Non-destructive Evaluation of Defects of Glass fiber Composites using Imaging System based on Photo-mixer Terahertz Technique

In this study, non-destructive evaluation using photo-mixer terahertz technique was studied to visualize the hidden damage in composite structures. A terahertz wave system was developed based on photo-mixer to detect the internal defects of the composite structure, and foreign material was simulated in a glass fiber-reinforced plastic (GFRP) specimen using PET film coated with silver nano-wire. For the visualization, an imaging algorithm for terahertz signal processing and stage control was developed using a GUI based on LABVIEW. The inspection was performed using the developed continuous terahertz inspection system and the terahertz waveform acquired in the single frequency was used to visualize defects.ope

Surface and inter-phase analysis of Composite Materials using Electromagnetic Techniques based on SQUID Sensors

In this thesis an electromagnetic characterization and a non-destructive evaluation of new advanced composite materials, Carbon Fiber Reinforced Polymers (CFRP) and Fiber-Glass Aluminium (FGA) laminates, using an eddy-current technique based on HTS dc-SQUID (Superconductive QUantum Interference Device) magnetometer is proposed. The main goal of this thesis is to propose a prototype based on a superconducting sensor, such as SQUID, to guarantee a more accuracy in the quality control at research level of the composite materials employed in the aeronautical applications. A briefly introduction about the superconductivity, a complete description of the SQUID properties and its basic working principles have been reported. Moreover, an overview of the most widely used non destructive technique employed in several industrial and research fields have been described. Particular attention is given to the eddy current testing and the technical improvement obtained using SQUID in NDE. The attention has been focused on two particular application, that are the main topics of this thesis. The first concerns with the investigation of the damage due to impact loading on the composites materials, and the second is the study of the corrosion process on the metallic surface. The electrical and mechanical properties of the tested advanced composite materials, such as Carbon Fiber Reinforced Polymers (CFRPs) and Fiber-glass Aluminium (FGA) laminates are investigated. The experimental results concern the non-destructive evaluation of impact loading on the CFRPs and FGA composites, by means of the electromagnetic techniques; the investigation of the electromechanical effect in the CFRPs using the SQUID based prototype and the AFM analyses; and the study of corrosion activity of the metallic surface using magnetic field measurement

Production accompanying testing of the ATLAS Pixel module

The ATLAS Pixel detector, innermost sub-detector of the ATLAS experiment at LHC, CERN, can be sensibly tested in its entirety the first time after its installation in 2006. Because of the poor accessibility (probably once per year) of the Pixel detector and tight scheduling the replacement of damaged modules after integration as well as during operation will become a highly exposed business. Therefore and to ensure that no affected parts will be used in following production steps, it is necessary that each production step is accompanied by testing the components before assembly and make sure the operativeness afterwards. Probably 300 of about total 2000 semiconductor hybrid pixel detector modules will be build at the Universität Dortmund. Thus a production test setup has been build up and examined before starting serial production. These tests contain the characterization and inspection of the module components and the module itself under different environmental conditions and diverse operating parameters. Once a module is assembled the operativeness is tested with a radioactive source and the long-time stability is assured by a burn-in. A fully electrical characterization is the basis for module selection and sorting for the ATLAS Pixel detector. Additionally the charge collection behavior of irradiated and non irradiated modules has been investigated in the H8 beamline with 180 GeV pions

Monitoring system for long-distance pipelines subject to destructive attack

In an era of terrorism, it is important to protect critical pipeline infrastructure, especially in countries where life is strongly dependent on water and the economy on oil and gas. Structural health monitoring (SHM) using acoustic waves is one of the common solutions. However, considerable prior work has shown that pipes are cylindrical acoustic waveguides that support many dispersive, lossy modes; only the torsional T(0, 1) mode has zero dispersion. Although suitable transducers have been developed, these typically excite several modes, and even if they do not, bends and supports induce mode conversion. Moreover, the high-power transducers that could in principle be used to overcome noise and attenuation in long distance pipes present an obvious safety hazard with volatile products, making it difficult to distinguish signals and extract pipeline status information. The problem worsens as the pipe diameter increases or as the frequency rises (due to the increasing number of modes), if the pipe is buried (due to rising attenuation), or if the pipe carries a flowing product (because of additional acoustic noise). Any system is therefore likely to be short-range. This research proposes the use of distributed active sensor network to monitor long-range pipelines, by verifying continuity and sensing small disturbances. A 4-element cuboid Electromagnetic Acoustic Transducer (EMAT) is used to excite the longitudinal L(0,1) mode. Although the EMAT also excites other slower modes, long distance propagation allows their effects to be separated. Correlation detection is exploited to enhance signal-to-noise ratio (SNR), and code division multiplexing access (CDMA) is used to distinguish between nodes in a multi-node system. An extensive numerical search for multiphase quasi-orthogonal codes for different user numbers is conducted. The results suggest that side lobes degrade performance even with the highest possible discrimination factor. Golay complementary pairs (which can eliminate the side lobes completely, albeit at the price of a considerable reduction in speed) are therefore investigated as an alternative. Pipeline systems are first reviewed. Acoustic wave propagation is described using standard theory and a freeware modeling package. EMAT modeling is carried out by numerical calculation of electromagnetic fields. Signal propagation is investigated theoretically using a full system simulator that allows frequency-domain description of transducers, dispersion, multi-mode propagation, mode conversion and multiple reflections. Known codes for multiplexing are constructed using standard algorithms, and novel codes are discovered by an efficient directed search. Propagation of these codes in a dispersive system is simulated. Experiments are carried out using small, unburied air-filled copper pipes in a frequency range where the number of modes is small, and the attenuation and noise are low. Excellent agreement is obtained between theory and experiment. The propagation of pulses and multiplexed codes over distances up to 200 m are successfully demonstrated, and status changes introduced by removable reflectors are detected.Open Acces