Gary L. Leatherman

Behaviour of carbon fiber reinforced cement composites in direct tension

Abstract The effect of carbon fibers on the tensile strength of cement paste matrix was experimentally and analytically investigated. The tensile strength values were obtained using the cementitious composites axial tensile technique (CCATT) [1,2]. The addition of 1, 1.5, 2, and 3 volume percent of polyacrylonitrite-based (PAN) carbon fiber to a cement matrix results in an increase in the uniaxial tensile strength of 32, 42, 48 and 56 percent, respectively. A predictive model based on the rule of mixtures is developed. The model accounts for the tensile strength of composites with short and randomly dispersed carbon fibers. In addition, the developed equation of the tensile strength accounts for the orientation and the length of fibers, the specimen geometry and the effectiveness of the reinforcement with increasing fiber content. The developed constitutive model compares satisfactorily with experimental results and it can be used as a practical tool for approximating the tensile strength of CFRC composites.

Strength of structural ceramics after exposure to sodium sulfate

Abstract A variety of advanced structural ceramics were treated in air at 1000°C for 500 h in the presence of various amounts of sodium sulfate. Room temperature flexure strength was determined before and after treatments. Results show that Ce-TZP and alumina are resistant to strength degradation after exposure to sodium sulfate, but Si 3 N 4 (NC-132) and, to a lesser degree, Y-TZP are not. The addition of sodium sulfate also has an adverse effect on the high temperature performance of the Y-TZP, by reducing its load carrying capabilities between 900 and 1000°C. For the Ce-TZP, alumina and even the Si 3 N 4 there appears to be no change in the high temperature performance when sodium sulfate is present.

Tensile Testing of Fiber Reinforced Cementitious Composites

A novel approach in tensile testing of cementitious composites using the ASCERA® hydraulic tensile tester is described. The test specimens are cylindrical bars. Steel pistons are adhesively bonded on either end of the specimens and inserted in a pressure chamber. The pressure is increased until the specimen is pulled apart by the hydraulic pressure exerted on the pistons. Advantages of this method are: large volume under load, self-alignment to minimize externally applied bending moments, and determination of the rupture stress exactly at the fracture initiation point. Glass reinforced cementitious composites were tested. Results are discussed with respect to curing time and fiber volume fraction. The tensile strength values obtained by hydraulic testing are compared to values obtained by traditional uniaxial tensile strength tests. A biaxial model is adopted to verify the results.

Effects of Sodium Sulfate Induced Corrosion on the Static Fatigue Life of Silicon Nitride Containing Different Dopants

Flexure testing was used to determine the effects of sodium sulfateinduced corrosion on the static fatigue life of two silicon nitride ceramics at 1000°C. The results show that the static fatigue life of the MgO-doped silicon nitride is significantly reduced when Na2SO4 is introduced. Conversely, the static fatigue life of the Y2O3 + A1203- doped silicon nitride is increased in the presence of Na2SO4.