Prediction of Crash Performance of Adhesively-Bonded Vehicle Front Rails

Adhesive bonding provides a versatile strategy for joining metallic as well as non-metallic substrates, and also offers the functionality for joining dissimilar materials. In the design of unibody vehicles for NVH (Noise, Vibration and Harshness) performance, adhesive bonding of sheet metal parts along flanges can provide enhanced stiffening of body-in-white (BIW) leading to superior vibration resistance at low frequencies and improved acoustics due to sealing of openings between flanges. However, due to the brittle nature of adhesives, they remain susceptible to failure under impact loading conditions. The viability of structural adhesives as a sole or predominant mode of joining stamped sheet metal panels into closed hollow sections such as hat-sections thus remains suspect and requires further investigation. As modern vehicle design is primarily driven by CAE (Computer-Aided Engineering), it is important to ensure that the experimental behaviors of adhesively-bonded components can be satisfactorily predicted. With the stated issues in mind i.e. gathering insight into the performance of adhesively-bonded steel hat-section components under impact loading and simulation of its behavior using an explicit FEA code such as LS-DYNA, a systematic experimental and numerical study is carried out comprising: (a) testing of single lap shear joints in a UTM and prediction of the average mechanical behavior of the joints till failure using a cohesive zone material modeling approach for the adhesive with independent Mode I and Mode II fracture criteria; (b) axial impact testing of double-hat section components with conventional spot welds, the same components with purely adhesively-bonded flanges in lieu of spot welds, and hybrid components with adhesive-bonding as well as sparse spot welds, and prediction of the detailed impact responses of the components mentioned; and (c) finally, implementation of the adhesive-based joining strategies in front rails of a validated finite element model of a commercially produced unibody passenger car and assessment of its performance vis-à-vis the baseline vehicle in full frontal NCAP test mode against a rigid barrier.