۱٫ Introduction

۲٫ Obtaining of loading signal during standard operational cycle

۳٫ Signal processing

۴٫ Damage model

۵٫ Calculation of fatigue life time distribution function

۶٫ Conclusion

Acknowledgment

Reference

Fatigue lifetime estimation of load bearing parts of construction is a key factor in a design of technique used for long term operation. Complex loading in combination with complex geometry of the most loaded parts represents only one of many problems that engineers have to deal with. One of the most commonly used approaches how to deal with this problem is to use the technical standards. This approach, despite its indisputable advantages (clear and comprehensible steps of calculation), has several significant shortcomings (non-economical oversized design). In this paper we propose procedure of how to estimate fatigue lifetime of construction parts that are loaded with random operational loading. The result of proposed procedure is distribution function of fatigue lifetime which takes into account the complex geometry of the designed part and random character of the complex loading (multiaxial stress state) in a hotspot. This approach is then demonstrated on fatigue lifetime estimation of bearing pin of a console manipulator loaded by random operational loading. Loading process was obtained using set of strain gages. The measured loading process was then transformed into stress histories in critical hotspot using FEM. Method of processing the stress loading histories in critical hotspot into a form usable in combination with hypotheses for fatigue damage calculation under multiaxial stress states is presented.

Introduction

Estimation of fatigue life time of mechanical components working under real operational loadings (usually multiaxial variable amplitude loading) could be considered as an ultimate task in a field of fatigue life time analysis. Due to the complexity of the problem, there are many factors that have crucial influence on the final lifetime estimation. Moreover, a great deal of these problems do not have widely accepted solution and usually there are multiple ways how to solve them. One way how to tackle these problems is to use the methodology given by standards. These standards normally use some simplification to make the estimation more feasible for engineers. However, as a result of these simplifications, the methodology given by standards is normally suitable only for infinite life calculation, and when used in finite fatigue life time estimation, it usually leads to oversized components, or in some cases, it can even lead to the design error on non-conservative side. Due to these facts, enormous effort was and still is put forth to postulate methodology for finite fatigue life estimation under variable non-proportional random loading [1,2,3,4,5]. In the pages below, authors show how to deal with problems that engineers have to overcome during fatigue life time estimation under multiaxial random loadings. Step by step, analysis of real component (bearing pin of pneumatic handler) loaded with random loading is shown. Usage of multiple techniques is shown for various problems and brief comparison of results and small critical discussion is provided.