振动场下微裂材料的非线性超声调幅特征

Nonlinear acoustic modulation feature of microcracking material under vibration

一般在材料损伤后,其非线性力学特征更加明显.在高频声波和低频振动位移场下,开裂材料会出现非线性超声调幅现象.介绍了非线性超声调幅现象,对微裂材料的非线性超声调幅特征进行探讨,提出以旁频能量与振动输入能量之比,作为描述材料损伤的定量参数,并进行试验研究,采用碱骨料反应对2根混凝土试件引入微裂缝损伤,与1根无损试件进行对比.试验结果显示,振动场下微裂材料的非线性超声调幅特征十分明显,2根损伤试件在不同损伤水平上的相对损伤参数有较大改变,且在相同损伤水平上两者十分接近;而对比无损试件的相对损伤参数变化很小.表明该方法对微裂缝损伤极为敏感,运用相对损伤参数能够对损伤的程度给出定量化的描述,且具有较好的一致性.

Generally material behaves more nonlinearity after damage. For material with microcracks, phenomenon of nonlinear acoustic modulation would appear under the mixture displacement of both high- frequncy acoustical wave and low-frequncy vibration. The nonlinear acoustic modulation is explained; and the chracterization of the damaged material with microcrack is discussed. A relative damage parameter is presented using the power spectrum energy ratio of sideband to vibration. Experimental tests were performed by two mortar samples with alkali-reactive aggregate and exposed to an aggressive environment to induce micro-cracking; and these two samples were compared to a control one with no damage. The test results show that acoustic modulation feature is very obvious for the damaged samples under vibration. The relative damage parameter increases greatly for the two damage samples and keeps good agreement for two samples with the same damage level, while changes little for the undamage one. The relative damage parameter can be used to clearly distinguish the damaged samples to undamaged ones. The method presented is sensitive to the micro-crack with good consistency; and the relative damage parameter demonstrates a good quantitative discription of the damage degree.