發(fā)布時間：2018-04-15 15:27

  本文選題：裂紋修復 + 疲勞壽命�。� 參考：《湖南大學》2016年博士論文

【摘要】：在機械結(jié)構(gòu)運行過程中,經(jīng)常會發(fā)生裂紋,從而降低結(jié)構(gòu)的使用壽命和安全性能。傳統(tǒng)的裂紋修復方法有鉆止裂孔、外貼鋼板、補焊等,這些方法都具有一定場合的應(yīng)用價值。但對于薄壁結(jié)構(gòu),如垃圾車箱體、洗掃車箱體等,傳統(tǒng)裂紋修復方法存在不少局限性。而碳纖維增強復合材料(CFRP)具有比剛度和比強度高、可設(shè)計性好、防腐蝕等優(yōu)點,CFRP加固鋼結(jié)構(gòu)采用粘接方式連接,不會產(chǎn)生次生應(yīng)力和缺陷,在裂紋結(jié)構(gòu)修復中具有廣泛應(yīng)用前景。CFRP修復裂紋鋼板通過膠層粘接將鋼板的部分載荷傳遞給CFRP,使鋼板、膠層和CFRP作為整體承受載荷。它的破壞形式非常復雜,包括鋼板裂紋擴展、碳纖維補片失效、膠層剝離等,其中膠層剝離和鋼板裂紋擴展是主要破壞形式。如果膠層剝離,就會造成CFRP無法承擔載荷,從而加劇修復結(jié)構(gòu)失效;鋼板裂紋擴展進一步減小有效承載截面,從而加劇縮短結(jié)構(gòu)使用壽命。因此論文在國家863計劃項目《工程機械共性部件再制造關(guān)鍵技術(shù)及示范》(2013AA040203)資助下,針對CFRP修復裂紋鋼板結(jié)構(gòu)的兩種主要破壞形式,以粘接膠層和裂紋鋼板為研究對象,采用理論推導、數(shù)值分析和實驗研究相結(jié)合的方法,對膠層剝離機理和CFRP修復裂紋鋼板的疲勞性能進行研究。論文主要研究工作和創(chuàng)新性成果如下:(1)根據(jù)線彈性力學理論,建立CFRP粘貼加固鋼板的理論應(yīng)力公式。將CFRP粘貼加固鋼板簡化為二維平面模型,詳細推導CFRP粘貼加固鋼板的膠層剪應(yīng)力、膠層正應(yīng)力和CFRP縱向應(yīng)力的理論公式,進而得到膠層最大剪應(yīng)力和最大正應(yīng)力的計算公式及其發(fā)生位置。(2)基于粘聚力理論模擬膠層,建立CFRP粘貼加固鋼板的三維有限元模型,揭示了膠層剝離機理和剝離過程,包括膠層剛度損傷規(guī)律、膠層應(yīng)力規(guī)律和CFRP應(yīng)變規(guī)律,膠層剝離過程可分為彈性變形、膠層軟化和膠層剝離三個階段。采用粘聚力理論模擬膠層,解決了膠層很薄計算難以收斂的難題,且可以統(tǒng)一描述界面損傷的萌生與擴展。(3)根據(jù)線彈性力學理論,建立CFRP階梯粘貼端部結(jié)構(gòu)的理論應(yīng)力公式。將CFRP粘貼加固鋼板簡化為二維平面模型,在CFRP對齊粘貼鋼板的理論應(yīng)力公式基礎(chǔ)上,推導出階梯粘貼各階梯端部膠層的剪應(yīng)力和正應(yīng)力理論公式、各階梯CFRP縱向應(yīng)力的理論公式,對比了階梯粘貼與對齊粘貼端部粘結(jié)性能,并分析了加固參數(shù)對各階梯膠層的最大剪應(yīng)力和最大正應(yīng)力的影響。(4)根據(jù)著名Paris公式,提出了基于有限元模型的CFRP加固裂紋鋼板疲勞壽命預測方法�；谡尘哿碚撃M膠層,建立CFRP加固裂紋鋼板的線性有限元模型和非線性有限元模型,線性有限元模型將鋼板當作線性材料,用于計算鋼板裂紋應(yīng)力強度因子,非線性有限元模型將鋼板當作非線性材料,用于分析膠層損傷機理�；诜抡娼Y(jié)果和試驗數(shù)據(jù),采用最小二乘法擬合得到疲勞參數(shù)C和n值,并準確預測了 CFRP加固裂紋鋼板的疲勞壽命,CFRP加固可以提高裂紋鋼板的疲勞壽命十幾倍到幾十倍。(5)提出了基于敏感度方法的止裂孔與CFRP修復裂紋鋼板的疲勞壽命預測模型�；谡尘哿碚撃M膠層,建立了 CFRP加固缺口鋼板的非線性有限元模型,分析了 CFRP加固缺口鋼板的理論應(yīng)力集中系數(shù);基于仿真結(jié)果和試驗數(shù)據(jù),計算了 CFRP加固缺口鋼板的疲勞缺口系數(shù)和疲勞敏感度,并建立了 CFRP加固缺口鋼板的疲勞S-N曲線,止裂孔與CFRP修復后的疲勞壽命是缺口鋼板的292倍,甚至比無缺口鋼板的疲勞壽命還長,遠遠優(yōu)于CFRP修復裂紋鋼板。(6)針對CFRP層合板鋪層設(shè)計問題,提出了 CFRP加固中心孔鋼板的多級優(yōu)化方法。優(yōu)化方法分兩步:第一步,采用拉丁超立方方法選取試驗樣本點,基于樣本點計算結(jié)果,利用移動最小二乘法擬合近似代理模型,在代理模型基礎(chǔ)上采用自適應(yīng)響應(yīng)面優(yōu)化方法優(yōu)化基本鋪層厚度,第二步,結(jié)合復合材料制造約束條件,利用Optistruct對鋪層順序進行優(yōu)化,得到最佳鋪層設(shè)計方案,優(yōu)化設(shè)計后鋼板中心孔處應(yīng)力分布更合理,最大Mises應(yīng)力減小了 47.2%。
[Abstract]:In the mechanical structure in the process of operation, often crack, thereby reducing the service life and the safety performance of the structure. The traditional method of crack repair crack drilling hole, sticking steel plate, welding, the application value of these methods have certain occasions. But for thin-walled structures, such as garbage truck box, sweeping vehicle case, the traditional methods have some limitations. The crack and carbon fiber reinforced composite (CFRP) has high specific stiffness and strength, good design, corrosion proof, CFRP reinforced steel structure by bonding connection, does not produce secondary stress and defects in the structure, with a wide range of crack repair application of.CFRP to repair the crack plate through an adhesive bonding transfer part of load plate to the steel plate, CFRP, and CFRP layer as a whole under load. Its failure form is very complex, including steel plate crack, CFRP sheet Failure, peeling, peeling and crack propagation of steel plate which is the main form of destruction. If peeling, it will cause CFRP unable to bear the load, thereby increasing the repair of structural failure; plate crack growth to further reduce the effective loading area, so as to shorten the service life of the structure increased. Therefore the remanufacturing and demonstration of key technologies in 863 countries. Project "construction machinery common components (2013AA040203) funding, according to the two main failure modes of CFRP repair crack on steel plate structure, the cementation layer and crack of steel plate as the research object, using the method of theoretical derivation, numerical analysis and experimental research combined with the fatigue properties of the layer stripping mechanism and CFRP repair of cracked plate. The main research work and innovative achievements are as follows: (1) according to the elastic mechanics theory, the establishment of CFRP strengthened steel plate theory stress public Type. CFRP strengthened steel plate is simplified as a two-dimensional model, detailed derivation of CFRP strengthened steel plate shear stress, normal stress layer theoretical formula of force and CFRP longitudinal stress, and then get the maximum shear layer calculation formula of stress and the maximum stress and its position. (2) to simulate dynamic cohesion based on the theory, establish three-dimensional finite element model of CFRP strengthened steel plate, reveals the peeling mechanism and the peeling process, including layer stiffness damage law, adhesive stress rule and CFRP strain law, peeling process can be divided into elastic deformation, rubber softening and peeling in three stages. The cohesion theory simulation layer. To solve the difficult problem of computing the convergence layer is very thin, and can describe the interfacial damage initiation and propagation. (3) according to the elastic mechanics theory, the establishment of CFRP ladder paste end structure theory of stress formula. The CFRP strengthened steel plate is simplified as a two-dimensional model, alignment in the CFRP plate theory based on the formula of stress, shear stress and normal stress theory formula of each end of the ladder ladder paste layer, each step CFRP theoretical formula of longitudinal stress, compared the ladder stick adhesive property with aligned paste at the end, and analyzes the reinforcement parameters of each layer of the ladder of maximum shear stress and the maximum normal stress. (4) based on the famous Paris formula, proposes the prediction method of the finite element model of fatigue crack based on CFRP reinforcement plate. Simulation layer cohesion theory based on the establishment of CFRP reinforced steel linear finite crack element model and nonlinear finite element model, linear finite element model of steel plate as a linear material for stress intensity factor of steel crack calculation, nonlinear finite element model of the steel plate as a nonlinear material, for The mechanism of damage layer analysis. The simulation results and the experimental data fitting based on fatigue parameters C and N values by using the least square method, and the fatigue life of CFRP steel plate reinforcement crack accurately predict, CFRP reinforcement can improve the fatigue life of crack plate ten times to several times. (5) proposed a fatigue life prediction model sensitivity method the stop hole and CFRP repair crack on steel plate. Based on simulation layer cohesion theory based on a nonlinear finite element model of reinforced steel plate gap CFRP, analyzes the theory of CFRP reinforced steel notch stress concentration coefficient; based on the simulation results and experimental data, fatigue notch factor CFRP reinforcement plate gap and fatigue sensitivity the calculation, and established the fatigue S-N curve CFRP reinforcement plate gap, crack fatigue life and CFRP repair after the hole is 292 times the gap plate, even more than the unnotched steel fatigue Life is long, far better than the CFRP repair crack plate. (6) for CFRP laminated design problems and puts forward a multi-level optimization method of CFRP reinforced steel plate. The center hole optimization method can be divided into two steps: the first step, the Latin hypercube method to select test samples, the results calculated based on the sample point, approximate model using agent moving least squares method, based on the model optimized by basic layer thickness, the response surface optimization method of adaptive second step, combined with the composite manufacturing constraints, the stacking sequence is optimized by Optistruct, the optimal layer design scheme, optimizing the distribution more reasonable stress plate center hole design, maximum Mises the force is reduced by 47.2%.

【學位授予單位】：湖南大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TB332;TG496

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