# Thermal-Mechanical Behaviour of Road-Embedded Wireless Charging Pads for EVs
###### Abstract
Due to the importance of power losses generated within IPT pads, multiple studies have been conducted to experimentally and numerically obtain their thermal response during operation. For temperature prediction, coupled electromagnetic-thermal simulations are typically used, because losses in the coil and ferrite are temperature-dependent [6; 7; 9; 10; 11]. [PERSON] et al. developed and validated finite element-based transient coupled simulations on a 1/4 -scale double-D (DD) IPT pad energized in a sandbox [6]. [PERSON] et al. used finite element (FE) simulations to evaluate the steady-state thermal response of the full-scale version of the pad used by [PERSON] [7]. [PERSON] et al. used a similar approach to obtain the transient temperature of the coil of an unpotted circular pad [9]. [PERSON] et al. compared the transient temperatures predicted from one-way and two-way coupled simulations on a secondary pad with a rectangular coil [10]. While most researchers used the finite element method for thermal simulation, computational fluid dynamics (CFD) have also been used [11; 12; 13]. Notably, [PERSON] et al. used CFD to predict the steady-state temperature of coupled primary and secondary DD pads [11]. There is very limited research on the structural behaviour of IPT pads. [PERSON] et al. developed an experimental methodology and an FE model for investigating the structural response of a 1/4 -scale DD pad to wheel loading [14]. The experimental characterization and optimization of the mechanical performance of individual litz wires and ferrite componentry were conducted by [PERSON] [15]. Several other studies have used finite element analysis (FEA) to investigate the structural behaviour of IPT roadways with wheel loading; however, they have focused on the response of the pavement surrounding the charging device [16; 17; 18]. The reviewed literature can broadly be split into two categories: thermal analyses of IPT systems for the determination of operating temperature [6; 7; 9; 10; 11; 12; 13], and structural analyses of IPT systems when under wheel loading [14; 15; 16; 17; 18]. There is a clear gap in the literature regarding the structural behaviour of IPT pads due to thermally induced loading. Given this, the objective of this paper is to present an experimental and FEA-based numerical investigation on the thermal-mechanical behaviour of a primary IPT pad. A focus was placed on the thermal-mechanical response of ferrite due to its brittleness, and hence potential for premature failure in service. The experimental results were used to validate the finite element (FE) model. It was anticipated that it would be difficult to pinpoint sources of any potential deviation between experimentally measured and numerically predicted strains, due to the multiple components and material systems within a road-embedded pad. The most complex components from a modelling perspective are the coil and the surrounding pavement. The coil is both heterogenous and anisotropic, while pavement materials are heterogenous. To ascertain the contribution of the coil and pavement materials to any differences between the experimental and numerical results, three sets of thermal load cases were investigated. First, a pad without a coil was heated to uniform temperatures within an oven. In the second experiment, a complete IPT pad (i.e., with the coil) was suspended inside an environmental chamber (i.e., can freely expand) and energized with an alternating current. In the final experiment, the same pad was embedded in a simulant asphalt material and re-energized to obtain the most realistic thermal-mechanical response. The pad without a coil will subsequently be referred to in this paper to as the 'partial pad', while the pad with a coil will be referred to as the 'complete pad'. The paper starts with a description of the structure of the double-D (DD) pad, followed by the multi-physics characterization of the materials within.