Misalignment-induced bending in pin-loaded tensile-creep specimens

In this paper, we have examined the possibility that elastic bending Induce d by load misalignment can affect creep measurements on pin-loaded tension specimens of silicon nitride (Si3N4). We have shown that elastic bending at room temperature can be as great as 42% of the axial strain when clean pin s were used but was reduced to similar to3% when lubricated pins were used. Creep tests at the same applied stress and temperature were conducted on t wo groups of Si3N4 test specimens: one group used clean pins, and the other group used lubricated pins. By measuring the shapers of the specimens befo re and after the creep tests, we have determined that the loading holes wer e slightly misaligned before the creep tests and that small amounts of bond ing were induced by the creep tests. Bending occurred both in the gauge sec tion of the specimen and in the transition region between the gauge section and the heads of the specimen (the latter phenomenon is defined as hinge b ending). Our study indicated that the secondary creep rate, the hinge bendi ng, and the bending of the gauge section was not dependent on pin lubricati on, because the results from the clean and lubricated groups were statistic ally indistinguishable. Hinge bending was dependent on initial misalignment of the loading holes, whereas bending of the gauge section was independent of such factors.