Study of the strength limit of the bark of a plum tree trunk under the action of normal compression

Purpose. Reduction of damage to trunks of tree bark due to substantiation of the parameters of the harvesting technique using the method of determining the strength limit of tree bark in field conditions during research and the device for its implementation. Methods. Standardized and improved methods of determining the strength limit of tree bark under normal load were used, as well as the basic provisions for conducting laboratory and field experiments. Results. During field research, the developed method of determining the strength limit of tree bark was applied. It was established that highly elastic deformation of the bark does not affect the functional properties of phloem, phelloderm and cambium, i.e. after removing the load, the bark is completely restored, and irreversible plastic deformation leads to the death of bark fibers. The transition to the region of plastic deformation is marked by a sharp increase in the rate of deformation at a constant rate of load application, i.e. the strength limit of the crust is overcome and the flow fluidity phase. To implement the improved method, the developed device was used to determine the strength limit of the crust under normal compression, which made it possible to substantiate the parameters of the overlays of working organs and modes of operation of shakers of fruit-harvesting means and machines during development. Conclusions. The proposed method and device made it possible to determine the bark strength limit during normal compression in the field without damaging the tree bark. It was established that for plum orchard trees with diameters of 50–200 mm, it is 0.68–1.74 MPa and depends on the thickness of the cork tissue, which increases with the age of the tree. The method of implementing the method and the device is universal, therefore it is advisable to use it during field tests to determine the limit of bark strength for other fruit and nut trees. Keywords: method, instrument, tree bark, normal pressure, strength limit.