在役轴疲劳裂纹超声非拆卸检测与定量评价

Large shaft components are under the condition of overload and alternate loading for a long time, the presence of a crack may cause serious damage to major equipment. Due to the bearing cannot be easily removed and detection space is limited, it is difficult to inspect crack using conventional nondestructive testing method, which bring a big challenge for non-disassembly ultrasonic inspection fatigue of in-service shaft. In this proposal, a few techniques are proposed to solve some key issues to meet the challenge. Firstly, the model for ultrasonic incident on pressure interface is established to reveal the relation between interface roughness, curvature, pressure and interfacial stiffness. The pressure interface is simplified with a periodically cracked interface, the finite element modeling of the simplified model is carried to decide the equality parameters; Secondly, a simulation method hybrid spatial impulse response and finite element is presented to predict transducer outputs of echo wave from crack surface, the pressure interface and complex structure, it is significant to reveal the propagation law of ultrasonic wave in complex cases and provide guidance for eliminate no-defects echo; Finally, sparse deconvolution method is used to extraction ultrasonic signal in this project, which transducer vibratory function as the kernel function. To overcome the ill-posed problems, the ultrasonic sparse deconvolution method based on majorization-minimization is proposed. The theoretical results of this research are applied in ultrasonic nondestructive testing system of key shaft compoments and all these achievements provide new ideas for ultrasonic evaluation of fatigue crack in-inservice shaft components.

大型轴类零部件长期在重载和交变载荷下运行，易产生疲劳裂纹，疲劳裂纹可能迅速扩展，发生突然断裂，造成灾难性后果。由于轴上有轴承等不能轻易拆除的部件，在现场安装条件受限的情况下，没有任何接触面可供常规无损检测方法对配合区域进行检测，因此在役轴内部疲劳裂纹的非拆卸检测成为一大难题。本项目建立超声波在承压界面传播的理论模型，揭示界面粗糙度、曲率、压力对超声波的影响规律，在此基础上将承压界面进行等效简化，通过有限元建模与计算机仿真，确定等效参数；建立有限元和空间脉冲响应相复合的声学模型，研究超声波在在役轴结构中的传播机制，揭示裂纹大小、裂纹走向、探头参数、承压界面和轴结构形式对超声回波幅度、相位和波形畸变的影响规律；利用探头响应特性函数，建立基于最优-最小化方法的超声信号反卷积模型，解决反卷积的盲问题和病态问题，分离高度重合回波。本项目预期成果为提高在役轴类零部件缺陷超声检测的可靠性奠定坚实基础。

大型轴类零部件长期在重载和交变载荷下运行，易产生疲劳裂纹，由于轴上有轴承等不能轻易拆除的部件，在现场空间受限的情况下，只能在轴端面布置探头对压装界面进行检测，界面压力会导致缺陷定量误差，因此对非拆卸超声检测相关的关键问题进行了研究。分析了承压界面超声传播特性，得到透射系数与界面压力的关系，分析了超声波在“周期间断”界面上的传播特性，得到“周期间断”模型参数与透射系数之间的关系，并与精确解进行了对比，当周期长度小于0.15倍纵波波长时等效模型精度较高，再根据实验获得的界面透射系数确定界面结合率，实现了承压界面有限元模型等效。建立了承压条件下的裂纹回波有限元模型，分析了界面压力对回波的影响规律，得到了界面压力与回波幅值的关系，随着界面压力增大，缺陷的回波幅值变小。针对缺陷超声回波在时域上重叠影响检测可靠性的问题，提出了基于高阶累积量和最优—最小化方法的超声信号反卷积算法，可以提取出重叠回波中的缺陷。针对采集到的超声信号易受到各种噪声影响的问题，提出基于果蝇优化算法（FOA）和正交匹配追踪（OMP）的超声信号去噪算法，引入自适应迭代停止条件和高维广义CAT映射提高寻优效率并避免局部最优，显著提高了超声回波信号的信噪比。相关研究成果不仅适应于在役轴类零件的超声检测，也适用于其他零部件超声无损检测模型的建立和超声信号的处理。