复合材料调制热像检测的数值模拟

为了给复合材料结构的调制热波成像检测提供基础理论依据和操作参数窗口,用基于有限单元法的计算机数值模拟研究了复合材料层压板分层、脱粘的调制热像检测规律。分析了相位差与调制频率及缺陷深度的关系,提出了最佳检测频率、半高频带和盲频的预测方法,验证了利用盲频来估计缺陷深度的方法,提出利用最佳检测频率来估计缺陷深度的新方法。研究结果表明：最佳调制频率和盲频近似与缺陷深度的平方成反比;最大相位差及半高频带宽随缺陷深度的增大而减小;利用盲频和最佳调制频率都可以对缺陷深度进行定量估计,在缺陷深度为1~4 mm的范围内,两种方法的估计误差分别在约9%和11%以内。     

热波检测缺陷定量识别与图像重建研究

基于红外热波方法对某型固体火箭发动机壳体含脱粘缺陷试件进行了数值仿真和实验研究。为了得到直观、精确的缺陷三维图像,采用同态滤波方法对原始图像进行降噪增强处理,利用粒子群模糊聚类算法对缺陷进行了分割,并对缺陷的大小和深度进行了定量识别,在此基础上,利用体绘制重建算法对缺陷进行三维重建。结果表明:同态滤波方法信噪比高,图像增强效果好;粒子群模糊聚类算法分割效果好,缺陷保真性高;缺陷定量识别的精度较高,三维重建效果较好,为实现缺陷的自动识别奠定了基础。     

面芯脱粘缺陷对复合材料夹芯圆柱壳屈曲特性影响分析

面芯脱粘是复合材料夹芯结构常见的损伤形式。本工作综合考虑面芯界面损伤演化、分层屈曲以及分层扩展的耦合作用,建立了深水静压载荷下复合材料夹芯圆柱壳极限承载能力预报方法。基于非线性极限载荷计算方法,通过预制初始缺陷,开展了含面芯脱粘缺陷复合材料夹芯圆柱壳屈曲特性分析,揭示了典型面芯脱粘缺陷对复合材料夹芯圆柱壳失效模式及极限承载的影响机理,得到不同面芯脱粘形式、脱粘尺寸、脱粘位置的影响规律。研究发现,随贯穿面芯脱粘长度增加,结构失效模式发生整体屈曲→混合屈曲→局部屈曲演化;外蒙皮/芯层面芯脱粘对含环向贯穿面芯脱粘复合材料夹芯圆柱壳极限承载敏感度更高,内蒙皮/芯层界面脱粘对含纵向贯穿面芯脱粘缺陷复合材料夹芯圆柱壳极限承载敏感度更高;对于多个局部圆形面芯脱粘,沿纵向分布越集中、沿环向分布越离散,结构极限承载损失率越高。研究成果对面芯脱粘缺陷复合材料夹芯圆柱壳的优化设计与可靠性评估具有很好的指导意义。     

火箭发动机装药包覆质量诊断的超声新技术

目的 研究火箭发动机装药包覆质量超声检测技术。方法 从发动机壳体外侧诊断内部推进剂包覆质量的超声技术。结果 研制了相应的检测设备并对实际物体实施了检测。结论 作者提出的板波诱发超声检测, 既可从发动机壳体外检测内壁涂敷的单层或多层包覆、绝热材料层厚度,也可识别各层界面的脱粘。     

利用黏弹性发热的复合结构脱粘的超声振动热像检测

相对于光激励的红外热像检测而言超声激励的振动热像（VT）检测是一种新兴技术,其产热机制一直为广大学者所争论。聚焦于黏弹性发热,研究了非金属材料复合结构脱粘缺陷的VT检测。以铝合金-软木复合结构脱粘的VT检测为例,通过数值模拟和实验,对缺陷的温升规律进行了分析。理论计算和实验获得了相似的结果,表明非金属材料的黏弹性发热是脱粘处产热的主导因素。这一结论为金属-非金属复合结构的脱粘及树脂基复合材料分层的VT检测提供了理论依据。     

涂层粘接质量红外热成像检测研究

随着科学技术的发展和国防需求的不断提升,军事装备的各项技术日益受到重视,对涂层粘接质量的有效监控手段研究具有重要意义。针对涂层粘接质量无法定量、定性的问题,制作不同缺陷的无损检测试块,同时调整基体与涂层的厚度进行实验,针对基体及涂层厚度对检测结果的影响,使用两种无损检测手段研究各参数对检测结果的影响。结果表明:红外热成像检测可有效检测出涂层脱粘的情况,并且涂层越厚,缺陷越容易被检出。基体越厚,缺陷越不容易被检出。     

油气管道聚乙烯层粘接缺陷的红外热成像检测方法和信号增强技术研究

为降低油气管道聚乙烯层粘接处的脱粘、粘接缝隙等面积型缺陷造成的安全事故发生概率,通过主动式红外热成像技术以及对不同深度的聚乙烯材料缺陷进行检测,采用主成分分析法和锁相技术对获取的原始红外图像进行处理,实现深度在5 mm处的粘接缺陷定量检测,该深度为油气管道聚乙烯层的标准尺寸大小。通过实验确定锁相频率与图像信噪比的关系,可为提高锁相检测效果提供依据。研究表明:激励频率在0.005～0.006 Hz范围内,锁相检测可以满足在役油气管道5 mm深的粘接缺陷检测,主成分分析法可以有效解决激励导致的温度分布不均匀带来的噪声干扰,弥补锁相检测方法的不足,提升缺陷可检测深度,该方法可以将原始温度分布图像的信噪比均值由0.637 dB提升至8.033 dB。     

金属夹心CFRP复合材料超声检测方法

新型机翼、弹翼等结构已采用金属夹心碳纤维增强（Carbon Fiber Reinfored Polymer，CFPR）复合材料结构。针对该类复合材料结构的材料组成和结构特点，分析和对比常用的超声穿透法和超声反射法能否对金属夹心CFPR复合材料内部质量进行检测，提出了先采用超声C扫穿透法确定缺陷的平面位置，然后采用高分辨率超声A扫反射法确定复合材料中分层缺陷及采用超声相位法确定复合材料与金属间的脱粘缺陷的方法。采用提出的方法检测带有预置缺陷的试样和实际产品。检测结果表明，提出的方法可准确检测试样中大小为5 mm×5 mm的预置人工分层和脱粘，且能准确检测实际产品中的缺陷。     

复合材料粘接缺陷的超声检测识别研究

超声检测无人机复合材料试件时,针对复合材料较薄、超声检测回波信号易发生混叠的问题,该文提出一种基于经验模式分解和小波包能量谱特征的脱粘缺陷识别方法。该方法首先对不同大小脱粘缺陷回波信号进行经验模式分解和小波包分解,分别提取其能量谱特征;然后,对提取的能量谱特征采用改进隶属度函数的径向基神经网络进行脱粘缺陷分类识别。实验结果表明:提取的能量特征能够有效提高不同脱粘面积缺陷的识别率。     

波在考虑热载荷和转动惯量效应的非线性大变形多层压电层合壳内的传播研究

研究了非线性大变形、层合壳的铺设形式、转动惯量及热载荷效应对波在压电层合壳中传播的影响。首先利用Hamilton最小势能变分原理推导了波在大变形压电层合壳内传播的非线性动力学平衡方程;通过求解方程特征值得到了波传播特征曲线;数值算例表明波在压电层合壳内传播与壳体大变形、转动惯量以及热载荷有关,并与线性小变形理论(Cooper-Naghdi壳体理论)进行了比较。     

A new approach for estimation of defects detection with infrared thermography

A new approach is proposed for a priori ascertaining the suitability of infrared thermography for the non-destructive evaluation purposes of materials. The novelty regards a cause/effect relationship between the thermal signature perceived by the infrared camera and a dimensionless group, which includes geometrical and thermal characteristics of the defect and host material. Such relationship, which was experimentally assessed through the evaluation of several specimens, is helpful to predict the thermal contrast associated with a type of defect embedded inside a certain material. This prediction of course is useful in decision making about the use of infrared thermography without preliminary feasibility tests and thus with economic benefits.     

A review of factors influencing defect detection in infrared thermography: Applications to coated materials

Infrared thermography is a technique that is used to nondestructively inspect parts for the presence of subsurface defects. The technique normally consists of applying heat to one surface of the part and observing the thermal response, using heat-sensing devices such as infrared cameras, as the part cools. Internal defects such as voids modify the thermal response and produce local hot or cold spots on the specimen surface. For the detection of subsurface defects, the sensitivity of the technique to different parameters such as defect depth, material properties, and heating methods has not been established due in part to the complex nature of the heat/flaw interaction. A finite element model is used here to examine the influence of these parameters on defect dectability. The model shows that the defect detectability decreases with increasing defect depth beneath the surface, and that the technique is most sensitive to the inspection of low thermal diffusivity coatings bonded to high thermal diffusivity substrates. The results also show that the heat pulse duration should be made as short as possible to maximize defect detectability.     

Semi-empirical modelling of the di-interstitial defect in silicon

Previous infrared spectroscopy studies of the defect spectrum of neutron irradiated Czochralski grown silicon (Cz-Si) revealed a band at 533 cm^?1, which disappears from the spectra at ~170 °C and exhibits a similar thermal stability with the Si-P6 Electron paramagnetic resonance (EPR) spectrum correlated with the di-interstitial defect. The proposed structural model for this defect consists of two self-interstitial atoms located symmetrically around a lattice site Si atom. The calculations reveal that the previously suggested structure of the Si-P6 defect has a vibrational frequency at about 513 cm^?1, which is close to the experimental value of 533 cm^?1. The modeling results indicate that the 533 cm^?1 infrared band originates from the same structure as that of the Si-P6 EPR spectrum.     

Modelling of the lock-in thermography process through finite element method for estimating the rail squat defects

Squats are a major problem on the world railways. The non-destructive evaluation technique is becoming increasingly attractive in the detection of near surface defects on track. Non-destructive thermal evaluation is one such method of inspection technique that can be used for the detection of near surface defects. Its sub-group of lock-in thermography is under analysis. Lock-in thermography utilizes an infrared camera to detect the thermal waves and then produces a thermal image, which displays the local thermal wave variation in phase or amplitude. There are few studies into the actual experimental representation of complex subsurface defects when concerning lock-in thermography processes. While this may be less of a concern given the purpose of numerical defect characterization to reduce the need for extensive experimental pre-tests, the necessity for (artificial) representations of a defect will inevitably be required for validation. The research outlined in this paper examines the use of 3D finite element modelling (FEM) as a potential flexible tool in simulating the lock-in thermography process for detecting squats in track. In addition, lock-in analysis proved that the correct frequency range had to be selected for the material to detect the defect. As maximum positive and negative phase angles were located at “optimum” frequencies, at certain frequencies lead to minimal phase angle difference to which the defects were not detectable (blind frequency) by using the incorrect testing. The 3D finite element method has advantage for determining the “optimum” thermal excitation frequencies compare with experimental investigation. The experimental results show that 3D FEM models can be used to defect the location and the depth of squats in the railway.     

基于机器视觉的内层包装缺陷检测光源的优化

目的 针对食品内层包装纸的缺陷特征,对机器视觉识别系统的照明光源进行优化,以提高内层包装缺陷的识别率,减少缺陷包装量。方法 基于计算机视觉识别技术,通过斑点检测不同光源下内层包装纸的常见缺陷特征,分别采用Matlab的三维绘图、相关性分析的方法,依次确定照明光源类型、形状和角度,并进行应用验证。结果 红外光源为纸铝复合内层包装纸缺陷特征识别的最适光源类型;条形光源与内层包装纸呈极显著相关,缺陷识别率达96.95%;60°的高角度照明位置与内层包装纸呈显著相关,缺陷识别率达96.96%。红外条形光源高角度照明,缺陷识别率达99%。结论 将红外条形光源高角度照明应用于纸铝复合内层包装纸的在线检测,与LED环形光源相比,其缺陷特征视觉识别率提高了0.51个百分点。     

火灾损伤混凝土结构红外热像检测与评估

根据红外检测原理，采用红外热像技术对混凝土结构火灾损伤进行实验研究，给出了火灾损伤混凝土红外热像平均温或随时间的变化曲线，建立了混凝土红外热像平均温升与其受火温度及强度损失的回归方程，并运用上述检测模型对火灾损伤的混凝土建筑物进行了检测和评估。     

Infrared absorption spectra of defects in carbon doped neutron-irradiated Si

Experimental data of infrared (IR) absorption measurements carried out on fast neutron irradiated carbon rich Cz–Si crystals were studied. Data from similar crystals, subjected prior to irradiation to thermal treatments at 1000 °C [(HT)] and thermal treatments at 1000 °C under high hydrostatic pressure [(HTHP)] of 11Kbar, were also studied. The time duration of both treatments was 5 h. After the irradiation the intensities of most of the observed bands were always stronger in the pre-treated material. Transformation of the defects upon post-irradiation isochronal anneals was investigated. Two out of six IR bands of the C_iC_s defect in the neutral charge state, at 543.5 and 635 cm⁻¹, were detected at room temperature [(RT)]. It is argued that another two bands at 918 and 1006 cm⁻¹ arising in the spectra upon annealing of the C_iC_s bands are associated with the same carbon-related structure giving rise to the Si-PT4 electron paramagnetic resonance (EPR) spectrum. A band at 533 cm⁻¹ shows the same thermal evolution with a defect giving rise to the Si-P6 EPR spectrum attributed to a multi-interstitial cluster in silicon. Differences observed in the evolution curves of the C_iC_s(Si_I) defect (987, 993 cm⁻¹) between the as-grown and the pre-treated samples are considered and discussed.     

Evaluation of gluing of CFRP onto concrete structures by infrared thermography coupled with thermal impedance

Carbon Fiber Reinforced Polymers (CFRPs) have been increasingly employed for structural strengthening, and are attached to structures using bonding adhesives. The aim of this work is to characterize defects in the bond between CFRP and concrete (after they are located by pulse infrared thermography), and assign the defects a “numerical value” (ranging from 0 for a complete air–gap to 1 for a fully glued bond). Quantitative characterization is performed by measuring the thermal impedance, and then identifying the thermophysical parameters of the system through fitting the measured impedance to a theoretical model. An inversion procedure is carried out to estimate the unknown parameters, without prior knowledge of sample properties. In particular, it is possible to estimate more accurately both the amount of glue within a defect and the thermal contact resistance.     

NDTE using pulse thermography: Numerical modeling of composite subsurface defects

The ability to predict subsurface defect information in composite materials through a non-invasive, efficient inspection protocol is fast becoming a vital research area. In numerically modeling the thermographic process associated with an infrared (IR) technique we can afford inspectors the ability to predict subsurface defect information associated with a specific material configuration. The research involved in this study looks specifically at the finite element modeling (FEM) of delaminations in a composite flat plate setup. To date the modeling of delaminations has been restricted to only two dimensional (2D) numerical representations and associated primarily with rear faced detection. The results of this research, however, clearly show that the rear faced detection technique has limitations in defect depth prediction and the 2D approximation associated with this technique ignores a paramount effect in the form of lateral thermal diffusion. It is also made clear that the representation of experimental flat plate models with flat bottomed holes, under pulse phase thermographic inspection, in simulating delaminations is misguided.     

基于Levenberg-Marquardt算法的内部缺陷导热反问题研究

在传热学的基础上,建立了三维的物理和数学模型,同时对LM(Levenberg-Marquardt)方法进行了修正.根据修正后的模型进行了导热反问题模拟研究,计算结果显示修正后的模型收敛速度更快;同时利用修正后的导热反问题的数学模型对材料内部不同性质缺陷的位置、几何形状及导热率对反问题求解的影响进行了分析,发现修正后的模型如果同时对缺陷位置、几何形状和导热率进行求解时,效果不好,但是对缺陷位置、几何形状与导热率分别进行求解时,可以获得比较好的结论;而测量误差对该方法求解结果有所影响,特别是对导热率影响较大.