PSI - Issue 54

Johannes Kaiser et al. / Procedia Structural Integrity 54 (2024) 26–33 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2.2. Crack tip heating The determination of the heat generated on pre-cracked test specimens has already been the subject of various research projects. For amorphous plastics, such as polycarbonate, polystyrene, polymethylmethacrylate, etc., temperature changes of a few Kelvin [6] up to 700 K [7] have been observed. However, problematic for a comparability of the results are the non-comparable test conditions (test specimen geometry, test specimen speed) and the measurement technique used. In addition to the use of embedded thermocouples [8], these are temperature sensitive foils which change their color when the temperature is increased [6] or thermographic cameras with different temporal and spatial resolution [9, 10, 11]. Some of the tests listed here show a temperature increase of the materials that far exceeds the glass transition temperature. However, it could not be shown in these tests at which stage of the crack growth and at which point of the crack the temperature changes occur. 2.3. Problem and objective Publications in the literature [7-11] and previous work [12] show that at least a softening locally before the crack tip is a realistic scenario. If, in addition, a transition temperature of the amorphous plastics is exceeded, a significant influence on the fracture mechanical properties, which has not yet been applied in design processes, would be possible. In the context of this publication, a setup is to be presented for the first time that can investigate the temperature with spatial and temporal resolution during the fracture initiation and research step on the basis of amorphous polymers by combining a high-resolution thermographic camera with an image correlation system. 3. Experimental setup 3.1. Materials and specimen preparation Three amorphous thermoplastics with high technical relevance were selected for the investigations. Due to the expected brittle material behavior, the impact modified polystyrene (PS) PS486N from Ineos Styrolution Group GmbH, Frankfurt am Main, was chosen. In order to be able to additionally map the influence of the molecular chain length and the pseudo-ductile material behavior on the crack spatter heating, two polycarbonate grades (PC) were used. These were PC1100, hereafter referred to as PC n (low viscosity), and PC1220, hereafter referred to as PC h (higher viscosity), from Lotte Chemical, Seoul, South Korea. The plastics were dried in vacuum ovens according to the manufacturer's instructions and then processed on an Allrounder 370s injection molding machine from Arburg, Lossburg, Germany. Type 1A tensile test bars were produced in accordance with DIN EN ISO 527-2 to determine the mechanical properties. For the fracture mechanics tests, both Single-Edge-Notched Tension (SENT; cf. Fig. 1, left) and Compact Tension (CT; cf. Fig. 1, right) were produced from the injection-molded plates using a milling machine. The geometry selected for this purpose is also shown in Fig. 1.

Figure 1. Test specimen geometry for the determination of fracture mechanical properties