An experimental procedure and test setup are used for investigating effect of using nanoparticle additives to the adhesive on the load transfer capacity (LTC) of bonded magnesium (Mg)–steel (St) single lap joints (SLJ). Investigated variables include the nanopowder material (alumina versus silica), particulate size (20 nm versus 80 nm), and concentration in the adhesive (2.5 wt.% versus 5.0 wt.%). Two different levels of surface roughness on the bonded area are used, namely, sanding the bond area with G60 or G180 sand paper. Test data and scanning electron microscopy (SEM) failure mode analysis are provided.
Segmented polyureas (PUa) are industrially important class of polymers widely used in coatings, sealant, and adhesive applications. Here, we report synthesis, characterization, and modeling of Isophorone Diisocyanate-Diethyl-Toluene-Diamine-Polyether amine (IPDI-DETDA-PO PUa) with varied hard segment contents of 20, 30, and 40 weight percent. For each of the three materials, we study its structure and phase behavior using FTIR, DSC, and TEM, and clearly show the presence of microphase separation between the hard and soft nanodomains. We then measure the linear viscoelastic response of the PUa-s using DMA (frequency sweeps at multiple temperatures). The DMA data are shown to obey the time-temperature superposition. Finally, we develop a new micromechanical model describing the DMA results; the model describes a phaseseparated PUa as two "Fractional-order Maxwell gels" branches, connected in parallel, with the first FMG branch representing the "percolated hard phase" and the second one modeling the "filled soft phase". In agreement with the earlier thermodynamic theories, the volume-fraction of the percolated hard phase is related to the hard segment weight-fraction (HSWF), defined as the combined mass of IPDI and DETDA normalized to the total mass of the polymer. The data and model are found to be in a good qualitative and quantitative agreement.adhesive, dynamic mechanical analysis, fractional calculus, hard domains, polyurea, time temperature superposition | INTRODUCTIONPolyurethanes (PU), polyureas (PUa), and poly (urethaneureas) (PUU) represent a fascinating family of polymers. [1][2][3][4] Their applications include coatings, 5 adhesives and sealants, 6,7 elastomers, 8 as well as rigid foams for thermal insulation 9 and flexible foams for furnishings
Abstract. Hydrogen induced cracking (HIC) has been a persistent issue in welding of high-strength steels. Mitigating residual stresses is one of the most efficient ways to control HIC. The current study develops a proactive in-process weld residual stress mitigation technique, which manipulates the thermal expansion and contraction sequence in the weldments during welding process. When the steel weld is cooled after welding, martensitic transformation will occur at a temperature below 400 °C. Volume expansion in the weld due to the martensitic transformation will reduce tensile stresses in the weld and heat affected zone and in some cases produce compressive residual stresses in the weld. Based on this concept, a customized filler wire which undergoes a martensitic phase transformation during cooling was developed. The new filler wire shows significant improvement in terms of reducing the tendency of HIC in high strength steels. Bulk residual stress mapping using neutron diffraction revealed reduced tensile and compressive residual stresses in the welds made by the new filler wire.
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