附录1 外文文献原文及译文原文：An evaluation of NDT methods for the location and sizing of forging discontinuitiesIn selecting an NDT method for flaw detection in forgings a number of variables must be considered:a) the type of discontinuity to be assessed;b) the method to be used for detection and evaluation, andc) the variables associated with the forging itselfThe variables in item a) will govern the location within the forging and its orientation with respect to a particular surface Item b) could include a considerable array of NDT methods, but for the purpose of this paper only the six most widely used are considered一visual testing (VT), penetrant inspection(PI), magnetic particle inspection(MI), eddy current testing (ET), radiographic inspection (RT) and ultrasonic inspection (UI). In the last item c) the component race include such things as condition, geometry access for inspection.a)Forging discontinuitiesThe location of the discontinuity will have a significant influence on the selection of the NDT method to be used and they are therefore grouped into three categories, to aid this selection:1. open to the surface: laps, seam, burst, slugs, cracks and inclusions2. slightly subsurface: seam, stringers, inclusions and grain structure variations3. internal: stringers, burst, lamination, grain structure, inclusions and pipingA brief review of these terms may be helpful:Lap: folded metal, flattened into the surface but not fusing with itSeam: linear flaws due to oxidized blow holes or ingot splashes, which are elongated by hot workingBurst:ruptures caused by failure of plastic deformation by processing at too low a temperature or excessive working of metalStringers: a bar stock defect, due to non metallic inclusions being squeezed out into long and thin stringsLamination: planar defect aligned parallel to surface, originating in the original ingot from rolled out pipingCracks: transgranular failure, due to localized stresses resulting from non-uniform heating or cooling and non-plastic deformationInclusions: impurities, such as slag, oxide and sulphides, often from the original molten stage in forming the billet used for forgingGrain structure: depending upon the extent of working, (deformation and recrystllisation) can be as small as 0.5mm or as large as 10mmPiping: a cavity at the centre of the ingot or billet, caused by shrinkage during solidification Slug: a piece of foreign matter that has been pressed or rolled into the surface of the material b)The NDT MethodVT—visual testing is the oldest of the NDT methods but still valid and widely used today The system is based upon observation, usually by a human observer, but now increasingly by digital/video cameras which use pattern recognition to locate dissimilar areas in a surface. The sensitivity will depend upon the method but typically a good observer with simplevisual aids can resolve 0.5mm differences aids will include magnifying glasses (up to x10), microscopes(up to x100) and fibred-optic bores copes and endoscopes for viewing internal details in hollow or complex sections. The system is used for surface inspection only with costs in the range $4 to $4000.PT一the surface is covered with brightly covered oil (typically red or fluorescent), which will penetrate any surface openings. After removal of excess, an absorbent, white powder is applied, which draws any trapped oil to the surface. This creates an indication of the presence of the surface opening. This process, like visual inspection, also requires visual acuity, but the indications are ‘enhanced’ by the process, since‘bleed-out’ spreads the visual image. Costs can range from as little as $4 for a couple of cans, to $8000 for a process ‘line’. Both VT and PT are surface inspection systems only arid will therefore detect only those discontinuities that have a definite surface opening Surface cleanliness is very important, particularly with PT.MT一ferromagnetic materials carrying a large flux density; retain the presence internally, with little external evidence other than at the poles. Any discontinuity in the material will disturb this uniform flux and create a small ‘leakage’ at the site of the discontinuity. This leakage can be detected by the fact that finely divided; ferromagnetic particles collect at the-site, creating an indication. As with PT, the particles can be colored, to increase contrast, which when viewed under suitable lighting, create a clear visual image of the discontinuity. However, unlike PT the leakage can pass through thin layers of paint or plating materials, so that the discontinuity does not have to be open to the surface. The system can therefore detect surface AND slight subsurface discontinuities. However this is only possible in ferromagnetic materials, such as iron, mild and tool steel, nickel, cobalt and martenstic stainless. It will not operate on Paramagnetic or Diamagnetic materials, such as copper, aluminum and austenitic stainless steel. A small electromagnet can cost as little as $200, but a large `bench type' machine can cost up to $10 000 and the cost of electricity can be substantial.ET一Direct current flowing in a coil, sets up a longitudinal magnetic, field through the coil, and exhibits a particular resistance to flow. If the current is alternating, then a further effect一inductive reactance, adds to this resistance, the total being impedance. This impedance also causes a lag between the current and the voltage, called a phase shift. This shift and impedance are characteristics of the coil.If the coil is now placed close to a conducting surface, the reversing magnetic field induces a reversing current in the conducting (eddy current) which opposes the inducing field. This opposition alters the impedance of the coil and a suitable instrument can detect these changes (both phase angle and/or impedance).For a given ,discontinuity-free surface , a specific alteration will be present which can be zeroed .If the coil now passes over a discontinuity, a change in induction will occur which will be registered by the instrument. However, a change in the conductivity of the material will also effect the induction, as will changes in permeability. Thus, non-uniform heat treatment, segregation and in homogeneities in material composition and structure will also effect the induction and create an ‘indication’. Another critical factor is the distance between the coil and the test surface. This ‘lift off’ can be used in a positive way to determine coating or paint thickness’, on conducting materials. But equally, differences in the coil/specimen gap can result in non-relevant signals. The system can therefore detect surface AND slight subsurface discontinuities. However this is only possible in conducting materials and the proximity of the test coil to the test surface is critical. This means that for any component (other than flat plate), special probes are usually designed to follow specific component contours. A small eddy current machine can cost as little as $2000, but a large automated machine can cost upto $20 000RT一Short wavelength, electromagnetic radiation will pass through many materials, depending upon density and thickness, and then create a range of exposures on either film or a fluoroscopic screen, to present a visual image of the internal composition of the item. Differences in absorption within the material due to such things as gas holes, cracks and bursts will create photographic density differences on the film or detector, which can be interpreted by trained personnel. The source of radiation can be an X-ray tube or a gamma source (such as Iridium or Cobalt) and the images can be generated on either film or as real-time images on fluoroscopic screens. Defect orientation is a vital factor in radiography since it is thickness differences, which the process detects. Hence, a lamination type defect, parallel to the film would be almost impossible to detect. On the other hand, a crack perpendicular to the film would almost certainly be detected. It is therefore often the case that a single component would have to be radio graphed from more than one direction, in order to detect most defects. Finally, the radiation used is highly hazardous and therefore any environment in which it is used, must suitably shielded, to prevent exposure of the operator. As well as shielding the use of X or gamma rays will also require, monitors, alarms, interlocks and personal dosimetry systems, which along with the film itself, adds to the cost.A basic X-ray set up would cost around $10000 and with ancillary equipment and film could cost $3000 per year to run.UT—At an interface between materials of differing acoustic impedance, a sound wave will have a proportion reflected and the remainder transmitted. Thus a gas hole or crack in a forging will reflect a sound beam because of their large difference in acoustic impedance with the metal structure containing them. Since ultrasound travels in a given material at a known (predictable) velocity, then the distance to a reflector will be a direct function of this time of flight of the pulse of sound. Its location can therefore be estimated .Since the amplitude of the returning signal is also related to the size of the reflector, then an approximation can be made of the extent of the reflector, in terms of length through-wall thickness and width. The data can be presented as an ‘A’scan, on a cathode ray tube (requiring skilled interpretation) or as a ‘B’ or ‘C’ scan, where the data are plotted on printers or strip charts as a permanent record. Depths of penetration can be adjusted (by calibration and probe selection) from 10mm to 3 meters in suitable, fine-grained material. However cast, or large grained forged material, could be attenuate signals to the extent that they are untestable. A typical portable flaw detector and probes would cost around $5000, a fully automated ‘C’ scan immersion system could cost $2000.c)The variables associated with the forging1.Surface conditionFor VT and PT surfaces better than 6.3um Ra would yield the best results. For MT a similar situation exists, where a confusing background could result from rough surfaces. ET also requires a smooth a surface for preference, since ‘lift-off’ effects could be unacceptable. For RT a surface roughness exceeding 1% of material thickness could result in a significant loon of sensitivity. However for UT, a suitably viscous ‘couplant’could assist in sound transmittance, but entry surface ‘noise’on the timebase and attenuation would reduce sensitivity.2.GeometryFlat surfaces are the simplest to inspect, by any method. However, PT is least influenced by geometry, being a liquid process. MT requires that the flux be at 90 to the discontinuity and thus, curved surfaces and hollow sections offer particular problems. VT may require special access equipment and ET will need specially designed probes for curved or irregular surfaces. Since RT relies on absorption differences, variations in thickness due to curvaturewill result in large variations in photographic density and a consequent loss of film contrast. In UT the probe has best transmittance when it is whole face is in direct contact with the surface. Any curvature will result in “rocking”of the probe and a consequent loss of “coupling” and reduced signal amplitude.plexityForged bar, billet, rod and plate offer simple shapes for inspection, but aircraft landing gear is an entirely different manner. PT is the least influenced by complex shapes when using the water washable system VT will require longer inspection periods and aids such as mirrors and bores copes. For MT, the more complex the shape, the more difficult it is to arrive at an all over procedure and individual flux/current tor the various sections ET will again require specially shaped probes and RT a larger number of film exposure and angled shots UT will need careful planning to ensure complete coverage and may not be possible if access is limited.4.ThicknessVT, ET, PT and MT are all unaffected by thickness since they are surface methods. RT has an approximate thickness limit of 300mm in steel and at 2% sensitivity (a typical value), will only record discontinuities of 6mm maximum section, in the plane of the radiation. UT is capable of inspecting beyond 2 meters in fine-grained material but is less effective below 10mm or so.5.Discontinuity OrientationVT and PT are unaffected by orientation. In MT, for maximum sensitivity the flux should be at right angles to the discontinuity. ET requires that the discontinuity be at right angles to the coil windings and RT has its maximum sensitivity when the discontinuity lies parallel to the radiation beam. UT has the maximum response when the reflector is at right angles to the sound beam.译文：对铸件缺陷位置和尺寸的无损检测方法的评价对铸件裂纹探测时，选择无损检测方法必须注意以下几点：a)评定缺陷类型；b)确定评定和探测缺陷的方法；c)铸件自身相关的变化。