PSI - Issue 42

Niklas Ladwig et al. / Procedia Structural Integrity 42 (2022) 647–654 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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rather brittle fracture, they evaluated their tests with help of numerical simulations by applying the concept of stress intensity factors from linear-elastic fracture mechanics (LEFM). Watson et al. [14] realized mixed-mode I+III loading in a geometric way by choosing a kind of out-of-plane scarf DCB test. Their setup is rather simple with respect to the experimental effort, but an individual pair of adherends is needed for each mode-mixity of interest. Our work, which is presented below, is based on the idea to perform dual-actuator tests on adhesively bonded joints subjected to mixed-mode I+III loading, which allows to prescribe (constant or variable) mode-mixity during testing. In addition, the energy release rate (ERR) is calculated in-situ during the experiment based on the J -integral, which is independent of crack length, and therefore allow a consideration of ERR within the test control. Details of the so called Mixed-Mode Controlled Double Cantilever Beam (MC-DCB) test have been published during the last couple of years [2][6][9]. In the next section, the most important information from these publications is briefly summarized in the next section and reference is made to the original work for further details. The recent work focusses on a comparison between two different kinds of adhesives and shows the applicability of the MC-DCB tests in case of brittle and ductile adhesive joints. In addition, the traction at the initial crack tip position has been identified for strictly monotonic mixed mode loading up to the start of crack propagation. 2. Theory The Out-of-plane loaded Double Cantilever Beam (ODCB) test was introduced by Loh and Marzi [6] to investigate adhesive joints loaded in pure mode III. A double cantilever beam is loaded by out-of-plane bending and thus induces a mode III loading in the adhesive layer. The Mixed-Mode-Controlled Double Cantilever Beam (MC-DCB) test [7] is a combination of a DCB test with an ODCB test to study mixed-mode I+III fracture.

Figure 1 illustrates the loading of such MC-DCB test. It is assumed that the external moment causes the mode III loading and the external force cause mode I the loading, respectively, while the contribution of all other external loading to fracture energy are of negligible order of magnitude. Loh and Marzi [7][9] proposed an additive mode partitioning = + with, = and = 2 2 1 (1) where describes the rotational angle of the upper adherend in the clamping, b describes the adhesive layer width, is the loading moment at the upper adherend clamping, the Youngs Modulus and the area moment of inertia of the cross section of the adherend. In addition, the mixed mode ratio Figure 1 – Specimen under loading condition