PSI - Issue 56

Tamas Krausz et al. / Procedia Structural Integrity 56 (2024) 71–77 Krausz/ Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction Thermal loads and their long-term effects often lead to certain material failures or defects, which despite not resulting in structural damage, might end up as a claim of the customer towards the manufacturer of the specific product. In general, engineers and material specialists limit the use cases of these temperature sensitive materials to applications which are meant to function in controlled environmental conditions. However, during the lifetime of these products, they can still be subjected to various extreme temperatures. For this reason, there are several international standards ( ISO 16750-4, Road Vehicles - Environmental Conditions and Testing for Electrical and Electronic Equipment - Part 4: Climatic Loads , 2010), specifying that all the electronic products, which rely on the usage of such thermoplastics, must withstand high numbers of thermal cycles, within the -40°C to +85°C temperature range, without producing mechanical failures. Polycarbonate is one of the most widely used thermoplastic materials, from the amorphous polymer category, which offers several benefits due to its physical properties which make it the material of choice for a wide variety of applications. These include low density, transparency, high impact resistance, chemical stability, and ease of processing (Allen et al., 1973; Davis & Golden, 1969; Shah, 2009). Although the very good properties it possesses, longer exposure of polycarbonate to temperature will alter its chemical, thermal, and mechanical properties (Jiang et al., 2018; Redjala et al., 2019, 2021). The aim of this paper is to investigate the variation of the elastic properties of the proposed polycarbonate grades, such as Young’s modulus, yield strength and Poisson’s ratio, during quasi-static tensile testing of thermally aged and non-aged samples. For the non-aged samples, the effect of the temperature increase over the mechanical behavior in tension of the materials has been studied (Cao et al., 2014; Krausz et al., 2021). The investigation concludes with the comparison of both test cases with the tensile behavior of the materials at room temperature condition. 2. Experimental investigations 2.1. Specimen preparations The specimens used for the experiments were produced by injection molding, directly in their final, dogbone shape, and kept at room temperature (22 ° C) and normal humidity conditions (~50%). The shape and dimensions of the specimens were selected according to the ISO 572-2 tensile testing standard ( ISO 527-2, Plastics - Determination of Tensile Properties - Part 2: Test Conditions for Moulding and Extrusion Plastics , 2012), with a total length of 150 [mm], a gauge length of 60 [mm], a width of 10 [mm] and a thickness of 4 [mm]. The thermal aging of the specimens has been conducted in a Vötsch VT3 7006 S2 type thermal shock test system. The system consists of two low and high temperature chambers, which permit very rapid temperature changes in the range of -80 ° C to +220 ° C. The specimens were placed on the shelves inside the cradle, which makes a translatory movement between the top (hot) and bottom (cold) chambers during the thermal cycles applied. The type and number of the cycles has been selected according to the IEC 60068-2-14 international standard ( IEC 60068-2-14, Environmental Testing - Part 2 14: Tests - Test N: Change of Temperature , 2009), applicable to environmental testing. (Fig.1). Nomenclature MK2405 Makrolon 2405, polycarbonate material without glass fiber reinforcement Makrolon 9415, polycarbonate material with 10% glass fiber Makrolon 8035, polycarbonate material with 30% glass fiber MK9415 MK8035