Research On Fatigue Life For Small Diameter Split Sleeve Cold Expansion Strengthening Hole

With the successful assembly of C919 aircraft, the civil aviation industry of our country has made a new chapter. However, the fast development of civil aviation industry will absolutely result in the high requirement of fatigue life increase of the aircrafts. The strengthening process of cold expansion on split sleeve can obviously increase the fatigue life of fastener holes on the aircrafts, as a result, this kind of technique has been widely used in the aviation industry. This article was mainly about numerical simulation of the cold expansion on split sleeve whose diameter is below 10 mm, and did some further research on the effects of split-sleeve cold expansion on fatigue life improvements of hole-specimens. More details about the work and main achievements are as follows.1. The finite element simulation models of cold expansion on split sleeve to different materials of specimens with holes were built. The main purpose in this period was to research the influence of cold expansion strengthening process with or without split sleeve on tangential stress distribution around the holes of specimens. Meanwhile, we also changed the degree of cold expansion in the process to analyse what kind of role it played on tangential stress distribution.2. Based on the result of finite element simulation, we made the whole life fatigue simulation and stress life fatigue simulation for the 7050 aluminium alloy specimens with holes and got the fatigue life results accordingly under different circumstances, such as the change of cold expansion degree or fatigue load with or without split sleeve. We also built the whole life fatigue simulation and stress life fatigue simulation for the TC4 titanium alloy hole-specimens. We changed the same parameters as those chosen in the process of 7050 aluminium alloy cold expansion and got the final results about their effects on the improvements of fatigue life.3. Fatigue crack growth simulation models were built in the cold expansion strengthening process on split sleeve for hole-specimens of 7050 aluminium alloy and TC4 titanium alloy. During the strengthening process of cold expansion on split sleeve, the related parameters, such as cold expansion degree or fatigue load, were changed to get the fatigue crack growth life in different situations. With the fatigue life results we got from the whole life fatigue simulation, stress life fatigue simulation and fatigue crack growth life simulation, we made a comprehensive comparison among those results.4. In terms of the whole life fatigue simulation, stress life fatigue simulation and fatigue crackgrowth life simulation, we made an analysis from the point of fatigue life enhancement factor to research the effects of split sleeve cold expansion strengthening process on the improvements of fatigue life to different hole-specimens materials.5. On the development platform of VS2010, using MFC class library, combining with ABAQUS script file, MATLAB engine and SQL language, we designed a fatigue life prediction system comprehensively in the language of C++. The system which integrated ABAQUS second development platform, fatigue prediction platform and data base, optimized the research methods and summarized the contents for the whole article.