Laser Thermomechanical Evaluation of Bonding Integrity

Thermal imaging for the nondestructive evaluation (NDE) of materials appears to be of ever increasing importance for industrial applications. The development of new materials. both metallic and ceramic. as thermal and oxide barrier coatings present new challenges to inspection techniques. Thermal imaging methods seem ideally suited for such applications. being particularly sensitive to surface and near surface material thermal inhomogeneities that may be defect-related. However, these same sophisticated materials can pose rather sever requirements upon the efficacy of any particular type of thermal imaging. Typical problems encountered include rough. optically scattering surfaces. surfaces ranging from highly reflective to absorptive, complex surface geometry and microscopic to very macroscopic (practical components) imaging requirements.</p

A Dipole Thermal Wave Source and Mirage Detection

The mirage technique (with a single modulated heating source) [1–3] has been successfully applied to study the thermal, optical and electronic properties of solid state materials. Its advantages of being nondestructive, noncontact and high sensitivity make it a powerful and versatile tool. In this paper, we propose a new technique which is the same mirage technique, but with a dipole source. It inherits the advantages of the traditional mirage technique but overcomes some of the shortcomings. The traditional mirage technique generally gathers data by positional scanning, which, in additional to being time-consuming, introduces noise associated with the mechanical movement and makes the analysis susceptible to the nonuniformity of the sample. The nonuniformity can be unevenness in optical properties, surface roughness, or simply grain boundaries. With a dipole source, it is possible to gather data by frequency sweeping. In doing so, the new technique is free from those shortcomings connected with positional scanning. Also, the use of a dipole heating source nearly doubles the signal magnitude with the same amount of unmodulated heating beam power. We use this technique to study the thermal properties of CVD diamonds, glass and silicon samples. The results show that this technique has capabilities of measuring thermal diffusivity with both good resolution and wide range

Laser Ultrasound Imaging of Lamb Waves in Thin Plates

Laser ultrasound offers many advantages over conventional piezoelectric ultrasound including the potential for rapid wide-area scanning, non-contacting (no couplant) generation and sensing, and large bandwidth [1,2]. Ultrasonic surface waves may be easily generated by a laser and can travel extended distances when the part is not immersed and loss to a surrounding water bath is eliminated. In addition, the geometric attenuation is significantly less as the sound energy spreads out in a circular annulus rather than in a spherical shell giving rise to an amplitude decay proportional to r −1/2.We have shown that synthetic focusing of laser ultrasound data [3] permits us to use this information to create images of near-surface defects outside the scan area. A single scan line can be used to image the complete surface of part with high speed, resolution, and sensitivity (Figure 1).</p

Persistent topology for natural data analysis - A survey

Natural data offer a hard challenge to data analysis. One set of tools is being developed by several teams to face this difficult task: Persistent topology. After a brief introduction to this theory, some applications to the analysis and classification of cells, lesions, music pieces, gait, oil and gas reservoirs, cyclones, galaxies, bones, brain connections, languages, handwritten and gestured letters are shown

Localization of a delamination and estimation of its length in a composite laminate beam by the VSHM and pattern recognition methods

The focus of this work is to investigate the delamination damage in laminate composite beams, to fix a Vibration-based Structural Health Monitoring (VSHM) method for the laminate structures. The analysis is concentrated on the vibration characteristics of the samples and, in particular, the attention is addressed on the first several natural frequencies of a composite laminate beam with a delamination damage. The core of this work is an experimental investigation on the vibration response of a composite laminate beam and its changes caused by delaminations with different sizes and in different locations of the beam. The study is divided in 3 sections: delamination detection, delamination localization, and delamination estimate. The aim is to determine how the first six harmonics frequencies change due to the delamination, and the results show that they can be successfully used to investigate the presence, the location and the dimensions of the delamination in a composite beam. A Pattern Recognition analysis is used to locate the damage, while the detection and the evaluation are done using the changes in the harmonic frequencies. A finite element analysis is performed, and the variations of the natural frequencies due to delamination are in good agreement with the experimental results

Progress Towards a Fiber-Based Laser-Ultrasonics System for Rapid NDE of Large-Area Composites

State-of-the-art integrally stiffened composite materials, manufactured for use in the next generation of commercial and military aircraft, are being increasingly used for structural components such as wings and fuselages. However, due to the complexity of the manufacturing process, small variations in the shape of integrally stiffened composite structures often occur. Thus, a prioriknowledge of the part shape often does not provide sufficient tolerance to allow an automated conventional ultrasonic inspection. Many of the advantages of laser-based ultrasonics, including its noncontacting nature and applicability to rapid scanning of contoured and integrally stiffened structures, have been described previously [1–5]. To further extend the utility of laser-based ultrasonics, enable limited access inspections and also provide an upgrade/retrofit path for existing ultrasonic scanning systems, it is desirable to reduce the size of current laser-based ultrasound (LBU) system scan heads and provide both generation and detection laser beam delivery via optical fibers. A promising approach is the use of a scanning head based on a Cassegrain optical collection system. This approach minimizes the load carrying requirements of the scanning assembly and is also well-suited for integration with fiber optics to allow the delivery and reception of the ultrasonic generation and detection laser beams via long lengths of optical fiber. This provides increased mobility of the LBU scan head and allows the ultrasonic generation and detection lasers and other sensitive equipment to be housed in a clean environment which potentially can be located hundreds of meters from the inspection area. The use of a pulsed CO2 laser has been reported previously for generation of ultrasonic waves in composite materials [4]. However, the CO2 laser wavelength (λ = 10.6 μm) and the high peak power laser pulses precludes the use of fiber-optic beam delivery over all but very short lengths (< 1.5 m) of specialized optical fiber. Consequently an alternative generating laser has been sought that can be transmitted efficiently over standard quartz optical fiber. An alexandrite laser, which is tunable over the 720–800 nm wavelength range, is being investigated for this application. Progress towards the implementation of a fiber-based LBU system for rapid NDE of large-area composites, and the use of an alexandrite laser for ultrasonic generation in composite materials are described below.</p

Analysis of Ultrasonic Waves in Arbitrarily Oriented or Rotating Anisotropic Thin Materials

Much work has been performed modeling thin anisotropic materials for use in nondestructive testing with plane wave excitation and detection [1–5]. There has been interest in the development of dispersion curve inversion and group velocity inversion procedures [6–8]. The general approach in many of these techniques is to align the excitation and detection along a known crystal axis, and analyze the detected signal to determine elastic constants, bond quality, thickness, or any number of other parameters [9–12]. Unfortunately, most of these approaches will fail to perform adequately when the target’s crystal axis is rotating with respect to the excitation axis, or when the coordinate frame of the crystal axis is unknown.</p

Role of cyclin D1 in conferring malignant phenotypes on immortalized esophageal epithelial cells

Cyclin D1 is commonly overexpressed in many types of human squamous cell carcinomas, including esophageal squamous cell carcinoma. Studies in the past mainly focused on the role of cyclin D1 in cell growth and regulation of the G1/S transition of the cell cycle. Recently, malignant transformation induced by classical oncogenes was shown to be associated with upregulation of cyclin D1. So far, there are still no reports on the direct contribution of cyclin D1 to malignant transformation of immortalized epithelial cells. In this study, the role of cyclin D1 in the early stage of esophageal carcinogenesis was investigated by stable overexpression of cyclin D1 in an hTERT-immortalized esophageal epithelial cell line, NE2-hTERT. Our results showed that ectopic expression of cyclin D1 stimulated anchorage-independent growth in soft-agar, which is a major hallmark of transformed cells. This finding was further supported by the decrease in colony number in an esophageal cancer cell line (KYSE510) with cyclin D1 knockdown by siRNA. Cyclin D1 overexpressing esophageal epithelial cells also acquired a higher ability to migrate through cellular matrix, and showed reduced adhesion to different substrates. Western blotting and pull-down assays were used to further explore the mechanism involved. The results showed that the overexpression of cyclin D1 was associated with upregulation of pERK1/2 and reduced Rac1 activity. Our findings suggest that cyclin D1 overexpression promotes invasive potential and migration ability in immortalized esophageal epithelial cells, and that these malignant phenotypes may be mediated by pERK1/2 and cytoskeletal signaling. [This study is supported by the Research Grants Council of the Hong Kong SAR, China (Central allocation Project No. HKUST 2/06C)