Abstract:
Polyethylene terephthalate glycol (PETG) is characterized by a double refraction effect which is used when modeling the stress states of building structures. This paper aims to study the mechanical properties of PETG due to the need for practical approval of the modeling results.
Experiments show that, for most plastics, the initial region of the stress-strain diagram significantly deviates from a straight line. However, an extended interval can be distinguished in this region, where the diagram is well approximated by a linear function. If the deviations of the diagram from the straight line are random, it is possible to test the statistical hypothesis of their correspondence. Only diagrams with valid hypothesis are applied in this study.
Twelve PETG samples have been tested using the fused deposition modeling (FDM) method. For the five diagrams, the hypothesis of the presence of the linear region in interval $\epsilon\in [0.0075; 0.0275]$ is confirmed at a deviation significance level of $1\%$. The Young's modulus determined using the diagrams is $2.044 \pm \genfrac{}{}{0pt}{}{0047}{0.027}\times 10^9$ Pa. This value falls within interval $2.01 \times 10^9\div 2.11 \times 10^9$ Pa presented on Wikipedia. The obtained yield strength is $49.71 \pm 1.81$ MPa, which is consistent with the results reported in the literature and reference data.
Keywords:statistical hypothesis testing, Pearson criterion, stress-strain diagram, Young modulus.
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