| The fatigue fracture of the fastening hole is one of the most common forms of structural damage to the aircraft fuselage,so it must be strengthened to improve the fatigue life of the place.However,traditional anti-fatigue strengthening methods like cold extrusion,interference fit and mechanical shot peening have problems such as high surface roughness,small processing range and high cost.While environmental protection and high-quality processing surface cavitation water jet technology can effectively overcome the shortcomings of the existing anti-fatigue strengthening methods.Therefore,in this paper,the cavitation water jet technology was applied to the fatigue strengthening process of the inner surface of the fastening hole,and the influence law of the process parameters in the technology on the inner wall of the fastening hole and the strengthening mechanism were studied.The anti-fatigue strengthening of the inner surface of the middle fastening hole provides a new processing method.The main research contents of the thesis are as follows:Firstly,the dynamic model of a single bubble in the submerged cavitation jet field was established by theoretical analysis,and the single bubble near the wall was numerically simulated by FLUENT to analyze the maximum collapse pressure,speed and the volume fraction of the bubble collapse caused by the external environmental pressure.Then still used FLUENT to simulate and analyze the flow field of the submerged cavitation water jet,exploring the influence of nozzle diameter and incident pressure on the flow field.Based on these results of the axial velocity,pressure of the flow field and the gas volume distribution of the external flow field,the incident pressure and the selection range of the nozzle diameter were determined.Secondly,taking the 7050 aluminum alloy sample with fastening hole as an example,the evaluation index was selected,different factors and corresponding levels were set.Then the orthogonal test was carried out to explore the influence of incident pressure,nozzle diameter dimensionless target distance and impact time on the surface roughness and microhardness of hole wall.Then the fuzzy comprehensive evaluation method was used to evaluate the results of orthogonal test and optimize the process parameter.Finally,the integrity of the inner wall surface of the fastening hole of each sample and the difference in the metallographic structure around the hole were analyzed.And then,the vibration fatigue test was done to compare the fatigue life of each sample and the first-order natural frequency,and make the micro-observation of each fatigue fracture and analysis of the differences,diffusion and fracture in each sample,and finally a comprehensive analysis to preliminarily determine the anti-fatigue strengthening mechanism of 7050 aluminum alloy fastening holes with cavitation water jet. |
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