Damage Development in a Cellular Axisymmetric Tank Additive-Manufactured from Plastic Filament. Part 1. Damage Development in Cellular Axisymmetric Multilayer Shells Under Critical Mechanical Loads and Quivalent Properties of Model Layers for Stress-Strain State Estimation

The paper analyzes the peculiarities of forming honeycomb structures by additive methods (in particular, from plastic filament (Fused Deposition Method, FDM) and shows that the engineering application of products with honeycomb structures should take into account the peculiarities of structural damage development under the influence of working loads. For typified products in the form of closed multilayer shells (tanks for various technological purposes), these are thermobaric effects that lead to a loss of the long-term strength of the product and to the development of damages on the initial defects. It is proposed to divide the latter into three groups: defects in the form of cavities of various volumes and shapes, as well as contact patch defects at the adhesion boundary of the laid-down layers under the conditions of stable technological process; defects formed by random factors of a technological nature; defects arising from heterogeneities and initial differences in the material used (plastic filament). It is concluded that the loss of the bearing capacity of shells made of structural plastics (except for highly elastic ones) can be described by the development of cracks in the interlayer areas of the product in accordance with Griffiths’ theory. It is in these areas that the presence of defects is greatest. Since there is a significant difference between the mechanical properties of plastic filament and the product made by extrusion, it is proposed to use the equivalent properties of the components of a cellular system in the form of a three-layer connected shell in analyzing the stress-strain state of the product model.