Bend Strength versus Tensile Strength of Fiber-Reinforced Ceramics

The bending strength of fiber‐reinforced glasses and ceramics is often observed to be higher than their tensile strength; the difference varies, however, from one material to another. To gain an understanding of the relationship between these two measure of strength, we have carried out an analysis of bending which accounts for the deviations from linearity that occur on the tensile side of the beam. The results of this analysis indicate that the strength ratio (bending strength/tensile strength) depends most sensitively on the rate at which the stress drops after the ultimate tensile strength. In particular, composites failing gracefully (with a gradual decay in stress) tend to have comparatively higher strengths in bending. A method of inferring the: tensile strength from simply the load‐deflection curve in bending is proposed. In addition, by accounting for the weakness in interlaminar shear, we can predict the variation in bend strength with beam aspect ratio. The various theories are compared with experimental data.