Birch plywood sample cyclic bending property investigation and analysis
2020
Zalcmanis, A., Latvijas Finieris, JSC, Riga (Latvia) | Abols, K., Riga Technical Univ. (Latvia) | Zudrags, K., Riga Technical Univ. (Latvia) | Krasnikovs, A., Riga Technical Univ. (Latvia)
In the present research several thicknesses sanded birch (Betula sp.) plywood samples were tested, having fibre directions of surface veneer both in longitudinal and transverse directions, in order to investigate dynamic strength, stiffness and damage accumulation properties. Sample dimensions were according to EN310 for static and also dynamic tests. Low Cycle Fatigue (LCF) 3-point bending tests with single cycle amplitude value not less than 85 % of specimen ultimate bending strength were carried out. Each cycle was characterized by “Quazi” linear load increase and decrease (saw type) and R value close to zero. Experimentally numbers of cycles up to rupture were obtained and corresponding stiffness degradation S-N curves were plotted. Analysis of the results indicates that stiffness degradation is a noteworthy factor to be taken into account when designing plywood structures. The experimental data show – when stiffness degradation occurs, remaining deformation also appears due to damage accumulation. It also shows that when the bending stress is approximately 85 % of ultimate strength, mean numbers of cycles up to rupture vary between 123 and 3490 cycles depending on thickness and lamina lay-up. If the stress level is lowered to 80 % ultimate bending strength, fatigue life should extend to 10000 cycles. Average stiffness degradation varies from 8.9 % to 20.0 % depending on thickness and lamina lay-up.
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