Lifetime prediction in creep-fatigue environment
The creep-fatigue interaction has been studied and innovative mathematical models are proposed to predict the operating life of aircraft components, specifically gas turbine blades subject to creep-fatigue at high temperatures. The historical evolution of the creep-fatigue lifetime prediction is given in order to place the present study in the context. A literature review of the life estimation under creep-fatigue environment is presented.
LIFE PREDICTION FOR THE TITANIUM ALLOY IMI 834 UNDER HIGH TEMPERATURE CREEP–FATIGUE LOADINGS
In the present investigation the life behaviour of the titanium alloy IMI 834 under loading conditions which are close to real service was considered. Different types of creep-fatigue loadings were applied at 600°c, i.e. balanced and unbalanced cycles with different ramping times into tension and into compression and stress hold Strain Range Partitioning (SRP) cycles. The testing was performed in laboratory air. The results of the creep-fatigue tests showed that life was reduced by the different types of creep-fatigue cycles. In the stress hold tests the mean stresses had a pronounced influence on life. The observed life of the stress hold SRP cycles could be predicted within a factor of ±2 of actual life by frequency-modified approaches. If mean stresses were considered in terms of maximum tensile stress or by a modified Morrow approach, life predictions remained within a factor of ±1.5 of the actual test results. A SRP approach which was frequency modified in the present study led to life predictions which fell within a band of a factor of ±1.35 of the actual test results.
La inseguridad jurídica en normas de contratación estatal
It is established by different studies that the issue of government procurement has been marred by several factors, the test objective to publicize these factors, we take as starting point the constant conflict between the branches of government to try and organize this subject; will collect and analyze diverse regulatory and case material in order to achieve evidence and demonstrate the different concepts of constant change that produces excessive regulation of the subject procurement and is in turn causing rapid changes that result in legal uncertainty for our law on the Contract Status.