Determination of the mechanical properties of 3d-printed polymer products by methods of structural mechanics

Mathematical models of stress-strain state (SSS) for modeling tests of polymer composite samples obtained by fused deposition modeling (FDM) in approximations of isotropic and orthotropic media are formulated. An algorithm for solving the inverse SSS problem to determine the effective mechanical properties in the orthotropic approximation of composite products printed by the FDM method has been developed. Numerical models have been developed to solve inverse SSS problems to determine the effective orthotropic mechanical properties of composite products with different degrees of reinforcement, obtained using additive technologies based on the FDM method. The grid convergence of the developed numerical models by the method of double recalculation is investigated. It is established that the used mesh of geometric models of product samples leads to errors in determining the vector of the modulus of elasticity in the range of 0–3.19%, and the vector of the shear modulus does not exceed 0.05–0.2%. Numerical experiments to determine the effective mechanical properties of samples of composite polymeric materials in the approximation of orthotropic homogeneous medium were performed. The obtained results are compared with the data of calculations by analytical dependences to determine the effective mechanical properties of composite materials. It is shown that the results of numerical studies agree satisfactorily with the corresponding data obtained from analytical dependences in the range of 0.081–5.696%. It is established that all three components of the vectors of modulus of elasticity and shear increase with the degree of reinforcement. The largest increase is observed for the components of vectors  and , which is due to the reinforcement in the direction , and the difference between the values ​​of the components of vectors  and  and  and  is due to the cross-sectional asymmetry of the strand. Dependences for operative prediction of effective orthotropic mechanical properties of composites based on PLA + KEVLAR 29 within the limits of change in the volume fraction of reinforcing fibers up to 5% are obtained. To develop new composite materials with predetermined properties, it is not necessary to perform multivariate, rather complex and cumbersome numerical experiments in solving the inverse SSS problem.