The mass application of FDM technology is slowed down due to the difficulty of selecting 3D printing parameters in order to manufacture an article with the required characteristics. This paper reports a study into the impact of 3D printing parameters (temperature, print speed, layer height) on mechanical parameters (strength, elasticity module), as well as on the accuracy of printing and roughness of the surface of a specimen based on thermoplastic (PLA plastic). Several batches of specimens were fabricated for this study in accordance with ASTM D638 and ASTM D695, which were tested for tension, geometric accuracy, and roughness. Based on the experimental data, regression analysis was carried out and the functional dependences of the strength, elasticity module, printing precision, roughness of a surface on 3D printing parameters (temperature, speed, thickness of the layer) were constructed. In addition, the derived mathematical model underlying a method of non-linear programming has established such printing parameters that could provide for the required properties of a structure. The analytical dependences reported in the current work demonstrate a high enough determination factor in the examined range of parameters. Using functional dependences during the design phase makes it possible to assess the feasibility of its manufacture with the required properties, reduce the time to work out the process of printing it, and give recommendations on the technological parameters of 3D printing. The recommendations from this study could be used to make PLA-plastic articles for various purposes with the required properties

Currently, we observe extensive use of products made of polymeric composite materials in various industries. These materials are being increasingly used to manufacture large-sized structural parts that bear significant loads. However, increase in the volume of composites used in critical structures is impeded by the instability of properties of the resulting products. In most cases, the reason for this is the residual thermal stress–strain behaviour of the composite structure. This paper deals with the development of a method to predict the residual stress–strain behaviour depending on the heating conditions and distribution of the temperature field over the thickness of the moulded composite package. The method establishes the relationship between moulding process parameters and the effect of the auxiliary and basic equipment on the distribution of the temperature field, stresses, and strains in the moulded product. It is shown that the rate of temperature change at the stage of heating has its effect on the amount of residual deformation of the structure. Experimental studies have been carried out to determine the influence of several factors (rates of heating and cooling) on the residual deflection of the composite panel. Experimental data proves that specimens moulded under conditions of an increased heating rate get a greater deflection than those moulded at a lower heating rate. The error of results during the full-scale experiment did not exceed 6.8%. Our results provide an opportunity to determine the residual thermal stress–strain behaviour of the moulded structure with the required degree of accuracy without a series of experiments. It allows us to significantly simplify the practical implementation of the developed method and avoid any additional production costs.

Modern additive technologies make it possible to create structures of variable thickness and of any shape. Thus, designers face problems of optimal design of a new type, and these are problems of topological optimization. Such problems are to determine the optimal form of the structure or the optimal distribution of material over the structure. As a rule, the criterion of optimality is the mass of the structure. However, the structure must retain its bearing capacity under a certain load. The symmetric two-shear adhesive joint of the main plate with two overlays of the same shape on both sides is the object of study in this article. The main goal of this study was to determine the optimal form of overlays with variable thicknesses under certain restrictions. The main restriction is the strength of the structure. Furthermore, additional restrictions are imposed on the minimum and maximum thickness of the overlay. Therefore, the solution to the problem is presented in the form of a set of the following tasks: building a mathematical model of the adhesive joint, building a numerical solution to the primal problem using the finite difference method, and building a genetic optimization algorithm. In the presented article, to improve the convergence of the genetic algorithm is proposed to use an island model that consists of several populations. The main feature of the proposed model of the genetic algorithm lies in the fact that on one of the "islands" mutations occur more frequently and with higher dispersion than on the other two "islands". On the one hand, this decision ensures a high rate of evolutionary selection, and on the other hand, the stability of the results is achieved. Several modeling problems are solved in this article. The main results of this research include the following: nonlinear dependence of the overlay length on the applied load was determined; restrictions on the minimum thickness of the overlay, which cause the appearance of a certain “plateau” at the edge of the overlay, the thickness of which is equal to the minimum allowable were defined.

The composite structures in the aerospace industry for in recent decades are widely applied however, at the beginning of the 21st century composites are growing rapidly. The largest companies in the aerospace industry are increasing the volume of composites application of in the structures, and nowadays the volume of composites reaches 50%. The different elements of aircraft and even highly loaded structures such as spars, ribs, skin, etc., are currently made from composites. First of all, this is due to the possibility of a significant reduction in the weight of the structure, as well as a decreasing in production costs. The advanced technologies in the engineering software allows to solute different complex problems. One of the main direct of research in the composites is optimization of composite structure due to improving the relative strength and relative stiffness of the composite structure, and improving the efficiency of manufacturing processes. There are a lot of methods of optimizations but currently the topological optimization is the most conceptual and forward-looking method. The main goal of the article is to analyze and estimate the approach for designing wing rib with symmetric laminated plates with the different fiber orientation based on the topology optimization. The following tasks were solved for this: firstly, a topological optimization model was determined. This model was based on maximum stiffness with a specified volume constraint is established. The next step was optimization by the solid isotropic material with penalization (SIMP) model and sensitivity filtering technique; as a result of optimization the topological structures of wing rib with different fibre orientations were obtained. The topological structure and stiffness of the wing rib depend on the fibre orientation. Finally, the corresponding morphing analysis of wing rib with laminated plates is implemented by adopting ANSYS, which verified the anti-deforming capability of topology structure and illustrated the feasibility for designing the wing rib. The result shows that the maximum deformation of optimized structure is 1.57mm, whereas the maximum deformation of the un-optimized structure is 2.02 mm. Under the condition of the same material removals, the optimized structure can decrease by more than 20% deformations.

Currently, prefabricated panel structures are typical products made of polymeric composite materials. The integrity of the composite panels, their structure and accuracy of making a contour are largely associated with the manifestation of residual technological stresses. The above phenomena and associated stress-strain behaviour inevitably occur in the process of moulding of the composite products. However, their value, nature, time of occurrence and dynamics of growth can be fully controlled and regulated. The paper deals with the study of the effect of moulding pressure on the quality of a composite product. A dependence is presented that allows us to determine the time for the degassing of the polymeric composite material package at the given temperature and pressure to obtain a monolithic and nonporous structure. It is shown that the peak of the maximum volatile-matter yield for the considered binder types lies in the temperature range where the degree of curing does not exceed 10%; that is, the viscosity values do not prevent the removal of volatile fractions. The effect of moulding pressure on the values of the volume content of the reinforcing material has been studied, and the dependence of the required thickness of the absorbent layer on the parameters of the package of polymer composite material and pressure has been obtained. The dependence of the required thickness of absorbent layer on the parameters of the package of polymeric composite material and pressure has been obtained. The mathematical model developed by us provides an opportunity to predict the stress-strain behaviour of a composite structure at any time during the moulding process. The model is closely related to chemo-viscous and thermal models. It allowed us to synthetize a method for choosing the rational parameters of the moulding process (temperature, pressure, and time), materials of additional layers and equipment. The experiments proved the presence of several defects, such as de-lamination of edges, waviness, swelling and poor adhesion of upper layers in the specimen of the composite panel cooled stepwise in the absence of the vacuum pressure. The surface quality of the specimen of the panel cooled stepwise under vacuum pressure was significantly better, and no visible defects were observed. The obtained theoretical values of deflections, considering the change in physic-mechanical characteristics that depend on the temperature and rheonomic properties of the material, showed an error that did not exceed 7%, compared to the experimental data. Our results can be applied at the enterprises engaged in designing and manufacturing panel structures of polymeric composite materials.

A novel approach to the calculation and optimization methodology of repairable elements of unmanned aerial vehicle (UAV) structures using pre-cured composite patches is proposed. These patches are glued to the damaged structure with adhesives filled with short fibers or particulate fillers. Compared with conventional repair procedures (in which composite prepregs or wet lay-up are used), the suggested method allows damaged UAV structures to be repaired relatively quickly in field conditions without the need for a vacuum or special equipment. In most scientific studies on this problem, significant attention is devoted to the investigation of rectangular patches used for reinforcing plates that have defects such as cracks and damage. This study focuses on the potential application of circular patches for reinforcing plates with defects or damage and includes further parametric optimization of the geometric parameters of the patch. A fundamental approach to the topological and structural optimization of adhesive bonding, along with an experimental study of adhesive properties, has been combined into a single model. This model includes the optimization of the shape and structure of patches for bonded repair, allowing for changes in adhesive thickness to restore the load-carrying capacity of the structure. The simulation and analysis of the results of the renovation of damaged structures for double-sided and single-sided repaired elements of the UAV structure were performed.