A temperature control device is to be made from a rectangular copper strip with a cross-section 4 mm times 8 mm, which is 100 mm long and is pinned at each end to rigid supports. How much axial pre-compression is required so that buckling will occur after a temperature rise of 50 degree C? Assume that the Euler equation is applicable. For copper E - 100 GN/m2 and the coefficient of thermal expansion = 18 times 10-6/ degree C.