Mechanical characterization of brushite cements: A Mohr circles' approach

Dry and wet brushite cements with various solid/liquid ratios were tested i n compression and tension. Two different testing techniques were used to de termine tensile strength: Direct Tensile test (DT) and Diametral Compressio n test (DC) (Brazilian test), which is an indirect way of measuring tensile strength on brittle materials. Statistical analysis of the results obtaine d on dry cements points out a constant ratio between the values measured by DT and Brazilian tests (DC/DT = 85%), The Mohr's circles representation al lows us to understand that, for a material like our cement, ultimate stress measured with the Brazilian test can only underestimate tensile strength, because the compressive/tensile strength ratio is lower than 8, The second consequence of this low ratio is that, in the Brazilian test, the plane alo ng which fracture initiates undergoes not only a normal tensile stress, but also a tangential stress component. Thus, the state of stress on the fract ure plane differs from the one taking place in the direct tensile test, Con sequently, with such a material (sigma (c)/sigma (t) < 8), the Brazilian te st does not estimate the true tensile strength. (C) 2000 John Wiley & Sons, Inc.