含LT型裂纹木梁起裂载荷确定方法的试验研究

木材裂纹萌生的准确判定对木材损伤断裂的评估具有重要的意义,起裂载荷是标定裂纹萌生的关键参数。本试验以杉木为研究对象,利用声发射技术(AE)、数字图像相关法(DIC)和电测法(EM),对含LT型裂纹木梁的损伤断裂特性进行了试验研究。通过研究木梁在加载过程中声发射参数变化规律以及裂尖区域的表面应变信息的演变,分析木梁裂纹萌生规律并确定起裂载荷Pini。结果表明:声发射累计振铃计数、幅度可有效反映木梁内部损伤的产生和演化,利用声发射参数的变化规律能准确确定含LT型裂纹木梁的起裂载荷Pini;数字图像相关法、电测法可以实时监测木梁表面裂缝尖端区域的应变变化,根据应变演变特征可以有效监测木梁表面裂纹的萌生和扩展。声发射技术、数字图像相关法、电测法在确定木梁起裂载荷Pini方面有较好的适用性,所确定的起裂载荷大小为:电测法>数字图像相关法>声发射。试验结果为研究监测含LT型裂纹木材裂纹萌生的试验方法提供了依据,应用时可结合实际工况选择合适的测量方法。

Experimental study for determining method of cracking load of wooden beams with LT crack

Cracking of wood due to flexural load is one of the clear physical indicators of loss of service life of timber components.The cracking prediction is therefore very important for service life evaluation of timber components.The accurate determination of wood crack initiation has a great significance to the evaluation of wood damage and fracture.The crack initiation load is the key parameter to judge the crack initiation.By taking Chinese fir as the research object,this study used the acoustic emission(AE),digital image correlation(DIC)and electrical measurement(EM)to examine the damage and fracture characteristics of wood beams with LT-type cracks.The variation law of acoustic emission parameters of wood beam during loading and the evolution of surface strain information in crack tip region were investigated in order to analyze the crack initiation law of wood beam and determine the cracking load(P ini).The results showed that the cumulative counts and amplitude of acoustic emission can effectively reflect the generation and evolution of internal damage of wood beams,and the variation law of acoustic parameters can accurately detect the micro-damages inside the wood and determine P ini of the wood beams with LT-type cracks.The digital image correlation and the electrical measurement method can be used to monitor the strain change in the crack tip region of the wooden beam surface in real time.It can effectively monitor the surface crack initiation and propagation of wood beams according to the strain evolution characteristics.The digital image method had the characteristics of full-field measurement and can further predict the location and propagation path of crack initiation.Acoustic emission,digital image correlation and electric measurement methods have good applicability in determining the cracking load of wooden beams.However,due to the different measurement principles and measurement accuracy of three measurement methods,the cracking load size determined by three methods can be ranked as:electrical measurement>digital image correlation>acoustic emission,and the experimental results provide a basis for the study of experimental methods for monitoring the crack initiation of wood.In practical engineering applications,the most suitable measurement method can be selected according to the actual working conditions.