Stress intensity factor determination methods for aircraft structures

Abstract

During calculations for the fatigue and residual strength of aircraft structural elements, it is necessary to establish a functional relationship between the structure’s loading data, crack configuration, and one of the parameters characterizing the material’s limit state at the crack tip the stress intensity factor (SIF). This paper provides an overview of methods for determining SIFs. Three main approaches are described here: analytical, numerical, and experimental. The appropriateness of each approach is analyzed. It has been found that for full-scale aviation thin-walled structures with a supporting longitudinal-transverse load set of variable stiffness, subjected to complex external loading conditions and with contact surfaces and contact stresses present between structural elements, the determination of SIFs is significantly complicated when using analytical and/or numerical models. It has been established that experimental methods using strain gauge techniques are most suitable for such tasks, particularly the method proposed by J. W. Dally and R. J. Sanford, known in English technical literature as DST. The theoretical formulations of this approach are described, recommendations for determining the strain gauge orientation are presented, and existing modifications of the method are considered. The applicability of the strain gauge method to different types of materials (brittle and plastic) and to various specimen configurations is demonstrated. The review revealed potential problems that may arise when applying this method. The authors present their vision regarding the prospects for developing experimental methods for real-time monitoring of the conditions of aviation structures. In particular, a hybrid approach is proposed that combines the strain gauge method with the finite element method and the digital image correlation method. Three possible application methods are described depending on the tasks. In addition, the importance of integrating these methods into the overall diagnostic system for the timely detection and analysis of defects occurring during the operation of aviation structures is emphasized.

Keywords

• тріщина
• коефіцієнт інтенсивності напружень
• тензодатчик
• механіка руйнування