PSI - Issue 68
Ihssane Kididane et al. / Procedia Structural Integrity 68 (2025) 358–364 Ihssane Kididane et al. / Structural Integrity Procedia 00 (2024) 000–000
359
2
Two dual-actuator test configurations are found in the literature that could be used to obtain a complete fracture envelope from a single experiment. The first one combines a Double Cantilever Beam (DCB) and an End-Loaded Split (ELS) test and was introduced by Singh et al. (2010) and later further improved by other research groups (Panettieri et al., 2018; Yang et al., 2022; Ansari et al., 2023; Yosra Rahali and Grognec, 2023). However, the cited works did not yet focus on determining fracture envelopes by smoothly varying the mode-mixity during the tests. The so-called Controlled Mixed-Mode Bending (CMMB) test, which was originally developed as part of a national German research project (Hahn et al., 2012), was recently further developed and examined in detail by Kididane et al. (2024). This test corresponds to the Mixed-Mode Bending test introduced by Crews and Reeder (1988) as superimposition of a DCB and an End-Notched Flexure (ENF) test, but using two independent actuators instead of a load jig. Kididane et al. (2024) obtained fracture envelops of a structural adhesive joint in di ff erent ways, namely by prescribing a constant mode-mixity and by varying the mode-mixity in a single experiment. The aim of the work presented here is to investigate the influence of the layer thickness on the fracture behavior in mixed mode I + II using the latter option of carrying out CMMB tests.
2. Experimental work
2.1. Sample manufacture
In the present research, joints made of the adhesive Henkel LOCTITE ® Hysol 9460 were investigated. This spe cial adhesive was selected in order to be able to compare the experimental results at di ff erent layer thicknesses with reference data from the literature (Ji et al., 2012). The adherends, which are made from a high-strength aluminum alloy (EN AW-7075 T6) to avoid plastic deformation in the substrates, were cleaned with methyl ethyl ketone (MEK), sandblasted with corundum and then cleaned again with MEK before applying the adhesive. According to the rec ommendations in the adhesive data sheet, the adhesive layer was first cured for 24 hours at room temperature before the samples were placed in an oven to post-cure at 60 ◦ C for one hour. A total of 23 samples with nominal layer thicknesses t adh between 0 . 1 and 1 . 2 mm were manufactured. The layer thicknesses were measured with a caliper at various locations between the initial crack tip and the position of force F 1 (Fig. 1) in order to be able to specify the average layer thickness with standard deviation for each individual sample.
2.2. Test setup
section A-A
2L
2L
c=
b=(1-
) 2L
W w
c
a
b-a
(W-w)/2
(W-w)/2
crack tip position
F 1 ,
F 2 ,
1
2
simple support (SLB): F 2 : support force F 3 =0 simple support (CMMB): F 2 : external loading F 3 : support force
A
H h
1
2
h H t adh
A
3
4
adhesive layer
adherends
F 4
F 3
x
Fig. 1. Sketch of CMMB and SLB test configurations.
Fig. 1 sketches a CMMB test setup with relevant nomenclature. In the most general case, the displacements δ 1 < 0 and δ 2 ≥ 0 are applied by independent actuators. A classic SLB configuration can be achieved by simply unmount ing the lower support location ”3” (marked blue), leading to F 3 ≡ 0, while keeping δ 2 ≡ 0, which corresponds to a simple support (marked green). The arrows of the symbols (forces, displacements and rotations) indicate the direc tion of action of positive quantities. The geometrical dimensions 2 L = 840mm, W = 25mm, w = 8mm, H = 10mm, h = 5 mm and the initial crack tip position a 0 = 280 mm were the same in all tests. The SLB tests were loaded at half
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