An acrylic (PMMA) window is clamped in a low carbon steel frame at T = 20 C.

An acrylic (PMMA) window is clamped in a low carbon steel frame at T = 20 C. The temperature falls toT = -20 C, putting the window under tension because the thermal expansion coefficient of PMMA is larger than that of steel. If the window was stress-free at 20C, what stress does it carry at -20 C? Use the result that the bi-axial stress caused by a bi-axial strain difference ∆ε is σ= E∆ε

where E is Young’s modulus for PMMA and Poisson’s ratio ν= 0.33.

You will find data for expansion coefficients in Table A7, and for moduli in UASSP, 5. Use mean values.