Which statement is NOT true about ceramics?

• A. Ceramics are typically brittle.
• B. Surface compressive stresses can greatly enhance fracture strength.
• C. The compressive strength is typically ten times the tensile strength.
• D. Ceramics are highly ductile.

Answer: (D)

The main idea here is that ceramics fail through brittle fracture: they are strong in compression but very weak in tension because cracks open and propagate with little to no plastic deformation. Small flaws on the surface act as stress concentrators, so the tensile strength is controlled by crack initiation and slow, unstable propagation, leading to low toughness. Techniques that introduce surface compressive stresses, like certain surface treatments or peening, help close those cracks at the surface and at crack tips, which can dramatically increase the fracture strength by resisting crack opening. The notion that the compressive strength is typically around ten times the tensile strength reflects this large gap between how ceramics behave under compression versus tension, though the exact ratio varies with material and flaw population. The only statement that doesn’t fit is that ceramics are highly ductile, since they do not undergo meaningful plastic deformation before failure.