Materials Reports  2020, Vol. 34 Issue (Z2): 447-452 |
| METALS AND METAL MATRIX COMPOSITES |
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| Composite Fatigue Strength Distribution and Fatigue Verification Test Load Enhancement Factor |
| HAO Xinchao, XUE Bin
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| COMAC Shanghai Aircraft Design and Research Institute, Shanghai 201210, China |
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Abstract The aim of the load enhancement factor (LEF) for fatigue verification of aircraft composite structure is to shorten the composite structure durability (fatigue) verification cycle by increasing the test load, and to ensure that the fatigue verification has sufficient reliability statisticly. It is a FAA approved method for the verification of composite aircraft structure. Because the fatigue strength distribution can not be directly obtained by fatigue test, the traditional LEF is derived from the composite static strength Weibull distribution combined with the fatigue life weibull distribution, which is called the static strength load enhancement factor(SLEF) method. On the basis of fatigue reliability theory, by studying P-S-N and P-Sa-Sm curves of fatigue strength and fatigue life, a method of LEF based on fatigue strength distribution and fatigue life Weibull distribution of composite structure is proposed, which is called fatigue strength load enhancement factor (FLEF) method. The method is verified by carbon fiber/epoxy composite structure fatigue test. Compared with the SLEF method, the FLEF method does not need to obtain the static strength probability distribution through the static strength test, only through the fatigue test, the LEF could be obtained. According to the analysis of test data, the LEF obtained by SLEF method can not guarantee the reliability of composite fatigue test verification without batch data. The LEF determined by FLEF method has smaller dispersion and higher reliability. The FLEF method is more suitable to determine the composite fatigue verification LEF in theory and practice.
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Published: 08 January 2021
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| About author:: Xinchao Hao, senior engineer of COMAC Shanghai Aircraft Design and Research Institute, has been engaged in the structural design of civil aircraft for a long time. |
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