Abstract
Because of the presence of graphite, the stress-strain properties of gray cast irons usually differ in compression and in tension. So, it can be considered that the neutral axis of a beam made of gray cast iron shifts toward the compression side under bending load. But the behaviors have not been made clear enough. Our experiments have been conducted to learn about the behaviors and the differences between the stress that occurs in a real beam and the stress that is calculated on the assumption of an ideal elastic material. The results may be summarized as follows ; (1) Even under a great bending load, the distribution of the strains in the beams made of gray cast irons display linearity. (2) Up to a certain stress, stress-strain diagrams in tension and in compression of cast iron tend to exhibit the same straight line and show the same elastic behaviors. In this case, no movement of the neutral axis is recognized. But on increasing the load, the neutral axis of the beam shifts towards the compression side. A beam of high tensile strength usually needs high bending load to move the neutral axis but even then the amount of its movement and its increasing rate are small. (3) Under a low bending load, the stress distributions of beams show straight lines and they are in approximate agreement with the stress assuming an ideal elastic material. But on increasing the load, the stress distributions gradually show a curved pattern. The stress which occurs in the compression side surface approximately agrees with the stress that is calculated by assuming an ideal elastic material but the stress which occurs in the tension side surface becomes less than that. Nodular graphite cast isons do not show much differences between the stresses in the compression side and in the tension side. (4) The fracture by bending load of a beam of gray cast iron occurs when the stress in the tension side surface comes close to the tensile strength of the beam material.
