Novel quantitative non-destructive testing method for composite structures

A novel QNDT (quantitative non-destructive testing) method is developed that is combined with a phase-shifting shearing speckle and thermograph, and, it aims at the detection of faults such as cracks, voids, delamination and weak areas. The technique is immune to ambient noise and is suitable for measuring the in situ environment. Some different depth defects that would produce deformation differing from other positions could be found with shearing speckle when the sample is loaded, however, a thermograph based on the thermal resistance effect of a defect can detect only those varisized defects embedded deeply in the composite structure by measuring the surface temperature distribution. The resolution is examined for artificial delaminated defects in carbon-fiber composite structures using a phase-shifting shearing speckle and thermograph. The experimental results have demonstrated that the technique is effective for revealing defects in composite structures.     

Active infrared thermographic inspection technique for elevated concrete structures using remote heating system

Conventionally, the inspection of elevated concrete structures requires the use of scaffolding or an aerial truck. In this study, elevated railway structures constructed of reinforced concrete were inspected using active infrared thermography. The inspection area corresponded to half of the middle slab covering an area of 16.8 m²; one inspection was carried out that took about 15 min. A remote heating system consisting of a 6-kW air-cooled xenon arc lamp and a scanner system was developed to detect hidden defects in elevated concrete structures without the need for an aerial truck or scaffolding. The generation of a thermal image and irradiation are carried out simultaneously by the beam scanning. High-contrast infrared thermal images can be obtained by the simple image processing procedure that is proposed.     

近高超声速高温蓝宝石窗口下中波红外成像退化分析仿真与性能测试实验

本文基于高温红外窗口热辐射红外成像探测器干扰机理,开展高温红外窗口成像分析、仿真与实验验证研究工作. 根据流体仿真计算获得的高温窗口温度及实验测得的窗口发射率、吸收率等参数,开展窗口热辐射计算;建立了光学窗口介质内部辐射传输路径和强度计算模型,并给出了窗口辐射出射模型以及相应红外成像模型;基于光学追迹方法,把窗口热辐射成像的计算问题转换成了光学计算问题;设计了一种基于高温蓝宝石红外窗口的加热实验,对红外成像仿真结果进行了检验. 通过仿真结果与窗口加热实验结果对照,将基于模型分析获取图像与实验结果图像作差,得到的平均每个像素误差值为0.45;实验发现在窗口约773 K条件下,设计的中波红外成像系统的信噪比、对比度分别降低到原来三分之一左右,而整个红外成像系统NETD值由原来的约52 mK上升到了954 mK. 本文提出的窗口热辐射分析方法可以有效估计窗口热辐射对中波红外成像的影响,设计的实验对成像系统的指标验证有较好的用途,同时对红外成像系统波段细化优选和成像参数调整,降低图像退化程度,都有着重要的指导意义. 关键词： 近高超声速 高温蓝宝石窗口 气动效应 仿真与实验     

基于小波变换的红外热波无损检测融合算法

在红外热波无损检测中获取的热像序列存在着背景噪声大、缺陷边缘模糊、对比度低等特点。为了提高由红外热像序列重构的数字图像的缺陷显示能力,以小波变换为热像处理工具,采用基于像素级和特征级的图像融合算法对热像序列进行了处理,并采用基于统计学的图像评估标准对处理效果作了定量评价。通过对铝合金试件的检测实验说明该方法可用于材料内部缺陷的红外热波无损检测。研究结果表明,此种图像融合算法可对不同深度缺陷所对应的两幅最佳热像进行有效地融合,在一幅融合图像中直观地反映出全部缺陷,并能有效地减少加热不均和背景噪声对缺陷识别的不利影响。     

空间目标抖动状态红外图像仿真建模研究北大核心CSCD

空间目标容易受到太空垃圾碰撞及干扰从而产生抖动。针对空间抖动目标红外图像的模型构建问题,对天基空间红外成像系统的主要噪声进行分析并考虑杂散光影响,基于Creator与Vega软件平台相结合,提出抖动状态下空间目标表面缺陷的红外图像的建模方法。依据空间目标基本特征分析其红外辐射特性,在Creator中对空间目标缺陷进行三维建模;根据目标以及背景红外辐射特性对三维模型进行温度场分析,将分析所得结果与Vega红外模块相结合获得红外图像模型;确定抖动图像数学模型并对仿真图像施加抖动影响,然后施加杂散光影响获得最终模拟图像。实验结果表明:该方法生成的抖动状态下空间目标红外图像与实验图像相似程度高,能为空间目标探测与态势感知提供一种有效的模拟系统。     

Defects inspection of the solder bumps using self reference technology in active thermography

With the decrease of solder bumps in dimension and pitch, defects inspection of the solder bumps become more difficult. A nondestructive detection system based on the active thermography has been developed for solder bumps inspection. However, heating non-uniformities and emissivity differences may impede the defects recognition. In this paper, we propose a method using a self reference technology based on a source distribution image (SDI) to eliminate the influence of unevenness in emissivity values and heating power distribution. Three thermograms captured right after the heat pulse are averaged to create the SDI. Then the SDI is subtracted from the original thermograms, and we get the thermal contrast images, in which eight points on the edge of each hot spot are selected as the feature points for the corresponding bump. Thermal difference between the feature points and the central point are adopted to quantify the thermal behaviors of the solder bumps, by which the missing bump is distinguished from the reference bumps. The results show that it is effective using the method to eliminate the impacts of emissivity unevenness and heating non-uniformities on defects identification in the active infrared test.     

Research on thermal wave processing of lock-in thermography based on analyzing image sequences for NDT

Lock-in thermography, an active IR thermography technique for NDT, is based on propagation and reflection of thermal waves which are launched from the surface into the inspected component by absorption of modulated radiation. In this paper, thermal wave image sequences were sampled by a Cedip JADE MWIR 550 FPA infrared camera. Thermal wave signal processing algorithms are investigated to obtain information on subsurface defects. The Fourier transform, four-point correlation, and digital lock-in correlation algorithms are applied to extract the amplitude and phase of thermal wave’s harmonic component. A novel method called the time constant method (TCM) is proposed to analyze subsurface defects by using lock-in thermography. The experimental results confirm the thermal wave signal processing algorithms’ efficiency on subsurface defect detection.     

New Ways of Detecting Cracks,Delaminations, and Other Defects in Materials and Objects via High Frame-Rate Thermal Imaging

A number of advanced nondestructive thermographic tools are described that are based on the video recording of surfaces using thermal imaging cameras in which infrared radiation is induced by shortterm heating with an electric current or a stream of hot air. The tools allow the detection of cracks, delaminations, gaps, and other types of defects both inside and outside the shell of a structure that cannot be reached for direct inspection.     

Nondestructive testing using air-borne ultrasound

Over the last two decades, more efficient transducers were developed for the generation and reception of air-borne ultrasound, thus enabling the non-contact, non-contaminating inspection of composite laminates and honeycomb structures widely used in the aerospace industry. This paper presents the fundamentals of making air-borne ultrasonic measurement, and point out special considerations unique to propagating ultrasound in air and through solids. Transducer beam profile characterization, thickness dependence and resonance effects in the transmission of air-coupled ultrasound through plates, and the detection and imaging of defects and damage in solid laminates and honeycomb sandwich will be discussed and illustrated with examples. Finally, a manual scan system developed for implementing air-borne ultrasonic imaging in the field and on aircraft will be introduced.     

Lock-in thermographic inspection of squats on rail steel head

The development of squat defects has become a major concern in numerous railway systems throughout the world. Infrared thermography is a relatively new non-destructive inspection technique used for a wide range of applications. However, it has not been used for rail squat detection. Lock-in thermography is a non-destructive inspection technique that utilizes an infrared camera to detect the thermal waves. A thermal image is produced, which displays the local thermal wave variation in phase or amplitude. In inhomogeneous materials, the amplitude and phase of the thermal wave carries information related to both the local thermal properties and the nature of the structure being inspected. By examining the infrared thermal signature of squat damage on the head of steel rails, it was possible to generate a relationship matching squat depth to thermal image phase angle, using appropriate experimental/numerical calibration. The results showed that with the additional data sets obtained from further experimental tests, the clarity of this relationship will be greatly improved to a level whereby infrared thermal contours can be directly translated into the precise subsurface behaviour of a squat.     

Infrared thermography-based visualization of droplet transport in liquid sprays

An infrared thermography-based technique for the characterization and visualization of liquid sprays was developed. The technique was tested on two atomizers: a high-speed rotary bell atomizer and a high volume low pressure air-assisted atomizer. The technique uses an infrared thermography-based measurement in which a uniformly heated background acts as a thermal radiation source, and an infrared camera as the receiver. The infrared energy emitted by the radiation source in traveling through the spray is attenuated by the presence of the droplets inside the spray. The infrared intensity is captured by the receiver showing the attenuation in the image as a result of the presence of the spray. The captured thermal image is used to study detailed macroscopic features of the spray flow field and the evolution of the paint droplets as they are transferred from the applicator to the target surface.     

EMIR: a photothermal tool for electromagnetic phenomena characterization

The heat-photon conversion phenomenon can be used to obtain a thermal image of an electromagnetic field. The electromagnetic field is partially absorbed by a sensitive paint or by a coating deposited on structures or on thin films. A map of the temperature increase of this absorbing medium is an image of the electric or magnetic intensity field distribution, depending on the electric and magnetic properties of the medium. A brief history of the various techniques used to obtain thermal images of electromagnetic fields is first presented. Emphasis is then put on infrared thermography which has been preferentially used in the past 20 years. An analysis of the thermal problems involved is presented. It appears that the solution to these problems is the key for the enhancement of the technique and for really quantitative work. Original solutions have been developed at ONERA, based on the combined use of optimised thin films with controlled electric conductivity, very sensitive infrared cameras, lock-in infrared thermography, and microwave interferometry. In these conditions, quantitative images of both amplitude and phase are obtained. Such an electromagnetic field imaging technique is a powerful tool which has no equivalent and which can be used for several types of applications such as: i) antenna radiation pattern characterization; ii) mode propagation characterization in waveguides; iii) study of absorption phenomena in complex materials; iv) nondestructive evaluation of dielectric structures (electromagnetic windows) or radar absorbing materials; v) knowledge of surface currents distribution on metallic structures.     

复合材料脱粘缺陷的红外热像无损检测

以固体火箭发动机中的玻璃纤维复合材料壳体/绝热层试件的脱粘缺陷为研究对象,利用脉冲闪光灯热激励方式对试件进行加热,用红外热像仪实时监测试件的表面温度场,由表面温度差异来判定试件内部缺陷,然后通过对热像图进行图像增强处理和分割以定量识别缺陷。将实验结果与超声C扫描检测结果进行的对比分析表明:红外热像无损检测方法能够快速直观地发现深度5 mm以内、直径10 mm以上的脱粘缺陷,而超声C扫描检测更适合于对特定缺陷进行准确定量检测。     

红外探测系统的激光辐照热效应仿真分析

为研究红外探测系统受激光辐照后的热效应与二次热辐射对探测器成像的影响,使用Ansys软件对红外探测器进行热辐射仿真和有限元结构仿真;采用黑体辐射定律和DO辐射计算模型模拟计算探测器内光学系统在不同激光辐照度下的温度随时间变化情况以及探测器内部温升对靶面成像的二次热辐射干扰情况;采用热弹性力学模型仿真计算探测器内部的热应力和热变形情况。结果表明:探测器受到1.06μm激光照射,矫正镜激光辐照度在50 W/cm²时,靶面受到二次热辐照度在0.6 s时达到100μW/cm²的量级,使红外探测器达到饱和;探测器受激光辐照后系统最高温度出现在矫正镜中心处,拟合得到系统最高温度与受照时间函数关系,可预测探测器升温结构破坏;最大热变形出现在矫正镜背面中心处,由外向内形成不等附加光程差,干扰探测器的成像效果;最大热应力出现在矫正镜前面中心处,得到最大热应力与激光辐照度间的线性关系曲线,为矫正镜热应力破坏提供预测参数。     

GaAs表面不同运动状态H2SO4-H2O2-H2O液滴的红外辐射特性

利用红外热像实时监测系统,研究了GaAs表面不同运动状态(包括静止状态、缓慢运动状态、快速运动状态)下H₂SO₄-H₂O₂-H₂O液滴的红外辐射特性,并对实验结果和研究价值进行分析.主要的实验结论包括：静止状态时,反应生成热在液滴内部向上对流,液滴顶部为红外辐射灰度峰值,并向液滴边缘陡降,同时,生成热将沿GaAs基片向周边扩散;缓慢运动时,液滴后存在类似于“彗尾”的热残留现象,表现为温度降低、灰度峰值与液滴运动同向的“双重运动特性”,灰度峰值位移曲线与液滴实际位移存在差异,温度最高点有可能位于“慧尾”中;快速运动时,液滴未与GaAs反应便脱离基片,表现为“液膜轨迹”现象,辐射灰度从液膜边缘到液膜中心为半椭圆面的平缓过渡,并分析了轨迹中心灰度值的分布与变化特性.液滴运动热行为红外监测方法的提出,在推动液滴自身研究的同时,也将进一步推动红外技术与材料科学、化学科学等交叉学科的融合. 关键词： 红外热像 实时监测 液滴 砷化镓     

Establishment and experimental verification of infrared BRDF model in rough surface

Because of the thermal radiation from materials, the influence of spontaneous radiation on infrared-material—BRDF could not be neglected. In this paper, the spatial distribution characteristics of the material spontaneous radiation energy are analyzed. Then a full infrared BRDF semi-physical model in rough surface is developed by incorporating the characteristic parameters of the material spontaneous radiation into the five-parameter BRDF model. Finally, the model is verified using experimental data. Experimental results demonstrate that the proposed model error is less than 1%. The semi-physical model is more suitable for describing real physical process, and can be applied to analyze stray radiation of infrared optical system and target infrared characteristics.     

气动热环境下共形整流罩热辐射特性研究

高温整流罩产生强烈的红外辐射,在探测器接收面上形成背景噪声,严重影响成像质量。为了评估气动热环境下高速飞行器共形整流罩热辐射对探测器性能的影响,建立了气动热环境下整流罩热流固耦合计算模型、整流罩热辐射发射以及传输模型,计算了整流罩非均匀温度场、形变场、应力以及应变场,仿真得到了共形整流罩热辐射对高速飞行器光学系统成像质量的影响。研究结果表明:随着时间的不断增长,探测器接收面的最大辐照度也逐渐增大。在第10 s时,0°攻角下共形整流罩热干扰辐照度最小值为0.094 W/m2,最大值为0.108 W/m2。和相同工况下的共形整流罩相比,球形整流罩10 s时的最大辐照度分别是椭球面和抛物面形整流罩最大辐照度的近12倍和7倍,即共形整流罩产生的干扰对探测系统的影响较小,不会对探测器的探测性能产生致命性的影响。     

Non-destructive inspection of drilled holes in reinforced honeycomb sandwich panels using active thermography

The aerospace industry is in constant need of ever-more efficient inspection methods for quality control. Product inspection is also essential to maintain the safe operation of aircraft components designed to perform for decades. This paper proposes a method for non-destructive inspection of drilled holes in reinforced honeycomb sandwich panels. Honeycomb sandwich panels are extensively employed in the aerospace industry due to their high strength and stiffness to weight ratios. In order to attach additional structures to them, panels are reinforced by filling honeycomb cells and drilling holes into the reinforced areas. The proposed procedure is designed to detect the position of the holes within the reinforced area and to provide a robust measurement of the distance between each hole and the boundary of the reinforced area. The result is a fast, safe and clean inspection method for drilled holes in reinforced honeycomb sandwich panels that can be used to robustly assess a possible displacement of the hole from the center of the reinforced area, which could have serious consequences. The proposed method is based on active infrared thermography, and uses state of the art methods for infrared image processing, including signal-to-nose ratio enhancement, hole detection and segmentation. Tests and comparison with X-ray inspections indicate that the proposed system meets production needs.     

零视距地物长波红外特征场景仿真研究

为仿真地物长波红外场景图像,根据地表温度随时间变化的规律,并结合气象状况、背景材质、热特性参量、热状态等参数,在对太阳辐射、大气长波辐射、大气温度和地表热传导等影响地表温度变化的因素进行分析的基础上,建立了基于热平衡理论和热传导过程的方程。解算出多种常见地表一日之中的温度变化情况,并将其应用于由相同景物可见光纹理图像反演出的相应红外纹理图像中。在考虑景物表面自身发射、反射的辐射计算模型的前提下,生成了具有相似红外纹理细节的地表红外场景。结果表明,该方法可生成接近真实感的红外场景,有效地模拟仿真地物的长波红外特征。     

辐射背景对岩石受力热红外光谱变化影响的实验研究

研究表明,岩石在加载过程中表面的红外辐射随应力发展而变化,而辐射信息的有效提取与辐射背景存在密切关系。通过理论分析不同实验环境对岩石受力热红外光谱变化影响,开展了花岗岩在室内外环境下的受力热红外光谱观测实验,分析了不同辐射背景下岩石红外辐射与应力的相关性以及由应力引发的辐射变化信息的强弱差异,并对两种环境下岩石应力热红外探测的优势波段进行了对比分析。结果表明,辐射背景对岩石受力热红外光谱探测结果有重要影响,室外环境因背景辐射较弱,相同应力作用下的红外辐射变化更加显著,与应力之间的相关程度更高,优势波段区间更宽,更加有利于岩石应力的热红外探测。8.0~11.8 μm波段是利用热红外遥感监测地表花岗岩应力变化的优势波段。