# Automotive Seat Comfort and Vibration Performance Evaluation in Dynamic Settings
## 2 Materials and Methods  
### Seat Sample Preparation  
Full-size pick-up truck seats were selected for this study. Three seats were built with base level attributes (i.e., only with simple adjustment functions, no heating, venting, or pneumatics were included) to eliminate potential bias on seating comfort perceptions (Figure 1). The three seats were identical except for the foam in the seat cushions, which were specially formulated for this study. Seat B used the current production foam, whereas Seat A and Seat C contained foams with different chemical formulations. All three foams had the same density of 58 \(\pm\) 3 kg/m\({}^{3}\).  
Three cushion foam pads were tested per ASTM D3574 [12] prior to being assembled into the seats. The mechanical properties are shown in Table 1 and their definitions are as follows:  
\(-\)Foam Firmness was evaluated by the indentation force (load) deflection test and summarized as 50% indentation load in newtons.  
\(-\)Support factor (also known as compression modulus) indicates foam's ability to support weight. The support factor was calculated by the ratio of 65% to 25% indentation loads obtained from the indentation force deflection test. The greater support factor measure ments indicate that the foam can better sustain the weight while the lower support factor indicates that the foam more easily bottoms out.  
\(-\)Hysteresis loss was also evaluated by the indentation force deflection test and defined as the difference between loading and unloading portion (energy) of the load-deflection curve expressed as a percentage of the loading energy. As hysteresis loss indicates how much energy the foam can absorb, the foam with the higher hysteresis loss can better absorb vibration.  
All three seats, which were in a new and unused state, were evaluated using basic mechanical characterizations according to SAE J2896 [11]. The overall seat cushion foam hardness (i.e., load-deflection curve) as well as vibration transmissibility are shown in Figure 2. The mechanical property measures showed that Seat A was the firmest, followed by Seat B, and Seat C was the softest (Table 1, Figure 2 Left). Although the three seats differed in the foam firmness, the support factors (defined as load ratio of 65% indentation over 25% indentation [12]) remained comparable. Seat A and Seat C had less hysteresis loss than Seat B. Differences in hysteresis may affect the effective stiffness and energy management of the foam while being exposed to vibration. Both Seat B and Seat C had lower vibration transmissibility than Seat A. Seat C also had lower resonance frequency than Seat A and Seat B (Figure 2 Right).  
Overall, these three seats were specially built so that, when comparing between the newly formulated seats (Seat A and C), the firmness and peak vibration transmissibility were the major differentiators. When comparing between Seat B (current production) and Seat C, the hysteresis loss and the resonance frequency were the major differentiators per standardized SAE J2896 testing specifications.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Seat ID** & **50\% Indentation Load** & **Support Factor 1** & **Hysteresis Loss (\%)** & **Thickness (mm)** \\ \hline A & 698.4 & 3.30 & 20.3 & 84.0 \\ B & 386.6 & 3.27 & 26.5 & 82.7 \\ C & 333.8 & 3.24 & 19.7 & 82.2 \\ \hline \hline \end{tabular} \({}^{1}\) Support Factor is defined as ratio of 65%/25% Indentation loads (ASTM D3574-17).  
\end{table}
Table 1: Mechanical properties of the cushion foam pads.  
Figure 1: Three seats tested: Seat (**A**) (Left), Seat (**B**) (Middle), Seat (**C**) (Right).