《材料科学基础英文版课件6.ppt

Creep of Materials Introduction Oxidation-resistant coating (usually, MCrAlY, M = Ni or Ni and Co; NiAl) Thermal barrier coating (usually, yttria-stabilized zirconia, YSZ) – to create a temperature gradient between the metal and the gas (~300-400oC) * Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Outline Introduction Mechanisms of creep Creep damage and creep fracture Effect of stress or temperature on creep Considerations in high temperature design Example: Prediction of creep lifetime Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 1. Stress – strain curve ? ? At room temperature Typical engineering stress – strain curve Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. So far we have just focused on the mechanical properties of materials at room temperature. However, some engineering structures – particularly those related to energy conversion, such as boilers and turbines in the power generation industry, operate at much higher temperatures Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. ? ? ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● Furnace windings 2. Creep curve Test conditions: A higher temperature A certain stress which is lower than the yield strength Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Typical creep curve at a constant stress (?) and a constant temperature (T) Steady-state creep (creep rate is constant) Creep rate decreases with time Creep rate increases with time Elastic strain Rupture time or creep lifetime Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. At room temperature, the deformation depends only on the stress At high t