DEFORMING AND FRACTURE OF LINDEN AND PINE UNDER INTENSIVE DYNAMIC IMPACTS
The paper presents the results of dynamic tests under compression of two wood species: linden and pine under loading along and across the fibers. Dynamic tests were carried out using the modified Kolsky method with the realization of multi-cycle loading of the sample during one test. As a result, strain diagrams were obtained for uniaxial stress state taking into account additional loading cycles The use of the multi-cycle loading mode made it possible to obtain a significantly greater degree of the sample deformation than with traditional single-cycle loading. To create a pulse load, a gas gun was used. According to the experimental results, dynamic deformation diagrams were obtained, as well as ultimate strength and deformation characteristics, fracture energy for linden and pine were determined depending on the cutting angle of the samples and the strain rate. A strong anisotropy of the properties of the tested materials is observed: the samples have the greatest strength when a load is applied along the fibers, and the least - across the fibers. A positive effect of the strain rate is noted. The module of the load branch is non-linear and, as a rule, is smaller than the module of the unload branch (while maintaining the integrity of the sample). The nature of the deformation and fracture of the samples strongly depends on the angle of cutting-out. At cutting angle across the fibers, the deformation diagram after reaching a certain threshold value is close to an ideally plastic diagram. At cutting angle along the fibers, the initial portion of the diagrams is close to linear, i.e. elastic deformation takes place. However, after reaching a certain value (“yield strength”), the diagram becomes nonlinear. This kind of behavior takes place in those experiments in which the destruction of the samples occurs. For both wood species, there is a significant excess of energy absorption by samples cut and tested along the fibers, compared with samples cut and tested across the fibers.