Design and Optimization of Door Trim Grab Handle

Abstract

Plastics are used in components of motor vehicles that may be impacted by passenger or pedestrians in road accidents. Improved performance specifications for these components are required to meet legislation aimed at increasing levels of protection in event of accident. Grab Handle is one of the components of a Door Trim used for occupants during ingress and egress. Although there is no specific regulation exists, its performance is validated based on criteria specified by OEM. Grab handle subjected to various forces during abusive and crash loading should be designed for strength and stiffness as measured by stress, strain and deflection. It is important to distinguish between the stiffness of a polymer and the strength of a polymer. The stiffness describes the resistance to elastic deformation; the strength describes the resistance to collapse by plastic yielding or fracture. Depending on the application, one or the other may be design limit. Much of the engineering design with polymer is based on stiffness and the aim is to keep elastic deformation below critical limit.

Finite element analysis with Topology optimization is used at the concept level of the design process to arrive at a conceptual design proposal that is then fine tuned for performance and manufacturability. The objective function of topology optimization is to minimize the mass of the component subject to stress and deflection constraint and is used as a guide in determining optimal distribution of stiffening ribs. CAD model of existing grab handle along with topology optimized one further considered for comparative study based on static loading, crash analysis and moldflow analysis.

In Static analysis grab handle is required to sustain excessive pull load of 1000N without failure. Alternate materials and mounting scheme, which can sustain higher stresses in abusive loading condition also studied. Crash analysis is performed to determine force level generated during impact, which should be within defined limits, to reduce occupant injuries due to stiffening of ribs. Moldflow software simulation is used for validating and optimizing the injection molding design process. The simulation set-up and results are used to interpret to show how changes to wall thickness, material and geometry affect manufacturability for thermoplastic materials.

Hypermesh 11.0 and Optistruct 11.0 is used for meshing and topology optimization. Static simulation is performed using Abaqus 6.11 to confirm stress and deflection behavior. Side impact crash analysis done in Pamcrash helped to establish performance of different material. Autodesk Simulation Moldflow software provided results for fill time and cavity pressure analysis.