Nondestructive evaluation,

Nondestmctive tests differ from methods of laboratory analysis and testing where specimens are generally sectioned, broken, damaged, or destroyed. Nondestmctive tests can be performed on materials, components, and stmctures or systems that actually are to be used. Thus, effective use of NDE requires engineering knowledge of the stmcture, the performance characteristics, and service environment, as well as the test method. More complete information on all of the topics discussed herein are available (1 6). 

An effective NDE program rehes heavily on periodic certification of the competence of its personnel (13,14). Certification programs designate levels of competence for all levels of personnel. Level I technicians are able to carry out instmctions in an NDE Level III supervisors are qualified to evaluate the needs of the test and devise a scheme that assures the desired level of quaUty or safety. 

Risk-Based Inspection. Inspection programs developed using risk analysis methods are becoming increasingly popular (15,16) (see Hazard ANALYSIS AND RISK ASSESSMENT). In this approach, the frequency and type of in-service inspection (IS I) is determined by the probabiUstic risk assessment (PRA) of the inspection results. Here, the results might be a false acceptance of a part that will fail as well as the false rejection of a part that will not fail. Whether a plant or a consumer product, false acceptance of a defective part could lead to catastrophic failure and considerable cost. Also, the false rejection of parts may lead to unjustified, and sometimes exorbitant, costs of operation (2). Risk is defined as follows  

In the simplest terms, a fault-tree for risk analysis requires the following information probabiUty of detection of a particular anomaly for an NDE system, repair or replacement decision for an item judged defective, probabiUty of failure of the anomaly, cost of failure, cost of inspection, and cost of repair. Implementation of a risk-based inspection system should lead to an overall improvement in the inspection costs as well as in the safety in operation for a plant, component, or a system. Unless the database is well estabUshed, however, costs may fluctuate considerably. 

Several nontechnical factors can significantly affect the results of a nondestmctive inspection. Many of these are classified as human factors (1,2,17). Operator experience affects the probabiUty of detection of most flaws. Typically, an inexperienced operator has more false rejects, known as Type II errors, than an experienced operator. A poor operator has few false rejects but is more likely to miss a defect in the inspection, known as a Type I error. Operator fatigue, boredom, or an unfavorable environment such as lighting, cold, or rain may further affect performance. Thus it usually is a good investment for the inspection company to assure that the operator environment is most amenable to inspection, that the equipment is suitable for the task, and that the operator is alert and well rested. 

The following sections review laboratory NDE, microscopy, and experimental stress analysis methods, which the engineer can use to obtain information about the presence and severity of flaws developed by test or parts when they are subjected to sustain mechanical loading. 

NDE methods have the advantage that they cause no harm to the specimen thus the same part can be nondestructively retested or subsequently tested destructively. However, NDE only reveals the location and severity of flaws. The experimenter must judge the importance of each particular flaw. Some times, the importance of a defect is obvious (harmless, or likely to shorten service lifetime, or likely to cause catastrophic frilure) otherwise, experimental stress analysis will quantify the severity of the flaw. The defects that are relevant to the strength of short/long fiber RPs are as follows  

Defects X-ray Neutron Gamma ray Ultrasonic Sonic Microwave Temperature differential Heat, photosensitive agent Penetrant 

Selection of the NDE method(s) depends on the specific type of material, the type of defect/flaw to be analyzed, the environment of the evaluation, the effectiveness of the evaluation method, the size and thickness of the product, and other factors. The selection should also include the economic consequences of structural failure. However, there are always increasing demands for more accurate characterization of the size and shape of defects that may require available advanced techniques and procedures, and may involve the use of more than one method. 

In some design situations, the locations of critical areas of stress are obvious. Proper mold design and choice of part geometry should ensure adequate strength in these areas, but microscopic observation of the 

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O Brien, T.K., Characterization of Delamination Onset and Growth in a Composite Laminate in Damage in Composite Materials, ASTM STP 775, p. 140-167,1982 Poursartip, A. Ashby, M. F., Beaumont P.W.R., The Fatigue Damage Mechanics of Fibrous Laminates in Proceedings of the European Workshop on Nondestructive Evaluation of Polymers and Polymer Matrix Composites, Polymer NDE (edited by Khg. Ashbee), Technomic Publishing, p. 250-260, 1984... 

Chan,R.W.Y., Hay,D.R., Matthews,J.R., MacDonald,H.A., (1988), Automated Ultrasonic System for Submarine Pressure Hull Inspection , Signal Processing and Pattern Recognition in Nondestructive Evaluation of Materials, C.H.Chen (ed). Springer-Verlag, pp. 175-187... 

Numerical Modeling of eddy current steam generator inspection Comparison with experimental data, P.O. Gros, Review of Progress in Quantitative Nondestructive Evaluation, Vol 16 A, D.O. Thompson D. Chimenti, Eds (Plenium, New York 1997) pp 257-261. 

Klaholz, S. Langenberg, K.. ]. Baum, P. Waite, F. Review of Progress in Quantitative Nondestructive Evaluation, 14 219-226, Plenum Press, New York, 1995... 

Nesvijski, E.G., Nogin, S.I. Acoustic Emission Technics for Nondestructive Evaluation of Stress of Concrete and Reinforced Concrete Structures and Materials. Third Conference on Nondestructive Evaluation of Civil Structures and Materials, Boulder, CO, 1996. Nesvijski, E. G. Failure Forecast and the Acoustic Emission Silence Effect in Concrete. ASNT s Spring Conference, Houston, TX, 1997. 

There have been numerous efforts to inspect specimens by ultrasonic reflectivity (or pulse-echo) measurements. In these inspections ultrasonic reflectivity is often used to observe changes in the acoustical impedance, and from this observation to localize defects in the specimen. However, the term defect is related to any discontinuity within the specimen and, consequently, more information is needed than only ultrasonic reflectivity to define the discontinuity as a defect. This information may be provided by three-dimensional ultrasonic reflection tomography and a priori knowledge about the specimen (e.g., the specimen fabrication process, its design, the intended purpose and the material). A more comprehensive review of defect characterization and related nondestructive evaluation (NDE) methods is provided elsewhere [1]. 

H.A. Sabbagh and R.G. Lautzenheiser. Inverse problems in electromagnetic nondestructive evaluation. International Journal of Applied Electromagnetics in Materials, 3 253-2614, 1993. 

R. Coulette, E. Lafond, F. Lepoutre, D. Balageas, M.-H. Nadal and C. Gondard, Laser ultrasonics NDE of two-layered samples . Review of Progress in Quantitative Nondestructive Evaluation, Vol 17, edsD. O. Thompson and D. E. Chimenti (Plenum, New York, 1998), to be published. 

F.A. Reed, T. Batzinger, R.W. Reed, and S. Jonsson. Porosity measurement of composites using attenuation methods. Review of Progress in Quantitative Nondestructive Evaluation, 12, 1993. 

Nondestructive Evaluation at SwRI, http //www.nde.swri.edu/index.html... 

GNETICMATERIALS - THIN FILMS AND PARTICLES] (Vol 15) -imaging techniques [NONDESTRUCTIVE EVALUATION] (Vol 17) -useinNDE [NONDESTRUCTIVE EVALUATION] (Vol 17)... 

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