The management of design rationale (DR) in engineering design is an important task since DR is often regarded as crucial information in design decision support and design analysis. The existing DR systems largely rely on human efforts in capturing DRs along design activities according to some predefined DR models. However, these systems require heavy human involvement and they do not have the capacity to extract DRs from design archival documents, which contain rich DR information but are usually unstructured or semistructured texts, e.g., design documents, service reports, and test reports. In view of such challenges, it has motivated us to propose a new DR model to intelligently discover DRs from design archival documents. In this paper, we propose an issue, solution and artifact layer (ISAL) model for DR representation and approaches for rationale information discovery from design archival documents. We also introduce a DR repository construction platform based on the ISAL model by integrating rationale information from both design archival documents and design processes. Using patent documents as our research data, we conduct a conceptual comparison and experimental study of DR discovery especially for artifact information extraction. Results demonstrate the merits of our proposal. Lastly, we discuss potential applications by taking advantage of our ISAL model.