describe the british standard proportional round test piece, indicating how it should be prepared?

well away from the grips. Obviously, the portion gripped is subjected to a severe crushing stress, so any results founded upon the load under which a test piece broke at this place would be misleading. marked Lo (Tables 1.1 and 1.2) is the gauge length on which, as explained later, all measurements are taken. which fracture occurs outside the 'middle half' of the gauge length is The length 0, The result of any test in usually ignored. The standa rd proportional test pieces recommended in BS 18: Part 2 have an original gauge length Lo which bears a specified relationship to the cross-sectional area So, because compa rable values for percentage elongation are obtained from different forms and sizes of test pieces in which this relationship is uniform. The primary gauge length a dopted is 5.65/So. Standard Proportional Test Pieces The cross-section of the test piece is preferably circular or rectangular, with a transition radius r between the gripped ends and the parallel length, where these differ in size. with a reduced central portion should not be less than the original length plus the diameter of the circle circumscribing the cross-section of the parallel portion; the diameter of the central portion should never be less than 3 mm; the gripped ends may be of any size to suit the holders of the testing machine. The pa rallel length of a test piece Table 1.1 gives the recommended sizes of machined round test pieces for steel. Test pieces with diameters other than those given in Table 1.1 may be used in special cases, provided that the gauge length Lo = 5.65/ So is approximately five times the diameter. Cast test pieces conform to the dimensions listed in Table 1.1, unless otherwise specified in the standard for the material; for unma chined test pieces of uniorm section, it is recommended that the elongation be measured to a gauge length of 5.65S0 (i.e. five dia meters for round test pieces), as for machined test pieces. Non-Propor- tional Test Table 1.2 gives the as,