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Proper orthogonal decomposition for model reduction of a vibroimpact system

The application that inspires this work is the percussion drilling. This problem has impacts and presents uncertainties. In this first analysis the focus is on the construction of an efficient reduced-order model to deal with the nonlinear dynamics due to the impacts. It is important to have an efficient reduced-order model to perform the stochastic analysis. The simplified full model is constructed using the finite element method, and three different bases are used to construct the reduced-order models: LIN-basis (composed by the normal modes of the associated linear problems), PODdir-basis (obtained through proper orthogonal decomposition -direct method) and PODsnap-basis (obtained through proper orthogonal decomposition -snapshot method). The shapes of the elements of LIN-basis, PODdir-basis, and PODsnap-basis are compared. One important conclusion is that the information necessary to represent the details of a vibroimpact dynamics, measured by the proper orthogonal values, is more than the usual 99% recommended.

Influence of the Martensite Volume Fraction on the Reciprocating Sliding Behavior of Ti-Nb Microalloyed Steel

The objective of this work was to evaluate the influence of martensite fraction on the wear mode and the energy dissipation by friction of dual phase (DP) steel tested under reciprocating sliding conditions. For this purpose, a Ti-Nb microalloyed steel was heat treated in a conventional furnace at temperatures between 780 and 880°C (intercritical annealing temperature) for 3 min to obtain DP microstructures with volume fractions of martensite between 25 and 90%. Wear tests were carried out in both DP and as-received samples, using a reciprocating tribometer with ball-on-flat geometry, at two constant applied loads, 2.5 and 4 N. The wear damage of each sample was measured through volume loss and the dissipated energy during the test. The obtained results evidenced a significant influence of the contact load over the wear mode, because at low load the DP wear was reduced with increased hardness but just up to 75% of martensite. At high load, the sliding process promotes an oxide mixture in the ferritic microstructure that acts as a factor in wear reduction.