Trapezoidal Bar Research Articles

Determination of tensile and compressive creep behaviour of ceramic materials from bend tests

We have developed equations that permit the determination of individual compressive and tensile creep rates from four-point bend test measurements made on trapezoidal bars. The equations developed are for the general stress dependence case. Finnie first proposed this type of analysis and solved the equations for the case of linear stress dependence. We present graphs that show solutions to the equations for the stress squared case. Creep measurements were performed on trapezoidal HS-130 Si3 N 4 bars to determine the ratio of compressive to tensile creep (β). The values determined on four separate tests using two different temperatures and beam dimension ratios b 2/b 1 gave fairly consistent results. The β′s for previously unstrained material are: 0.24, 0.14, 0.17, and 0.17 with the average value of β=0.18. For the case of prestrained Si3N4, β is 0.48. To further test the usefulness of this analysis, data from a conventional (rectangular bars) four-point bend test were taken from the literature and analysed using the equations developed in this paper and the average determined value of β. The individual tensile and compressive creep rates determined in this manner were found to agree very closely with other literature data measured in direct tension and compression tests.