Holographic inspection of laminated plates containing two fully-overlapping identical debonds

Debonds in laminated plates, particularly those made of glassfiber-reinforced plastics, can be readily detected using double-exposure holography when an incremental vacuum pressure is applied between exposures. With the aid of a model developed in this paper, a method is presented for inspecting a laminated plate containing flaws in the form of two identical circular debonds which are fully overlapped. Two holograms are taken, one on each side of the plate; the anomalous fringe patterns enable not only the detection of the presence of fully-overlapping debonds, but also an estimation of their size and depths. The technique can be applied during the shop testing, i.e., for the detection of defects occurring during the manufacturing of composite laminates, because both sides of the laminate must be inspected. This capability contributes further to realizing the potential of holography in nondestructive testing and evaluation of components.     

Meeting the challenges related to material issues in chemical industries

Reliable performance and profitability are two important requirements for any chemical industry. In order to achieve high level of reliability and excellent performance, several issues related to design, materials selection, fabrication, quality assurance, transport, storage, inputs from condition monitoring, failure analysis etc. have to be adequately addressed and implemented. Technology related to nondestructive testing and monitoring of the plant is also essential for precise identification of defect sites and to take appropriate remedial decision regarding repair, replacement or modification of process conditions. The interdisciplinary holistic approach enhances the life of critical engineering components in chemical plants. Further, understanding the failure modes of the components through the analysis of failed components throws light on the choice of appropriate preventive measures to be taken well in advance, to have a control over the overall health of the plant. The failure analysis also leads to better design modification and condition monitoring methodologies, for the next generation components and plants. At the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, a unique combination of the expertise in design, materials selection, fabrication, NDT development, condition monitoring, life prediction and failure analysis exists to obtain desired results for achieving high levels of reliability and performance assessment of critical engineering components in chemical industries. Case studies related to design, materials selection and fabrication aspects of critical components in nuclear fuel reprocessing plants, NDT development and condition monitoring of various components of nuclear power plants, and important failure investigations on critical engineering components in chemical and allied industries are discussed in this paper. Future directions are identified and planned approaches are briefly described     

A novel X-ray technique for inspection of steel pipes

The corrosion-induced material loss in crude oil carrying steel pipelines was originally studied by making use of the backscatter X-ray technique. The steel thickness can be determined by studying the density profile of the backscatter intensity vs. the depth location of a voxel. There are, however, some practical limitations to the above method, and a new method for evaluating steel thickness, namely, the transcatter technique is described. This technique uses the intensity of the beam which is transmitted by the pipe wall and subsequently scattered by the hydrocarbon inside the pipeline. The thickness is evaluated using three techniques, namely, the sequential technique, the dual angle technique, and the reference technique. Of the three techniques, the sequential technique has been studied in detail. The mathematical equations and experimental results related to the transcatter technique show that the thickness can be measured with an accuracy of better than 10% for a nominal steel thickness of 8 mm with a measurement time of several minutes.     

A novel method of processing pulse echo data in adhesive bond inspection

A novel method for evaluating nondestructively the quality of bonded assemblies is presented. It is shown that a combination of HOC (higher order crossing) analysis and another frequency domain parameter can distinguish between different surface treatments, as well as predicting cohesive or adhesive failure of bonds. It is believed that this method will open the way to predict the durability of bonded structures at the manufacturing or inservice stages.     

Shearography: A novel and practical approach for nondestructive inspection

This paper presents an optical technique referred to as shearography for nondestructive inspection. Shearography is an interferometric method which allows full-field observation of surface displacement derivatives. It reveals flaws in materials by looking for flaw-induced strain anomalies. Both surface and interior flaws can be detected. Because of its numerous advantages, shearography is more practical than holography. The simplicity and the alleviation of vibration isolation requirement make shearography a practical approach for nondestructive testing in field/plant environments.     

机电装备的失效分析、安全评定和无损检测

从认识论的高度阐明失效、失效分析和预防在人类科学技术发展中的属性、地位和作用。失效分析和预防具有多学科交叉综合的属性,它的发展依赖于应用学科、应用基础学科、甚至于基础学科的发展,但又对它们的发展起重要反转作用和影响。因此,它是科学技术第一生产力中最积极、最活跃的因素之一。从方法论的角度进一步叙述了失效分析与失效预防之间的辩证关系。失效分析是一种事后的逆向思维过程,它是从异常现象（结果）到因素（模式、原因和机理）的反向科技探索,而失效预防（安全评定）则是从因素到结果的一种事先的正向思维过程。逆向思维与正向思维协同并用,事后分析转化为事先分析,构成科学技术研究活动和科技发展的全过程,两者不可偏废。综述了失效分析和失效预防（安全评定）的主要内容、技术、方法和它们的发展趋势,并提出它们与无损检测技术之间的关系。     

在役绝缘子失效特征与无损检测

在电网各个环境中运行的不同种类绝缘子，长期服役后都会不同程度地产生失效，导致故障事故的发生，对电网可靠性带来了极大地潜在威胁，研究绝缘子的失效特征对于指导绝缘子安全检测具有十分重要的意义。本文基于在役绝缘子种类繁多和结构复杂的特点，分析绝缘子失效特征和损伤部位，提出了利用无损检测技术检测绝缘子损伤缺陷的方法。     

计算机X线摄影(CR)后处理技术在颈椎常规摄影中的应用

目的:评价计算机X线摄影(CR)后处理技术在颈椎常规摄影中的应用价值。方法:随机选取50例颈椎正、侧位CR片,并经密度仪测得标准测试点的密度值,观察其是否分布在胶片特性曲线的直线部分。结果:所测得的标准测试点的密度值均投影在胶片特性曲线的直线部分。结论:经过CR系统处理的颈椎正、侧位片完全符合诊断要求,并可满足不同的临床诊断需求。     

超声检测信号的特征分析

目的 在无损检测中提高疵病实时检测和识别的正确性和可靠性。方法 提出了利用检测信号的波形特征分析进行疵病实时检测和识别的方法。结果 通过一应用实例,表明该方法对于提高检测可靠性是行之有效的。结论 用波形特征分析的方法可实现疵病的实时检测和提高检测精度。     

国外工业射线胶片概况

本文扼要介绍了国外几家主要感光器材工业公司，如：爱克发、柯达和富士生产，用于无损探伤的工业射线照相胶片系列的品种、性能、规格和应用范围。     

考虑时间和温度影响的复合材料开孔层板压缩失效分析

鉴于复合材料性能的时间-温度相关性,对固化后的树脂基体(5228A)进行了动力学分析(Dynamic Mechanical Analysis,DMA),得到了试验窗口中不同温度下的储能模量曲线片段,利用封闭平移(Closed Form Shifting,CFS)方法对其进行扩展,建立了主曲线并得到了曲线片段对应的平移因子。根据加速试验方法(Accelerated Testing Methodology,ATM),分别以两种铺层的准各向同性开孔层板(CCF300/5228A)为研究对象,建立了匀应变率(Constant Strain Rate,CSR)压缩强度主曲线。借助微距拍摄和超声波C扫描,对其渐进损伤过程和不同温度下的破坏形貌进行了观测。结果表明:即使温度低于玻璃态转变温度,树脂基体动态力学性能也会随时间的增加而降低;单层较厚的开孔层板压缩强度对时间和温度更加敏感,而单层较薄的开孔层板则具有更好的损伤容限性能;温度升高、加载速率降低时,开孔层板压缩最终破坏主导因素从分层损伤趋于纤维屈曲。     

Deformation and failure of blast-loaded metallic sandwich panels—Experimental investigations

Metallic sandwich panels with a cellular core such as honeycomb have the capability of dissipating considerable energy by large plastic deformation under impact/blast loading. To investigate the structural response of sandwich panels loaded by blasts, a large number of experiments have been conducted, and the experimental results are reported and discussed in this paper. Quantitative results were obtained based on the measurement in the tests by a ballistic pendulum with corresponding sensors, and then the deformation/failure modes of specimen were classified and analysed systematically. The experimental programme was designed to investigate the effects on the structural response of face-sheet and core configurations, i.e. face-sheet thickness, cell size and foil thickness of the honeycomb, and mass of charge. The experimental data were then compared with the predicted data from finite element simulations, and the results show a good agreement between the experimental and computational studies.     

Correlating bonded joint deformation with failure using a free surface strain field mining methodology

In this work we present a strain field mining methodology where the intensities and spatial distributions of strains in double lap strap epoxy (EA 9394) bonded joints are measured, analysed and correlated with bond strength. While the global behaviour of the bonded joints was linear elastic at room temperature, discrete regions of elevated (relative to the full field average) shear strains were observed. The size, spatial distribution and other features of these strain ‘hot spots’ were described with a metric called the homogeneity index. This index captures the uniformity of the strain field with respect to regions of positive and negative strain at a specific stress level. The linearity of the progression of the homogeneity index and its magnitude was correlated with a joint's fracture strength and failure mode. The index was a robust predictor of double‐lap strap bonded joint performance between 30% and 90% of a specimen's strength and can be used to improve joint design, manufacturing, quality assurance, maintenance and inspection.     

改进射线数字成像系统的图像质量

目的 改善射线数字成像系统的图像质量。方法 在射线数字成像系统中,存在许多影响图像质量的因素,这些因素来源于系统的各个成像环节,如CCD相机、成像屏、X射线源、被测物体、控制电路、射线散射等,它们对成像质量造成严重影响。作者针对DR成像系统降低图像质量的因素作了分析,并通过校正和图像处理的方法使其得到了抑制。结果 提出了改善射线数字成像系统图像质量的方法。结论 通过实际应用,表明所提出的方法是有效的。     

2-D biaxial testing and failure predictions of IM7/977-2 carbon/epoxy quasi-isotropic laminates

In previous research, a series of a thickness-tapered cruciform specimen configurations have been used to determine the biaxial (two-dimensional, in-plane) and triaxial (three-dimensional) strength of several carbon/epoxy and glass/vinyl-ester laminate configurations. Refinements to the cruciform geometry have been shown capable of producing acceptable results for cross-ply laminate configurations. However, the presence of a biaxial strengthening effect in quasi-isotropic, [(0_N/90_N/ ± 45_N)_M]_S, laminates have brought into question whether the cruciform geometry could be used to successfully generate two-dimensional strength envelopes. In the present study, a two-dimensional failure envelope for a IM7/977-2 carbon/epoxy laminate was developed at the Air Force Research Laboratory, Space Vehicles Directorate, using a triaxial test facility. The electromechanical test frame is capable of generating any combination of tensile or compressive stresses in σ₁:σ₂:σ₃ stress space and can evaluate the uniaxial (one-dimensional, in-plane), biaxial or triaxial response of composite materials. Results are promising as they indicated that failure in the majority of the IM7/977-2 specimens occurred in the gage section. This leads the authors to believe that maximum biaxial stress states were correctly generated within the test specimen. In addition to the experimental data presented, multi-continuum theory (MCT) was used to predict and analyze the onset of damage and ultimate failure of a biaxially loaded IM7/977-2 laminate. Multi-continuum theory is a micromechanics based theory and associated numerical algorithm for extracting, virtually without a time penalty, the stress and strain fields for a composites’ constituents during a routine structural finite element analysis. Damage in a composite material typically begins at the constituent level and may, in fact, be limited to only one constituent in some situations. An accurate prediction of constituent failure at sampling points throughout the laminate provides a genesis for progressively analyzing damage propagation in a composite specimen allowing identification of intermediate damage modes. A constituent-based, quadratic, stress-interactive, failure criterion was used to take advantage of the micro-scale information provided by MCT. There was reasonable correlation between analytically and experimentally developed IM7/977-2 2D failure envelope which leads us to believe that the thickness-tapered cruciform specimen can be used to determine the biaxial strength of quasi-isotropic laminates.     

Optimal inspection and preventive maintenance of units with revealed and unrevealed failures

The maintenance of a single unit system that alternates operating and idle periods is studied. In the former case the failures are detected as soon as they occur and only by special testing or inspection in the latter. This paper aims at minimizing the cost per unit of time for an infinite time span by selection of a unique interval, for both inspection and maintenance. A special feature of this model is the possibility of a less than perfect testing as the inspections may fail and give a wrong result. It is further assumed that both preventive and corrective maintenance make the unit as good as new with the durations of inspections and maintenances being negligible. The existence of an optimum interval and how it depends on both the cost parameters and the reliability characteristics of the unit is discussed.     

Treatment of false calls in evaluating nondestructive inspection proficiency

A test designed to evaluate nondestructive flaw detection proficiency by ultrasonic and eddy current methods has been conducted. Test data for each participant are reduced to contingency table format, and analysis of these tables via traditional measures of association is used to rank individual performances. The presence of false calls in an inspection record introduces a random inflation in flaw detection results. Measures are required which compensate for that fact. Proficiency rankings based on two such measures, Somers'd coefficient and the mean square contingency coefficient, show reasonable consistency with intuition-based rankings by experienced observers. Finally, a weighted generalization of Somers'sd is suggested, although optimal selection of weights remains an open problem.     

超声检测中的兰姆波层析成像

兰姆波作为超声导波，可以对薄板类结构实现大范围快速的检测。然而，从兰姆波数据中提取定量信息时对检测人员的技术素质提出了很高的要求。文章用兰姆波层析成像仿真实现了铝板中不同缺陷的重建图像。结果表明：采用滤波反投影算法得到的层析图像给出了关于缺陷位置和类型的信息，从而使技术人员可以方便地识别出材料中的缺陷。     

浅谈某产品用50SiMnVB钢横向断裂原因分析

通过对某军工产品用50SiMnVB铜在加热过程中,横向断裂疵病产生的原因机理进行了分析与验证,准确地找到了该问题产生的原因,并在后续生产中增加无损检测技术,可有效地剔除该类缺陷,保证产品质量。