually require significant effort and time.

Abstract: The fiber optic smart structures allow engineers to add nerve systems to their designs, giving structures capabilities that would be very difficult to achieve by other means, including continuous assessment of damage processes. In this study, we evaluated the potentiality of the application of the optical fiber sensors to the monitoring of the fatigue crack growth behavior of composite patch repaired structures. The composite patch with embedded optical fiber sensors can be considered as a smart patch which has both repairing and monitoring functions. We used recently developed Transmission-type Extrinsic Fabry-Perot Interferometric (TEFPI) optical fiber sensors for the monitoring of fatigue crack growth behavior of cracked thick aluminum plate repaired with bonded composite patch. The sensing principle and the senor construction of the optical fiber sensor are presented. The experimental results show that it is possible to monitor the fatigue crack growth behavior of structures repaired with composite patch using the optical fiber sensor

Abstract: Structural health monitoring for carbon nanotube (CNT)/carbon fiber/epoxy composite was verified by the measurement of electrical resistivity. This study has focused on the preparation of carbon nanotube composite sensors and their application for structural health monitoring. The change of the electrical resistance was measured by a digital multimeter under tensile loads. Although a carbon fiber was broken, the electrical connection was still kept by distributed CNT particles in the model composites. As the number of carbon fiber breakages increased, electrical resistivity was stepwise increased. The CNT composites were well responded with fiber damages during the electro-micromechnical test. Carbon nanotube composites can be useful sensors for structural health monitoring to diagnose a structural safety and to prevent a collapse.

Abstract: This paper presents the feasibility of an artificial intelligence technique for processing and interpretation of non-destructive evaluation (NDE) data from assessments of engineering structures. The technique used is a learning and reasoning approach with belief network. With this technique, causal factors and consequent indicators in the data structure in relation with structure/material condition can be modelled, and their causal relationship can be established using the NDE data as the learning resource. Fundamentals of the technique are briefly presented, and then the potential applications of the technique to NDE data are demonstrated in two case studies.

Abstract: Concrete runways are subject to material deterioration or structural problems, which lead to surface cracks and scaling of a concrete pavement. In this study, seismic techniques including the SASW method, the impact-echo method and the impulse-response method were integrated into a systematic nondestructive approach, which is designed for the assessment of structural integrity of concrete runway pavements. Numerical simulation of the employed seismic methods was performed to verify the validity. For feasibility, the integrated approach was applied to a concrete runway which has surface cracks at pavement segments not subject to airplane loading. The approach verified that the surface cracks were attributed to reduced subgrade stiffness, which may not be detected by conventional pavement tests. The validity of the integrated approach was also proven in lieu of forensic engineering for concrete runway pavements.

Abstract: Concrete lining of underground structures is one of structural elements to require the structural integrity assessment. In this paper, for the structural-integrity assessment of concrete lining, the resonance search (RS) technique based on stress-wave propagation is proposed. The RS technique is the combination of the Spectral-Analysis-of-Surface-Waves (SASW) method and the resonance method. In the RS method, the shear-wave velocity profile is first determined by the SASW measurements. Then, the thickness of concrete lining is determined using the search technique to match the measured resonant frequency and the theoretical resonant frequency evaluated by the numerical modeling. The validity of the proposed procedure was verified by the numerical simulations of the method, the field test at a test concrete lining and the practical application to a real concrete lining of tunnel ManDeok in Korea. The slab thicknesses obtained by coring and Ground Penetrating Radar (GPR) scanning were also compared with the thickness by the RS technique.

Abstract: The behavior of a jointed rock is different from that of an intact rock, and the characteristics of elastic wave propagation in a jointed rock are different from those of an intact rock. In this study, a rock resonant column testing device is designed to measure the longitudinal and flexural wave velocities of jointed rocks under different states of stress. A column of more than 12 rock discs is stacked on a steel base, which acts as a free-fixed system. This configuration ensures that waves propagate under an equivalent continuum condition, thereby rendering a constant and unique velocity. The effect of joint conditions on the wave velocities is investigated through rock resonant column testings. The results show that velocities are sensitive to the state of stress and increase nonlinearly with stress. The velocities are also affected by joint conditions such as roughness, spacing, and filling. The results are useful for rock mass classification based on near-surface geophysical characterization.

Abstract: Alternative construction methods and a simple method for identifying pole’s subsurface end condition using elastic wave propagation test were proposed. After twelve prototypes of poles having different subsurface end conditions were constructed, horizontal loading tests and elastic wave propagation tests were performed. It was found that there was a close correlation between the 1st resonant frequency and maximum pulling force. The results of this study will provide a key to identify the telecommunication pole’s foundation.

Abstract: A modified one-sided measurement technique is proposed for Rayleigh wave (R-wave) velocity measurement in concrete. In this study, the maximum energy arrival concept is adopted to determine the wave velocity by employing its continuous wavelet transform. Experimental study was performed to show the effectiveness of the proposed method. Results reveal that the proposed method can be effectively used to measure the R-wave velocity in concrete structures.