CFRP修复裂纹钢板的粘接和疲劳性能研究

发布时间：2018-04-15 15:27

本文选题：裂纹修复 + 疲劳寿命　；参考：《湖南大学》2016年博士论文

【摘要】：在机械结构运行过程中,经常会发生裂纹,从而降低结构的使用寿命和安全性能。传统的裂纹修复方法有钻止裂孔、外贴钢板、补焊等,这些方法都具有一定场合的应用价值。但对于薄壁结构,如垃圾车箱体、洗扫车箱体等,传统裂纹修复方法存在不少局限性。而碳纤维增强复合材料(CFRP)具有比刚度和比强度高、可设计性好、防腐蚀等优点,CFRP加固钢结构采用粘接方式连接,不会产生次生应力和缺陷,在裂纹结构修复中具有广泛应用前景。CFRP修复裂纹钢板通过胶层粘接将钢板的部分载荷传递给CFRP,使钢板、胶层和CFRP作为整体承受载荷。它的破坏形式非常复杂,包括钢板裂纹扩展、碳纤维补片失效、胶层剥离等,其中胶层剥离和钢板裂纹扩展是主要破坏形式。如果胶层剥离,就会造成CFRP无法承担载荷,从而加剧修复结构失效;钢板裂纹扩展进一步减小有效承载截面,从而加剧缩短结构使用寿命。因此论文在国家863计划项目《工程机械共性部件再制造关键技术及示范》(2013AA040203)资助下,针对CFRP修复裂纹钢板结构的两种主要破坏形式,以粘接胶层和裂纹钢板为研究对象,采用理论推导、数值分析和实验研究相结合的方法,对胶层剥离机理和CFRP修复裂纹钢板的疲劳性能进行研究。论文主要研究工作和创新性成果如下:(1)根据线弹性力学理论,建立CFRP粘贴加固钢板的理论应力公式。将CFRP粘贴加固钢板简化为二维平面模型,详细推导CFRP粘贴加固钢板的胶层剪应力、胶层正应力和CFRP纵向应力的理论公式,进而得到胶层最大剪应力和最大正应力的计算公式及其发生位置。(2)基于粘聚力理论模拟胶层,建立CFRP粘贴加固钢板的三维有限元模型,揭示了胶层剥离机理和剥离过程,包括胶层刚度损伤规律、胶层应力规律和CFRP应变规律,胶层剥离过程可分为弹性变形、胶层软化和胶层剥离三个阶段。采用粘聚力理论模拟胶层,解决了胶层很薄计算难以收敛的难题,且可以统一描述界面损伤的萌生与扩展。(3)根据线弹性力学理论,建立CFRP阶梯粘贴端部结构的理论应力公式。将CFRP粘贴加固钢板简化为二维平面模型,在CFRP对齐粘贴钢板的理论应力公式基础上,推导出阶梯粘贴各阶梯端部胶层的剪应力和正应力理论公式、各阶梯CFRP纵向应力的理论公式,对比了阶梯粘贴与对齐粘贴端部粘结性能,并分析了加固参数对各阶梯胶层的最大剪应力和最大正应力的影响。(4)根据著名Paris公式,提出了基于有限元模型的CFRP加固裂纹钢板疲劳寿命预测方法。基于粘聚力理论模拟胶层,建立CFRP加固裂纹钢板的线性有限元模型和非线性有限元模型,线性有限元模型将钢板当作线性材料,用于计算钢板裂纹应力强度因子,非线性有限元模型将钢板当作非线性材料,用于分析胶层损伤机理。基于仿真结果和试验数据,采用最小二乘法拟合得到疲劳参数C和n值,并准确预测了 CFRP加固裂纹钢板的疲劳寿命,CFRP加固可以提高裂纹钢板的疲劳寿命十几倍到几十倍。(5)提出了基于敏感度方法的止裂孔与CFRP修复裂纹钢板的疲劳寿命预测模型。基于粘聚力理论模拟胶层,建立了 CFRP加固缺口钢板的非线性有限元模型,分析了 CFRP加固缺口钢板的理论应力集中系数;基于仿真结果和试验数据,计算了 CFRP加固缺口钢板的疲劳缺口系数和疲劳敏感度,并建立了 CFRP加固缺口钢板的疲劳S-N曲线,止裂孔与CFRP修复后的疲劳寿命是缺口钢板的292倍,甚至比无缺口钢板的疲劳寿命还长,远远优于CFRP修复裂纹钢板。(6)针对CFRP层合板铺层设计问题,提出了 CFRP加固中心孔钢板的多级优化方法。优化方法分两步:第一步,采用拉丁超立方方法选取试验样本点,基于样本点计算结果,利用移动最小二乘法拟合近似代理模型,在代理模型基础上采用自适应响应面优化方法优化基本铺层厚度,第二步,结合复合材料制造约束条件,利用Optistruct对铺层顺序进行优化,得到最佳铺层设计方案,优化设计后钢板中心孔处应力分布更合理,最大Mises应力减小了 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%.

【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB332;TG496

【参考文献】