ASTM E21-2020 pdf free download.Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials.
4. Significance and Use
4.1 The elevated-temperature tension test gives a useful estimate of the ability of metals to withstand the application of applied tensile forces. Using established and conventional relationships it can be used to give some indication of probable behavior under other simple states of stress, such as compression. shear. etc. The ductility values give a comparative measure of the capacity of different materials to deform locally without cracking and thus to accommodate a local stress concentration or overstress: however, quantitative relationships between tensile ductility and the effect of stress concentrations at elevated temperature are not universally valid. A similar comparative relationship exists between tensile ductility and strain-controlled, low.cycle fatigue life under simple states of stress. The results of these tension tests can be considered as only a questionable comparative measure of the strength and ductility for service times of many hours. Therefore, the principal usefulness of the elevated-temperature tension test is to assure that the tested material is similar to reference material when other measures such as chemical composition and microstructure also show the two materials are similar.
5. Apparatus
5.1 Testing Machine:
5.1.1 The accuracy of the testing machine shall he within the permissible variation specified in Practices E4.
5.1.2 Precaution should be taken to assure that the force on the specimens is applied as axially as possible. Pertèct axial alignment is difficult to obtain especially when the pull rods and extensorneter rods pass through packing at the ends of the furnace. However, the machine and grips should be capable of loading a precisely made specimen so that the maximum bending strain does not exceed 10 % of the axial strain, when the calculations are based on strain readings taken at zero force and at the lowest force for which the machine is being qualified.
4. Significance and Use
4.1 The elevated-temperature tension test gives a useful estimate of the ability of metals to withstand the application of applied tensile forces. Using established and conventional relationships it can be used to give some indication of probable behavior under other simple states of stress, such as compression. shear. etc. The ductility values give a comparative measure of the capacity of different materials to deform locally without cracking and thus to accommodate a local stress concentration or overstress: however, quantitative relationships between tensile ductility and the effect of stress concentrations at elevated temperature are not universally valid. A similar comparative relationship exists between tensile ductility and strain-controlled, low.cycle fatigue life under simple states of stress. The results of these tension tests can be considered as only a questionable comparative measure of the strength and ductility for service times of many hours. Therefore, the principal usefulness of the elevated-temperature tension test is to assure that the tested material is similar to reference material when other measures such as chemical composition and microstructure also show the two materials are similar.
5. Apparatus
5.1 Testing Machine:
5.1.1 The accuracy of the testing machine shall he within the permissible variation specified in Practices E4.
5.1.2 Precaution should be taken to assure that the force on the specimens is applied as axially as possible. Pertèct axial alignment is difficult to obtain especially when the pull rods and extensorneter rods pass through packing at the ends of the furnace. However, the machine and grips should be capable of loading a precisely made specimen so that the maximum bending strain does not exceed 10 % of the axial strain, when the calculations are based on strain readings taken at zero force and at the lowest force for which the machine is being qualified.
6. Sampling
6.1 Unless otherwise specified the following sampling procedures shall be followed:
6.1.1 Samples of the material to provide test specimens shall be taken from such locations as to be representative of the lot from which it was taken.
6.1.2 Samples shall be taken from material in the final condition (temper). One test shall be made on each lot.
6.1.3 A lot shall consist of all material from the sank heat, nominal size, and condition (temper).
7. Text Specimens and Sample
7.1 The size and shape of thc lest specimens should be based primarily on the requirements necessary to obtain representative samples of the material being investigated.
7.2 Unless otherwise specified, test specimens shall be oriented such that the axis of the specimen is parallel to the direction of
fabrication, and located as follows:
7.2.1 At the center for prtxlucts 1L5-Va in. (38 mm) or less in thickness, diameter, or distance between flats.
7.2.2 Midway from the center to the surface for products over +1.5.14 in. (38 mm) in thickness, diameter, or distance between flats.
7.3 Specimen configurations described in Test Methods 1i8/IiXM. are generally suitable for tests at elevated emperatures:
however, tighter dimensional tolerances are recommended in 7.6. The particular specimen used should he mainly governed by the requirements specified in 7.1. When the dimensions of’ the material permit, except for sheet and strip, the gauge length of the specimens should have a circular cross section. The largest diameter specimen consistent with that described in 7.1 should be used. except that the diameter need not be greater than 0.500 in. (12.7 mm). The ratio of gauge length to diameter should be 4, as for the standard specimens described in Test Methods EXIE8M. If different ratios are used, the specifics should be reported in the results. (See 11.1.4)
Noit 5—Specimen size in itself has little effect on tensile piopenies provided the material is not subject to appreciable surface corrosion. lac& of soundness, or oncnlatian effects. A small number of grains in the specimen cross section, or preferred orientation of grains due to fabrication conditions. can have a pronounced effect on the test results. When corrosion is a factor in testing. the results do become a function of specimen size. Likewise, surface preparation of specimens. if aft.xling results, becomes more important as the specimen size is reduced.
7.4 Specimens of circular cross section should have threaded, shouldered, or other suitable ends for gripping which will meet the requirements of 5.1.2.
Non 6—Satisfactory axial alignment may he obtained with precisely machined threaded ends. But at temperatures where oxidation and creep are readily apparern. precisely tilted threads are difficult to maintain and to separate after test. Practical considerations require the USC of relatively loose-lilting threads. Other gripping methods have been successfully uscd
7.5 For rectangular specimens sonic modifications of the standard specimens described in Test Methods L8/l8N1 are usually necessary to permit application of the force to the specimen in the furnace with the axiality specified in 5.1.2. lIthe material available is sufficient, the use of elongated shoulder ends to permit gripping outside the furnace is the easiest method. When the length of the specimen is necessarily restricted, several methods of gripping may be used as follows:
7.5.1 A device that applies the force through a cylindrical pin in each of the enlarged ends of the specimen. The pin holes should he accurately centered on extensions of the centerline of the gauge section. Grips of this type can provide good axiality of loading.ASTM E21 pdf free download.