Lecture 9 Flashcards
(3 cards)
What thermal effects does temperature have on composites?
Themo-mechanical properties can be designed for in composites. i.e. zero thermal expansion.
The glass transition temperature (Tg) is the reference point when the matrix is solidified or indeed liquified.
Explain the coefficient of thermal expansion (CTE) in isotropic and orthotropic materials.
It is a material constant and equal in all directions for isotropic materials (thermal strains are not causing stress).
In an orthotropic material there is a CTE in the fibre direction, transverse direction and in-plane. The fibre and matrix put a constraint on each other and so the local stresses are created. The layers are considered homogenous so no residual stress is considered when a single layer’s temperature is changed.
How does moisture effect a composite?
Polymer matrix composites absorb moisture, which results in hygroscopic expansion.
It is treated exactly in the same manner as thermal expansion. The hygroscopic strains are assumed to be proportional to the percent of moisture absorbed.
