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Saint-Jacques-de-la-Lande, France

Dubourg L.,Institute Maupertuis | Merati A.,NRC Institute for Aerospace Research | Jahazi M.,NRC Institute for Aerospace Research
Materials and Design | Year: 2010

This paper focuses on the results of process optimisation and mechanical tests that were used to ascertain the feasibility of using friction stir welding (FSW) to join stringers to skin. The effects of process parameters on weld quality of 1.5-mm 7075-T6 stringers lap-joined on 2.3-mm 2024-T3 skins were investigated. Advancing and retreating side locations on the joint configuration were alternated to determine optimal design arrangements. The effects of travel and rotation speeds on weld quality and defect generation were also investigated. Weld quality was assessed by optical microscopy and bending tests. It was found that: (i) the increase of the welding speed or the decrease of the rotational speed resulted in a reduction of the hooking size and top plate thinning but did not eliminated them, (ii) double pass welds by overlapping the advancing sides improved significantly the weld quality by overriding the hooking defect, and (iii) change of the rotational direction for a counter clockwise with a left-threaded probe eliminated the top sheet thinning defect. Subsequently, FSW lap joints were produced using optimum conditions and underwent extensive mechanical testing program. Several assembly configurations including discontinuous and continuous welds as well as single and double pass welds were produced. The results obtained for cyclic fatigue performance of FSW panels are compared with riveted lap joints of identical geometry. S-. N curves, bending behaviour, failure locations and defect characterisation are also discussed. It was found that: (i) the tensile strength of FSW joints approached that of the base material but with a significant reduction in the fatigue life, (ii) the probe plunge and removal locations served as the key crack nucleation sites in specimens with discontinuous welds, and (iii) double pass welds with overlapping advancing sides showed outstanding fatigue life and very good tensile properties. The present work provided some valuable insight into both the fabrication and application of FSW on stringer/skin lap joints. © 2010 Elsevier Ltd.

Diot G.,Institute Maupertuis | Walaszek H.,CETIM de Senlis | Kouadri-David A.,CNRS Civil and Mechanical Engineering Laboratory | Guegan S.,CNRS Civil and Mechanical Engineering Laboratory | Flifla J.,ECAM RENNES Louis de Broglie
Journal of Physics: Conference Series | Year: 2014

Laser welding of aluminium generally creates embedded welding defects, such as porosities or cracks. Non Destructive Inspection (NDI) after processing may ensure an acceptable weld quality by defect detection. Nowadays, NDI techniques used to control the inside of a weld are mainly limited to X-Rays or ultrasonics. The current paper describes the use of a Laser Ultrasound (LU) technique to inspect porosities in 2 and 4-mm thick sheet lap welds. First experimentations resulted in the detection of 0.5-mm drilled holes in bulk aluminium sheets. The measurement of the depth of these defects is demonstrated too. Further experimentations shows the applicability of the LU technique to detect porosities in aluminium laser welds. However, as the interpretation of raw measures is limiting the detection capacity of this technique, we developed a signal processing using Time-Reversal capabilities to enhance detection capacities. Furthermore, the signal processing output is a geometrical image of the material's inner state, increasing the ease of interpretation. It is based on a mass-spring simulation which enables the back-propagation of the acquired ultrasound signal. The spring-mass simulation allows the natural generation of all the different sound waves and thus enables the back-propagation of a raw signal without any need of filtering or wave identification and extraction. Therefore the signal processing uses the information contained in the compression wave as well as in the shear wave. © Published under licence by IOP Publishing Ltd.

Diot G.,Institute Maupertuis | Koudri-David A.,CNRS Civil and Mechanical Engineering Laboratory | Walaszek H.,CETIM de Senlis | Guegan S.,CNRS Civil and Mechanical Engineering Laboratory | Flifla J.,ECAM RENNES Louis de Broglie
Journal of Nondestructive Evaluation | Year: 2013

Embedded welding defects, such as porosities and cracks, are generally formed during aluminium laser welding. It is challenging to test these defects with current non-destructive evaluation (NDE) methods. This work features the creation of defects and their study with the help of NDE methods. The chosen method should be able to detect porosities in lap-welded sheets of 5754 aluminium alloys. The welding process is described and the samples were first characterised with X-ray techniques to choose those containing defects of various sizes and densities. Secondly, these welds were tested with the Laser Ultrasonic Technique (LUT). The first results show that LUT gives defect signatures. Based on raw measurements only, our results show that it is difficult to give any precise description of the defects' size or position. To aid in the interpretation of the results, a frequency-bandwidth analysis has been performed because of the broadband nature of laser ultrasonic signals. © 2013 Springer Science+Business Media New York.

Belchior J.,CNRS Civil and Mechanical Engineering Laboratory | Guillo M.,Institute Maupertuis | Courteille E.,CNRS Civil and Mechanical Engineering Laboratory | Maurine P.,CNRS Civil and Mechanical Engineering Laboratory | And 2 more authors.
Robotics and Computer-Integrated Manufacturing | Year: 2013

In this paper, a coupling methodology is involved and improved to correct the tool path deviations induced by the compliance of industrial robots during an incremental sheet forming task. For that purpose, a robust and systematic method is first proposed to derive the elastic model of their structure and an efficient FE simulation of the process is then used to predict accurately the forming forces. Their values are then defined as the inputs of the proposed elastic model to calculate the robot TCP pose errors induced by the elastic deformations. This avoids thus a first step of measurement of the forces required to form a test part with a stiff machine. An intensive experimental investigation is performed by forming a classical frustum cone and a non-symmetrical twisted pyramid. It validates the robustness of both the FE analysis and the proposed elastic modeling allowing the final geometry of the formed parts to converge towards their nominal specifications in a context of prototyping applications.© 2012 Elsevier Ltd. All rights reserved.

Diot G.,Institute Maupertuis | Kouadri-David A.,INSA Rennes | Walaszek H.,CETIM | Dubourg L.,Institute Maupertuis | And 3 more authors.
30th International Congress on Applications of Lasers and Electro-Optics, ICALEO 2011 | Year: 2011

Embedded welding defects, such as porosity, cracks, are generally observed during laser welding of aluminium. Non Destructive Inspection (NDI) after processing could be a way of assuring an acceptable weld quality. Nowadays, NDI techniques to control the inside of a weld are often limited to X-Rays or ultrasounds. However, these techniques are expensive (X-rays) or not contact-less (ultrasounds) limiting the applicability. The present paper shows the use of a Laser Ultrasound (LU) technique to inspect porosities in 2-mm thick sheet lap welds. The LU technique implements a pulsed Nd:YAG laser to generate ultrasounds in the material and a heterodyne Nd:YAG laser interferometer to measure the echo. This contactless technique improves the NDI flexibility in regard of the geometry and surface quality of analyzed components while increasing the inspection speed. First experimentations resulted in the detection of 2-mm holes drilled in bulk aluminium sheets and the measurement of the shape and size of these defects is possible. On-going investigation shows the applicability of the LU technique to detect porosities in aluminium laser welds. Finally, the use of signal processing is also carried out to increase, in a first step, the signal-to-noise ratio and therefore enhances the defect detection.

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