What is the effect of temperature on composites and how does it influence performance?

• A. Elevated temperatures can reduce stiffness and strength (especially above Tg), while low temperatures can increase stiffness but may introduce thermal mismatch stresses.
• B. Temperature has no effect on stiffness or strength.
• C. Temperature always increases stiffness and strength.
• D. Temperature only affects color and odor of materials.

Answer: (A)

Temperature affects composites mainly through how the polymer matrix behaves and how the fiber and matrix expand or contract differently with temperature. As temperature rises, especially above the matrix’s glass transition temperature, the matrix softens and loses stiffness, so the overall modulus and strength of the composite drop and load transfer becomes less efficient. This is why elevated temperatures can noticeably weaken performance. At lower temperatures, the matrix becomes stiffer, so the composite can show higher stiffness and strength, but the different thermal expansions of fiber and matrix create thermal-mismatch stresses. Those stresses can drive microcracking or debonding and shorten life, even though the material appears stiffer.

So the best description is that elevated temperatures reduce stiffness and strength (especially above Tg), while low temperatures increase stiffness but may introduce thermal mismatch stresses. Temperature doesn’t have no effect, nor does it only affect color or odor, and it does not always increase stiffness and strength.