PSI - Issue 23

C. Skotarek et al. / Procedia Structural Integrity 23 (2019) 463–468 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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a) load-displacement curve

b) development of contact pressure

Fig. 6: Insertion process

a) schematic representation of the cohesive zone model

b) stress-displacement curve

Fig. 7: Cohesive zone model

a) comparison of simulation and experiment; bore hole opening corresponds to dL hole in Fig. 4b

b) scatter of experimental results; different colors refer to different specimens

Fig 8: Pin tip opening curves

4. Results The physical dimensions of each pin and each bore hole deviate from the expected values in a random manner. However, these values strongly influence the contact pressure and the area of the cold-welded zone in each case. The relevance of this effect was investigated by scanning 10 different pins in the computer tomograph. These pins were then inserted into printed circuits. Test specimens were cut out and loaded according to the procedure outlined above. Fig. 8b shows the recorded displacement curves. It can be seen that the characteristic form of the curves is the same in all cases, but that the stiffness of the system is significantly affected by the individual size and shape of the pin and the hole. This is especially true for the ascending part of the curve in which the crack develops in the cold-welded zone. A physical explanation for this behavior can be derived from the fact that the size and shape of the cold-welded zone is obviously influenced by the geometrical matching between the bore hole and the pin. Simulated and measured contact areas are compared with each other in Fig. 9 with the experimental case obtained by fracturing the bore hole.