Experimental and numerical study concerning the anisotropic behavior of an AA2024-T351 thick sheet using the unified formalism, a multi-mechanism model and a polycrystalline approach

The purpose of this work is to evaluate the anisotropic mechanical behavior of an AA2024-T351 thick plate using three multi-scales approaches: a Macroscopic Unified formalism (HILL 48), a Multi-Mechanisms Model and a Polycrystalline plasticity model. The experimental results obtained from uniaxial tensile tests are first described. Thereafter, the theoretical formulations and numerical identification of studied elastoplastic approaches are presented. Finally, finite element simulations of tensile tests and analysis of the thick sheet stretching forming process are performed

Laser ultrasound and simulated time reversal on bulk waves for non destructive control

International audienceLaser 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

FEM Prediction of Temperature and Residual Stresses Distribution During Friction Stir Welding of 2017A Aluminum Alloy

International audienceThe structures integrities containing welds are evaluated using numerical methods to characterize the residual stresses field induced during welding. These methods are mainly based on coupled thermal and mechanical analysis using the finite element method. The present paper deals with the case study of a straight welding of two plates in 2017A aircraft aluminum alloy

Non-destructive Testing of Porosity in Laser Welded Aluminium Alloy Plates: Laser Ultrasound and Frequency-Bandwidth Analysis

International audienceEmbedded 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

Defect Detection and Sizing in Laser-Welded Aluminum Welds, Using Laser-Generated Ultrasounds

International audienceEmbedded welding defects, such as porosity, cracks, are generally observed during laser welding of aluminum. 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 contact-less 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 aluminum 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 aluminum 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