A Study on the Joint Structures for the Improvement of Stiffness and ...

Session: B2A <strong>Study</strong> on the Joint Structures for the Improvement of Stiffness andCrashworthinessPark, Chang-Wook * An, Yongdok Kim, Dae SeungHyundai∙Kia Motors, 772-1, Jangduk-Dong, Hwaseong-Si, Gyeonggi-Do, 445-706, KoreaKey Word: Body-in-White, BIW, Load-Path Analysis, Joint Stiffness, CrashworthinessABSTRACTJoint structures in BIW play a significant role in the NVH and crashworthiness of vehicle. Theresearches on the design of joint structures, however, are very limited. The main drawbacks in thedesign of joint structures are complexity and difficulty in assessment of effectiveness to globalperformance. For example, B-pillar lower joint connects rocker with B-pillar. This joint partgenerally effects to the torsional stiffness of BIW and also contributes in side impact situation.However, it is very difficult to decide a certain joint structure is well-designed or has enoughrigidity. Load-path analysis can be a good alternative to this problem. The characteristics, functionsand the robustness of each joint structure are identified by employing load-path analysis. Using thishelpful methodology, we suggest new BIW design with improved joint structures. We first selected9 joint structures in BIW (Fig. 1) to be modified as following;1) Front apron ~ A-pillar: load-path improvement,2) Cowl ~ Strut tower ~ A-pillar: increasing section and connectivity improvement,3) A-pillar ~ Rocker ~ Rear wheel house: increasing joint stiffness,4) Rear floor cross member: increasing section,5) ~8) Rear structures: supplement of connectivity for discontinuous parts,9) Package tray: increasing section for ring structures and additional load-path.Fig. 1 Improved joint structures*Corresponding author. Tel.: +82-31-368-3349; fax: +82-31-368-3327,E-mail : cwpark66@hyundai.com

Fig. 2 Changes in rear structuresFor example, analysis results showed that load-path is not continuous in rear structures (5~8). Newparts are added to connect above discontinuous structures. (Fig. 2) These modifications completethe ring structure in rear body and also provide new load-paths. Mainly above problems are causedby manufacturing reasons; limited approaching range of resistance spot welding and/or cycle timeconstraint of arc welding. Laser welding is applied to overcome these issues. Performance of newBIW is increased 83 % in static rigidity and 13 % in dynamic aspect. For crashworthiness, intrusioninto compartment in IIHS OFFSET test is decreased by 14 %. Total mass increase is 4.3 kg, butthere was no major change in previous parts. This means that our future works is to optimize bothnew and previous part.