PSI - Issue 40

S.A. Bochkareva et al. / Procedia Structural Integrity 40 (2022) 61–69 Bochkareva S. A., Panin S. V. / Structural Integrity Procedia 00 (2019) 000 – 000

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Thus, the observed macro- and micro-bending depended on the interlayer thickness and its properties. Both factors influenced the distribution of strains and stresses and, as a consequence, the fracture behavior of the welded joint. Calculated dependences of the failure loads on the adhesion level and the number of contacting nodes at the adhesion level equal to the PEEK yield point are shown in Figure 10 for the ‘PEEK -PEEK film- PEEK’ welded joint under tension. The adhesion level equal to one correlated with both ultimate stresses and the PEEK yield point. The fracture loads changed nonlinearly on the adhesion level and linearly on the number of contacting nodes. With a decrease in the adhesion level and contacting nodes delamination occurred only.

Fig. 10 – The dependences of the failure loads on the adhesion level (a) and the number of contacting nodes (b) for the ‘PEEK -PEEK film- PEEK’ welded lap joint under tension

Figure 11 presents the calculated dependences of the fracture loads on strains at the adhesion level equal to the PEEK yield point. Curve 1 is presented for the PEEK plate for comparison, which indicated the correctness of the implemented model. All other curves reflected the fact that the maximum strength could be achieved by different USW procedures for joining the PEEK plates at the adhesion level corresponding to the PEEK yield point. The lowest tensile strength was found for the ‘PEEK -PEEK film-PEEK prepreg/USW-PEEK film- PEEK’ welded joint due to the high thickness and stiffness of the interlayer, while the greatest one was observed for the ‘PEEK -PEEK film- PEEK’ composition. Thus, it is necessary to obtain the minimum possible interlayer thickness when using PEEK films as a binder in the USW procedures or to form the highest adhesion level at the interface.

Fig. 11 – Stress-strain diagrams for the PEEK sample (1) and the following welded lap joints: (2) ‘PEEK - PEEK’; (3) ‘PEEK -PEEK film- PEEK’; (4) ‘PEEK -PEEK prepreg/USW- PEEK’; (5) ‘PEEK -PEEK film-PEEK prepreg/USW-PEEK film- PEEK’ 3. Conclusions The developed and implemented model of the welded lap joints, considering repreg as a CF-reinforced composite, discontinuities at the interface, the adhesion level and fracture patterns, enabled to study the effect of the