Analytic techniques for sizing the walls of advanced composite electronicsenclosures

Electronic enclosures for space or avionics application can be designed usi ng laminated composites to reduce weight, provide a modular design that has equal or better thermal and mechanical performance, and has a lower cost p er enclosure than the standard "black'' aluminum design. Initial sizing of an enclosure to determine the number of plies and ply orientation can be ac complished by subdividing the structure into simple shapes and analytic clo sed-form equations used to calculate bending stresses and deflections, unia xial and shear buckling allowables, and natural frequencies. This initial s izing was performed on a three-sided enclosure with integral mounting flang es. The walls were analyzed using static equivalent of random vibration loa ds in closed-form analytic approximate or exact equations and compared with those using finite element analysis (FEA). Depending on the degree of orth otropy, i.e., how close the off-diagonal flexural stiffnesses are to zero, the analytic predictions for laminae stresses vary with finite element resu lts. Two different hybrid PAN/pitch fiber/epoxy laminates and a carbon fabr ic/epoxy laminate with varying degrees of orthotropy were chosen for compar ison. The margins of safety for the analytic results was within 5% of the F EA results for the orthotropic laminate but was different by factors of 1.5 to 13 for the non-orthotropic laminates. There was good comparison between analytic solutions and FEA for buckling, natural frequency, deflection, an d stresses, in all cases the analytic predictions were conservative. These analytic equations were used for initial sizing of an enclosure, and a deta iled FEA was performed on the electronics enclosure under actual random vib ration loads. The final enclosure was fabricated and tested under these ran dom vibration loads. (C) 1999 Elsevier Science Ltd. All rights reserved.