Materials In Today's World

Mechanical Behavior of Ceramics


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.

Stress (y-axis) and Strain (X-axis) Diagram. Aluminum oxide (0.0007, 240MPa) line is steeper than glass (0.0009, 55MPa)
Stress-Strain curves for two brittle materials.
Credit: Callister & Rethwisch

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.

Three-point bending apparatus. Push up at both ends and down in the middle on the test material
Three-point bending apparatus used determine stress-strain behavior.
Credit: Adapted from Fig. 7.18, Callister & Rethwisch

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.