Detectability of FSW defects with NDE methods

Peer reviewed: YesNRC publication: Ye

Non-destructive evaluation of friction stir welds for aerospace applications

Peer reviewed: YesNRC publication: Ye

Assessment of friction stir welds with nondestructive methods

Peer reviewed: YesNRC publication: Ye

Assessment of friction stir weld integrity for process control

Peer reviewed: YesNRC publication: Ye

Telocytes and putative stem cells in the lungs: electron microscopy, electron tomography and laser scanning microscopy

This study describes a novel type of interstitial (stromal) cell — telocytes (TCs) — in the human and mouse respiratory tree (terminal and respiratory bronchioles, as well as alveolar ducts). TCs have recently been described in pleura, epicardium, myocardium, endocardium, intestine, uterus, pancreas, mammary gland, etc. (see www.telocytes.com). TCs are cells with specific prolongations called telopodes (Tp), frequently two to three per cell. Tp are very long prolongations (tens up to hundreds of μm) built of alternating thin segments known as podomers (≤ 200 nm, below the resolving power of light microscope) and dilated segments called podoms, which accommodate mitochondria, rough endoplasmic reticulum and caveolae. Tp ramify dichotomously, making a 3-dimensional network with complex homo- and heterocellular junctions. Confocal microscopy reveals that TCs are c-kit- and CD34-positive. Tp release shed vesicles or exosomes, sending macromolecular signals to neighboring cells and eventually modifying their transcriptional activity. At bronchoalveolar junctions, TCs have been observed in close association with putative stem cells (SCs) in the subepithelial stroma. SCs are recognized by their ultrastructure and Sca-1 positivity. Tp surround SCs, forming complex TC-SC niches (TC-SCNs). Electron tomography allows the identification of bridging nanostructures, which connect Tp with SCs. In conclusion, this study shows the presence of TCs in lungs and identifies a TC-SC tandem in subepithelial niches of the bronchiolar tree. In TC-SCNs, the synergy of TCs and SCs may be based on nanocontacts and shed vesicles

Inductive and solid-state sensing of pulsed eddy current : a comparative study

In recent years, solid-state devices made their way in the development of electromagnetic non-destructive evaluation (NDE) probes. This fact was evidenced especially for pulsed eddy current, where magneto-resistive and Hall effect devices are used as sensing elements. Their low frequency range and small surface area are suitable to improve the detection of buried and small discontinuities. Although their properties are expected to enhance detectability over simple induction coils, this was still to be proven or demonstrated in a comparative study. This work compares the sensing capabilities of an induction coil to those of two solid-state devices: giant-magneto-resistive (GMR) and Hall effect sensors. All of them are used as detectors in pulsed eddy current probes that have the same excitation mechanism, a ring-type copper coil driven by a constant amplitude square waveform. While the excitation part of the probe is fixed, the sensing components are inter-changeable. Although both induction coils and solid-state sensors output a voltage value as an indication of the magnetic field they are detecting, the voltage for pick-up coils is directly proportional to the rate of change of the magnetic flux. For solid-state sensors the output is in direct relation to the detected magnetic field. Under this study, all three sensing elements are used to detect the driving coil's magnetic output (magnetic field or flux) in air, on planes perpendicular and parallel to the face of the driver coil. The results obtained by all three sensors are quantitatively compared. Then the sensing devices are inserted in the inner space of the driving coil and, subsequently, used for detection of artificially made defects. Finally, the results are compared in terms of magnetic field sensitivity and inspection performance.Peer reviewed: YesNRC publication: Ye

Enhanced image processing and archiving capabilities of magneto-optical imaging for non-destructive evaluation

In its current state, the wide acceptance of the Magneto-Optical Imaging (MOI) technique is hindered due to noise, lack of recordable results, and impossibility of data post-processing. This paper presents some add-ons made to a commercial MOI system to ease the image interpretation, archiving and reporting of the results. In addition, a few image processing techniques are also employed in an attempt to perform automatic flaw detection. The recording capability of the MOI instrument output images was addressed by digitizing the video signal in video or image files. To help with the identification of the damage location and distance between images, a rotary quadrature encoder was mounted onto the MOI scan head. The use of the encoder allowed the identification of the inspection location with respect to a reference position, such as the beginning of the scan. Moreover, it allowed saving images at fixed intervals, which were then stitched into a single image, thus simplifying the post inspection analysis process. Both live and post-inspection image processing capabilities were made available. Implemented image processing included background subtraction, de-noising, contrast adjustment and morphological operation, among others. Contrast stretching transform and background subtractions were found to be among the most powerful techniques that could be used in simplifying the image interpretation.Peer reviewed: YesNRC publication: Ye

Crack Growth Monitoring with Structure-Bonded Thin and Flexible Coils

Structural health monitoring with thin and flexible eddy-current coils is proposed for in situ detection and monitoring of fatigue cracks in metallic aircraft structures, providing a promising means of crack sizing. This approach is seen as an efficient replacement to periodic inspections, as it brings economic and safety benefits. As such, printed-circuit-board eddy-current coils are viable for in situ crack monitoring for multi-layer, electrically conductive structures. They are minimally invasive and could be attached to or embedded into the evaluated structure. This work focuses on the monitoring of fatigue crack growth from a fastener hole with structure-bonded, thin, and flexible spiral coils. Numerical simulations were used for optimization of the driving frequency and selection of crack-sensitive coil parameters. The article also demonstrates the fatigue crack detection capabilities using spiral coils attached to a 7075-T6 aluminum coupon

Improvements in weld quality control based on NDE techniques : correlation between inspection results and mechanical properties for friction stir welds in aluminium alloys

FrictionStirWelding(FSW) is gaining acceptance as an established joining process of aluminium alloys in different configurations such as continuous butt or lapjoint sand discontinuous FS-spot welds as an alternative solution to resistives pot welding. Applications of this joining process can be found for parts production in the aerospace, automotive and marine sectors. However, inspite of its great potential to favourably replace conventional welding processes and also its capacity to join materials which cannot be welded by fusion welding, wide use of FSW of aluminium is still limited. Main limiting factors for larges cale FSW are: welding equipment capital cost, fixture design and cost, re-design of joints to be FS-welded and lack of standards for FS-welds quality control.Le soudage par friction-malaxage [friction stir welding ou FSW] est de plus en plus accept\ue9 comme proc\ue9d\ue9 \ue9tabli d\u2019assemblage d\u2019alliages d\u2019aluminium dans diff\ue9rentes configurations comme la soudure continue bout \ue0 bout ou avec recouvrement et la soudure discontinue par friction-malaxage par points. Ce proc\ue9d\ue9 constitue une solution de rechange au soudage par r\ue9sistance par points. On peut trouver des applications de ce proc\ue9d\ue9 d\u2019assemblage dans la production de pi\ue8ces dans les domaines de l\u2019industrie a\ue9rospatiale, automobile et maritime. Toutefois, malgr\ue9 son potentiel consid\ue9rable pour remplacer avantageusement les proc\ue9d\ue9s de soudage classiques et sa capacit\ue9 \ue0 assembler des mat\ue9riaux impossibles \ue0 souder au moyen du soudage par fusion, un usage r\ue9pandu du FSW de l\u2019aluminium se fait encore attendre. Les principaux facteurs qui limitent l\u2019utilisation du FSW \ue0 grande \ue9chelle sont : le co\ufbt en capital de l\u2019\ue9quipement de soudage, la conception et les co\ufbts des montages, la modification des joints pour permettre le soudage par friction-malaxage et l\u2019absence de normes relatives au contr\uf4le de la qualit\ue9 des soudures par friction-malaxage.Peer reviewed: YesNRC publication: Ye