CHAPTER 5 RELIABILITY-BASED DESIGN OF COMPOSITE LAMINATES FOR CRYOGENIC ENVIRONMENTS This chapter presents reliability-based designs of composite laminates for hydrogen tanks in cryogenic environments, comparison between deterministic and reliability-based design, identification of uncertainty parameters that have the largest influence on the optimum design, and quantification of the weight penalty associated with level of uncertainty in those parameters. The results indicate that the most effective measure for reducing thickness is quality control (refer also to Qu et al., 2001). The reliability-based optimization is carried out using response surface approximations combined with Monte Carlo simulation described in chapter three. Reliability-Based Design Optimization Problem Formulation The reliability-based optimization is formulated as minimize h= 4(tz +t2) such that P < P" 0.005 < t, 51 0.005 < t2 where h is the laminate thickness, tl is the stack thickness of lamina with ply-angle 6, and has a lower limit of 0.005 inch on it, t2 is the stack thickness of lamina with ply-angle 82 and has a lower limit of 0.005 inch. The limits on tl and t2 alSo ensure that the laminate has a minimum thickness of 0.04 inch to prevent hydrogen leakage. The reliability