Measured and simulated examination of the propagation paths of structure‐borne sound using the structural intensity for fibre reinforced injection moulded thermoplastic parts

Abstract

AbstractIn product development e.g. electromobility, engineers need to place special emphasis on acoustics. A large number of automotive interior components consist of injection‐moulded thermoplastic parts. If required these lightweight components are reinforced with fibres or fillings. This reinforcement leads to a higher vibration sensitivity and higher natural frequencies. Due to the fact that the auditory threshold decreases with a rising excitation frequency, a conflict of objective between acoustics and lightweight components exists. In order to influence the acoustic behaviour in early development stages, the structure‐borne sound including its source and propagation paths have to be analysed. An appropriate parameter by which to visualise these pieces is the structural intensity (STI) which is calculated by the product of velocity and stress. Previous investigations have mainly focused on the behaviour of isotropic materials e.g. steel calculated using FEM. An experimental determination of the STI is a challenge since the stress of a vibrating structure cannot be directly measured. Furthermore the experimental determination is limited to the surface of the structure. First investigations using FEM were carried out to examine composite materials with a unidirectional fibre orientation and revealed a high potential to influence the structural behaviour in acoustic matters, i.e. the transmission of structure‐borne sound. Therefore a current research project deals with the opportunities to influence the vibro‐acoustic behaviour of injection moulded parts using the structural intensity. In this paper a method is presented to examine the influence of fibres, fillings and geometric modifications on the STI for injection moulded parts using FEM. A method to measure the STI for orthotropic parts is also presented. In addition to a comparison between the measured and the simulated results, a look‐ahead at planned future investigations in the research project is given.