PSI - Issue 66

Carl H. Wolf et al. / Procedia Structural Integrity 66 (2024) 26–37 2 Carl H. Wolf, Sebastian Henkel, Christian Düreth, Maik Gude and Horst Biermann / Structural Integrity Procedia 00 (2025) 000–000

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direction lead to interlaminar shear stresses, which can cause delamination which can ultimately yield fatigue failure of the material. To investigate the influence of these bolt-rivet connections on the fatigue properties of FRP components, specimens made of carbon fiber-reinforced plastic composite (CFRP) specimens with a hole-notch arrangement were tested. For this purpose, a test setup developed for this load case was used, which represents the superposition of stresses on the connecting elements [1, 2, 10]. So far, there are no established test specifications and analysis methods for this test method to determine the critical energy release rates based on the external loads. As soon as a crack is present in a specimen, the crack tip loading is currently only determined using finite element (FE) calculations. The aim of the current study is therefore to develop a measurement method for determining the crack tip loading using a local measurement concept. The measurement concept is validated by a stress analysis using FE analysis and a comparison with fatigue data of Sutton [8], who investigated fatigue crack propagation in an epoxy polymer, Yao [16], who investigated Mode I fatigue delamination growth in composite laminates with fiber bridging and DCB-specimen under pure Mode I fatigue delamination growth made of the same material [12].

Figure 1: Schematic illustration of a joint of two CFRP components with possible interlaminar cracks/delamination (red lines). Nomenclature CFRP carbon fiber-reinforced plastic composite DIC digital image correlation E Youngs’s modulus E I , E II Youngs’s modulus in direction of Mode I or rather Mode II crack opening direction FE finite element FRP fiber-reinforced plastic composites f camera image acquisition frequency of the camera f machine test frequency of the servo-hydraulic testing system F compression, F tension compressive or rather tensile force F tension, amplitude amplitude of the tensile force F tension, mean mean tensile force G energy release rate G I (t), G II (t), G eq (t) time dependant Mode I, Mode II or rather equivalent energy release rate  G general cyclic energy release rate  G eq equivalent energy release rate  G eq, Clip ,  G eq, FE equivalent energy release rate determined by virtual measuring clip or FE analysis, respectively  G I ,  G II Mode I or Mode II energy release rate K general stress intensity factor K eq, min (t), K eq, max (t) time dependant Mode I, Mode II or equivalent stress intensity factor  K eq equivalent stress intensity factor K I (t), K II (t), K eq (t) time dependant Mode I, Mode II or equivalent stress intensity factor  K general cyclic stress intensity factor  K I ,  K II Mode I or Mode II stress intensity factor  4 crack opening displacement with a gauge length of 4 mm  5 crack opening displacement with a gauge length of 5 mm  S ,  4, S crack opening displacement (with a gauge length of 4 mm) perpendicular to crack