红外热像法快速确定45#钢的疲劳性能

红外热像法作为一种无损、实时及非接触的测试技术,在疲劳研究领域得到广泛的应用.该方法克服了传统试验方法周期长、所需试验试件和费用多的困难.本文利用红外热像仪测量了疲劳试验中45#钢试件表面温升变化,根据红外疲劳极限快测法得到疲劳极限,并由累积塑性功和塑性温升之间的相关假设,推导出了试件疲劳寿命的计算公式.试验结果表明,红外热像法可以快速、准确地确定材料的疲劳极限和S-N曲线.     

疲劳热像法研究综述

能量方法是疲劳研究的重要方法,新兴的红外热像技术则是实现这一方法的重要手段.红外热像法作为一种无损、实时及非接触的测试技术,已被广泛地应用于疲劳研究中. 近年来,提出了一些用于快速确定材料及构件疲劳极限的热像法,并得到了很好地开发与推广.文中介绍了疲劳热像法的兴起、发展与深入研究,讨论了该领域出现的主要问题及当前的研究热点,并展望了疲劳热像法的研究前景.      

利用红外热像技术快速确定材料疲劳极限

基于能量理论，阐述了利用红外热像方法确定材料疲劳极限的原理，并利用红外热 像仪对具有矩形截面的钢试件进行了疲劳试验，通过记录疲劳试验过程中试件表面的温度变 化，经处理后得到了该种材料的疲劳极限. 试验表明，利用红外热像技术可以快速、准确地 确定材料的疲劳极限. 同时，该方法还具有可靠、经济、便捷等优点.     

碳纤维增强混凝土中裂纹的红外热像检测方法与机理研究

本文利用碳纤维机敏混凝土的功能特性，采用红外热像无损检测方法检测机敏混凝土构件中的裂纹损伤，该方法利用机敏混凝土的导电性和电热效应，给试样通电造成其裂缝尖端区域与其它正常部位的温差，以及温差所导致的试样表面温度的非均匀分布，借助红外热像仪，通过对试样表面温度的分析对试样内部的裂纹进行无损检测，文中对温差产生的机理也进行了分析。     

封面图片说明

封面图为高分辨率热像仪所拍摄的某结构的红外热像图,从中可以清晰地看到物体经过时因热弹性效应导致的结构表面温度场的变化,进而判断出结构局部的高应力区域。疲劳热像法作为一种无损、实时、全场、非接触的测试手段,不仅可在较     

几种应变检测的光力学测试方法及其比较

应变测量技术在工程应用中有重要意义.一是它可以直接用来获得应力场,可以用来评价材料的安全性和可靠性;二是应变梯度很大的部位往往又是材料破坏的起始点,所以应变测量又可以用于进行材料的无损检测.当前几种光力学方法受到了重视,即云纹干涉法、电子剪切散斑干涉法和数字相关散斑法,对上述方法的原理、光路设计、特点作了介绍,以便这些传统方法的进一步推广,文中还特别介绍了一种作者近来在国内率先开展的微压痕应变花法.这一方法可以方便用于金属等材料上,可以较精确定量研究测试物体的应变而且对刚体位移不敏感,应用起来更加直接和方便,更有推广和应用前景.本文有利于针对研究对象的特点,选用更加合适的应变测量方法.     

基于红外热像的自由剪切湍流被动标量高阶谱分析

利用红外热像仪对高压水射流进行了连续探测.对红外热像序列表征的标量脉动场进行双谱分析,检测湍射流的相干结构、射流不同截面内相干结构的尺度关联性以及射流不同发展阶段的特征尺度.研究表明,以红外热像为样本的全局自双谱表征了射流不同波段能分量对相干的贡献;按三列对图像采样的横断面局部互双谱给出了沿流向的大涡区、小涡区、以及各向同性湍流区的频率耦合特征;按三行对图像采样的纵向局部互双谱给出了射流的轴心线区、剪切层、空气湍流区大涡层和各向同性湍流层等各纵向断面的相干特征;通过红外热像序列的双谱分析,由流场相干结构的尺度关联性,得到了射流诱导的空气湍流场在不同发展阶段的特征尺度.     

SUS304钢表面粗糙度对红外图像的影响

为提高红外热像仪图像及测温精度,根据红外热像仪的测温原理和红外辐射原理,通过使用红外热像仪、CCD相机以及激光表面形状测量显微镜,研究了SUS304钢在单轴拉伸塑性变形过程中表面粗糙度与目标发射率的关系;并用热电偶和红外热像仪对塑性变形过程中的温度分布进行了测量。研究结果表明,目标发射率随表面粗糙度成比例增大,造成红外热像仪测定的塑性变形区域比实际变形区域大;通过预先设定材料的表面粗糙度,以提高有效目标发射率,能得到较好的红外图像和测温精度。     

基于应力波传播机理的混凝土无损检测研究综述

混凝土结构在基础设施中应用广泛,但环境与荷载导致材料和结构的老化损伤问题,势必影响材料性能及耐久性和结构完整性及安全性．构建有效的混凝土材料性能评估和结构损伤识别体系是当前研究热点．现有研究因对应力波传播机理不深入理解、损伤定位定量模型理想化、损伤形式简化等问题仍存在局限性．因此,开发普适全面、稳定可靠的无损检测系统,对在建或既有混凝土结构服役状况进行长期、实时跟踪,具有重要学术意义和工程应用价值．本文结合混凝土无损检测领域的国内外研究现状及进展,从智能压电材料振动机理研究、混凝土无损检测方法发展、基于应力波的无损检测研究进展这三个逻辑层面,即按照研究手段到研究方法再到具体研究方案的顺序,循序渐进地对混凝土材料性能评估和结构损伤识别的研究进行了成果总结和方法提炼;基于此进一步概述了该领域所存在的瓶颈问题、研究重难点,最后提出了针对这些局限性的混凝土无损检测研究展望．     

用超声波方法测量螺栓应力

1.引言近年来有很多资料介绍了测定作用应力和残余应力的超声方法.由于实际构件应力分布的复杂性和材料组织结构对声速测量的影响,超声波应力分析方法的实际应用受到了限制,发展比较缓慢.然而,对于像螺栓、立柱等主要承受轴向应力的构件,用超声波方法测量其应力具有很大实际意义,它具有快速、简便和无损测量的特     

纤维增强复合材料的破坏机理

纤维增强复合材料本身是一个非均匀各向异性力学结构。复合材料的研制、设计和使用都与力学密切相关。复合材料的破坏机理比金属材料复杂,不同组分的构成使其在加工中存在和使用中带来的缺陷比金属多。它的破坏机理与纤维、基体组分的性能,粘结强度,纤维铺设方向和顺序,工作条件等有关。需要采用有效的试验和分析方法,研究复合材料在不同      

Rapid evaluation of the fatigue limit in composites using infrared lock-in thermography and acoustic emission

Fatigue limit determination via the conventional Wöhler-curve method is associated with extended experimental times as it requires testing of a large number of specimens. The current paper introduces a methodology for fast, reliable and experimentally economic determination of the fatigue limit in monolithic and composite materials by means of combined usage of two nondestructive inspection methods, namely infrared (IR) lock-in thermography and acoustic emission (AE). IR thermography, as a real-time and non-contact technique, allowed the detection of heat waves generated due to thermo-mechanical coupling as well as of the energy dissipated intrinsically during dynamic loading of the material. AE, on the other hand, was employed to record the transient waves resulting from crack propagation events. Aluminum grade 1050 H16 and cross-ply SiC/BMAS ceramic matrix composites were subjected to fatigue loading at various stress levels and were monitored by an IR camera and AE sensors. The fatigue limit of the monolithic material, obtained by the lock-in infrared thermography technique and supported by acoustic emission was found to be in agreement with measurements obtained by the conventional S–N curve method. The fatigue limit of the ceramic matrix composite was validated with acoustic emission data.     

Thermo-mechanical measurement of elasto-plastic transitions during cyclic loading

The surface temperature of stainless steel SS304 low cycle fatigue specimens subjected to cyclic loading was studied using infrared thermography technique. The thermal data mapped onto the various stages of cyclic stress-strain curve shows the ability of these measurements to identify the yield points in both the compression and tension loading. Based on the results of this study, it is possible to identify the state of stress for materials such as elastic tension, plastic tension, elastic compression, plastic compression during cyclic loading using infrared thermographic data. The thermo-elastic slope and thermo-plastic slope was observed to be dependent on the prior loading cycles.     

Energy Dissipation Measurement in Improved Spatial Resolution Under Fatigue Loading

Experimental Mechanics - Recently, a technique for rapidly determining a material’s fatigue limit by measuring energy dissipation using infrared thermography has received increasing interest....     

Rapid Determination of Fretting Fatigue Limit by Infrared Thermography

This paper demonstrates the feasibility of infrared thermography to determine the so-called fretting fatigue limit. Fretting fatigue tests are performed on aluminum and steel specimens. The coupled fatigue and tangential loads are sequentially increased (block loading) whilst the normal load is kept constant for all blocks. The temperature data is processed and analyzed using a Fast Fourier Transform (FFT) algorithm implemented in the commercial software Matlab. It is demonstrated that the second harmonic of the temperature signal can be linked to the specific loading block below which no or negligible damage is generated in the specimen. The stress amplitude of this block is considered to be a best estimate of the fretting fatigue limit. A constant amplitude fretting fatigue test with this stress amplitude confirmed that the specimen remains intact at 10⁷ cycles.     

Deformation and dissipated energies for high cycle fatigue of 2024-T3 aluminium alloy

During the high cycle fatigue of aluminium alloys, an energy dissipation occurs. This dissipation is hard to be estimated because of the high diffusivity of such alloys and the importance of the thermoelasticity effects in comparison with others standard metallic materials (e.g., steels). Nevertheless the study of the energy balance gives valuable information about the nature of deformation mechanisms facilitating the construction of constitutive models associated with the microplasticity and damage of the aluminium alloy. In this work, the different energies involved in the energy balance were deduced from two complementary imaging techniques. The dissipation and thermoelastic sources were derived from an infrared thermography system, while the deformation energy was estimated from a digital image correlation system. Three tests with various loading blocks were carried out and a comparison between deformation and dissipation energies was systematically performed.     

An Analytical Model for Defect Depth Estimation Using Pulsed Thermography

The use of pulsed thermography as a non-destructive evaluation tool for damage monitoring of composite materials has dramatically increased in the past decade. Typically, optical flashes are used as external heating sources, which may cause poor defect definition especially for thicker materials or multiple delaminations. SMArt thermography is a new alternative to standard pulsed thermography as it overcomes the limitations on the use of external thermal sources. Such a novel technology enables a built-in, fast and in-depth assessment of both surface and internal material defects by embedding shape memory alloy wires in traditional carbon fibre reinforced composite laminates. However, a theoretical model of thermal wave propagation for SMArt thermography, especially in the presence of internal structural defects, is needed to better interpret the observations/data measured during the experiments. The objective of this paper was to develop an analytical model for SMArt thermography to predict the depth of flaws/damage within composite materials based on experimental data. This model can also be used to predict the temperature contrast on the surface of the laminate, accounting for defect depth, size and opening, thermal properties of material and defect filler, thickness of the component, and intensity of the excitation energy. The results showed that the analytical model gives good predictions compared to experimental data. This paper is one of the first pioneering work showing the use thermography as a quantitative non-destructive tool where defect size and depth could be assessed with good accuracy.