PSI - Issue 68

Pascal Franck et al. / Procedia Structural Integrity 68 (2025) 119–125 P. Franck et al. / Structural Integrity Procedia 00 (2025) 000–000

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(DIC) were used. The arrangement of the two camera systems can be seen in Fig. 1c. One camera system was used to record the surface reactions of the bamboo material itself and the second camera system recording from the side was able to record possible material reactions between the bamboo lamellas the LBL contains.

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(b)

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Fig. 1. Experimental setup: (a) laminated bamboo lumber specimen; (b) testing setup; (c) top view of the arrangement of the digital image correlation systems.

3. Results and discussion 3.1. Multiple amplitude tests (MAT)

To get an overview of the capability of the LBL material in tensile direction, the described specimens were tested in quasi-static tests. The specimens have shown an average tensile strength σ tensile,max of about 90 MPa. According to the results that could be achieved in the tensile tests, the multiple amplitude tests (MAT) were conceived. This led to a starting maximum stress σ max of 20 MPa with the previously mentioned load ratio R = 0.1. After the specimen reached 10 4 cycles in the current load level, the maximum stress was increased by Δσ max = 5 MPa. This procedure was continued until the failure of the specimen occurred. The results of an exemplary MAT are shown in Fig. 2. It can be seen that the LBL material was capable of withstanding the first load levels without significant material reaction. The maximum strain ε max recorded using the glued-on displacement sensors (Fig. 2a) showed the typical gradual ascent to the increasing load. Within the load levels, the strain did not show a rise, which would have been an indicator of fatigue-induced damage to the LBL material. This response can be further observed till the end of the load level with a maximum stress of 50 MPa. During the last cycles of the load level, the recorded strain starts to slowly increase and, with the transition into the next higher load level, the strain shows a sudden peak. In the following load level, the strain shows an increase that led to the assumption of a plastic material reaction and thus the LBL getting damaged. This assumption may be supported by apparent observations made during the test since cracks in the curves of the test specimen happened and led to the first remarkable material reaction. Afterwards, the specimen was able to further withstand the load for a limited duration, since the transition to the next higher load level resulted in a higher rash of the maximum strain. The described behavior of the LBL could be observed within the calculated value of the dynamic stiffness C dyn as well. Again, the first load levels did not lead to a significant change in the specimen’s stiffness. At the end of the test, the described stronger material reaction to the increased load led to a decreased dynamic stiffness. Finally, the specimen did fracture at a load level with a maximum stress of 65 MPa. The fracture of the specimen could be reproduced at the same load level with the following multiple amplitude tests conducted following the described test execution.