宏细观振动对选择性热激励效果的影响

Influences of macro and micro vibration on selective thermal excitation effect

激振频率是选择性激励红外热成像检测技术的控制参数。从结构共振的角度选取含微裂纹的混凝土简支梁作为激励对象,以简支梁自振频率作为激振频率,测试激励效果;并选用40 k Hz激振频率进行对比试验。试验结果显示,40 k Hz频率激振下的简支梁出现了显著热激励效果,但自振频率未出现激励效果。结合这一试验现象,在机理层面计算分析了简支梁宏观整体振动、梁内细观质点波动两种振动状态对热激励效果的影响以及它们之间的相互作用规律。分析结果表明:在整个激励过程中,结构整体振动的热激励能力弱于质点波动,并持续消弱质点波动的强度;细观质点波动是热激励效果出现的原因,可选用40 k Hz超声频率激振来降低宏观整体振动强度,消除整体振动对质点波动的弱化作用。

An excitation frequency is one of the control parameters of the selective thermal excitation detection technology. The study was started from the perspective of structural resonances. A simply supported concrete beam having micro-cracks was chosen as an incentive target and its natural frequency as the excitation frequency,which tested the incentive effect. And a 40 k Hz excitation frequency was chosen as an objective of the comparison tests.The experiment results show that the simply supported concrete beam excited by the 40 k Hz frequency has a significant thermal excitation effect,but this effect is not excited by the natural frequency. Both macroscopic overall vibration and microscopic particles fluctuations in the simply supported beam influence the excitation effect. Based on the experimental phenomenon,the influences of two vibration conditions on the thermal excitation effect and the interaction between two vibrations were analyzed in the aspect of mechanism. Analysis results show that the thermal excitation ability of the overall vibration is weaker than that of the particles fluctuations during the whole process of excitation,and the overall vibration continues to weaken the strength of the particles fluctuations throughout the whole excitation process. The microscopic particles fluctuations can excite the thermal excitation effect. The 40 k Hz ultrasonic frequency can be used to reduce the overall vibration strength,so as to eliminate the attenuation of the overall vibration to the particles fluctuations.