基于非对称椭圆的应力波木材缺陷断层成像算法

Wood stresswave nondestructive testing tomography algorithm based on asymmetric ellipse

木材中的空洞、腐朽等缺陷在很大程度上影响着木材的力学性能。为实现木材内部缺陷的无损检测,提高木材利用率,提出了一种基于非对称椭圆的木材应力波无损检测算法。选取3个不同缺陷的原木样本作为实验材料,其中两个分别为位于中心以及边缘的人工圆形缺陷,一个为偏边缘的自然缺陷,采用自制的应力波检测设备获取木材截面内的波形数据。首先根据得到的射线速度值计算分段后的线段和交点的速度值,并进行校正;然后计算射线两侧不同的控制系数,确定射线影响区域;最后根据网格单元的速度值生成断层图像。数值仿真与实测结果表明,基于非对称椭圆的应力波断层成像算法能够精确地检测出原木样本的缺陷。从重建的断层图像可以看出:与基本椭圆插值方法相比,提出的算法能够更清晰地显示缺陷的大小及位置,应用混淆矩阵定量分析,在准确率、精确度和查全率3个参数指标上分别有7.46%,4.04%和22.24%的提升。基于非对称椭圆的木材应力波无损检测算法可以提高断层图像的精度,准确反映缺陷情况,对于木材缺陷的无损检测具有较好的参考作用。

Defects such as voids and decay in wood affect the mechanical properties of wood products to a great extent.In order to realize the non-destructive testing of wood internal defects accurately and improve the wood utilization rate,a wood stress wave nondestructive testing algorithm based on asymmetric ellipse was proposed.In order to verify the effectiveness of the algorithm,a circular defect model and a square defect model with three different positions and sizes were used for imaging,and then three log samples(Toona sinensis and camphor)with three different defects(artificial defects and natural defects)were selected as experimental materials,and the lab-made stress wave detection equipment including sensor,amplifier and data acquisition card was used to obtain the waveform data in the wood section.Firstly,the velocity value was calculated and modified according to the collected waveform data,and the imaging area was meshed at the same time,then the ray was segmented according to the intersection in the imaging area,the velocity values of the ray intersection point and each segment after the segmentation were calculated,and the velocity values of the line segment and the intersection point were modified.Then the control coefficient of the semi-ellipse on both sides of the ray was calculated according to the maximum distance from the defect point to the ray,and the line segment of the grid element in the ellipse was judged.Finally,the sectional images were generated according to the velocity values of the grid elements.The numerical simulation and experimental results showed that the stress wave tomography algorithm based on asymmetric ellipse can accurately detect the defects of log samples,and the reconstructed tomography results showed that,compared with the basic ellipse interpolation method,the proposed algorithm can show the size and location of defects more clearly.The accuracy,precision and recall have been improved by 7.46%,4.04%and 22.24%,respectively.The wood stress wave nondestructive testing algorithm based on asymmetric ellipse can improve the accuracy of sectional images and reflect the location and size of defects more accurately,so this algorithm is an improved method for wood stress wave nondestructive testing.It can be a good reference for the non-destructive testing of wood defects.