Enhanced Development Process for UPDs – Digital Approach

Underrun Protections devices (UPDs) are specially designed barriers fitted to the front, side, or rear of heavy trucks. In case of accidents, these devices prevent small vehicles such as bikes and passenger cars going underneath and thus minimizing the severity of such accident. Design and strength of UPD is such as to absorb the impact energy and minimise deflection to avoid the under run. Compliance to UPD safety regulations provides stringent requirements in terms of device design, dimensions, and its behaviour under loading. Since accuracy of Computer Aided Engineering (CAE) predictions have improved, use of numerical tools like Finite element method (FEM) are extensively used for design, development, optimisation, and performance verification with respect to regulatory requirements. For improved accuracy of prediction of results through FEA, correct representation of sub-systems is very important. One such sub-system in UPDs is bolted connections, which require accurate methods to represent critical characteristics, especially under extreme loading situations. The two primary characteristics in the bolted connections are a pretension and a mating part contact. The paper describes the UPD analysis with two types of bolt modelling methods, a) solid elements method b) a combination of beam, shell and constrained spot-weld elements. The solid element method can accurately predict the physical behaviour of the structure through mating part contact. The failure behaviour of the solid models is based on an elasto-plastic material, defined by a piecewise stress-strain curve and a strain rate dependency and the bolt failure can be predicted through strain-based failure criteria. In improved method mating part contact is achieved through shell elements modelling and failure is based on the “constrained spot-weld failure”. It requires only the values of maximum axial and shear force at failure, usually known from component level physical tests on bolt. The advantage of improved method is that pretension can be introduced in this method. Prediction of performance with both methodologies is validated in physical tests and correlation between CAE and Test is established.