Which statement is true about fracture of polymers?

• A. Crazing cannot occur before fracture.
• B. All polymers are ductile at all temperatures.
• C. Fracture strengths of polymeric materials are low relative to metals and ceramics.
• D. Only brittle fracture is possible.

Answer: (D)

In polymers, how they fracture depends strongly on temperature and loading rate. They can fail brittly with little plastic deformation, especially at low temperatures or high strain rates, or they can fail in a ductile manner with significant plastic flow and sometimes visible necking or crazing before fracture when loaded more slowly or at higher temperatures. Crazing—the formation ofextended, void-like regions connected by fibrils—is a common energy-absorbing process in many polymers and can precede fracture, so it is not true that crazing cannot occur before fracture. The statement that fracture strengths of polymers are always low relative to metals and ceramics is too general—many polymers have modest strengths, but there are high-performance polymers with substantial strength, so this isn’t a universal rule. Overall, fracture behavior in polymers is not limited to one mode; it varies with temperature, rate, and the material’s molecular structure, leading to either brittle or ductile failure under different conditions.