It is difficult to measure the yield strength of ceramics as they tend to fracture before they enter the plastic deformation region, i.e., they are brittle. Examples of two brittle materials that fracture before entering the plastic deformation region are aluminum oxide and glass, as shown in the figure below.
Tensile tests of brittle ceramics are usually not performed. It is difficult to shape these materials into the proper test structure, difficult to grab the brittle material without breaking it, and it is difficult to align the test samples to avoid bending stresses which can destroy the sample. For brittle ceramics, a three-point bending apparatus (shown in the figure below) is used determine the stress-strain behavior, and the measurement results are used to calculate an equivalent modulus of elasticity.
This image is a technical diagram illustrating the concept of midpoint deflection in a beam subjected to a central load. The beam is supported at both ends and experiences a downward force F applied at its midpoint. The distance from each support to the point of force application is labeled L/2, indicating that the load is symmetrically placed. The diagram includes two types of beam cross-sections: one rectangular, defined by dimensions b (width) and d (depth), and one circular, defined by radius R.
The deflection at the midpoint is represented by δ, which measures the vertical displacement from the beam’s original horizontal position to its deflected shape under the load. This visual helps convey how different cross-sectional geometries and loading conditions affect the structural behavior of beams, particularly in terms of bending and deformation. It is commonly used in engineering and physics to analyze material strength and structural performance.
To Read
Now that you have been introduced to the mechanical behavior of ceramics, please go to your e-textbook and read more on this topic on pages 84 to 86 in Chapter 4 of Materials for Today's World, Custom Edition for Penn State University. When finished with the reading proceed to the next web page.