涂层界面刚度的超声数值仿真检测

针对涂层结合界面刚度在非破坏条件下难以精确测量的问题,提出了一种超声检测特征参量表征刚度系数的方法。利用声波在n层各向同性介质中的反射、透射原理,结合界面的弹簧模型,建立了多层介质界面刚度系数的超声检测数学模型。基体选用钢、铸铁、铝合金,表面选用不同喷涂工艺得到的Al2O3陶瓷涂层,获得了不同界面刚度系数的超声反射频谱。仿真结果表明:分离界面和理想界面时,谐振频率都具有周期性,但周期大小不同;弱结合界面时,随着界面的刚度系数逐渐增加,谐振频率逐渐增多,这些谐振频率均向高频方向移动。与频率较高处相比,频率较低处的谐振频率随着刚度系数的增加向高频移动的速度更快。因此建立了第一个谐振频率与刚度系数之间的关系。在同一刚度系数下,由谐振频率与材料的特性阻抗关系获得如下规律:当涂层材料不变时,谐振频率随着基体特性阻抗的增大而增大;当基体材料不变时,谐振频率随着涂层特性阻抗的增大而减小。给出了以指数函数形式拟合的刚度系数与谐振频率的变化曲线。通过对该指数函数参数与材料特性阻抗之间关系的分析,获得了弱界面时谐振频率与刚度系数和材料特性阻抗三者之间的函数表达式。该方法为涂层复合材料弱界面的超声检测提供了理论支持。

Testing stiffness coefficient of coating interface based on ultrasonic numerical simulation

Aiming at the problem that stiffness coefficient of bonding interface is difficult to be accurately measured under the condition of nondestructive,a method using ultrasonic to test stiffness coefficient have been proposed.Mathematical model of the ultrasonic testing stiffness coefficient for multilayer medium has been established by the reflection and transmission of acoustic wave propagation in layered medium and the bonding interface spring model.Ultrasonic reflection spectra under different bonding interface have been obtained when the substrate material is steel,cast iron,aluminum alloy,and the coating material is Al2O3 ceramic obtained by different spraying processes.The simulation results show that the resonant frequency is periodic on the condition of the debonded or perfectly bonding interface,but the periodicity is different.When the interface is weakly bonded,many resonant frequencies emerge and move to high frequency with the increment of stiffness coefficient.The lower resonance frequencies move faster than the higher ones.The relations between resonance frequency and stiffness coefficient have been established.The variation rules of resonance frequency with the substrate and coating impedance are as follow: the resonance frequencies increase with the increasing of the substrate impedance,and decrease with the increasing of the coating impedance in the same stiffness coefficient.The relation between stiffness coefficient and resonance frequency is fitted using the exponential function.The function including the substrate and coating impedance,stiffness coefficient and resonance frequency was obtained in weakly bonded interfaces.The results will provide theoretical support to ultrasonic testing of the coating composites with weakly bonded interfaces.