Implementing design automation systems to automate repetitive and time consuming design tasks enables engineer-to-order manufacturers to perform custom engineering in minimum time. To maintain a design automation system, regular updating of design information and knowledge is necessary. Consequently, there is a need of principles and methods to support capturing and structuring associated knowledge, specially, design rationale. In this paper a method for capturing, structuring, and accessing to design rationale in order to support maintenance of design automation systems is presented. The method is tested through a design automation system that develops FEA (finite element analysis) models automatically. The results are evaluated in a case company which is a supplier to the automotive industry serving many brands and car models which each more or less requires a unique solution.