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The aging characteristics of Al/UHSS resistance rivet welding (RRW) joints are investigated for the first time in this paper. Microstructure studies have shown that the aging treatment does not change the phase composition of the Al/steel mixed nugget still remaining the ferrite structure, while the precipitation, growth and dissolution occur for the microstructure of Al alloy varying with the distance from the rivet. Mechanical tests revealed that for interfacial fracture (IF) and button pullout fracture (BPF) joints, the maximum peak load increased by 13% and 26% with the prolonged aging time, respectively. The improvement in the joint strength after aging can be attributed to the relaxation of the residual stress for IF joint and the age hardening of Al sheet for BPF joint. In addition, interestingly, the accelerated artificial aging is discovered firstly in Al/steel RRW joint. The phenomenon can be attributed to the higher solid solubility of Mg and Si in softening zone of Al sheet, resulting in faster and more precipitation during the aging treatment. The precipitation kinetics indicated that the average Avrami exponent was 1.25, proving the one-dimensional linear growth of fresh nuclei of the hardening phase β''. The block shear model analysis suggested that the Canadian Standards Association, giving the calculating/test values ratio ranged from 0.88 to 1.08, could provide a more reasonable calculation, which showed that the shear failure was mainly determined by the yield of the gross shear plane, and the tension plane failed because of tensile rupture during the lap-shear test.

Tests simulating exposure to severe weather conditions have been relevant in seeking new applications for particleboard. This study aimed to produce particleboards with residues of CCB (chromium-copper-boron oxides) impregnated Pinus sp. and castor oil-based polyurethane resin, and to evaluate their performance before and after artificial accelerated aging. Panels were produced with different particle mass, resin content and pressing time, resulting eight treatments. Particles moisture and size distribution were determined, beyond panel physical and mechanical properties, according to NBR14810-3: 2006. After characterization, treatments B and G (small adhesive consumption and better mechanical performance, respectively) were chosen to artificial aging tests. Statistical results analysis showed best performances were achieved for waterproof aged samples, of both B and G treatments. As example, in treatment B, MOR and MOE values were 23 MPa and 2,297 MPa, samples before exposure; 26 MPa and 3,185 MPa, 32 MPa and 3,982 MPa for samples after exposure (non-sealed and sealed), respectively.

This study evaluated the effect of artificially accelerated aging (AAA) on the surface hardness of eight composite resins: Filtek Z250, Filtek Supreme, 4 Seasons, Herculite, P60, Tetric Ceram, Charisma, and Filtek Z100. Sixteen specimens were made from the test piece of each material, using an 8.0 × 2.0 mm teflon matrix. After 24 hours, eight specimens from each material were submitted to three surface hardness readings using a Shimadzu Microhardness Tester for 5 seconds at a load of 50 gf. The other eight specimens remained in the artificially accelerated aging machine for 382 hours and were submitted to the same surface hardness analysis. The means of each test specimen were submitted to the Kolmogorov-Smirnov test (p > 0.05), ANOVA and Tukey test (p < 0.05). With regard to hardness (F = 86.74, p < 0.0001) the analysis showed significant differences among the resin composite brands. But aging did not influence the hardness of any of the resin composites (F = 0.39, p = 0.53). In this study, there was interaction between the resin composite brand and the aging factors (F = 4.51, p < 0.0002). It was concluded that notwithstanding the type of resin, AAA did not influence surface hardness. However, with regard to hardness there was a significant difference among the resin brands.