曲面构件早期损伤的空耦非线性表面波检测理论及评价方法

Curved components are widely used in military, aviation and rail industries, and it is essential to detect and evaluate effectively the early-state-damages in these components to avoid the aggravation of damages and ensure the service safety of curved components. Nonlinear surface acoustic technique has been accepted as a potential tool to characterize the early-state-damages in materials. In this research, nonlinear surface wave evaluation method suitable for curved components using air-coupled receivers will be developed. The nonlinear properties of surface wave propagating in curved surface is analyzed using the WKB(Wentzel-Kramers-Brilloin) method and perturbation theory, and the nonlinear surface wave fields generated by angle beam wedge transducers are modeled using the Green’s function method, so that the effects of curvature on the propagations and diffractions of nonlinear surface waves can be clarified. The air-coupled transducer is calibrated based on the reciprocity theory, and a method of measuring surface wave absolute nonlinear parameters of curved components is proposed. The fatigued plane-specimens are evaluated using nonlinear surface waves and a dislocation-related evaluation theory is proposed, and then, a multi-parameter evaluation model for early-state-damage using surface wave absolute nonlinear parameter, velocity and attenuation coefficient is developed. A method for correcting the effects of curvature on the measured nonlinear surface wave parameters is researched, and the early-state-damages in curved components can be accurately evaluated using the proposed multi-parameter evaluation method. The aim of the research is to clarify the detection theory of nonlinear surface wave in curved surface, and propose a detection and evaluation method suitable for curved components using nonlinear surface wave and air-coupled ultrasonics. It is expected this research will be of practical significance to ensure the service safety of curved components.

曲面构件广泛应用于军工、航天和轨道交通等领域，只有及时检测和评价其早期损伤才能有效地避免损伤加剧并消除安全隐患。非线性表面波检测技术是评价材料早期损伤的有效手段。本项目拟研究适用于曲面构件的空耦非线性表面波评价方法：首先，利用WKB方法和微扰理论研究曲面上表面波非线性特性，采用格林函数法建立楔块探头辐射至曲面的非线性表面波声场模型，分析曲率对非线性表面波传播和衍射特性的影响；然后，采用互易理论对空耦探头进行校验，研究曲面构件表面波绝对非线性系数的测量方法；接着，开展损伤试块的检测实验并研究位错相关评价理论，建立基于表面波绝对非线性系数、声速和衰减系数的材料损伤多参数评价模型；最后，研究曲率对非线性表面波测量结果的修正方法，实现曲面构件早期损伤状态的有效评价。项目预期成果将揭示曲面构件早期损伤的非线性表面波检测机理，建立基于空耦探头接收的评价方法，对保证曲面构件的服役安全具有重要的应用价值。

材料或者构件早期损伤的检测，尤其是疲劳损伤的检测和寿命评价是保证安全的重要基础。本项目主要以动车组轮对等曲面构件和材料的疲劳损伤检测为例，提出了利用空气耦合超声探头检测方法和非线性超声表面波检测理论的曲面构件早期损伤评价方法。研究主要内容包括超声表面波在曲面表面传播特性，空气耦合超声探头灵敏度校验方法，曲面传播的非线性表面波非线性系数的检测方法，疲劳损伤的非线性表征方法等。重要的研究成果包括提出了空气耦合超声探头的校验方法，实现了利用空耦探头测量绝对非线性系数的技术；深入研究了曲面曲率对表面波传播特性的影响，保证了曲面构件下表面波所有参数的准确测量；建立利用表面波声速、衰减和非线性系数于一体的材料损伤状态综合检测和评价体系，可实现材料或构件早期损伤状态的有效评价。项目所取得的成果可用于指导广泛应用于军工、航天和轨道交通等领域中曲面构件的早期损伤的检测和评价，以及时发现早期损伤并避免安全事故发生。