Test Piece

Contrast Ratio Cq The contrast ratio is established on the basis of the ratio of the amplitude of the unattenuated radiation to the amplitude after attenuation through a test piece. This test piece is a lead disk which is mounted in the middle of the image converter it masks approximately 10% of the surface of the image converter. 

Contrast Sensitivity S For this purpose a test piece is used whose least material thickness to be resolved in the video signal corresponds to the contrast sensitivity. The test piece can be a step/hole image quality indicator as per EN 462-2. 

In general, the performance of a radioscopic system should always be checked via test pieces with natural flaws. To ensure an additional comparability, standardized image quality indicators have to be used to control the essential image quality parameters such as spatial resolution (unsharpness) and contrast sensitivity. 

Detection of this particle accumulation has so far been done visually. To make the particles more easily visible, they have been chemically treated in order to make them light up or flouresce when struck by an ultraviolet light. The operator sits in a darkened room in which the test pieces are illuminated by ultraviolet light. Cracks show up very clearly and in principle this method of inspection is acceptable. Despite the effiency of this method it is well known that a large number of defective pieces pass this test. Why is it so ... 

In addition, the mirrors are adjustable, so that unimportant areas can be ignored. Light re-emmited from the surfaee is detected, and the detector signal is transmitted to a computer programmed with acceptable deviation levels for comparison with a reference component. Tolerance levels can vary for different areas of the same test piece they may, for example, be higher on a ground section than on adjacent unmachined areas. 

When directed towards the test piece the laser beam passes through a centre hole in a 45 degree fixed-angle mimor. Between this mirror and the test piece the laser beam and the flourescence follow a common beam path. A photodetector is aimed at the 45 degrees angle mirror and, therefore, looks along the laser in this common beam path, see Fig 3. 

The computer also can leam from a defect-free test piece by rutming such a piece in a readmode. For example, if a drilled hole for lubrication purposes is present at the same location on all parts, the computer will recognise this signal and accept it on all test pieces. The computer will actually be comparing the test piece under scrutiny with standard non-defect master. In addition a reference test piece should be used to check that the specified reference defects really will be detected. This is needed to adjust the settings and sensitivity of the system. 

The method was applied for determination of the quality of the detection media on test pieces following the type testing of the European standard [4] in order to check the validity of the method. The other application was the determination of the visibility in dependance of the variations of the inspection parameters (application of the detection medium, magnetization, inclination, viewing conditions) in a range which may appear in the practical inspections. The results leads to conclusions on the visibility level which is a measure of the probability of recognition for the indication that means of the reliability of the method. 

The experimental investigations are carried out in order to get an idea about the variations of the visibility of the indications during practical inspections. The specimen where a test piece with spare eroded artificial defects (Width 25 pm depth d = 30, 60, 120 pm) and other specimen with natural cracks, a forged steering lever and a weld. As an example, in Fig 4 the steering lever with 2 cracks can be seen and below the dependance on the visibilty of a weak indication and a part of the bright indications on the field strenght H. 

Shoe Delay. Defines the shoe, or wedge, delay, in tenths of microseconds, of the prohe being used. This control is used to adjust the zero point of time interval measurement to correspond to the instant that the ultrasound pulse enters the test piece. 

Material Veloeity. Defines the velocity, in metres/sec, of ultrasound in the material of the test piece used to convert A-scan signal time to distances within the test piece. 

Before the data can be visualised, ie displayed in a two or three-dimensional representation, the ultrasonic responses from the interior of the test-piece must be reconstructed from the raw ultrasonic data. The reconstruction process projects ultrasonic indications into 3D space. As well as reconstructing the entire ultrasonic data set within an acquisition file, it is possible to define an arbitrary sub-volume of the test object over which reconstruction will take place. The image resolution may also be defined by the user. Clearly, larger volumes or greater resolution will increase the computation time for both the reconstruction and visualisation processes. 

The CamuS system is currently in the form of a laboratory prototype and is undergoing a series of validation tests using an extensive set of test-pieces covering a range of geometries and classes of defect which has been manufactured for the purpose. 

As the sensitivity can be adjusted according to the surface condition of the test piece, repeat-able and reliable ultrasonic results are achieved. 

Another fundamental characteristic ofNDT data is that it is spatial. It is the use of an NDT signal, together with its location, which provides insight into the hidden nature of the test-piece. Any discussion of NDT inspection data assumes the spatial component is included. 

Test pieces for Brinell testing must have two parallel sides and be reasonably smooth for proper support on the anvil of the test machine. Minimum sample thickness must be 10 times indentation depth. Successive indentations must not be closer than three indentation diameters to one another or to the edge of the test piece. 

For contact testing a couplant normally is used between the probe and the test piece. This material may be oil, water, or some gel or other Hquid or paste. Compatibihty with the test object is important, so that no unexpected chemical attack occurs, causing a crack to initiate. Whereas the frequency range for ultrasonic tests may extend from approximately 50 kH2 to 50 MH2, the range most commonly used for metallic test materials is 0.5—25 MH2. 

For some dipped work, wet gel strength measurement is carried out, where the gel is deposited onto preformed, tissue paper dumbeUs, and the load necessary to break the dumbeU-shaped test piece is measured. 

If the test piece contains many holes, gas is indicated and the melt may be flushed with nitrogen to control this situation. SmaE amounts of deoxidi2er should be added to the gas-free melt untE shrinking of the test piece occurs. 

Eor colorfastness to perspiration, ISO 10S-E04, the specimen is immersed in a solution of 0.5 g/L of 1-histidine monohydrochloride monohydrate and 5 g/L sodium chloride buffered to either pH 8.0 (alkaH perspiration test) or pH 5.5 (acid perspiration test) in a dish at 50 1 Hquor-to-goods ratio, at room temperature for 30 min. The specimen is removed and, as in the water test EOl, left for 4 h between plates at 37°C before drying and assessing both test piece and adjacents. 

Examples of artificially soiled test pieces used to test the performance of amylases include cocoa /milk/sugar, cocoa/sugar/potato starch, cocoa /milk/sugar/potato starch, and starch/carbon black, all on cotton or polyester/cotton. 

Test Piece The size and the shape of specimens will vaiy with the purpose of the test, nature of the material, and apparatus used. A large surlace-to-mass ratio and a small ratio of edge area to total area are desirable. These ratios can be achieved through the use of rectangular or circular specimens of minimum thickness. Circular specimens should be cut preferably from sheet and not bar stock to minimize the exposed end grain. 

Corrosion-resistance test This can be done with the help of a salt spray test. The test piece is suspended in a salt spray chamber (Figure A13.6) for. seven days in 100% relative humidity (IS 101 and IS 11864). After the test, the surface should have no signs of deterioration or corrosion. 

Acid resistance This can be checked by using N/IO (H2SO4) solution. When a few drops are spilt on the test piece, or when the test piece is dipped for almost half an hour in the solution. It should develop no corrosion spots on the surface. 

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