Use of extensometers with spherically pointed pin ends for accurate determination of material qualities

Highly accurate FFA 10 mm inductive extensometers with spherical tips are used for materials testing. The pin ends are ground conical and spherically pointed ends of 16tm radius are then honed. The specimen is indented with a slightly greater cone angle and with the same nose radius by a similar conical‐spherical taper shank. The extensometer is mounted in these indentations under a spring pressure that plasticises the spherical contact area and squeezes out unevennesses. The shear modulus of steel was evaluated from four values of Young's modulus and four of Poisson's ratio in tension and compression, determined with such extensometers in 16 different tests under dead weights calibrated by the official standards institute. The four shear modulus values obtained have root mean square errors within ±0.5%.