摘要
木材弹性模量是表征其力学性能的重要指标之一,应力波因其操作简便、成本低、测量结果准确等特点广泛应用于木材弹性模量的测量。目前,应力波技术测量木材弹性模量主要通过应力锤激励法实现,事实上应力锤激励法在测量木材弹性模量时无法实时分析测试试件的振动状态,且敲击易造成应力集中,不适用于厚度较小且材质较轻的木材试件。基于此,依据振动理论并结合压电材料的压电效应,从激振源和信号处理方式两个方面,构建了一种基于压电晶片激振测量木材横向弯曲弹性模量的方法。通过比较不同激励频率下激振与响应信号的幅值,获取木材试件的固有频率,根据梁的横向振动方程计算出弹性模量,并对比应力锤共振法测量结果验证该方法的可行性。两种方法测量结果的相对误差在2.5%以内,平均误差仅为1.54%。实测数据表明,基于压电晶片激振法可以有效地测得木材的弹性模量,且该方法测量时使用压电晶片激振产生的振幅较小,更加满足弹性力学微小变形的假设。后期的信号处理方面克服了应力锤法不能有效处理一些突变和不平稳信号的不足,使得检测方式更加灵活,重复性较好。
Wood elastic modulus is one of the several important indicators to characterize its mechanical properties. Stress wave technology was widely used in the measurement of wood elastic modulus due to its simple operation, low cost and accurate measurement results. At present, using the stress wave technology to measure wood elastic modulus is mainly conducted by the stress hammer excitation method, which can effectively measure the bending elastic modulus of wood according to national standards. However, in fact, the stress hammer resonance method cannot analyze the vibration state of the test specimen in real-time when measuring the elastic modulus of wood, and the energy generated by the percussion was not easy to control. Therefore, it is not suitable for some wood specimens with small thickness and light weight. Based on this, according to the vibration theory and combined with the piezoelectric effect of piezoelectric materials, this study constructed a method for measuring the elastic modulus of wood based on piezoelectric wafer excitation from two aspects, namely, excitation source and signal analysis method. This method used a single harmonic vibration wave to excite the specimen, collected the response signal, and calculated the amplitude ratio of the response signal to the excitation signal. When the amplitude ratio reached the maximum, it was determined that the specimen reached resonance. At this time, the excitation frequency could be considered as the natural frequency of the tested specimen. The elastic modulus was calculated according to the transverse vibration equation of the beam, and the feasibility of this method was verified by comparing with the measurement results of the stress hammer resonance method. The relative error of the two methods was less than 2.5%, and the average error was only 1.54%. The measured data showed that the piezoelectric wafer excitation method could effectively measure the elastic modulus of wood. According to the formula of the average energy flow of the wave, the amplitude of each specimen under the excitation of the piezoelectric wafer was calculated and the maximum amplitude generated was only 362 μm. Therefore, this method was used to measure the limited range that was close to the assumption of the small deformation in elastic mechanics. The signal processing in the later period overcame that the stress hammer method cannot effectively deal with some abrupt and unstable signals, and made the detection method more flexible and repeatable.
作者
王晓羽
徐兆军
骆立
周康
那斌
WANG Xiaoyu;XU Zhaojun;LUO Li;ZHOU Kang;NA Bin(College of Materials Science and Engineering,Nanjing Forestry University,Nanjing 210037,China)
出处
《林业工程学报》
CSCD
北大核心
2022年第6期74-79,共6页
Journal of Forestry Engineering
基金
国家重点研发计划(2016YFD0600703)。
关键词
压电晶片
弹性模量
压电晶片激振法
响应信号
激励信号
piezoelectric wafer
modulus of elasticity
piezoelectric wafer excitation method
response signal
excitation signal
