Browsing by Author "Wang, Z."

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    Fatigue life improvement in fatigue-aged fastener holes using the cold expansion technique
    (Elsevier Science B.V., Amsterdam., 2003-09-01T00:00:00Z) Zhang, Xiang; Wang, Z.
    The use of cold expansion process as a life extension technique on aircraft structural joints was investigated. The primary focus was an experimental test programme consisting of open-hole and low-load transfer joint specimens made of 2024-T351 aluminium alloy and pre-fatigued to 25, 50 and 75% of the baseline fatigue life for plain holes. The FALSTAFF loading spectrum was applied. The results indicate that significant life improvements can be obtained through cold expansion applied at all percentages of fatigue life tested in this work with the optimum stage being around 25% of the baseline life. The major life extension was obtained through slower crack growth in the short crack stage. The life improvement factors for the open-hole and joint specimens were comparable provided that the degree of cold expansion is the same. Crack growth life of the open-hole specimen was predicted by employing an analytical residual stress model and the AFGROW computer code. The prediction results showed good agreement with the experimental results for cold expansion at build cases.
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    Predicting fatigue crack growth life for cold-worked holes based on existing closed-form residual stress models.
    (Elsevier Science B.V., Amsterdam., 2003-09-01T00:00:00Z) Wang, Z.; Zhang, Xiang
    This paper studies the capability of four closed-form solutions for calculating cold expansion-induced residual stresses. The aim is to check whether these models are able to provide accurate solutions of residual stresses for three aerospace grade aluminium alloys of medium thickness so that fatigue life can be estimated using these residual stress models without going to the formidable finite element analysis. Based on these studies, crack growth lives for three different kinds of specimens are predicted by the AFGROW computer program and compared with experimental tests. Factors affecting the capability of these closed-form solutions are examined, and modifications to these models based on the fatigue tests and parametric studies are suggested. The study demonstrates that good prediction of crack growth life can be obtained if a suitable closed- form model is used.