Test-pieces types

Tests were carried out on test pieces (Type No. II, 10 mm. thick) taken from sheets of that thickness having been cold worked to the extent of 100 and 300 %. 

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. 

All ceramic materials are elastic, and hence show very little bending under load. They do not exhibit any creep under load. The modulus of rupture type of test is the routine test most commonly used in the ceramic industry, and gives the figure generally quoted for the strength of the material. It must be remembered that the value obtained for any particular body depends on the cross-sectional area of the test piece thus figures quoted from test results may be higher than those obtained on actual articles, which usually have a thicker section than the test piece. 

A weld bead included in a test-piece is, to some extent, peculiar to itself and may not necessarily be representative of nominally similar welds to be made by other welders under other circumstances. To this extent, results of tests on welds must be subject to some qualification in interpretation, having in mind that what will be disclosed principally will be the overall ability of the composition of the weld metal to resist the corrosive environment. In some cases, entrapped flux, craters, fissures, folds, surface oxides etc. may introduce localised corrosion that may or may not occur with all welds of the type studied (see Section 9.5). 

Velocity effects can be achieved either by having the test-piece move through a presumably stationary liquid or by having a moving liquid come into contact with a stationary test-piece. Occasionally tests may involve both types of exposure. Details of test procedures are given in NACE TM 0270-70 Method of Conducting Controlled Velocity Laboratory Corrosion Tests. 

An earlier study by Gafa and Lattanzi [6] describes the use of commercial AOS, AS, SAS, and LAS surfactants. Three types of cotton test pieces were washed with a formulation containing surfactant (25%), silicate (8%), sodium... 

A type of test for determining abrasion resistance. Fixed knives, under constant load, scrape across a rotating rubber test piece. The resulting loss in weight is a measure of the abrasion resistance. 

A-4 One required for each welding procedure, for each type of filler metal (i.e., AWS E-XXXX classification), and for each flux to be used. Test pieces shall be subjected to essentially the same heat treatment (including time at temperature or temperatures and cooling rate) as the erected piping will have received. 

The great majority of durability tests (indeed all types of test) are made on test pieces rather than on the complete product. There are several reasons for this, not least the cost of... 

Because oxygen is used up in the ageing process it is important that an air flow is maintained and the test pieces are exposed to air on all sides. With either type of oven, there must be a steady flow of air through the oven. IEC 60216 [2] specifies between 5 and 20 complete changes per hour which means that some general purpose laboratory ovens would not be suitable. The air velocity will also affect the rate of ageing but this is said to be under consideration in IEC 60216-4 [7]. 

The number and type of test pieces exposed for each measurement point will depend on the property being measured. If measurement is non-destructive, e.g., loss of mass or colour, then the same specimens can be used throughout the test, being replaced in the oven after each measurement. If the measurement is destructive then one set of specimens must be prepared for each combination of duration and temperature. It is recommended to expose at least two reserve sets in case the threshold level has not been reached by the end of the last planned duration. Usually the number specified in the relevant test method standard is chosen but, again, the more the better. An example and some of the problems are described in Section 12.2. 

An important difference between apparatus of, for example, type (a) and type (d) of Figure 6.1 is that in the former case, the test piece is continuously and totally in contact with the abradant and there is no chance for the heat generated at the contact surface to be dissipated. 

Processing variables can affect to a very great extent the results obtained on the rubber product or test piece and, in fact, a great number of physical tests are carried out in order to detect the result of these variables, for example state of cure and dispersion. In a great many cases, tests are made on the factory prepared mix or the final product as it is received but, where the experiment involves the laboratory preparation of compounds and their moulding, it is sensible to have standard procedures to help reduce as far a possible sources of variability. Such procedures are provided by ISO 2393 which covers both mills and internal mixers of the Banbury or Intermix type, and also procedures for compression moulding. 

ASTM D318316 deals only with cutting test pieces from rubber that is not in the form of sheets, but the content is very similar to the relevant parts of ISO 4661, covering slicers, skiving machines, buffing wheels and abrasive bands. Apparently, buffing wheel apparatus is known as an Emerson type rubber buffer in the USA, presumably after a manufacturer. 

In principle the usual type of circulating air laboratory oven can be used for conditioning test pieces when temperature only is controlled. However, for temperatures near to ambient, enclosures equipped with cooling coils would be essential. If a cabinet has to be used it would probably be more... 

The principle of the compression plastimeter is very simple - the test piece is compressed between parallel plates under a constant force and the compressed thickness measured. This simplicity accounts for the early adoption of this type of instrument and its subsequent continued popularity. The work of Williams16 led to the first widely used parallel plate instrument and eventually to various modified forms all working on the same principle. Apart from simplicity, the compression principle has no real inherent advantages but a number of disadvantages ... 

ISO 200722 specifies a rapid plastimeter procedure using an instrument with one platen either 7.3, 10 or 14 mm diameter and the other platen of larger diameter than the first (i.e. disc type method). The size of the first platen is chosen such that the measured plasticity is between 20 and 85. The test piece is cut with a punch which will give a constant volume of 0.40 0.04 cm, the thickness being approximately 3 mm and the diameter approximately 13 mm. The test piece is pre-compressed to a thickness of 1 0.01 mm within 2 sec and heated for 15 sec. The test load of 100N is then applied for 15 sec when the test piece thickness is measured. The usual temperature of test is 100°C and the result is expressed as the thickness of the test piece at the end of the test in units of 0.01 mm and called the rapid plasticity number. The Wallace rapid plastimeter, and presumably other commercial instruments, conform to this specification but it would be sensible to check with the manufacturers. A technically identical method is given in BS 903 Part A5923. 

ISO 732324 specifies a parallel plate test based on the Williams plastimeter with plates 4 cm in diameter. The test piece is 2.00 0.02 cm3 in volume and can conveniently be a cylinder 16 mm diameter and 10 mm thick. As discussed above, a close tolerance on volume is necessary for this type of plastimeter. The test piece is preheated for 15 min (the temperature of test is usually 70°C or 100°C) and compressed under a force of 49N. The thickness of the compressed test piece is measured in mm and this value multiplied by 100 quoted as the plasticity number. The preferred time of application of the force is 3 min. The correction to the standard in 2003 was to change the tolerance on the force from 0.05N to 0.5N. 

A number of plastimeters of this type have been used for rubbers, often for research purposes, but one instrument, the Mooney viscometer, gained virtually universal acceptance and has been extensively used for routine quality control purposes for several decades. The principle of the Mooney is shown in Figure 6.4 together with several other possible geometries for a rotational instrument. The rotor turns at a constant rate inside a closed cavity containing the test piece so that a shearing action takes place between the flat surfaces of the rotor and the walls of the chamber. The torque required to rotate the rotor is monitored by a suitable transducer. 

Tests for scorch and rate of cure should be distinguished from tests for degree of cure or optimum cure measured on the vulcanised material. The latter type of test estimates degree of cure by measuring the physical properties of test pieces vulcanised for various times, tensile properties, swelling and set measurements being the parameters most commonly used. 

The reciprocating paddle instrument is now largely a matter of history and a third type, the rotorless curemeter, has rapidly become the most popular. The rotorless type is a curemeter in which one half of the die enclosing the test piece, rather than a paddle or disc within the test piece, oscillates or reciprocates (Figure 6.7). 

The standard briefly covers the significance of hardness in terms of its relation with modulus, and the practical use of hardness tests. The hardness tests for rubber that are standardized by ISO are introduced and the distinction between dead load and durometer type instruments is explained to help with selection of a test method for particular circumstances. The effect of test piece, use of standard hardness blocks and comparison of hardness scales is also outlined. 

Three different types of stand are specified, a) test piece pushed onto the indentor, b) the indentor pushed onto the test piece and c) as b) but with a damping mechanism. The type M must be used with a type c) stand. 

In the interests of standardisation it is desirable to limit as far as possible the variety of test piece sizes allowed. Success in this direction has not always been possible, as illustrated by the tensile test pieces detailed in ASTM D412. However, there would be no need to limit dimensions at all if it were not a fact that the size of test pieces can affect the magnitude of the result obtained, or at least the variability. In the case of tensile tests, the difference in level between results from rings and dumb-bells has already been mentioned. The variability of the two types of test pieces has been found to be similar. The measured tensile strength has a tendency to decrease with increasing cross-sectional area of the test piece and it is desirable to make comparisons only between groups of test pieces of nominally the same type and thickness. The difference between the results from type 1 and 2 dumb-bells is not normally significant but Bartenev and... 

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