Electric guitar neck from densified poplar? Experimental and numerical analysis

Electric guitar necks (EGNs) and parts are usually made of hardwoods (i.e., maple, ash, etc.), including protected exotic species coming from overseas (mahogany, etc.), due to their aesthetics, high stiffness and density. Additionally, EGNs typically include a truss rod – a metal bar stiffening the neck against bending caused by string tension. In order to reduce the environmental impact of guitar production, we believe that EGNs can be made from local and fast grown plantation wood modified using a thermo-hydro-mechanical (THM) process. In this paper, we analyze the potential of using THM densified poplar wood as a substitute material for EGN. We believe our approach for EGN production may be (i) more convenient due to higher mechanical properties of densified wood while preserving similar vibrational performance; (ii) more economical due to local and cheap resources use and absence of a truss rod; (iii) more environmentally friendly due to reduced logistics and energy costs. To analyze the hypothesis resulting from (i), we performed both experimental tests and numerical analyses. Experiments consisted of poplar wood densification (dens. ratio 2) to obtain the elastic orthotropic material model of densified poplar suitable for finite element analyses (FEA). We carried out compression tests accompanied with digital image correlation which provided a set of elastic material coefficients – 3x normal elastic moduli (EL, ER, ET), 3x Poisson’s ratios (μLR, μRT, μLT); 3x shear elastic moduli (GLR, GRT, GLT) were calculated from measured values. Developed material models were employed in FEA of (i) guitar neck deflection induced by string tension and (ii) modal analysis of a neck including sensitivity study for the role of density and elastic moduli on eigenfrequencies. FEA showed the highest 1st principal stress (PS1) is located on the bottom of the neck. Further, PS1 changes with change of EL – deflection decreased 40 % and PS1 increased ~ 11 % as EL increased from 12.4 GPa to 22 GPa. Eigenfrequencies decrease with density but increase as EL increases (1st freq 17.4 %, 2 nd freq. 21.4 % and 3rd about 27 %).