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Tepedino A.C.M.A.,Usiminas | Tepedino A.C.M.A.,Federal University of Minas Gerais | Takahashi R.H.C.,Federal University of Minas Gerais | Carrano E.G.,Federal University of Minas Gerais
2013 IEEE Congress on Evolutionary Computation, CEC 2013 | Year: 2013

This work investigates the conjecture that the employment of geometry-based operators can be worthy for the construction of efficient and stable evolutionary algorithms for scheduling problems in parallel machines. The effort reported here is an instance of a broader study which investigates the role of geometric concepts in combinatorial problems. This work considers multiobjective versions of the scheduling problem, which are solved using a variation of the classical NSGA-II with the geometric operators. The achieved results are encouraging, showing a repeatable good performance in several problem instances of different sizes, for both identical and unrelated machines. It is also shown some empirical evidence that the proposed geometric operators are able to regularize the space, which is a possible explanation for the algorithm good performance. © 2013 IEEE. Source

Godefroid L.B.,Federal University of Ouro Preto | Andrade M.S.,CETEC | Machado F.A.,Fumagalli Wheels | Horta W.S.,Usiminas
Materials Science and Technology Conference and Exhibition 2011, MS and T'11 | Year: 2011

Fracture toughness (J integral, R-curve) and fatigue crack growth (da/dN) resistance have been studied in two ferrite-martensite DP-600MPa steels broadly used in the automotive industry, with 7% to 12% of martensite volume fraction, and with different silicon and chromium additions. The effect of 10% prestrain followed by a bake hardening heat treatment was verified. This thermo-mechanical treatment was used to simulate the stamping and the paint baking of the wheels. All the mechanical properties are affected by the thermo-mechanical history for both steels. An inverse relationship was found between yield stress and J integral, and between yield stress and fatigue threshold. This behavior was related with small changes in the microstructure of the steels. Copyright © 2011 MS&T'11®. Source

da Silva T.A.,Usiminas | Modenesi P.J.,Federal University of Minas Gerais
Soldagem e Inspecao | Year: 2010

Steels coated with zinc and zinc-iron alloys are being increasingly used by the car industry due to their excellent corrosion resistance and good workability. Spot welding of coated steels has the disadvantage of increasing electrodes wear when compared to uncoated steels. Such wear is caused by the reaction of the zinc coating with the copper of the electrode forming an alloy Zn-Cu (brass). Spot welding tests were carried out in IF steels coated in an industrial hot-dip galvanizing line with pure zinc (GI) and a Zn- Fe alloy (GA). Three welding joints were evaluated: GA/GA, GI/GI and GA/GI. Dynamic weldability diagrams and electrode life were determined for each kind of joint. The results indicated that welding current increased more quickly with the number of welds for the GI/ GI joints. This result was associated with the fastest contamination of the electrode by zinc. For the GA/GI joints, welding current levels for adequate welding increased faster than for GA/GA joints but slower than for GI/GI joints. In general, the spot welding tests with GA/GI joints presented results closer to that of the GA/GA joints than to the spot welding tests with GI/GI joints. Such results showed the positive influence of the GA coating, even for joints including both coatings to improve the spot weldability of zinc coated steels. Source

Nunes E.,General Motors | de Oliveira A.F.,Usiminas | Sekeres T.,University of Sao Paulo | Wichern C.,NanoFocus Incorporated | Plaut R.L.,University of Sao Paulo
Materials Science Forum | Year: 2014

The aim of this research work is to study the inter-relationship, under controlled industrial conditions, among skin pass reductions, surface topography (characterized by 2D and 3D) roughness parameters, stampability and painted surface finish quality for automotive steel sheet stampings. Different surface textures obtained from cold rolling finishing have been evaluated in terms of paintability tests (rating and spectral curve) and tentatively related to roughness parameters (2D and 3D) obtained from the cold finished sheets. Some relevant tendencies have been established amongst these parameters. The results presented here are in accordance with other recently published research showing that there is a clear relationship between these parameters, and that further detailed studies are needed. © (2014) Trans Tech Publications, Switzerland. Source

Gutz A.E.,Federal University of Ouro Preto | Machado F.A.,FUMAGALLI | Gritti J.A.,FUMAGALLI | De Melo T.M.F.,Usiminas | And 2 more authors.
65th ABM International Congress, 18th IFHTSE Congress and 1st TMS/ABM International Materials Congress 2010 | Year: 2010

Automotive industry has demanded the development of new steels with good formability and high strength, aiming to obtain smaller thickness without performance loss, mainly concerning about safety and comfort of the passengers, and to obtain automobile weight reduction. The main challenges to develop these steels are not only to reach the traditional mechanical properties requirements, but also satisfy the additional requirements such as fracture toughness and fatigue crack growth resistance. This work shows results about J Integral and da/dN-dK curves of a ferritebainite microstructure steel, and compare its performance with two ferrite-martensite microstructure steels, with different silicon and chromium contents. The bainitic steel presented the best behavior. Source

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