锁相热成像无损检测方法的基础实验研究

红外热成像技术是一种新型的无损检测技术,能够成功应用于各种类型材料缺陷检测,但随着无损检测要求的不断提高,特别是对于新型航空航天材料的缺陷检测,如微小尺度缺陷和疲劳损伤等,因此需要加强各种无损检测技术在检测微弱信号方面的能力.锁相热成像技术是一种高灵敏度的热成像技术,在此主要探讨了锁相热成像技术的原理、实现方法以及实验中注意的问题.     

Research on the quantitative analysis of subsurface defects for non-destructive testing by lock-in thermography

This paper describes the quantitative analysis of the boundary, location and depth of subsurface defects by lock-in thermography. The phase difference between defective areas and non-defective areas illustrates the qualitative analysis of the boundary and the location of the subsurface defect. In order to accurately estimate the size, location and depth of the defects, the phase is normalised, the heat transfer partial differential equation (PDE) model is used to filter the noise of normalised phase image and the differential normalised phase profile is employed to determine the boundary and location of the defect. The profile of the differential normalised phase distribution has maximum, minimum and zero points that help to quantitatively determine the boundary and location of the subsurface defect. An artificial neural network (ANN) is proposed to determine the depth of the subsurface defect. Experimental results for a steel plate, a carbon fibre-reinforced polymer (CFRP) sheet-foam sandwich, and honeycomb structure composites with artificial subsurface defects show good agreement with the actual values.     

Quantitative determination of a subsurface defect of reference specimen by lock-in infrared thermography

This paper describes the quantitative determination of the sizes and locations of subsurface defects using lock-in infrared thermography. A phase (or temperature) difference between the defect area and the healthy area indicates the qualitative location and size of the defect. To accurately estimate these parameters, the shearing-phase technique has been employed, where the inspected image is shifted by a certain number of pixels to obtain a shifted image while subtraction of one image from the other gives the shearing-phase distribution. The shearing-phase distribution has maximum, minimum, and zero points that help determine quantitatively the size and location of the subsurface defect. Experimental results for a steel plate with artificial subsurface defects show good agreement with actual values.     

超声检测图像分辨率的维纳滤波去卷积研究

为了研究改善超声检测横向分别率以及缺陷检测精度的方法，对聚焦换能器和非聚焦换能器的超声检测成像结果进行了比较，结果表明聚焦换能器在焦点位置具有较高的横向分辨率。为了提高平面非聚焦换能器的成像分辨率，根据平面换能器的平底孔散射模型，计算出换能器的点扩展函数，并利用维纳(Wiener)滤波进行去卷积研究。结果表明，只要选取适当的滤波参数，去卷积处理能有效改善成像检测的横向分辨率。     

Defect characterization in infrared non-destructive testing with learning machines

It is well known that thermal contrast-based quantification methods are strongly affected by the non-uniform heating, the sample shape and the chosen sound area. In this work we propose a reference-free thermal contrast by using the thermal quadrupoles theory and evaluate the limits of defect detection in composite samples by using dynamic principal components analysis (DPCA) and k-nearest neighbor algorithm. Additionally, we propose and validate the radial basis functions (RBF) networks and support vector machines (SVM) for the detection and quantification of defect depth in composite material samples affected by non-uniform heating and with complex shapes.     

Infrared thermographic investigation of railway track ballast

A theoretical study was undertaken to determine if infrared thermography is an appropriate method to identify the condition of railway track ballast. Within this study the optimal conditions for an infrared survey were established.A laboratory experiment was undertaken to identify clean and spent ballast using an infrared camera. By cooling the ballast and watching it heat up to room temperature over time a difference in the rate of heat transfer between the two types of ballast was observed.A field trial of the infrared camera was undertaken over an operational track as part of the work within a normal track maintenance possession. The field trial identified an area of dirty ballast within a section of clean ballast and the findings were also confirmed by using ground penetrating radar and a trial pit. The laboratory and fieldwork are described in detail and sample infrared images as well as visual images of the same area are given — along with calculated values for the emissivity.The findings proved that it is possible to calibrate an infrared camera so that it can determine the condition of the ballast. Also from the success of the field trial it was shown that infrared thermography is a suitable method of identifying the condition of ballast on an operational track     

Variable emissivity infrared electrochromic device based on polyaniline conducting polymer

The use of polyaniline (PANI) as active layer in the electrochromic (EC) devices operating in the mid-infrared (mid-IR) ranges (3–5 μm, 8–12 μm) was investigated. The optical properties of the device were characterized by spectrophotometry in the wavelength range from 0.4 μm to 15 μm. Results show that upon reversible doping and undoping, the devices yield an average emissivity dynamic range of ca. 0.24 in the 8–12 μm region. The lowest emissivity of the devices in this region can be adjusted from 0.4 to 0.68 according to the preparation conditions. The average reflectance dynamic range is 18% in the 3–5 μm and 34% in the 8–12 μm regions.     

激光、微波和红外热成像检测技术在中国——庆祝中国机械工程学会无损检测分会成立三十周年

介绍学会成立30年来激光、微波和红外等无损检测新方法的发展进程。着重介绍了激光全息干涉、电子散斑干涉、微波探地雷达、红外热成像和热波成像等新技术近年来在国内的研究应用情况。对新技术的应用前景进行了展望。     

A novel method for solidification rate measurement of weld pool surface

设计了低碳钢激光点焊工艺, 显示了小尺寸液态熔池均匀回缩的凝固过程, 以此作为平台, 进行了 焊接熔池表面温度与凝固速率测量方法的研究. 采用红外测温仪从熔池表面直接获取熔池凝固过程温度曲 线; 利用金属固相与液相表面发射率的差异从熔池凝固温度曲线中提取能准确反映液--固转变的特征信息, 以此推算了熔池表面的凝固速率; 并通过进一步的工艺实验, 验证了凝固速率与焊点背面直径之间的良好 对应关系. 该方法亦适用于其它热加工过程金属凝固速率的测量与分析.     

锁相红外检测中相位检测方法

介绍了调制加热阶段的一维热波导热方程。为了减少图像序列采集数量,针对相位法红外热成像检测提出了获取热波信号相位信息的方法,即相关检测算法。利用噪声信号与参考信号不相关的原理,有效地提取微弱被测信号。通过对同一组图像序列的处理,将其与4点平均算法比较,证实该算法采集信息少,具有较高检测精度。同时也验证了相位信息对样品表面非均匀性不敏感,使得相位法红外热像技术在无损检测中有广泛应用。     

An artificial neural network interpreter for transient thermography image data

It is shown that an artificial neural network can be used as an expert system to obtain details of defect size and depth from transient thermography data. The neural network was trained on a comprehensive range of finite difference modelling results and is shown to provide a simple means of interpreting practical experimental measurements. An assessment is given of the sensitivity of the method to likely uncertainties in experimental measurement.     

超声热成像检测应用实例

简要介绍了超声热成像检测方法的基本原理和特点。该方法利用激励超声波在缺陷处产生机械振动,使缺陷处因热弹效应和滞后效应等原因释放出热量,用红外热像仪对此局部发热过程进行监测,最后对图像进行分析。由于激励信号的频率调制和特殊的图像处理方法,超声热成像检测法优势独特。对某航空碳纤维增强复合材料的检测表明,该方法能有效检测出裂纹、分层或破裂等缺陷,应用前景广阔。