ASTM-A956:06 pdf free download – Standard Test Method for Leeb Hardness Testing of Steel Products.
Xl .1.4 For the standard single coil rebound hardness testing devices, a typical induction voltage curve is sketched in Fig. Xl.2 where the shape of this curve is unique for all impact devices of this type. The impact and rebound velocities are assumed to he proportional to the extremal values A and B of the signal curve, which is a good approximation, if the device is constructed so, that the extremals are near the signal step caused by the impact. If they are too near, however, the reproducibility of the measurement suffers, because the signal is often disturbed short after the impact. The width of the signal curve has some influence on the result, because it determines, how good the proportionality between mimimum value B and rebound velocity is.
Xl. 1 .5 Another parameter of paramount importance determining the actual L value for a material of a given hardness is the impact energy, which follows from the impact velocity, the mass of the impact body, and its stiffness (which determines how much energy the impact body absorbs). In order to reproduce the standard direction dependency, it is necessary to specify velocity and mass separately and w have a specific free flight length. This means that the impact energy in general is the most important parameter for significance of L-values for all rebound hardness testers working in units of the seven different standard impact devices listed in 5.1 and given in Table X I. I. Furthermore, the L value depends on the geometry of the indenter and its material properties, predominantly hardness and elasticity.
X 1.1 •6 Finally, the effect of deceleration by eddy currents may affect the result. So the tube material must be specified, too, as well as special precautions have to bee taken to reduce eddy currents.
XI.2 Specifications of Standard Single Coil Hardness Testers
X1.2.1 Table X1.1 compiles the relevant specification for impact devices D/DC, E, D+15, DL, C, and G. Coil and permanent magnet are not explicitly specified. They have to he chosen in such a way, that the specified parameters of the induction voltage signal are fulfilled. For the definition of some of the parameters refer to Fig. Xl.2.
X1.3 Impact Direction Compensation
X1.3.1 Rebound hardness testing devices designed according to the above specifications will not only give correct readings for vertical downward impacts, hut will also have a characteristic dependency on the impact angle as shown in Tables Xl.2-Xl.8.
X 1.3.2 Tables X1.2-X 1.8 can be used for instruments determining only the velocity ratio in order to correct the readings manually for other directions than vertically down.