Evaluation of overload effects on fatigue crack growth and closure

Fatigue crack propagation tests with single tensile peak overloads have been performed in 6082-T6 aluminium alloy at several baseline [Delta]K levels and stress ratios of 0.05 and 0.25. The tests were carried out at constant [Delta]K conditions. Crack closure was monitored in all tests by the compliance technique using a pin microgauge. The observed transient post-overload behaviour is discussed in terms of overload ratio, baseline [Delta]K level and stress ratio. The crack closure parameter U was obtained and compared with the crack growth transients. Experimental support is given for the hypothesis that plasticity-induced closure is the main cause of overload retardation for plane stress conditions. Predictions based on crack closure measurements show good correlation with the observed crack growth rates for all the post-overload transients when discontinuous closure is properly taken into account.http://www.sciencedirect.com/science/article/B6V2R-46WPH0W-3/1/82b49d3e31362370a08505d5d300b60

Fatigue analysis of thin AlMgSi welded joints under constant and variable amplitude block loadings

This paper reports the fatigue behaviour of thin AlMgSi1 aluminium alloy weldments and the improvement in fatigue strength due to post-weld treatments. Several fatigue tests were performed using two distinct types of thin welded joints, T and single lap, manufactured using a 6xxx series aluminium alloy, and the efficiency of fatigue life improvement techniques, such as post-weld heat treatment and weld toe's burr dressing, was studied. Both the post-weld heat treatment and the burr dressing produced a fatigue strength improvement. This fact is discussed, for both geometries, in the context of the initiation and propagation phases contribution to total fatigue life. Finally, several fatigue tests were performed under variable amplitude block loading using T6 post-weld heat-treated single lap joints, and the correspondent fatigue lives were compared with the predictions of Miner's rule.http://www.sciencedirect.com/science/article/B6V59-480CN2C-2/1/ef6815883b0431d9a8aa0d0d77743ff

Milhocultores optam por híbridos com alto teto produtivo.

bitstream/item/70667/1/Milhoculturores-optam.pd

Estudo dos solos do município de Santa Vitória do Palmar.

bitstream/item/41413/1/Santa-vitoria-do-palmar.pdf; bitstream/item/41414/1/mapa-capacidade-de-uso.pdf; bitstream/item/41415/1/mapa-geomorfologia-e-solos.pdf; bitstream/item/41416/1/mapa-solos.pd