起重机金属结构裂纹复合修复方法探讨

本文针对起重机金属结构在长期疲劳交变荷载作用下易产生疲劳裂纹的问题为主要研究对象,采取碳纤维复合材料加固止裂孔的方式来复合修复裂纹。构建不同荷载下的止裂孔、CFRP和负荷修复的有限元模型,分析计算应力应变状态以及系数,制定止裂孔打偏情况下的复合修复有限元模型,研究CFRP加固对于止裂孔修复产生的影响。通过开展静拉伸强度试验,研究复合修复方法对损伤构件的修复效果,并且和仿真结果相互比较,验证了CFRP和止裂孔复合修复这一技术的可行性。经过相关结果表明,复合修复方式和止裂孔以及CFRP修复效果相比较来看,不但能够提升试件的承载性能,还能够弥补钻止裂孔修复焊缝裂纹的不足。     

CFRP修复裂纹钢板的疲劳试验及参数研究

薄壁钢板结构运行一段时间后,其母材或焊缝附近容易产生疲劳裂纹,而传统修复方法无法适用于薄壁钢板疲劳裂纹的修复。由于CFRP加固方法对钢板不会产生附加应力,可应用于薄壁钢板疲劳裂纹的修复。论文研究在裂纹尖端钻止裂孔再粘贴CFRP方法对裂纹钢板剩余疲劳寿命的影响,首先通过五组对比疲劳试验,分析"止裂孔联合CFRP加固"方法与其他修复方法对裂纹疲劳寿命的增强效果;然后基于粘聚力理论建立CFRP加固钢板的有限元模型,对CFRP加固后的止裂孔直径、CFRP刚度、CFRP尺寸等参数进行研究。研究结果表明:采用"止裂孔联合CFRP加固"方法,裂纹钢板的剩余疲劳寿命比仅钻止裂孔和仅粘贴CFRP都提高了数十倍,甚至超过无裂纹钢板的疲劳寿命,该方法尤其适于薄壁钢板的短裂纹修复。     

止裂孔与CFRP复合修复含裂纹钢结构的疲劳性能

起重机金属结构在长期服役过程中易产生疲劳裂纹,使用止裂孔与碳纤维复合材料(CFRP)对含疲劳裂纹的金属结构进行复合修复能获得比单一修复方式更好的效果.针对复合修复后止裂孔边缘裂纹萌生阶段,使用Abaqus与Fe-Safe建立有限元分析模型,分析了加固方式、止裂孔半径、疲劳裂纹长度及裂纹尖端到止裂孔边缘的距离等因素对裂纹萌生寿命的影响,并通过试验进行了验证.结果 表明,利用Abaqus与Fe-S～e对复合修复后的结构进行耐久性分析具有可行性,能够为制定修复方案提供参考.     

CFRP加固含裂纹钢板疲劳性能研究

基于Paris公式估算钢构件剩余疲劳寿命。通过对试件裂纹尖端应力强度因子和裂纹扩展长度的估计,用积分计算其剩余寿命。试验证明加固的钢板受疲劳载荷的过程中CFRP板能有效发挥作用且不易剥离。单侧加固和双侧加固钢板疲劳寿命分别提高了1.1倍和4.9倍。因此用CFRP加固修复疲劳载荷下的损伤构件是一种行之有效的方法。     

残余热应力对复合材料双面胶接含裂纹铝合金板修复结构疲劳寿命的影响

为研究残余热应力对复合材料双面胶接修复损伤金属结构疲劳寿命的影响,利用T300/E51复合材料补片对含中心裂纹的LY12CZ铝合金板进行双面胶接修复,研究了修复结构的疲劳寿命,并通过断口分析反推出了疲劳裂纹的扩展情况;利用Abaqus软件建立了考虑残余热应力的修复结构的三维有限元模型,分别计算了应力强度因子随裂纹长度的变化关系,并利用二次多项式拟合得到了应力强度因子幅值与裂纹长度的关系式;最后,利用Pairs公式材料常数修正法,对修复结构的疲劳寿命进行了预测。结果表明:在相同的疲劳载荷条件下,裂纹板修复结构的疲劳寿命约为未修复裂纹板的23倍;残余热应力会增加裂纹尖端的应力强度因子;有限元模拟的裂纹板修复结构的疲劳寿命与试验结果吻合较好,相对误差为3.7%。     

CFRP修复港口起重机箱形结构疲劳裂纹的数值仿真及实验研究

箱形结构是港口起重机的主要结构形式之一。其长期承受疲劳交变载荷,容易诱导裂纹扩展,最终导致疲劳断裂失效,严重威胁人类财产安全和经济效益。文中应用碳纤维增强复合材料(CFRP)对箱形结构上的疲劳裂纹进行修复,通过数值仿真计算裂纹尖端应力强度因子,结合Paris公式计算裂纹扩展的速率,随后通过疲劳载荷下裂纹扩展实验对仿真结果进行验证。结果表明,CFRP修复能够显著降低箱形结构上的裂纹扩展速率,延长其使用寿命。     

金属构件裂纹的修补

金属结构的裂纹可以用加强板进行修补,但有限元程序计算表明:选择加强板的参数应按照最大限度降低裂纹尖端应力的原则进行。笔者用实例说明修补裂纹只能延缓裂纹的扩展速度而不能根除裂纹的存在。 1.修补裂纹的方法 当金属构件由于长期承受交变载荷而产生疲劳裂纹时,修补裂纹的方法有: (1)在裂纹尖端钻止裂孔(按要求还应铰孔)。     

双高强螺栓止裂法对疲劳性能的影响研究

采用钢板做的拉伸试样,并在裂纹前端打孔,并在孔上拧上高强度螺栓.通过有限元仿真,对比分析单止裂孔,单高强度螺栓,双高强度螺栓三种方法的止裂效果,研究了双高强度螺栓对疲劳性能的影响,发现施加高强螺栓后,钢板表面与螺栓垫板之间产生的摩擦力遏制了裂纹的张开,相较与止裂孔和单高强度螺栓止裂,双高强度螺栓止裂更能减小应力集中,能够更好的提高试样的疲劳性能.可以通过此方法提高含裂纹结构的使用寿命.     

CFRP布加固钢箱梁的疲劳试验设计研究

钢箱梁长期运营后,不可避免地出现疲劳裂纹,疲劳裂纹出现后使得钢箱梁运营具有一定的安全隐患。钢箱梁疲劳裂纹处治包括补焊法、钻孔法和CFRP布加固法等,其中CFRP布加固法充分利用了复合材料的优越性,是一种较为有效的加固方法。根据某节段式钢箱梁构件,选择了CFRP布加固材料,确定了CFRP布加固的5个步骤(表面处理、配胶、涂胶、粘贴CFRP布及锚固),并设计了疲劳加固试验的装置和加载方案。通过对加固构件进行疲劳试验,可研究加固构件的疲劳性能,验证加固构件的加固效果,并对疲劳损伤演化过程进行理论分析。     

随机风载下齿轮副接触疲劳裂纹萌生寿命研究

对随机风场进行了模拟,得到了正常发电工况下主轴扭矩的时间历程;建立了齿轮副的三维有限元模型,计算了在静态载荷下齿轮副的应力应变。采用随机载荷雨流计数法对齿轮载荷进行雨流计数,并对结果进行了统计学分析,得到应力均值符合三参数威布尔分布。研究了服从三参数威布尔分布的分布参数对齿轮接触疲劳裂纹萌生寿命的影响。结果表明采用随机载荷相对于采用载荷均值齿轮的接触疲劳裂纹萌生寿命疲劳寿命下降,形状参数增大齿轮接触疲劳裂纹萌生寿命增大,尺度参数和位置参数增大齿轮的接触疲劳裂纹萌生寿命减小。     

Evaluation of stress and crack behavior using the extended finite element method in the composite layer of a type III hydrogen storage vessel

To facilitate the widespread use of fuel cell vehicles, it is necessary to ensure the safety of high-pressure hydrogen storage vessels. Because the composite layer experiences the highest internal pressure, cracks in the carbon fiber reinforced plastic (CFRP) layer of type III high-pressure vessels directly affect their safety. In this study, we evaluate the crack behavior in a type III high-pressure hydrogen vessel using a ply modeling method and the extended finite element method. The failure criteria were determined from the maximum principal stress and displacement that exceed the allowable tensile strength, considering the fiber and the transverse directions of each ply. The weak point of the CFRP composite layers was in the transverse direction on the 17th ply at a helical winding angle of 35° in the boundary of the dome and the cylinder. The crack extension was resulted from exceeding the allowable transverse stress at 35° winding angle. These results may be valuable for ensuring the safety of high-pressure hydrogen vessels.     

Crack tip shielding and anti-shielding effects of parallel cracks for a superconductor slab under an electromagnetic force

In this letter, the shielding or anti-shielding effect is firstly applied to obtain the behavior of two parallel cracks in a two-dimensional type-II superconducting under electromagnetic force. Fracture analysis is performed by the finite element method and the magnetic behavior of superconductor is described by the critical state Bean model. The stress intensity factors at the crack tips can be obtained and discussed for decreasing field after zero-field cooling. The shielding or anti-shielding effect at the crack tips depend on the distance between two parallel cracks and the crack length. The results indicate that the shielding effects of the two parallel cracks increase when the distance between the two parallel cracks decreases. It can be also obtained that the superconductors with shorter cracks has more remarkable shielding effect than those with longer cracks.     

固体发动机药柱表面裂纹分析

为确保含表面裂纹的固体发动机能正常点火发射，基于线粘弹性三维有限元。确定发动机药柱点火发射时的危险部位，在危险部位设置不同深度的裂纹，于裂纹尖端构建奇异三维裂纹元。模拟裂纹扩展，分别计算随着裂纹扩展所对应裂纹深度的各类应力强度因子，由此判断裂纹的稳定性。通过对某翼锥柱组合型并含前后伞盘的固体发动机药柱在点火发射时的数值分析，评估了药柱表面裂纹的稳定性。     

Finite element simulation of crack propagation based on phase field theory

The finite element approach is applied to predict crack patterns in a single or composite material under loadings. Crack patterns are represented as variations of a field variable. These variations are determined from the solution of a coupled system of equations consisting of an Allen-Cahn or Ginzburg-Landau type field equation and elasticity equations based on phase field theory. This representation does not require tracking crack tips as in the conventional finite element approach for the modeling of crack propagation problems. For a numerical solution for the system, a finite element algorithm is proposed and implemented into the finite element program “FEAP”. Several numerical simulations are performed and analyzed to predict the crack patterns in 2D single or composite materials under the loadings.     

多轴变幅应力状态下连杆微动疲劳全寿命研究

提出了一种适用于多轴变幅疲劳应力作用下的疲劳全寿命计算模型；结合有效应力强度因子幅理论和雨流计数技术处理应力谱，修正了Paris疲劳裂纹扩展速率公式使其适用于多轴变幅应力条件；在修正的Paris公式中引入短裂纹修正尺寸，得到全寿命计算模型；以斜切口式柴油机连杆齿形配合面处的寿命计算为工程算例，基于材料试验和有限元分析，计算得到配合面危险节点的寿命。结果表明，该模型可进行复杂工况下结构表面裂纹从任意初始尺寸扩展到任意设计尺寸的寿命计算，对指导关键性零部件寿命设计和确定检修时间具有重要意义。     

Nonlinear finite element analysis of a laminated cylindrical shell with transverse matrix cracks

A clamped laminated cylindrical shell is presented to investigate nonlinear structural behavior involving geometrically nonlinear deformation. In the investigation, transverse matrix cracks are considered in the stiffness of the laminated cylindrical shell. Stiffness degradation is examined for several laminated angles and transverse crack density. Micro-mechanics theory on the composite material was used to derive the degraded stiffness of the laminated cylindrical shell due to the crack density. Iterative numerical scheme was developed to calculate the degraded composite stiffness which is a complicated relation with the crack density. A nonlinear finite element program was developed using 3-D degenerated shell element and the fist order shear deformation theory to consider the large deformation of the clamped laminated cylindrical shell. The updated Lagrangian method is used for nonlinear finite element analysis. Nonlinear structural responses of the laminated cylindrical shell were examined for various stacking sequences and crack density under transversely loaded pressure. Also, the effect of crack opening/closed was considered in the examination. Through this study, it is realized that the transverse matrix crack causes moderate stiffness reduction and affects the responses of the composite shell.     

Second Generation Wavelet Finite Element and Rotor Cracks Quantitative Identification Method

The presence of cracks in the rotor is one of the most dangerous and critical defects for rotating machinery. Defect of fatigue cracks may lead to long out-of-service periods, heavy damages of machines and severe economic consequences. With the method of finite element, vibration behavior of cracked rotors and crack detection was received considerable attention in the academic and engineering field. Various researchers studied the response of a cracked rotor and most of them are focused on the crack detection based on vibration behavior of cracked rotors. But it is often difficult to identify the crack parameters quantitatively. Second generation wavelets (SGW) finite element has good ability in modal analysis for singularity problems like a cracked rotor. Based on the fact that the feature of SGW could be designed depending on applications, a multiresolution finite element method is presented. The new model of SGW beam element is constructed. The first three natural frequencies of the rotor with different crack location and size were solved with SGW beam elements, and the database for crack diagnosis is obtained. The first three metrical natural frequencies are employed as inputs of the database and the intersection of the three frequencies contour lines predicted the normalized crack location and size. With the Bently RK4 rotor test rig, rotors with different crack location and size are tested and diagnosed. The experimental results denote the cracks quantitative identification method has higher identification precision. With SGW finite element method, a novel method is presented that has higher precision and faster computing speed to identify the crack location and size.     

聚氨酯泡沫填充的碳纤维增强复合材料锥管吸能性能数值模拟及试验验证

提出了一种新型的碳纤维增强复合材料（CFRP）填充聚氨酯（PU）泡沫的汽车前部吸能结构，通过材料性能试验获得了PU泡沫、CFRP复合材料的力学性能参数及PU泡沫填充的CFRP锥管的准静态压缩吸能结果。应用LS-DYNA进行复合材料准静态压溃仿真分析，仿真结果与试验结果吻合较好，验证了复合材料填充结构有限元模型和材料模型的正确性，并且发现泡沫填充的CFRP锥管具有良好的吸能性能，填充结构比吸能高于两种材料单独使用时的比吸能之和。     

Characterization of fracture behavior in repaired skin/stiffener structure with an inclined central crack

Finite element analysis for the stress intensity factor (SIF) at the skin/stiffener structure with inclined central crack repaired by composite stiffened panels is developed. A numerical investigation was conducted to characterize the fracture behavior and crack growth behavior at the inclined crack. In order to investigate the crack growth direction, maximum tangential stress (MTS) criterion are used. Also, this paper is to study the performance of the effective bonded composite patch repair of a plate containing an inclined central through-crack. The main objective of this research is the validation of the inclined crack patching design. In this paper, the reduction of stress intensity factors at the crack-tip and prediction of crack growth direction are determined to evaluate the effects of various non-dimensional design parameter, including; composite patch thickness and stiffener distance. We report, the results of finite element analysis on the stiffener locations and crack slant angles and discuss them in this paper. The research on cracked structure subjected to mixed mode loading is accomplished and concludes that more work using a different approaches is necessary. The authors hope the present study will aid those who are responsible for the repair of damaged aircraft structures and also provide general repair guidelines.     

碳纤维带状弹簧的特性计算及实验

针对空间展开机构轻量化、小型化、简单化等的发展需求,通过理论分析实例设计了碳纤维带状弹簧,并结合有限元模拟及实验对其屈曲特性进行了研究。首先,根据薄壳弯曲理论推导了各向异性材料下碳纤维带状弹簧的弯矩计算公式,并分析了影响其屈曲特性的敏感参数;然后,针对工程需要进行了单根碳纤维带状弹簧的实例设计,并建立了其有限元分析模型,得出了其弯矩-转角曲线;最后,加工出了碳纤维带状弹簧实物并对其屈曲过程进行了实验研究。结果表明:实验测得的该碳纤维带状弹簧的临界弯矩值为1 237.6Nmm,与理论分析及有限元模拟结果符合的较好,最大误差为8.7%,验证了理论分析及有限元模拟的准确性及一致性,为之后碳纤维带状弹簧的设计及应用提供了理论依据及技术支持。