## 3 Results
### Validation of FE Analysis  
In order to validate the finite element analysis, the flexural test was carried out by applying a deformation, and the maximum force values at the previously determined deflections (2, 4, 6 and 8 mm) were compared. The results of the experimental and the simulated investigation with the unloaded and the loaded (8 mm deflection) door handle are presented in Figure 8. The simulation results were shown on a solid body model with the distribution of stress presented on the deformed body with a colour ramp, while the undeformed figure was a solid green colour. It can be seen from the compilation that the correspondence was notable; however, quantitative values were compared for an exact comparison.  
Figure 6: Explanation of measurement of fibre orientation in a section of one fibre, based on [16], (**a**) and one measured optical microscope image (**b**).  
Figure 7: Validation of fibre orientation across the thickness, 10 mm from the end of product (“c”—calculated data with AMI; “m”—measured data according to optical microscopy with standard deviation).  
The generated force as a function of time at a 4 mm deflection is presented in Figure 9. In both experimental and simulated investigations, force continuously increased until it reached a maximum; then, the force started to decrease until a constant value was achieved in the experimental investigation, while, in the simulation, it remained constant. This difference may possibly be because our simulation did not take stress relaxation into account; therefore, the reaction force remained constant after reaching the set deflection, while, in reality, the force would have relaxed, as shown in the diagram. Stress relaxation is a phenomenon in which a constant deformation at a constant temperature and humidity to a plastic is applied; then, the stress required to maintain a constant deformation decreases with time [32]. Some models, for example, the VAMUCH (variational asymptotic method for unit cell homogenisation), can calculate stress relaxation [33], but we used the built-in Abaqus model instead.  
Figure 8: The unloaded and loaded (8 mm deflected) door handle in reality (**above**) and in simulation (**below**).  
Figure 9: The force–time curves at 4 mm deflection.  
The flexural rigidity (EI) of the door handle was derived from the deflection formula for a cantilever beam (4) [34], based on the measured and the finite element analysis results:  
\[f=\frac{FL^{3}}{3 EI} \tag{4}\]  
where \"f\" is the determined deflection, \"F\" is the maximum reaction force and \"L\" is the distance between supports (55 mm).  
The calculated flexural rigidity values and relative errors are presented in Table 1. The EI values from the door handle simulation showed less than a 15% difference from the measured rigidity values, which was an acceptable difference. The relative errors at an 85% confidence level were between 6.06% and 15.84%. From the results, it could be concluded that for the 8 mm deformation of a door handle with such geometry, applying a relatively small force was enough (223.8 N), which could easily be reached by not opening the door carefully. However, it has to be mentioned that a short period load (which is typical in reality) would not cause a residual deformation, so the door handle would not suffer damage.