1st ICAI 2020

International Conference on Automotive Industry 2020

Mladá Boleslav, Czech Republic

tested under comparable conditions. A typical bio-material, a polylactic-acid based polymer, was chosen. For better comparison to the state-of-the-art, not only literature values of shear-strength were collected but also reference materials were acquired to be tested accordingly. These materials were then joined with the joining methods shown in Table 1. Table 2 gives an overview of the plastic materials used within the study. PLA, PET and PP were joined with the aluminium alloy AW6082 T6 (thickness: 1.5 mm) and tested destructively. As shown in Figure 2 all plastic specimen had the same thickness of 0.5 mm, but melting temperature as well as the strength of the basic material were different. These characteristics influence the process parameter for thermal joining and the maximal possible joining strength.

Table 2: Overview of the plastic material properties PLA PET

PP 22

Strength [MPa]

61

57

Melting temperature [°C]

149

250

143

Thickness [mm]

0,5

0,5

0,5

Source: own measurements 2.1 Test specimen design

To be as comparable as possible to other sources, typical lap-shear tests and geometries were used in accordance to DIN-EN-1465-2009. A limitation of this method is a superposition of shear and peel load during testing of thin and flexural slack materials. In addition, the base strength of thin plastic specimen can cause problems. Higher joint strength in the overlap area sometimes leads to cohesive failure in the plastic base material next to the joint. Thus, the results cannot show the actual shear strength possible (e.g. in industrial applications with more bulky geometries). To overcome this limit and to acquire area-independent shear strength values, double-lap joints where used: A plastic sample plate was joined to metal plates on both sides, Figure 2. While the conditions on the metallic-plastic interface are the same, tensile forces are now transmitted into the joining interface only by the metal plates and not by the (weak) plastic part. As a result, the metal-plastic interface can be directly tested even with thin plastic plates.

Figure 2: Test specimen design for adhesive bonding (left) and thermal direct joining (right). green: plastic; grey: aluminium alloy; black: adhesive

Source: own elaboration

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