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- Genet, Gwenaelle, 1980, et al.
(author)
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An approach to multidimensional equivalent fatigue loadings
- 2005
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In: American Society of Mechanical Engineers, Design Engineering Division (Publication) DE. ; 118 A:1, s. 53-61
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Conference paper (peer-reviewed)abstract
- In the automotive industry, temporal, financial and human constraints require continuous improvements in the design process of new vehicles, by delivering relevant specifications and providing reliability and robustness in design. In order to analyze factors like behaviors of drivers and types of roads and guarantee the reliability of car components, measurements of forces from wheels are stored when the vehicle is tested on tracks and used by customers. The measurements represent the time history of multi-dimensional forces on the four wheels in the longitudinal, vertical and transversal directions. They are applied on structures (suspensions or motoring for instance) during the design life of the vehicles. The context of this paper is the fatigue analysis of multi-input loadings. The study will be focused on random and possibly correlated multi-input processes, representing multidimensional forces. The goal of this paper is to present an approach to generate simple multi-input loadings equivalent to measurements In terms of damage. The simple loadings have to be equivalent for any arbitrary structure, satisfying the reliability requirements imposed by the car manufacturer. Copyright κ 2005 by ASME.
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| 4. |
- Johannesson, Pär, 1969, et al.
(author)
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Variation mode and effect analysis: an application to fatigue life prediction
- 2009
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In: Quality and Reliability Engineering International. - : Wiley. - 0748-8017 .- 1099-1638. ; 25:2, s. 167-179
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Journal article (peer-reviewed)abstract
- We present an application of the probabilistic branch of variation mode and effect analysis (VMEA) implemented as a first-order, second-moment reliability method. First order means that the failure function is approximated to be linear around the nominal values with respect to the main influencing variables, while second moment means that only means and variances are taken into account in the statistical procedure. We study the fatigue life of a jet engine component and aim at a safety margin that takes all sources of prediction uncertainties into account. Scatter is defined as random variation due to natural causes, such as non-homogeneous material, geometry variation within tolerances, load variation in usage, and other uncontrolled variations. Other uncertainties are unknown systematic errors, such as model errors in the numerical calculation of fatigue life, statistical errors in estimates of parameters, and unknown usage profile. By treating also systematic errors as random variables, the whole safety margin problem is put into a common framework of second-order statistics. The final estimated prediction variance of the logarithmic life is obtained by summing the variance contributions of all sources of scatter and other uncertainties, and it represents the total uncertainty in the life prediction. Motivated by the central limit theorem, this logarithmic life random variable may be regarded as normally distributed, which gives possibilities to calculate relevant safety margins.
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| 7. |
- Sandström, Johan, 1978, et al.
(author)
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Probability of subsurface fatigue initiation in rolling contact
- 2009
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In: Proceedings of the 8th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. - 9788890437007 ; 2, s. 419-424
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Conference paper (peer-reviewed)abstract
- Subsurface initiated rolling contact fatigue cracks initiate in the vicinity of material defects. As these exist randomly in the material, fatigue will appear randomly under otherwise constant conditions. By combining statistical methods with a contact mechanics and fatigue analysis, probabilities of fatigue initiation are evaluated. The developed model takes as input contact geometry, contact load and the statistical properties of the material defects. It is shown that under some well-defined presumptions the probability of rolling contact fatigue initiation in a rolling wheel can be expressed by a simple formula. Based on this, the parametric influence is assessed and it is found that the mean material defect size has a large influence. The benefit of material cleanliness testing procedures and the influence of the allowed defect size on the risk of subsurface initiated rolling contact fatigue in railway wheels are then quantified with the aid of numerical simulations.
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- Svensson, Thomas, 1950, et al.
(author)
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On the choice of difference quotients for evaluating prediction intervals
- 2008
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In: Measurement: Journal of the International Measurement Confederation. - : Elsevier BV. - 0263-2241. ; 41, s. 755-762
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Journal article (peer-reviewed)abstract
- The use of the Gauss approximation formula for prediction intervals of a function of several variables includes the determination of the partial derivatives. In many cases there may be difficulties to find these derivatives and they need to be replaced by difference quotients. The natural choice of step size in such quotients is to make it as small as possible that, however, may lead to numerical problems. Here, it is demonstrated that there is usually no reason for choosing small step sizes. Instead the best choice with respect to linearisation errors is proportional to the standard deviations of the variables involved. It is recommended that the difference quotient should be used with the step size equal to two standard deviations for an approximate 95% prediction interval. © 2007 Elsevier Ltd. All rights reserved.
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