金属构件裂纹的修补参数研究

金属结构的裂纹可以用加补强板的方法修补，但有限元程序计算表明：选择补强板的参数应按照最大限度降低裂纹尖端应力的原则。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。     

用有限元研究金属构件裂纹的修补参数

金属结构的裂纹可以用加补强板的方法修补 ,但有限元程序计算表明 :选择补强板的参数应按照最大限度降低裂纹尖端应力的原则。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     

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)。     

剪板机压料板裂纹的补焊

我厂生产用剪板机在实际生产中压料板产生了200mm的裂纹，该压料板长2．5m，宽1m，厚150mm，材质为灰铸铁（HT200）。为保证生产的正常进行，我们对压料板进行修补。     

含中心裂纹铝合金板的复合材料补片单面修补效果

利用袋压工艺、采用单向碳纤维/环氧复合材料补片对含中心裂纹的铝合金板进行了修补,测试了胶接修补前后板的静态力学性能和疲劳性能.结果表明:经过修补后,铝合金板抵抗静态拉伸破坏和疲劳破坏的能力均有显著的提高,其静态抗拉强度从258.35 MPa增加到349.69MPa,提高了35.35%;其疲劳寿命从25 446周次增加到63 868周次,提高了1.51倍,裂纹起始扩展速率从0.34μm/周次降低到0.16μm/周次,临界裂纹长度从20.20 mm增加到28.05 mm.     

复合材料补片参数对裂纹尖端应力强度因子的影响

利用有限元法对复合材料补片修补前后的铝合金薄板的裂纹尖端应力强度因子KI进行研究,分析各类补片参数对裂纹尖端应力强度因子的影响.结果表明,在正确选择复合材料补片的参数后,修补后铝合金板裂纹尖端的应力强度因子有显著地下降.     

用有限元确定起重机裂纹补强板的参数

采用ANSYS有限元分析软件，对因出现裂纹的起重机主梁而添加的补强板进行系列计算，得出修补后主梁裂纹的应力及应力强度因子的变化规律。结果表明，采用参数适当的补强板，可降低起重机主梁裂纹尖端的应力，从而保证起重机的安全。     

复合材料胶接修补技术的实验研究

通过静强度和疲劳寿命对比试验,证实了在含裂纹的铝合金的裂纹部位,胶接碳／环氧复合材料补片的修理方法的可行性和有效性。实验结果表明,裂纹板经胶接修补后,其静强度和疲劳寿命均有显著的提高,这为实际结构的胶接修补工作积累了可靠的实验数据。     

汽缸体和汽缸盖裂纹的修复

柴油机运转过程中,汽缸体与汽缸盖容易产生裂纹,造成漏气、漏水、烧坏汽缸垫,甚至发生机械事故。汽缸体与汽缸盖出现裂纹应及时进行修复,方法主要有以下4种。1.补板法补板法主要用于修补裂纹较多且相对集中或有部分破洞的机体平整的外表面。具体步骤是：①清除裂纹附近准备补板部位的油污、漆皮等物;     

补片参数对含穿透性裂纹层压板修补强度的影响研究

针对含穿透性裂纹的损伤层压板，采用“两板”模型建立起机械连接修补结构有限元分析模型，分别计算补片大小、厚度、铺排方式以及连接件位置等修补参数对修补效果的影响。采用自编有限元程序得出的计算结果及所得结论对实际复合材料修补具有很好的指导意义。     

Investigation of closure of internal cracks during rolling by FE model considering crack surface roughness

Internal cracks often appear in cast slabs, and their evolution during hot deformation directly affects the product quality. In this paper, the authors investigate the closure behavior of internal cracks during plate rolling using a finite element (FE) model that takes into account the roughness of the crack surface. Influences of the roughness and reduction ratio on the closure of cracks are analyzed. The simulated results show that the models with consideration of the initial crack roughness can be used to investigate the formation of residual voids around the crack after rolling. The simulation results are validated by experimental observations. Finally, we propose an explanation of the crack closure mechanism during rolling.     

带有两个共线裂纹载流薄板的温度场及热应力强度因子

采用复变函数的方法,给出带有两个等长度共线穿透裂纹的无限大载流薄板在瞬间电流作用下,裂纹尖端附近产生的温度场的表达式,得到温度在裂纹尖端的奇异特征.在通入垂直于裂纹的均匀电流作用下,由于裂纹的存在,裂纹尖端出现绕流现象,产生焦耳热,瞬时高温形成点热源.通过点热源在金属薄板内形成的温度场,可以导出裂纹尖端产生的热应力强度因子表达式.将其与外载荷产生的应力强度因子叠加,可建立通电状态下的断裂判据.算例分析表明,点热源在裂纹尖端附近产生的热应力强度因子为负值,可以部分抵消无穷远处施加的拉应力产生的应力强度因子的作用,进而达到止裂的目的.文中建立带有两个等长度共线穿透裂纹载流薄板的热应力强度因子的概念.其研究结果对工程结构实施电磁热效应裂纹止裂具有理论意义和实用价值.     

不锈钢表面裂纹方向电磁检测方法

针对传统交流电磁场检测表面不定方向裂纹容易出现漏检的问题,研究了旋转磁场下感应电流方向、裂纹方向变化对平板表面裂纹检测幅值的影响,推导了裂纹走向角度与平面磁场分量波谷幅值的关系表达式,从检测机理角度提出了裂纹方向判定方法及影响因素.建立了奥氏体不锈钢表面裂纹交流电磁场检测有限元仿真模型,开发了基于双U形激励和高分辨率隧...     

基于双轴 TMR 电磁传感器的裂纹检测方法研究

针对单一激励交流电磁探头检测任意方向裂纹容易出现漏检问题,设计了用于检测奥氏体不锈钢表面斜裂纹的新型双激励传感器,建立了奥氏体不锈钢表面裂纹交流电磁场检测仿真模型,开发了基于新型双激励传感器和高分辨率隧道效应磁阻传感器的金属平板表面裂纹检测系统。基于理论模型和试验系统研究了试件上裂纹走向和裂纹宽度对传感器拾取到磁场分量幅值的影响规律,研究了裂纹检测与方向判定方法。仿真和实验结果表明,利用磁场分量B_x、B_y畸变特征能够以相同的灵敏度检测出试件表面尺寸为15 mm×0.2 mm、深度大于3 mm的微小裂纹,并实现裂纹方向判定。引入宽度补偿参数后减小了横向、纵向裂纹判定误差,判定误差最大为3.9°。     

Constrained zones in a periodic array of collinear equal cracks

Thin plates made of Perspex and containing an array of collinear equal cracks were subjected to a combined mode of loading consisting of biaxial tension and shear at infinity. The thickness variation of the plates was depicted by the reflected shadow method developed by the author. According to this method a coherent monochromatic light beam was diffracted along the thickness when the plate was traversed and partly reflected on the rear face. The reflected part, which was again refracted through the thickness and afterwards emerged from the plate, was retarded according to Neumann's law. The retarded light rays created deviating wave-fronts which followed the Eikonal equation of geometric optics. If these rays were received on a ground-glass screen, they created a bright envelope, a caustic, which was related to the constrained zones surrounding the crack tips of the plate. In this paper the case of an array of collinear equal internal cracks was studied and especially the influence of neighbouring cracks on the shape and size of the caustic of each crack. The dimensions of the envelope are directly related to the stress-intensity factor corresponding to each crack tip which can be derived from the dimensions of the caustic. Experimental evidence with cracked Perspex plates corroborated the theory.     

08Al热轧板表面纵裂纹原因分析

对08Al热轧板出现表面纵裂纹的试样进行系统分析,结合生产工艺,找出了影响热轧板产生纵裂的主要因素:连铸坯表面裂纹严重,经过高温长时加热内氧化严重,在轧制过程未轧合而形成表面裂纹。     

Detection for transverse corner cracks of steel plates’ surface using wavelet

An algorithm is presented for detecting transverse corner cracks at a steel plate surface using wavelet transform. According to characteristics of transverse corner crack images, the wavelet transform is used for the multi-scale analysis of detecting the image edges and disintegrating the image into four directions at the same time. The proper threshold value is chosen to segment the image into vertical components to obtain the final detection result. The experiment shows that transverse corner cracks of steel plates can be more effectively extracted by the proposed method than the other two common methods.     

Detection for transverse corner cracks of steel plates’ surface using wavelet

An algorithm is presented for detecting transverse corner cracks at a steel plate surface using wavelet transform. According to characteristics of transverse corner crack images, the wavelet transform is used for the multi-scale analysis of detecting the image edges and disintegrating the image into four directions at the same time. The proper threshold value is chosen to segment the image into vertical components to obtain the final detection result. The experiment shows that transverse corner cracks of steel plates can be more effectively extracted by the proposed method than the other two common methods.