How does low temperature affect stiffness and residual stresses in composites?

How does low temperature affect stiffness and residual stresses in composites?

• A. Low temperatures always decrease stiffness.
• B. Low temperatures can increase stiffness but may introduce thermal mismatch stresses due to different CTEs.
• C. Low temperature has no impact on stiffness or residual stresses.
• D. Low temperature cures resin.

Answer: (B)

Lowering temperature tends to make composites stiffer because the polymer matrix and the overall composite become less compliant as molecular motion slows and the modulus increases. This is especially true below the resin’s typical operating range, where the matrix stiffens and the reinforced structure carries more of the load. At the same time, different constituents in a composite (for example, fibers and the resin) have different coefficients of thermal expansion. When the material cools, each component wants to shrink by a different amount. The bond between them keeps the layers and fibers from contracting independently, so stresses build up inside the material. These are residual stresses that remain after cooling. So, low temperature can increase stiffness, but it can also introduce residual stresses due to thermal-mismatch between the constituents.

Lowering temperature tends to make composites stiffer because the polymer matrix and the overall composite become less compliant as molecular motion slows and the modulus increases. This is especially true below the resin’s typical operating range, where the matrix stiffens and the reinforced structure carries more of the load.

At the same time, different constituents in a composite (for example, fibers and the resin) have different coefficients of thermal expansion. When the material cools, each component wants to shrink by a different amount. The bond between them keeps the layers and fibers from contracting independently, so stresses build up inside the material. These are residual stresses that remain after cooling.

So, low temperature can increase stiffness, but it can also introduce residual stresses due to thermal-mismatch between the constituents.