The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
Youssef Hammi - One of the best experts on this subject based on the ideXlab platform.
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Welding parameters influence on fatigue life and microstructure in resistance spot welding of 6061-T6 aluminum alloy
Materials & Design, 2013Co-Authors: R.s. Florea, A. Yeldell, Kiran N. Solanki, Douglas J. Bammann, Youssef HammiAbstract:The fatigue behavior of resistance spot welding (RSW) in aluminum 6061-T6 alloy (AlMg1SiCu per International Standard Office nomenclature) was experimentally investigated. Three welding conditions, denoted as “nominal”, “low” and “high”, were studied to determine the microstructure of the weld nuggets. The process optimization included consideration of the forces, currents and times for main weld and post-heating. By successive iterations and “witness samples” collected, the optimum welding parameters were determined. Load control cyclic tests were then conducted on single weld Lap-Shear Joint coupons to study the microstructure and fatigue life properties. These tests were used to characterize the fatigue behavior in spot welded specimens to elucidate the influence of the process parameters. This work revealed that the welding process parameters have a great influence in the microstructure and fatigue life of the 2mm-thick aluminum sheet resistance spot welded Joints. Different fatigue failure modes were observed at several load ranges and ratios for a constant frequency and three welding currents.
Robert E. Prud'homme - One of the best experts on this subject based on the ideXlab platform.
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The adhesion of amorphous polystyrene surfaces below Tg
Polymer, 2003Co-Authors: Gerald Guerin, Frédéric Mauger, Robert E. Prud'hommeAbstract:Abstract The bonding of polystyrene (PS) surfaces below T g was investigated by two different fracture tests: the Lap-Shear Joint method and the cantilever beam method. Adhesion energy values obtained by the two methods are in agreement and develop with (time) 1/2 , at temperatures as low as T g −16 °C. Even if the double cantilever method is the most common test found in the literature for adhesions above T g , for low adhesion values, below T g , the Lap-Shear Joint geometry is more appropriate. Moreover, when the glass transition temperature is used as a reference temperature, polydisperse and monodisperse PS adhesion energy curves are superposable, suggesting that the auto-adhesion is not significantly favored by the presence of numerous chain ends at the surface (due to the low molecular weight chains provided by the polydisperse PS).
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Morphology of fractured polymer surfaces self-bonded below the glass transition temperature
Mechanics of Composite Materials, 1998Co-Authors: Yuri M. Boiko, Robert E. Prud'hommeAbstract:Previosly noncontact surfaces of polystyrene (PS) and poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) were self-bonded in a lap shear Joint geometry below the glass transition temperature T_g The Joints were then fractured in tension at room temperature and the contact area was analyzed by means of scanning electron microscopy. Zones of plastic deformation were revealed on the surfaces of PS and PPO which had been bonded at T_g−33 and T_g−70°C, respectively, thus indicating interdiffusion across the interface. This result points to the lower T_g of the surface layer as compared with that of the bulk sample, in agreement with our previous studies. The unusually high self-bonding ability of PPO (at very low temperatures related to the bulk T_g) is presumably due to the low depth of penetration required to establish entanglements.
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Strength Development at the Interface of Amorphous Polymers and Their Miscible Blends, below the Glass Transition Temperature
Macromolecules, 1998Co-Authors: Yuri M. Boiko, Robert E. Prud'hommeAbstract:Bonding amorphous polystyrene (PS) and poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) has been carried out in a broad range of temperatures and contact times (t), but always below the glass transition temperature (Tg), in a lap−shear Joint geometry. Strength at the symmetric and asymmetric polymer/polymer interfaces develops with t1/4 and, hence, is diffusion controlled. The development of strength at the homopolymer/miscible blend interface below Tg can be simulated from data for homopolymer/homopolymer interfaces, taking into account the wetting (and “fast diffusion”) and diffusion contributions to the development of strength.
R.s. Florea - One of the best experts on this subject based on the ideXlab platform.
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Welding parameters influence on fatigue life and microstructure in resistance spot welding of 6061-T6 aluminum alloy
Materials & Design, 2013Co-Authors: R.s. Florea, A. Yeldell, Kiran N. Solanki, Douglas J. Bammann, Youssef HammiAbstract:The fatigue behavior of resistance spot welding (RSW) in aluminum 6061-T6 alloy (AlMg1SiCu per International Standard Office nomenclature) was experimentally investigated. Three welding conditions, denoted as “nominal”, “low” and “high”, were studied to determine the microstructure of the weld nuggets. The process optimization included consideration of the forces, currents and times for main weld and post-heating. By successive iterations and “witness samples” collected, the optimum welding parameters were determined. Load control cyclic tests were then conducted on single weld Lap-Shear Joint coupons to study the microstructure and fatigue life properties. These tests were used to characterize the fatigue behavior in spot welded specimens to elucidate the influence of the process parameters. This work revealed that the welding process parameters have a great influence in the microstructure and fatigue life of the 2mm-thick aluminum sheet resistance spot welded Joints. Different fatigue failure modes were observed at several load ranges and ratios for a constant frequency and three welding currents.
Ephraim Suhir - One of the best experts on this subject based on the ideXlab platform.
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Approximate evaluation of the interfacial shearing stress in cylindrical double lap shear Joints with application to dual-coated optical fibers
International Journal of Solids and Structures, 1994Co-Authors: Ephraim SuhirAbstract:Abstract A simplified analytical model is developed for the evaluation of the interfacial shearing stress in a cylindrical double lap shear Joint, with application to dual-coated optical fiber specimens subjected to pull-out testing, in situ measurements of Young's (shear) modulus of the primary coating material, and stripping of the coating from the glass. The objective of the analysis is to assess the effect of the material properties and specimen's geometry on the magnitude and distribution of the shearing stress. It is shown that the longitudinal distribution of this stress is nonuniform and that, for the given specimen's length, its maximum value increases with a decrease in the thickness of the primary coating. As far as the pull-out testing and Young's modulus evaluations are concerned, it is concluded that, while 1 cm long specimens with approximately 30 μm thick primary coating (such specimens are currently used in pull-out tests) are acceptable, shorter specimens will result in a more uniform stress distribution and, as a consequence of that, in more stable experimental data. As to the coating strippability, it is desirable that the stripping area be short, although satisfactory strippability is often achieved even for long stripping areas. It is concluded that a multiblade stripping tool might be worthwhile to consider if long portions of coating have to be removed from the fiber. The obtained results can be useful for comparing the adhesive strength of the primary coating in fibers of different lengths and with different coating designs, for the in situ evaluation of Young's modulus of the primary coating material from the measured axial displacement of the glass fiber, and for the assessment of the effect of material properties and fiber geometry on the strippability of the fiber coating.
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Interfacial shearing stress in a cylindrical double lap shear Joint, with application to dual-coated optical fiber specimens
1994 Proceedings. 44th Electronic Components and Technology Conference, 1Co-Authors: Ephraim SuhirAbstract:A simple analytical model is developed for the evaluation of the interfacial shearing stress in a cylindrical double lap shear Joint, with application to dual-coated optical fiber specimens subjected to pull-out testing and in-situ measurements of Young's (shear) modulus of the primary coating material. The purpose of the analysis is to assess the effect of the materials properties and specimen's geometry on the shearing stress. It is shown that the longitudinal distribution of this stress is nonuniform and that, for the given specimen's length, its maximum value increases with a decrease in the thickness of the primary coating. It is concluded that while 1 cm long specimens with approximately 30 /spl mu/m thick primary coating (these are currently used as pull-out test specimens) are acceptable, shorter specimens will result in a more uniform stress distribution, and, as a consequence of that, in more stable experimental data. The obtained results can be useful for comparing the adhesive strength of the primary coating in fibers of different length and with different coating designs, for the in-situ evaluation of Young's modulus of the primary coating material from the measured axial displacement of the glass fiber. >
Krishnan Balasubramaniam - One of the best experts on this subject based on the ideXlab platform.
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Bond stiffness estimation with shear horizontal guided waves generated using PPM-EMATs
International Journal of Adhesion and Adhesives, 2021Co-Authors: Dileep Koodalil, Prabhu Rajagopal, Krishnan BalasubramaniamAbstract:Abstract This paper aims to develop a technique for estimating an aluminium/epoxy/aluminium lap shear Joint stiffness. Shear horizontal guided waves are employed using periodic permanent magnet electromagnetic acoustic transducers (PPM EMATs). Based on the source influence of the EMATs and sensitivity of SH-like mode to adhesion, an appropriate transduction regime is selected. Different modality of inspection, such as reflection and transmission mode, is explored. The arrival time of the received signal in transmission mode depends on the adhesion level. A procedure for calculating the energy velocity in the bond and inverse calculation of bond stiffness is proposed. Experiments were performed on samples of different surface treatments. Based on the proposed method, the stiffness of the samples was estimated. Results show the technique's potential to quantify the adhesion level rather than merely classifying as good, weak, and bad bonds.
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Detection of interfacial weakness in a Lap-Shear Joint using shear horizontal guided waves
NDT & E International, 2020Co-Authors: Dileep Koodalil, David Barnoncel, Prabhu Rajagopal, Krishnan BalasubramaniamAbstract:Abstract This study aims to develop a shear horizontal guided wave based technique to evaluate the interfacial adhesion of aluminium-epoxy-aluminium tri-layer in a lap shear Joint. A 3-D Multi-physics finite element model was developed to investigate the physics of the interaction of SH modes with a tri-layer structure. By employing the boundary stiffness approach, different cases of interfacial adhesion-ranging from perfect bond, intermediate and weak bond, were simulated. Frequency-wavenumber analysis reveals that at the bond overlap region, the incident SH0 wave mode-converts to fundamental (SH0-like) and first-order(SH1-like) modes. The dispersion characteristics of first-order mode (SH1-like) was found to be dependent on the adhesion level, and this influences the time responses collected on a receiver plate in guided wave through-transmission configuration. Experiments were carried out on aluminium-epoxy-aluminium lap shear Joints using PPM-EMAT transducers. The analysis shows that this technique can detect and quantify different levels of adhesion, rather than merely classifying as good or bad bonds.
