Simulation and Modelling of Injection Molded Components : Fiber Reinforced Polymers in Powertrain Mounts

Abstract: Powertrain mounts' purpose is to mount the engine and the gearbox in the car. Besides that, it isolate the body from the powertrain movements and road excitation. The most common material in powertrain mounts bracket is aluminum but lately, fibre reinforced polymer (FRP) has been acting as a substitute for the aluminum. The major drive forces for the change is the possibility to decrease the weight and improve the attribute noise, vibrations and harshness (NVH). The main objective of this study was to compare aluminum and FRP in order to find advantages and disadvantages for use in a powertrain mount bracket. FRP's have in earlier investigations at Volvo Cars been assumed to be isotropic, although it is orthotropic due to fiber orientation. Hence, a comparison between isotropic and orthotropic material properties for the powertrain mount bracket was conducted. There was no established method for modelling orthotropic materials available at the powertrain mount department, so a suggestion of a work process was presented in this thesis. Information regarding FRP, as well as a comparison to aluminum was presented in a literature study. The different materials and material models were compared in series of stress-strain and eigenmode FEM analyses. The results from the stress-strain analyses evinced that the design for the aluminum bracket can withstand the loads without exceeding the design limit. In the FRP bracket with orthotropic material properties, the design limit was exceeded for the load cases with the highest load. The results from the stress-strain and eigenmode analyses of the isotropic and orthotropic material models showed significant differences. According to the isotropic material model, the bracket could withstand the loads, and the eigenfrequencies was 25-30% higher compared to the orthotropic material model. The conclusions drawn from this study was that FRP's may be an advantageous material for the powertrain mount bracket, compared to aluminum. The FRP's bracket will decrease the cost, weight, and carbon footprint as well as improve the NVH. However, difficulties of using FRP's have been observed and need to be further investigated. The main difficulties identified are creep, fatigue, moisture absorption, and aging. This study has also proved that orthotropic material properties must be included in order to understand the material behavior and find critical areas.