Análisis estadístico de fatiga

INTRODUCTION

During development of the subject of data Analysis in Engineering it has been studied methods for making inferences from smaller groups of data to possibly larger ones. Today, this Knowledge is more important than ever because it provides tools to take decisions that are based on empirical (observed) evidence and not on biases or beliefs.

In this work the intention is toapply concepts of inferential statistics like determination of the number of elements of the sample by using formulations, the test of fitness, reliability intervals for the parameter considered, to the analysis of the results in an engineering experiment and to determine if an experimental value of a mechanical property of a material follows a certain behavior or if is close to a certain theoristvalue.

For development of this inform it was necessary to attend to the laboratory of resistance of materials in order to obtain samples of the real values of the resistance to fatigue of a particular material, the test of resistance to fatigue brings some complications and requires several time to be done, because of this we based in a theory of mechanical design which states that for most ofthe steels the resistance to the fatigue is approximately half of the resistance to traction.

The Structure of this work starts with the description of the experiment, antecedents, it is followed by the problem; after that, objectives, Limitations, Analysis, Conclusions and recommendations and finally annexes and bibliography.

DESCRIPTION OF THE EXPERIMENT

What is fatigue?

One way toexplain fatigue is based on the definition of the ASTM standard definition of fatigue which is stated as: the process of progressive localized permanent structural change occurring in a material subjected to conditions that produce fluctuating stresses and strains at some point or points and that may culminate in cracks or complete fracture after a sufficient number fluctuations.

The ideathat fatigue is a process is critical to dealing with it in design and to the characterization of materials as a part of design. In fact, this idea is so critical that the entire conceptual view of fatigue is affected by it. Another critical idea is the one of fluctuating stresses and strains. The need to have fluctuating stresses acting under either constant amplitude or variable amplitude iscritical to fatigue. When a failure is analyzed and attributed to fatigue, the only thing known at that point is that the loads were fluctuating. Nothing is necessarily known about the nucleation of damage that forms the origin of fatigue cracks.

The experiment
The testing used to this types of experiments, the tensile strength test, involves taking a small sample with a fixed cross-sectionarea, and then pulling it with a controlled, gradually increasing force until the sample changes shape or breaks.
When testing metals, indentation hardness correlates linearly with tensile strength. This important relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment.

ANTECEDENTS

There is little doubt that fatigueplays a significant role in all industrial applications. Many components are subjected to some form of fluctuating stress or strain, and thus fatigue potentially plays a role in all such cases. However, it is still imperative that all designs consider those aspects of nucleation processes other than fatigue that may act to nucleate cracks that could propagate under the influence of cyclic loads.The intrinsic state of the material and all potential sources of cracks must be evaluated. Nonetheless fatigue is a significant and often a critical factor in the testing, analysis and design of engineering materials for machines, structures, aircraft and power plants. An important engineering advance of this century is also the transfer of the multi-stage fatigue process from the field to the...