# Static Factors in Sitting Comfort: Seat Foam Properties, Temperature, and Contact Pressure
## 3 Experimental Campaign
### Experiment 1: Mechanical Properties Assessment  
Following both Refs. [58; 59] ISO 2439 and ISO 3386 recommendations, an experimental setup was developed to measure and calculate foam hardness, SAG factor, and hysteresis loss. The setup consists of a hydraulic actuator (1) connected to a 200 kN load cell (2) and a posterior 5 kN load cell (to increase the measurement resolution) (3). A circular plate (4) was attached to the 5 kN load cell, which performs complete contact with the seat sample (5). The actuator's internal LVDT measured the plate displacement. A control-and-acquisition system was used to control the actuator speed and record the force. Figure 2 illustrates the experimental setup. Both Refs. [58; 59] ISO 2439 and ISO 3386 experiments perform the vertical movement of the plate (200 mm diameter) at a constant speed of 100 mm/min. Figure 3a,b shows the experimental tests conducted on both current AP seats, namely on comfort and standard foam cushions without and with seat covers, respectively. In its turn, Figure 3c,d represents the experimental tests conducted on the older AP seats without and with seat covers, respectively. Hysteresis loss and SAG factor experiments run only in foams without cover. These were applied to the 25% ILD hardness experiments to avoid damage to the covers. Table 1 presents the hysteresis loss percentage and the force was achieved at 75% deformation. Figure 2: Experimental setup developed for measuring foam mechanical properties. Similar results were obtained regarding the cushions of the same foam type, which may indicate that the foam thickness does not influence the hysteresis loss percentage, complying with the observations conducted by [PERSON] [26]. Comparing the results of the current and older seats, the latter presented slightly higher, but not significant, hysteresis loss. Therefore, considering only this property, both seats are expected to perform well and similarly. Moreover, the results have demonstrated lower values than those reported by [PERSON] and [PERSON] [13] and [PERSON] et al. [4]. Figure 4a,b illustrates the hysteresis loss of current and older AP seat cushions, respectively. \begin{table}
\begin{tabular}{c c c} \hline
**Seat Cushion** & **Hysteresis Loss \%** & **\(\mathbf{F_{75\%}}\) (N)** \\ \hline Current comfort seat & 13.7 & 1024 \\ \hline Current standard seat & 13.8 & 598 \\ \hline Older comfort seat & 15.1 & 1255 \\ \hline Older standard seat & 14.9 & 542 \\ \hline \end{tabular}
\end{table} 
Table 1: Hysteresis loss percentage and force at 75% deformation for the four analysed cushions. Figure 3: Experimental tests were conducted on current AP seats, without a cover (**a**) side and with a cover (**b**); and older AP seats, without a cover (**c**) and with a cover (**d**). Regarding the SAG factor, as mentioned above, it should be, ideally, superior to 2.8 for seating applications [4; 7; 13; 23; 24]. Table 2 presents the calculated values for both foam types. \begin{table}
\begin{tabular}{c c} \hline \hline
**Seat Cushion** & **SAG Factor** \\ \hline Current comfort seat & 2.7 \\ \hline Current standard seat & 2.0 \\ \hline Older comfort seat & 3.2 \\ \hline Older standard seat & 2.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: SAG factor results. Figure 4: Hysteresis loss illustration of (**a**) current AP seats and (**b**) older AP seats. Observing the results, the older foams demonstrated a higher SAG factor than the new ones. Its results are closer and superior to 2.8 regarding the standard and comfort cushions, respectively. Current and older seat foams are different in terms of density but equal in dimensions. Therefore, based on the current results, it may be concluded that density is affecting the foam-supporting capacity. Moreover, the current standard seat has the lowest supporting factor of all foams. When comparing both seat types' (comfort and standard) SAG factors, an increase is noticed for the thicker seat, which may indicate the influence of foam thickness on this physical property. The 25% ILD hardness evaluated hardness.