Wyniki wyszukiwania - Biblioteka Nauki

1

Ply thickness tolerances in stacking sequence optimization of multilayered laminate plates

100%

Latalski J.

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2013

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tom Vol. 51 nr 4

1039--1052

EN

The paper deals with the impact of manufacturing tolerances of plies thicknesses on optimal design of multi-layered laminated plates in compression. It is assumed that the considered tolerances are represented by the maximum acceptable deviation of every individual ply thickness from its nominal design value. The robustness of the optimum is achieved diminishing the buckling load amplitude factor by the product of arbitrary assumed tolerances and appropriate sensitivities. The discussed optimization problem is solved numerically by the direct enumeration method. The proposed approach is illustrated with examples of the rectangular multi-layered laminated plate design under uni- and biaxial compression. The achieved results emphasise the robustness of the proposed method compared to the approaches with ignored tolerances.

2

Influence of Manufacturing Tolerances on Vibration Frequencies of Turbine Blade

86%

Moneta G. , Jachimowicz J. , Osiński J.

Machine Dynamics Research

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2014

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tom Vol. 38, No. 1

105-118

EN

High Cycle Fatigue is one of most common mechanism of turbine blade failures. The reason are vibrations, which cause cyclic displacements and though that also variable stresses and strains. The most dangerous are excitation frequencies around resonances - that can cause failure in a very short time. About 70 years of jet engine development and more than one century of steam turbine history, was not enough to fully eliminate that problem. This paper shows an influence of manufacturing tolerances and accuracy of manufacturing technology on blade frequencies. Additionally, few methods for avoiding resonances have been presented and its implementation effort have been compared.

3

Modal measurements and model corrections of a large stroke compliant mechanism

81%

Wijma, w. , Boer S. E. , Aarts R. G. K. M. , Brouwer D. M. , Hakvoort W. B. J. , Wijma, w. , Boer S. E. , Aarts R. G. K. M. , Brouwer D. M. , Hakvoort W. B. J.

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tom 61

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nr 2

4

Impact of Manufacturing Tolerances on Stress in a Turbine Blade Fir-Tree Root

72%

Moneta G. , Jachimowicz J.

Fatigue of Aircraft Structures

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2020

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tom Iss. 12

92--101

EN

Low Cycle Fatigue (LCF) is one of most common mechanisms behind turbine blade failures. The reason is high stress concentration in notch areas, like fir-tree root groves, which can cause cyclic stress beyond the safe threshold. The stress levels strictly depend on the manufacturing accuracy of the fir-tree lock (for both fitted together: blade root and disk groove). The probabilistic study aimed at determination of stress was performed using Finite Element Method (FEM) simulation on a population of 1000 turbine models (disk + blades +friction dampers), where fir-tree lock dimensions were sampled according to the normal distribution, within limits specified in the documentation. The studies were performed for different manufacturing quality levels: 3-Sigma, 6-Sigma and 3-Sigma with tolerance ranges reduced twice. Based on the results, the probabilistic distributions, probabilities and expected ranges of values could be determined for: material plastification, stress, strain, LCF lifetime, etc. The study has shown how each tooth of the root is loaded and how wide a stress range should be expected in each groove. That gives information on how the definition of tolerances should be modified to make the construction more optimal, more robust, with lower likelihood of damage, taking into account the cost-quality balance. It also shows how the Six Sigma philosophy can improve the safety of the construction, its repeatability and predictability. Additionally, the presented numerical study is a few orders of magnitude more cost- and time-effective than experiment.

5

Optimum weight design of multilayered fiber composite plates with discrete ply angles and uncertainty in ply thicknesses

72%

Latalski J.

Composites Theory and Practice

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2014

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tom R. 14, nr 4

183--188

EN

The presented paper discusses the minimum weight design of multilayered fiber composite plates with tolerances in individual ply thicknesses. These tolerances are given by the maximum acceptable deviation of every individual ply thickness from its nominal value. The robustness of the design is achieved by diminishing the design state variable (buckling load factor) by the product of arbitrary assumed tolerances and appropriate sensitivities. The proposed approach is illustrated with examples of a simply supported rectangular laminated plate design under uni- and bi-axial compression. The minimum weight identified by the total number of layers is found to assure plate stability. For the discussed analysis, buckling load sensitivity formulas with respect to ply thicknesses are given. Based on these relations, the impact of the discussed variations on the optimal laminate stacking sequence and buckling mode shape is studied in detail. The achieved results emphasize the importance of robust design opposed to merely nominal approaches.

PL

Przedstawiono zagadnienie optymalizacji wielowarstwowych płyt kompozytowych z włóknami ukierunkowanymi dyskretnie z uwzględnieniem występowania tolerancji grubości poszczególnych lamin. Rozważane tolerancje zostały zdefiniowane jako maksymalne dopuszczalne odchylenia rzeczywistej grubości każdej z warstw od jej wartości nominalnej. W zaproponowanym podejściu do zagadnienia rozwiązanie optymalne uzyskano poprzez zmniejszenie zmiennej stanu zadania o wartość iloczynu przyjętych arbitralnie tolerancji i odpowiednich wrażliwości tej zmiennej stanu. Metodę rozwiązania zilustrowano przykładami ściskania jedno- i dwuosiowego płyty prostokątnej, swobodnie podpartej czterostronnie. Jako kryterium optymalizacji przyjęto minimum ciężaru (grubości) płyty. Zapisano rekurencyjne zależności na wrażliwość siły krytycznej względem grubości poszczególnych warstw laminatu. Następnie, na podstawie tych zależności, wyznaczono zmodyfikowaną wartość siły krytycznej obciążenia. Szczegółowo omówiono wpływ badanych tolerancji na układ i kolejność warstw w laminacie wielowarstwowym. Uzyskane wyniki w pełni potwierdzają zasadność stosowania optymalizacji odpornościowej jako metody projektowania gwarantującej lepsze (bezpieczniejsze) rozwiązania niż standardowe ujęcie nominalne zagadnienia.