Deployment of Structural Foam in a Vehicle Roof System for Weight Reduction: Analytical/Experimental Verification

The effect of structural foam (both polyurethane foam and Epoxy-based foam) on roof-crush resistance, when injected in the cavities of principal roof crush components, is investigated. Previously established design guide-lines have been used to optimize foam benefits by selecting appropriate foam density, and location of foam application. Finally, feasibility of downgaging a roof-crush system through optimized foam deployment and without affecting strength is evaluated. Two identical body-in-white (B-I-W) vehicles were used in this evaluation. One vehicle was considered as a base, while the other was injected with 9 pcf polyurethane foam at several critical locations. The foam density selection was based on the component study findings, while the foam location was determined based on a CAE analysis of the base model to locate plastic hinge formation and their sequence of occurrence. It was found that the maximum load was increased by 27% due to foam filling and the buckling strength increased by confining support. The total absorbing energy was increased by 25% due to the increase in the plastic moment capacity. Similar observations were registered when a 5 mm layer of Epoxy Based Foam was deployed in the same roof system. CAE roof-crush analysis performed on the tested (B-I-W) came in good correlation with the test results. Similar CAE analysis was performed on another vehicle roof-crush model; the maximum load was reported to increase by 26% and the total absorbed energy increased by 22% when the vehicle was injected with 9 pcf polyurethane foam at the pre-determined locations. Finally, the latest model was downgaged selectively by 20% with a minimum thickness of 0.68 mm. This resulted in a total weight saving of 6 Kgs. CAE analysis showed that the resulting loss in functionality of the system due to downgaging (resistance in this case) was totally compensated by foam deployment at the predetermined locations.