本文選題：復(fù)合強(qiáng)化　切入點(diǎn)：結(jié)構(gòu)孔　出處：《江蘇大學(xué)》2017年碩士論文

【摘要】：孔是結(jié)構(gòu)件上易產(chǎn)生疲勞斷裂的地方之一,飛機(jī)上存在著相當(dāng)數(shù)量的孔構(gòu)件,為提高其疲勞壽命,激光沖擊強(qiáng)化技術(shù)及冷擠壓強(qiáng)化技術(shù)都是較為高效的強(qiáng)化方法,本文嘗試將這兩者結(jié)合起來,實(shí)現(xiàn)全新的復(fù)合強(qiáng)化。本文通過理論分析、數(shù)值計算方法,研究了復(fù)合與非復(fù)合強(qiáng)化方式對孔結(jié)構(gòu)件應(yīng)力分布及疲勞壽命的影響,探索了超聲振動輔助傳統(tǒng)芯棒擠壓強(qiáng)化過程的力學(xué)特性,并進(jìn)行了復(fù)合擠壓強(qiáng)化相關(guān)試驗(yàn)。本文的主要研究工作及成果如下:(1)從理論上分析了激光沖擊強(qiáng)化、冷擠壓強(qiáng)化機(jī)理及其影響因素,分析了強(qiáng)化處理后的殘余應(yīng)力的分布,及其對疲勞壽命的影響,提出采用復(fù)合強(qiáng)化實(shí)現(xiàn)激光沖擊與芯棒擠壓強(qiáng)化的互補(bǔ),分析了復(fù)合強(qiáng)化對疲勞裂紋的抑制作用。(2)基于ABAQUS軟件進(jìn)行復(fù)合與非復(fù)合強(qiáng)化數(shù)值模擬,分析了不同工藝參數(shù)對其殘余應(yīng)力分布的影響規(guī)律。結(jié)果顯示,激光沖擊強(qiáng)化時峰值壓力高、作用時間長,其強(qiáng)化效果好;冷擠壓強(qiáng)化時擠入端與擠出端的應(yīng)力分布不一致,3%~4%左右的擠壓量較為合理;復(fù)合強(qiáng)化時,先激光沖擊強(qiáng)化后芯棒擠壓強(qiáng)化產(chǎn)生了激光沖擊作用完全被芯棒擠壓強(qiáng)化所覆蓋,但其強(qiáng)化效果稍優(yōu)于單芯棒擠壓強(qiáng)化;先冷擠壓后激光沖擊強(qiáng)化工藝順序,可以有效改善冷擠壓引起的擠入端與擠出端的差異,同時有效解決激光沖擊強(qiáng)化造成孔壁中部殘余拉應(yīng)力問題,實(shí)現(xiàn)了激光沖擊強(qiáng)化與芯棒擠壓強(qiáng)化的相互補(bǔ)充。試驗(yàn)結(jié)果表明,7050-T7451試樣經(jīng)過復(fù)合強(qiáng)化后,其疲勞壽命有很大的提高。(3)芯棒擠壓強(qiáng)化采用超聲振動輔助芯棒擠壓強(qiáng)化,降低了拉拔力,有效防止芯棒的斷裂;超聲擠壓強(qiáng)化的呼吸振動和縱向振動模態(tài)比較研究,結(jié)果認(rèn)為采用呼吸式超聲振動擠壓形式,其效果更好,在工程實(shí)際中可優(yōu)先采用呼吸式超聲振動;不同擠壓量下,隨著超聲頻率的增加拉拔力降低幅度明顯;芯棒擠壓強(qiáng)化后激光沖擊復(fù)合強(qiáng)化過程中,加入防變形芯棒能夠有效降低孔角的變形情況的發(fā)生。
[Abstract]:The hole is one of the places where fatigue fracture is easy to occur on the structural parts. In order to improve the fatigue life of the aircraft, the laser shock strengthening technology and the cold extrusion strengthening technology are more efficient strengthening methods.This paper attempts to combine the two to achieve a new compound strengthening.Through theoretical analysis and numerical calculation, the effects of composite and non-composite strengthening modes on stress distribution and fatigue life of pore structure are studied, and the mechanical properties of ultrasonic vibration assisted traditional mandrel extrusion strengthening process are explored.The related experiments of composite extrusion strengthening were also carried out.The main research work and results of this paper are as follows: (1) the mechanism of laser shock strengthening, cold extrusion strengthening and its influencing factors are theoretically analyzed, and the distribution of residual stress after strengthening treatment and its influence on fatigue life are analyzed.The complementary effect of laser shock and mandrel extrusion strengthening is proposed by using composite strengthening. The restraining effect of composite strengthening on fatigue crack is analyzed. The numerical simulation of composite and non-composite strengthening is carried out based on ABAQUS software.The influence of different process parameters on residual stress distribution was analyzed.The results show that the peak pressure is high and the action time is long, and the strengthening effect is good, the stress distribution of the extrusion end and extrusion end is not consistent with the extrusion end during cold extrusion strengthening, the extrusion quantity of about 4% is reasonable, and when the laser is strengthened,The laser impact effect was completely covered by the extrusion strengthening of the mandrel rod, but the strengthening effect was slightly better than that of the single mandrel extruding strengthening.It can effectively improve the difference between the extrusion end and the extrusion end caused by cold extrusion, at the same time, it can effectively solve the problem of residual tensile stress in the middle of the hole wall caused by laser impact strengthening, and realize the mutual supplement between laser impact strengthening and mandrel extrusion strengthening.The test results show that the fatigue life of the specimen 7050-T7451 has been greatly improved after the composite strengthening. The extrusion strengthening of the mandrel adopts ultrasonic vibration assisted extrusion strengthening, which reduces the drawing force and effectively prevents the fracture of the mandrel.The comparative study on the modes of respiratory vibration and longitudinal vibration strengthened by ultrasonic extrusion is made. The results show that it is better to adopt the mode of ultrasonic vibration of breathing type, which can be preferred in engineering practice.With the increase of ultrasonic frequency, the pull-out force decreases obviously, and the deformation of hole angle can be effectively reduced by adding anti-deformation mandrel in the process of laser impact composite strengthening after extruding and strengthening of mandrel.
【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG665;TG379

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