## 3 Results and Discussion
### Thermal Behavior
#### 3.3.2 Ageing Tests  
The thermal behavior of Ultem 9085 was evaluated after different artificial ageing treatments:  
* Warm storage, which had the aim of verifying the maintenance of high mechanical properties of the components after a long period at high temperature;
* Cyclic climate change, which allowed evaluation of the stability of the material under investigation under a constant and periodic variation of both the temperature and humidity. These variations could in fact cause reactions of hydrolytic degradation or cracks due to water penetration and freezing;
* Thermal shock, which aimed to verify the resistance of Ultem 9085 to sudden temperature variations. In order to evaluate the effect of different ageing treatments on mechanical behavior of Ultem 9085, three-point flexural tests were performed on samples with XZ orientation (they showed the highest flexural properties, as reported in Table 5) after each ageing step (sets A, B, and C in Table 6). A set of samples was tested after the three ageing treatments (set D in Table 6). Figure 5 compares the average stress-strain curve of as-printed samples with those of specimens after different ageing treatments. The statistical analysis was performed by considering the flexural properties of Ultem 9085 samples before and after ageing treatments. The results of one-way ANOVA (Table 7) showed that the ageing factor had a significant effect on the average values of flexural strength and elastic modulus. Therefore, the [PERSON]'s HSD post hoc test was performed with the aim of identifying which environmental conditions are significantly different from the others, mainly affecting the mechanical performances of the material. The results in term of flexural strength, elastic modulus, and elongation at failure are reported in Table 8; these outcomes are compared to the mechanical properties of as-processed samples. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Ageing Treatment** & \multicolumn{2}{c}{**Set of Tested Samples**} \\ \hline Warm storage & A & \\ \hline Cyclic climate change & B & D (A + B + C) \\ \hline Thermal shock & C & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Tested samples after different ageing treatments. Figure 5: Stress–strain curves of samples after different ageing treatments. The maintenance of samples at high temperature (100 \({}^{\circ}\)C) for a long period in a dry environment (Figure 5, curve A) did not involve a significant variation of flexural properties with respect to those observed for as-printed specimens (Table 5). However, differently from these latter samples, samples A showed break at an elongation value close to the maximum that can be reached (as previously reported, the load was applied until the breakage of samples occurred or until a maximum strain of 9% was reached). On the contrary, a significant variation of mechanical properties can be observed for samples C: the stay at the temperature of 70 \({}^{\circ}\)C for a long time followed by a sudden temperature variation up to \(-\)20 \({}^{\circ}\)C (Figure 5, curve C) leading to a significant decreasing of elastic modulus and flexural strength with respect to the as-printed samples. Specimens that withstood cyclic climate change (Figure 5, curve B) also experienced a significant variation of temperature (the difference between minimum- and maximum-reached temperatures was 90 \({}^{\circ}\)C) accompanied by a change of relative humidity. The so-conditioned specimens showed a significant improvement of elastic modulus and flexural strength with respect to as-printed and aged samples. The material with increased stiffness broke at a strain value of 7.5%. These outcomes suggest that an important thermal variation, independently from the thermal gradient, has a significant effect on Ultem 9085. The results of [PERSON]'s HSD post hoc test did not show a significant difference in term of elastic modulus for samples which underwent warm storage, cyclic climate change, thermal shock (Figure 5, curve D), and thermal shock only (Figure 5, curve C).