Energy input during friction stir spot welding

Friction stir spot welding is performed on thin plates of an aluminum alloy. This paper presents the results on how the number of tool rotations affects the quality of the resulting spot weld. Different combinations of rotation rate and dwell time are investigated. A linear relationship was found to exist between the number of tool rotations completed during the spot weld and the resulting tensile shear strength. Spot welds that only completed 10 rotations were 177% stronger than those created at 50 tool rotations. The energy generated during the welding operation was quantified and also found to have a linear relationship with tensile shear strength. A modified open-loop position control system is proposed that monitors and limits the energy generated during friction stir spot welding by adjusting the dwell time.     

Comparison of mechanical properties of pure copper welded using friction stir welding and tungsten inert gas welding

The objective of this research is to investigate the mechanical properties including bonding, tensile strength, and impact resistance of pure copper welded using friction stir welding (FSW) method and compare them with that of tungsten inert gas (TIG) welding. Micro-hardness tests are performed on pure copper, TIG welded copper and FSW welded copper to determine the effect of heat on the hardness of welded coppers. Tensile strength tests and notch tensile strength tests are performed to determine the mechanical properties of different weld process.In this experiment, it is found that the notch tensile strength and the notch strength ratio for FSW (212 MPa, 1.10) are significantly higher than those (190 MPa, 1.02) of TIG welding. For the impact tests, the weld zone and heat-affected zone energy absorption values for FSW (2.87 J, 2.25 J) are higher than those (1.32 J, 0 J) of TIG welding. XRD tests are performed to determine components of copper before and after welding process for TIG and FSW.     

Screening for antioxidant and detoxification responses in Perna canaliculus Gmelin exposed to an antifouling bioactive intended for use in aquaculture

Polygodial is a drimane sesquiterpene dialdehyde derived from certain terrestrial plant species that potently inhibits ascidian metamorphosis, and thus has potential for controlling fouling ascidians in bivalve aquaculture. The current study examined the effects of polygodial on a range of biochemical biomarkers of oxidative stress and detoxification effort in the gills of adult Perna canaliculus Gmelin. Despite high statistical power and the success of positive controls, the antioxidant enzymes glutathione reductase (GR), glutathione peroxidase (GPOX), catalase (CAT), and superoxide dismutase (SOD); thiol status, as measured by total glutathione (GSH-t), glutathione disulphide (GSSG), and GSH-t/GSSG ratio; end products of oxidative damage, lipid hydroperoxides (LHPO) and protein carbonyls; and detoxification pathways, represented by GSH-t and glutathione S-transferase (GST), were unaffected in the gills of adult P. canaliculus exposed to polygodial at 0.1 or 1 × the 99% effective dose in fouling ascidians (IC₉₉). Similarly, GR levels, thiol status, and detoxification activities were unaffected in mussels exposed to polygodial at 10 × the IC₉₉, although GPOX, CAT, and SOD activities increased. However, the increases were small relative to positive controls, no corresponding oxidative damage was detected, and this concentration greatly exceeds effective doses required to inhibit fouling ascidians in aquaculture. These findings compliment a previous study that established the insensitivity to polygodial of P. canaliculus growth, condition, and mitochondrial functioning, providing additional support for the suitability of polygodial for use as an antifouling agent in bivalve aquaculture.