Reduction of Errors in Ceramic Bend Tests

Abstract

Mechanical tests of most ceramics are subject to more stringent requirements than tests of materials which can undergo plastic deformation. The present paper identifies and discusses sources of stress concentrations and spurious displacements which may be imposed during 4-point bend tests of ceramic materials. Particular areas of concern involve unequal moments at the inner loading points, twisting resulting from skewed contact lines, wedging stresses at point contacts, and counter moments produced by friction at the loading-point-specimen interface. A bend fixture incorporating design features which significantly reduce these effects is described, and results of measurements of the surface stresses in calibration specimens under load in the fixture are presented.

Method to determine hot permeability and strength of ceramic shell moulds

“…Furthermore, this test may lead to errors caused by unequal moments at the inner loading points, twisting resulting from skewed contact lines, wedging stresses at the contact points, and counter moments produced by friction at the loading points/specimen interface (Hoagland et al, 1976). Calculating the strength from the maximal bending torque located in the middle of the sample may also lead to an over-estimation of the strength.…”

The Miniaturisation of the 4‐point‐bend Test

“…Eccentric loading with a pivoting loading head will result in a non-constant bending moment between the inner rollers [6]. From the present design concept of the fixtures it follows that the deviations of span lengths and the amount of eccentricity can be determined by the clearance of the rollers in the slots of the guide, as shown in the inset of Fig.…”

Factors affecting strength and shape retention of zirconia micro bending bars during thermal debinding

“…Considering the standard deviation of random errors, as measurement of width and height of the samples' cross-sections and the deviation of the signal repeat accuracy of the load cell [13], a relative error of maximum 2% of the bending strength was calculated. As friction at the sample-loading point interface may largely affect the measured values, it gives rise to an increase of the apparent strength [14][15][16][17]. Considering a coefficient of friction of 0.3 for the tribosystem 3Y-TZP against hard metal at ambient conditions [18] and the fact that friction is minor for 3-point bending compared to 4-point bending, the overestimation of the bending strength due to friction was calculated to be not higher than 9% [14].…”