温度补偿翻转电位法低温疲劳裂纹扩展速率微机测试

A New Microcomputer Aided System for Measuring Low Temperature Fatigue Crack Propagation Rate

本文对所研制的微机辅助低温疲劳裂纹扩展速率测试系统的硬件和软件做了介绍。系统采用了温度补偿翻转电位技术,控温信号锁存技术,低通滤波加数值补偿数据平滑技术以及坐标变换旋转放大卷积割线求导技术,从而大大提高了测试精度。文末还介绍了上述系统用于LY12CZ铝合金及16Mn钢的低温疲劳测试结果。

The low temperature fatigue crack propagation rate (LTFCPR) ofmaterials has been paid some attention in recent years. The measurementmethods used include compliance method (CM), ultrasonic method (UM) and Krak-Gauge analog electrical potential method (KGAEPM). When using CM,the signal noise of measurement is relatively large, because conversion ofmechanical movement to electrical signal is involved. When using UM, theaccuracy of temperature control may be affected by heat generated in cracktip; besides, continuous monitoring and measuring by UM is difficult. Whenusing KGAEPM, it often occurs that crack length measurement value lagsbehind actual value, because the ductilities of Krak-Gauge, binding glue, andmeasured materials differ greatly. In order to overcome the shortcomings of the above-mentioned methods,the traditional electrical potential method has beon modified to becometemperature compensation reversal electrical potential method (TCREPM),and a microcomputer aided system for measuring LTFCPR in near-thresholdregion has been developed; as a result, LTFCPR is more accurately measured.Furthermore, the system has been used successfully for measuring LTFCPRof LY12 aluminium alloy and 16Mn steel (see figures 8 and 9 in full paper). The special features of the authors measuremeat system are the followingfive points (the last point is successfully transplanted from the first author'sprevious research [6]; the other four points are presented for the first time): (1) By using the temperature compensation technique, the measurementerror caused by temperature effect of resistivity can be eliminated. (2) By using reversal electrical technique, the zero drift and thermalelectrical potential effect can be eliminated. (3) By using signal latching technique on temperature controller, themeasurement error caused by electric network fluctuation induced by start-upand shut-off of motor can be eliminated. (4) By using data smoothing technique of low-pass filtering and numericalcompensation, the degree of smoothness of numerical date can be conspicuouslyincreased, and the phenomenon of crack length displying value lagging bebindactual value can be eliminated. (5) By using the coordination rotation and amplification convolutionsecant method, the derivative (da/dN) accuracy is effectively improved.