Split sleeve hole cold extrusion strengthening technology is one of the most commonly used fatigue resistance technology for metal structures. The residual stress field of the hole cold extrusion strengthening structure needs to be analysed, which is an important part of the fatigue life study. Finite element analysis for the 7075 aluminum alloy cold extrusion strengthening plate is carried out in this paper. The effects of split sleeve and reaming process are considered in the analysis process, and the residual stress field at the hole edge is obtained. The numerical results are verified by the experimental results, which show that the two are in good agreement. It is show that the residual stress is the compressive stress near the extrusion hole while the tensile stress far away from the extrusion hole. Additionally, the compressive stress value is the largest in the middle layer, the smallest in the squeeze layer, and the value in the extrude layer is between the two.
The calendar safety life of the surface protection system in aircraft structures is the time limit for it to be used without functional failure at a certain level of reliability and confidence. The reliability of such protection systems and the operational safety and economy of the structure are closely related. This paper firstly establishes two methods for determining the calendar safety life of aircraft structural protection systems under a single service environment and in multiple service environments. A method for determining the reliability of the calendar safety life of the aircraft structural protection system was proposed, and an expression of the relationship between the maintenance costs for the aircraft fleet and the reliability of the calendar safety life of the aircraft structural protection system based on the relationship between the amount of corrosion damage to the structural substrate and the corrosion time and the expression of the calendar safety life of the protection system was established. Finally, taking a hypothetical aircraft fuselage wall plate connection structure as an example, an alternating corrosion fatigue test with protection system specimens was carried out. The process for determining the calendar safety life of the structural protection system and its reliability are given. This method is important to ensure the safety of aircraft structures, improve the efficiency of use, and reduce maintenance costs. Generally speaking, the reliability of the calendar safety life of the structure is 99.9%, and after the analysis in this paper, the reliability of the structural protection system is about 70%.
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