Wyniki wyszukiwania - BazTech

Ograniczanie wyników

1 Computer Methods in Materials Science

1 2009

Znaleziono wyników: 1

Liczba wyników na stronie

Wyniki wyszukiwania

Sortuj według:

Ogranicz wyniki do:

Thermo-mechanical forming of sheet metal -- modelling of warm forming, heat treatments and transformations

Van Den Boogaard A. H., Kurukuri S., Ghosh M., Miroux A. G.

Computer Methods in Materials Science

2009

Vol. 9, No. 1

5-11

Although basically all sheet forming processes are thermo-mechanical forming processes, the influence of temperature changes can most often safely be ignored. Two cases are considered, in which the interaction between thermal and mechanical behaviour cannot be neglected: 1. if the material is heated or cooled with the purpose to get different mechanical properties and 2. if the material properties vary considerably in the range between 20 and 100 °C, which is the range in industrial sheet forming processes without external heating or cooling. An example of the first one is temperature enhanced forming of aluminium sheet. In this process, parts of the tools are heated and other parts are cooled, in order to increase the formability. For simulations, this requires a material model that is suitable for the complete range of temperatures between 20 and 250 °C. Three models: a completely phenomenological model, the Bergström model and the Alflow model are evaluated with respect to temperature enhanced deep drawing of cylindrical cups of both Al-Mg and Al-Mg-Si alloys. A yet unexplained observation in experiments was that the earing profile changed between low temperature an elevated temperature deep drawing. Another type of temperature influence to enhance the formability of aluminium is an intermediate annealing step. Here, the thermal and mechanical loading is separated in time, but still they influence eachother, especially when aging materials are used. Experiments on, and models for an Al-Cu alloy are presented. The initial approach to completely reset the mechanical material properties after a heat treatment needed only very little correction. An example of the second type is the forming of austenitic stainless steels. Although the temperature dependence of austenite is not significant in ordinary industrial sheet forming situations, the material experiences a strain induced martensitic transformation which is highly sensitive to the temperature, exactly in the temperature range which is industrially the most common. Although progress is recently made in micro-scale modeling of the martensitic transformation, including transformation induced plasticity; these models are not feasible for full-scale forming simulations. Therefore, macroscopic models are developed that model the most relevant aspects in deep drawing: temperature, strain and stress dependent transformation and the influence on the macroscopic mechanical behaviour. The influence of stress is experimentally determined with a biaxial testing machine, in which several strain paths between simple shear and plane strain can be imposed.

Temperatura oraz rozkład prędkości odkształcenia podczas formowania aluminium na ciepło charakteryzują się duża niejednorodnością. Wykorzystywane do analizy modele naprężenia uplastyczniającego powinny uwzględniać wpływ tych niejednorodności. Opracowany w niniejszej pracy fizyczny model Nes wykorzystano do symulacji tłoczenia aluminium AA6061-T4 w warunkach odkształcenia na ciepło. W trakcie analizy zaobserwowano znaczące różnice w kształcie wypływki uzyskanej podczas odkształcenia w temperaturze pokojowej oraz 250 °C. Analiza z wykorzystaniem modelu plastyczności kryształów wykazała aktywności dodatkowych systemów poślizgu w podwyższonych temperaturach. W pracy przedstawiono wyniki analizy numerycznej dla procesów rozciągania oraz tłoczenia.