【作者】 赵小矛；

【导师】 赵东；

【作者基本信息】 北京林业大学 ， 机械设计及理论， 2018， 博士

【摘要】 在木材加工制造中对木制构件的质量检测和可靠性评估,是木材加工机械装备实现自动化和智能化的主要问题之一。声发射无损检测先进技术已在木材加工装备中得到应用,而且在评估木质材料品质和木材强度方面也有一定研究,但对使用中的实木结构健康状况的研究还不多。在结构损伤检测方面,损伤源的定位与损伤程度的测评是各种无损检测技术追求的最终目标,也受到国内外学者的普遍关注。近来,声发射信号特征参数的相关研究表明:能量是声发射信号的一个重要的特性参数,可以利用损伤过程中的能量释放规律进行材料结构损伤断裂的预测。由于木结构榫卯接合的部位属于隐藏部位,当其发生损伤时,肉眼无法观测。为了准确地预测榫卯结构的健康状况,可以根据榫卯结构在破坏前,木材所释放出来的声发射能量传播特性进行信息源位置的判定。为此,本文以我国家具业常用木材为研究对象,应用声发射技术探讨其声发射特性,并基于能量衰减特性对声发射源进行准确定位。论文的主要研究内容和创新点如下:1.研究了木材声发射信号特征,基于小波理论及人工神经网络技术提出了木材声发射信号的去噪及特征提取方法,采用LabVIEW/Matlab平台研制了木材声发射信号采集处理系统。2.利用木材声发射信号采集处理系统,结合断铅试验研究了孔洞、节子和含水率等主要因素对木材声发射信号传播特性的影响。阐明了孔洞、节子和含水率对能量衰减的影响规律:孔洞、节子和含水率的值越大,能量衰减越明显。3.研究了楸木木材的能量衰减特性,提出了用能量比量化确定木材声发射信号源(破坏源),推导并计算得到能量衰减系数α的取值范围为1.0-2.4,明确了声发射信号在楸木中传播时能量随着距离的增加而衰减,从理论上建立了木材能量衰减模型。这是本论文的创新点之一。4.基于木材能量衰减模型研究了方榫结构破坏源的定位方法,采用预制裂纹实验验证了能量衰减模型的有效性,对比了两点定位法和三点定位法的定位精度。通过定位L型和T型方榫结构破坏源,得到三点定位法比两点定位准确。这是本论文的又一创新之处。榫卯结构作为建筑、家具结构中的主要连接结构,其接合部位的健康状况直接影响到结构整体的安全性、可靠性以及使用寿命。本文为榫卯结构的加工制造,以及现场健康监测提供了参考依据,也为木结构破坏源的定位提供了一种新的方法。更多还原

【Abstract】 Acoustic emission technology has some research on the evaluation of wood material quality and wood strength,but there is not much research on the health status of solid wood furniture in use.In the aspect of structural damage detection,the location of damage sources and the assessment of damage extent are the ultimate goals pursued by various non-destructive testing technologies,which has attracted widespread attention from scholars at home and abroad.The existing acoustic emission localization methods mainly include time difference localization method and regional localization method.Since these two methods are susceptible to factors such as wave velocity,attenuation,waveform and component shape,the error of damage location detection is big.Recently,the related research on the characteristic parameters of acoustic emission signals shows that:Energy is an important characteristic parameter of acoustic emission signals,and the energy release law in the process of damage can be used to predict the damage of material structure damage.Since the tenon joint of the wood structure is a hidden part,when it is damaged,it cannot be observed by the naked eye.In order to accurately predict the health of the tenon structure,the position of the information source can be identified according to the acoustic emission energy propagation characteristics released by the tenon structure before the destruction.Therefore,in this paper we take the wood commonly used in China’s furniture industry as the research object,and use acoustic emission technology to explore its acoustic emission characteristics.The relevant contents and main innovations are as follows:1.The propagation modes of acoustic emission signals and the main factors affecting acoustic emission signals were discussed.According to the characteristics of wood acoustic emission,we designed and constructed a signal acquisition system.Based on wavelet theory and artificial neural network technology,the real-time acquisition of low-frequency acoustic emission signals of wood and its structure was realized.The sound emission signal processing platform was constructed by LabVIEW/Matlab software.The function of processing the collected acoustic emission signal,the system mainly includes three modules of signal playback,feature extraction and pattern recognition.2.Based on the wood acoustic emission signal acquisition and processing system developed in this paper,the effects of main factors such as holes,knots and water content on the propagation characteristics of wood acoustic emission signals were studied.The results show that the effect of holes and knots on energy attenuation is obvious.The larger the hole or knot is,the more obvious the attenuation effect is.The water content has a great influence on the velocity,amplitude and energy in the acoustic emission signal.The larger the water content is,the faster the attenuation rate is.3.The lead-emission simulated acoustic emission experiment was carried out with the self-processed wood specimens.The distance-attenuation curve was measured by the wave velocity measurement and attenuation experiment of the acoustic emission wave.The distance and signal amplitude were obtained.The relationship between the values and the energy attenuation coefficient a is in the range of 1.0 to 2.4.The results show that when the AE signal propagates in the eucalyptus(Juglans mandshurica),its energy shows a decreasing trend with the increase of the distance.The energy attenuation formula is applicable to the eucalyptus,and the wood energy attenuation model is theoretically established.4.Two-point and three-point positioning experiments were carried out on the L-shaped and T-shaped square eucalyptus components without gluing.The pre-crack experiment method was used to verify the correctness of the energy attenuation model.The wood energy attenuation model is used to calculate the location of the damage source under different conditions.The results show that the energy attenuation model can be used to determine the location of the damage source of the L-shaped and T-shaped square uncoated wood components.The three-point positioning method can obtain a more accurate location of the damage source than the two-point positioning.As the main connection structure in the building and furniture structure,the concrete structure of the concrete structure directly affects the safety,reliability and service life of the whole structure.This paper provides a reference for the on-site health monitoring of mortise structure,and also provides a new method for the location of wood structure damage sources.更多还原