润滑剂对直升机螺栓相控阵超声检测能力的影响

Effect of Lubricant on Helicopter Bolt Phased Array Ultrasonic Detection Capability

实现在役直升机桨毂阻尼器螺栓的原位检测能够降低维护成本,但在螺栓−机油润滑剂−紧固件的装配结构中,润滑剂引起的声阻抗差异可能引起螺栓表面缺陷的漏检和误判。为实现对在役直升机桨毂阻尼器螺栓裂纹的检测,采用超声相控阵探头分别对螺栓“R”型倒角的裂纹与螺杆表面的裂纹进行检测。同时为了验证润滑剂对裂纹检测的影响,利用超声相控阵探头对润滑剂耦合的装配螺栓进行检测,并与暴露在空气中的螺栓检测结果进行对比。结果表明:在2种耦合状态下,超声相控阵扇扫都可有效检出螺栓“R”型倒角与螺杆表面刻深0.1 mm以上当量的缺陷;螺栓表面涂有润滑剂时,缺陷回波幅值与无润滑剂时相差1%~6%,两者回波幅值之差在1 dB左右。因此,为降低润滑剂对刻深0.1 mm当量的桨毂阻尼器螺栓表面裂纹检测的不利影响,可以在参数设置中增加1 dB增益进行检测。

The on-site inspection of the hub shock absorber bolts for in-service helicopters can reduce maintenance costs.However,in the assembly structure of bolts-lubricating oil-fasteners,the difference in acoustic impedance caused by lubricating oil may lead to missed inspection and misjudgment of bolt surface defects.To detect the bolt cracks in the hub damper of the in-service helicopter,the cracks of the bolt“R”chamfer and the screw of the blot are detected by the phased array ultrasonic test(PAUT).Meanwhile,to verify the influence of lubricant on crack detection,the PAUT results of the bolts which screw surface coated with lubricant was compared with that found in the air.The results show that,regardless of the presence or absence of lubricant,the phased array fan scan image can find defects in the bolt“R”chamfer and screw with a depth of more than 0.1 mm.And by comparing the percentage difference between the echo amplitude of the surface coated with lubricant and the defect in the air,the difference ranges from 1%to 6%.After conversion,the difference between the two echoes is about 1 dB.Therefore,a 1 dB increase in the parameter settings can be set for eliminating the negative influence of the lubricant on the screw detected.