TY - THES

T1 - Environmental stress cracking of high-impact polystyrene and polycarbonate polyurethane in application-oriented media

AU - Huemer, Martin

N1 - embargoed until 06-06-2023

PY - 2022

Y1 - 2022

N2 - In practice, materials are exposed to various environmental influences, including different temperatures and environmental media. Depending on the chemical structure of the polymer, this can significantly change the behaviour of the material. For this reason, it is of great interest to determine the properties of materials under conditions that are as close to reality as possible. For this purpose, two different polymer types were investigated regarding their mechanical behaviour under real environmental conditions. In the first part, the environmental stress cracking resistance (ESCR) of impact-modified polystyrene was analysed. Two polystyrene types, differing in the size of the rubber particles, were subjected to both static and cyclic loads in air and in sunflower oil. Under long-term static loading in sunflower oil, it was found that, as the size of the rubber particles increases, ESCR increases. However, without the influence of the oil, smaller particles resulted in significantly higher resistance to crack growth. The detection of the crack tip during tests in oil proved to be very difficult. There is still potential for improvement with this regard for future investigations. In the cyclic "cracked round bar" tests, the larger particles proved to be significantly more effective in air and also in oil. In the second part of this work, a thermoplastic polycarbonate polyurethane was investigated for possible future use as as bone and tissue replacement via additive manufacturing. Again, two different types were investigated, differing in their hard-to-soft segment ratio. To simulate material behaviour in the application condition, the materials were tested at elevated temperatures immersed in a simulated body fluid. Conditioning studies, tensile tests and high-cycle fatigue tests were performed to analyse the influence of the media. It was shown that absorption of body-like fluids resulted in a decrease in stiffness and tensile strength and an increase in elongation at break. Similar effects were observed for the material with a lower proportion of hard segments due to increased temperature. For the material with the higher hard segment content, the tensile strength and elongation at break increased at the elevated temperature. The high-cycle fatigue tests showed that as the amount of liquid absorbed increases, the fatigue behaviour deteriorates considerably. The fatigue strength of the fully saturated specimens showed a parallel shift compared to that of the untreated specimens to 20 % lower stress values. Even an absorption of around 20 % of the maximum possible absorption quantity of simulated body fluid causes the same decrease in the tolerable stresses.

AB - In practice, materials are exposed to various environmental influences, including different temperatures and environmental media. Depending on the chemical structure of the polymer, this can significantly change the behaviour of the material. For this reason, it is of great interest to determine the properties of materials under conditions that are as close to reality as possible. For this purpose, two different polymer types were investigated regarding their mechanical behaviour under real environmental conditions. In the first part, the environmental stress cracking resistance (ESCR) of impact-modified polystyrene was analysed. Two polystyrene types, differing in the size of the rubber particles, were subjected to both static and cyclic loads in air and in sunflower oil. Under long-term static loading in sunflower oil, it was found that, as the size of the rubber particles increases, ESCR increases. However, without the influence of the oil, smaller particles resulted in significantly higher resistance to crack growth. The detection of the crack tip during tests in oil proved to be very difficult. There is still potential for improvement with this regard for future investigations. In the cyclic "cracked round bar" tests, the larger particles proved to be significantly more effective in air and also in oil. In the second part of this work, a thermoplastic polycarbonate polyurethane was investigated for possible future use as as bone and tissue replacement via additive manufacturing. Again, two different types were investigated, differing in their hard-to-soft segment ratio. To simulate material behaviour in the application condition, the materials were tested at elevated temperatures immersed in a simulated body fluid. Conditioning studies, tensile tests and high-cycle fatigue tests were performed to analyse the influence of the media. It was shown that absorption of body-like fluids resulted in a decrease in stiffness and tensile strength and an increase in elongation at break. Similar effects were observed for the material with a lower proportion of hard segments due to increased temperature. For the material with the higher hard segment content, the tensile strength and elongation at break increased at the elevated temperature. The high-cycle fatigue tests showed that as the amount of liquid absorbed increases, the fatigue behaviour deteriorates considerably. The fatigue strength of the fully saturated specimens showed a parallel shift compared to that of the untreated specimens to 20 % lower stress values. Even an absorption of around 20 % of the maximum possible absorption quantity of simulated body fluid causes the same decrease in the tolerable stresses.

KW - Environmental stress cracking

KW - high-impact polystyrene

KW - polycarbonate polyurethane

KW - long-term properties

KW - fracture mechanics

KW - S-N test

KW - Umgebungsbedingte Spannungsrissbildung

KW - hochschlagfestes Polystyrol

KW - Polycarbonat

KW - Polyurethan

KW - Langzeit Eigenschaften

KW - Bruchmechanik

KW - Wöhlerversuche

U2 - 10.34901/mul.pub.2023.106

DO - 10.34901/mul.pub.2023.106

M3 - Master's Thesis

ER -