Abstract
Flexural test of brittle material have been usually carried out by third-point loading of a rectangular beam.The modulus of rupture is usually estimated by Navier's formula assuming symmetric loading. But, as the results of an elastic analysis and of a photoelastic study, it was reported by the authors that Navier's formula was not so exact and an asymmetric loading usually takes place in this test.The objectives of this paper are to propose an elastic analysis method of beam subjected to asymmetric load and to define the effect of degree of asymmetry on the modulus of rupture.Stress of a beam subjected to asymmetric load was estimated by superposing the stress for symmetric load on that for inversely symmetric load.Numerical results obtained indicated that the value and the position of the maximum horizontal normal stress axmax at the lower face of the beam varied depending on the degree of asymmetry of load.The value of σxmax for asymmetric load was greater than that for symmetric load, and it varied within 20%.But it varied only 2% when cracking appeared within middle sixth-point.If Navier's formula is used, the value of the modulus of rupture estimated by the third-point loading is 75-89% of that obtained by the central loading. This result corresponds to that reported by flexural test.
