PSI - Issue 47

Johannes Wiener et al. / Procedia Structural Integrity 47 (2023) 253–260 Johannes Wiener/ Structural Integrity Procedia 00 (2019) 000–000

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2. Experimental 2.1. Materials

In this contribution, investigations focused on various composites with a matrix of polypropylene (PP) with a high percentage of talcum particle reinforcement (ca. 60wt%, �� 6967 MPa, σ y � 25.4 MPa). As IL materials, a standard type of PP (PP-St, �� 1444 MPa, σ y � 23.9 MPa) as well as a very compliant PP grade (PP-Soft, �� 242 MPa, σ y � 6.8 MPa) were used. While multilayer composites with a smaller number of layers can easily be produced via co-extrusion, microlayer composites require advanced methods. Nonetheless, layer architectures with thicknesses in the micron range can be produced using a static mixer tool (Fig. 3), as demonstrated by e.g. (Köpplmayr and Miethlinger 2014). By repeatedly folding the melt strands, composites with a variable number of layers could be produced, resulting in different layer thicknesses, t . In these microlayer composites, only PP-Soft was used as toughening agent, while both IL materials were used in multilayer composites. However, the investigation of microlayer composites was also extended to blends of the base materials, which were not investigated for multilayer composites.

Fig. 3. Multiflux static mixer for the production of microlayer composites (reprinted with permission of (Wiener et al. 2021)).

2.2. Methods The analysis of microlayer composites was conducted comparably straight forward using impact strength, a c , according to ISO 179 and the bending modulus, E b , according to ISO 178 as measures of toughness and stiffness. However, detailed investigation of multilayer specimens called for advanced methods from elastic plastic fracture mechanics. Since J tip cannot be measured directly, an experimental measure for fracture toughness is required. Therefore, the experimental J -integral, J exp , according to the multispecimen method (ESIS TC4 recommendation, (Hale and Ramsteiner 2001)). The tests were carried out on single edge notch bending (SENB) specimens and evaluated using Eq. 2 and Eq. 3. The parameter ٠according to Eq. 4 was introduced as a measure for the relative increase in the critical J exp for specimen failure of multilayer composites compared to the homogeneous matrix material. Simultaneously, an equivalent modulus E eq was generated based on the bending modulus from ASTM E1820 as a measure of stiffness. More detailed descriptions of all presented methods and results can be found in previous contributions (Wiener et al. 2020; Wiener et al. 2021; Wiener et al. 2022; Wiener 2023). � � ��� � � � � � � (2) ��� � � � 1 � �� . ����������� � � (3) �� � ������������ � � �� � � ���� (4)