应用AE和DIC原位监测含横纹裂纹木构件的裂纹演化规律试验研究

Experimental study on in situ monitoring of the evolution law of cracks in wood components with transverse cracks based on acoustic emission and image correlation

【目的】含横纹裂纹木构件的缺陷会使其在弯曲载荷下发生横纹断裂,研究含横纹裂纹木构件在载荷作用下微裂纹的萌生和扩展规律,对含横纹裂纹木构件断裂损伤的预判和评估具有重要的意义。【方法】以杉木为研究对象,基于声发射(AE)技术和数字图像相关法(DIC)对已预制横纹裂纹的木试件三点弯曲损伤过程进行了实时原位监测,采用声发射参数分析法研究了加载过程中微裂纹萌生和失稳扩展的声发射特征,同时结合裂尖区域的应变和位移变化信息分析木试件表面裂纹起裂和扩展的应变特征。【结果】含预制横纹裂纹木试件的损伤演变过程中的声发射和数字图像测量结果,所反映的微裂纹萌生、扩展规律一致,验证了声发射振铃计数、能量和幅度对裂纹损伤过程的预判。其中声发射振铃计数、能量、幅度可有效预报木试件微裂纹的萌生,木试件表面应变的变化可以有效观测裂纹萌生和扩展区域的演变。【结论】建立了木材微裂纹萌生、扩展行为与声发射参数和表面应变之间的对应关系,并成功地构建了基于声发射技术和数字图像相关法的原位监测含横纹裂纹木构件裂纹损伤演化的测量和评价体系,试验结果为进一步研究含横纹裂纹木构件裂纹演变行为的损伤机理和原位监测方法提供了参考依据。

[Objective] The defects of the wood component with transverse cracks will cause fracture damage under bending load. It is important to study the law of crack initiation and propagation to predict and evaluate the fracture damage of the timber-containing members. [Method] This paper was performed on Chinese fir and damage was monitored in-situ in real time based on acoustic emission(AE) and digital image technology(DIC) during three-point bending failure of wooden beams with prefabricated transverse cracks. The AE parameter analysis method was used to study the characteristics of AE signals during the crack initiation and propagation of Chinese fir. The strain characteristics of the surface of the wooden beam are also analyzed according to the strain and displacement changes of the crack tip region. [Result] The results showed that the crack initiation and propagation laws reflected by the AE and DIC measurements during the damage evolution of prefabricated cracks in wood beam specimens were consistent, the digital images of damage evolution from monitoring the crack tip region of wooden beams verify the prediction of AE signals, and AE ring count, energy and amplitude were effective indicators to predict the crack initiation of wooden beams. The strain of the wooden beam surface can effectively observe the evolution of crack initiation and extension. [Conclusion] The results of this study establish the relationship between wood microcrack initiation, propagation behavior and acoustic emission parameters and surface strain, and it successfully construct the evolutionary measurement and evaluation system for in-situ monitoring of cracks in wood components with transverse cracks based on acoustic emission technology and digital image correlation method. The experimental results provide a reference for the further study of the damage mechanism and in-situ monitoring methods for the crack evolution behavior of wood components with transverse cracks.