The goal of this work is an analysis of modern technologies and problem definitions of mechanics of composite materials for production of outlet guide vane for new domestic aviation propulsion PD-14, planned for installation on the short-range and mid-range jet aircraft MS-21. Outlet guide vanes (OGV), also called flow straightening vanes, are radially disposed behind the fan to straighten out the airflow to reduce losses in the outer contour of the engine. Considering a large number of vanes in the engine, the weight reduction can be very significant due to using polymer composite materials (PCM) instead of the metal in OGV. It is predicted that the weight reduction of each vane, at certain approach to design, can reach 40 %. The results of literature search of composite materials application in the details of fan for aircraft jet engines of world top manufacturers are presented in this paper. The analysis of advanced techniques for production of composite outlet guide vane, such as prepreg technology with autoclave molding, resin transfer molding (RTM), the use of thermoplastic binders and press-materials was carried out. It was noted that the formulation and solution of complex problems of engineering mechanics of composite materials are necessary for high-rate realization of mechanical properties in constructions and reducing the occurrence of defects. The possible problem definitions of deformable solid body mechanics, describing such processes as filtration, physical and chemical conversion, visco-elastic-plastic deformation in heterogeneous medium, typical for composite materials production cycle were considered. The influence of autoclave molding parameters on the mechanical properties of several types of carbon fiber reinforced plastics (CFRP) was analyzed. Using the equations of mechanics of laminated composite plates and shells we calculated effective elastic and strength properties of quasi-isotropic CFRP. A comparative estimate of the effectiveness of composite materials application in the design of OGV was obtained.

The numerical model of fluid-saturated porous brittle materials is proposed. The model is based on a hybrid approach combining the particle-based numerical method with finite difference method. In the framework of the model an enclosing porous solid is described with the discrete element method. An ensemble of discrete elements is used to model the processes of deformation of a porous solid and filtration of single-phase fluid in interconnected network of “micropores” (which are the pores, channels and other discontinuities enclosed in the volume of discrete elements). Relations between stress and strain of a discrete element, the change in volume of its pore space and fluid pore pressure in the “micropores” are proposed. Fluid mass transfer between the “micropores” and “macropores” (which are considered as the areas between spatially separated and non-interacting discrete elements) is calculated on the finer grid freezed in the laboratory system of coordinates. The developed coupled model was applied to study the mechanical response of samples of elastic-brittle material with water-saturated pore space under uniaxial compression. It is shown that the strength of fluid-saturated samples is determined by not only the strength properties of “dry” (unfilled) material and the fluid pore pressure, but largely by sample aspect ratio, rate of deformation and the characteristics of porosity of the material. Analysis of simulation results allowed authors to suggest a generalizing dependence of the uniaxial compressive strength of water-saturated permeable brittle material on the reduced diameter of filtration channels, which is the ratio of the characteristic diameter of the filtration channels to the square root of the sample strain rate. Presented results demonstrate the ability of the developed model to study nonstationary processes of deformation and fracture of fluid-saturated materials under dynamic loading.

The derivation of the kinematic relations for the martensitic transformations in steels is considered. Martensitic transformations are diffusion-less solid-state phase ones, occur at speeds close to the sonic speed and lead to changes in the type of the metal lattice. Therefore, when describing the kinematics of the martensitic transition, on the one hand, we are to take into account the basic physical phenomena such as restructuring lattice, accommodation of residual stresses caused by the restructuring; and on the other hand, - the existence of invariant (habitus) plane, making the transition possible at such high speeds. The derived kinematic relations are the part of a two-level mathematical model of solid-state phase transformations during thermomechanical processing of steels. The model is based on physical approaches of the theory of plasticity, allowing taking into account the physical mechanisms of deformation due to introduction of additional internal variables at the mesolevel. The derivation of the relations for the gradient of transformation deformation of mesolevel representative volume as a deformation with an invariant plane is presented. Analogues to the plastic deformation, the transformation deformation is given by a corresponding system of vectors, i.e. the vector normal to the invariant plane and the vector of the sliding direction (these vectors are not mutually perpendicular). These vectors are not known from crystallography, as their analogues in the theory of plastic shear on slip planes. They are calculated taking into account the magnitude of the changes in the lattice parameters at the phase transition and accommodative mechanisms. The results of calculation of transformation systems resulting due to accommodation of residual stresses by plastic shears and twinning on various possible systems in the martensite are given. After calculating transformation systems, gradients of deformation for the martensitic transition in steel and their geometric interpretation are made. The found eigenvalues of gradients give an insight into the volume change at the martensitic transformation. The results are compared with the available experimental and theoretical data.

We consider the criteria of the estimation of surface strengthening influence on the endurance limit stress increase of the solid and hollow cylindrical specimens with cuts under the bend for the symmetrical cycle of loading. We check the possibility of “check test piece” method using forecasting of the tested standard specimens endurance limit stress. The “check test piece” method allows preventing the destruction of standard specimens when the residual stresses are determined experimentally. In this case the endurance limit stress of the standard specimens can be calculated by the residual stresses of “check test piece” that is strengthened simultaneously with the standard specimens by the same technology. We assume the standard specimens and the “check test piece” having the equal isotropic initial strain, the shear strains are small and we do not take them into account for the initial strain determination. We explore the solid and hollow cylindrical specimens of different diameters made of steel 20 and steel 45. The circular cuts of the specimens were strengthened by the anticipatory surface plastic deformation technology using the air/hydraulic shot blasting. The obtained results make it possible to conclude that the compressive residual stresses, calculated for smooth cylindrical specimens by the initial strains of “check test piece”, do not differ much from those that have been determined experimentally (up to 7 %). We compute the increment of the endurance limit stress of the strengthened specimens with cuts by the developed procedure using the mean integral residual stresses criterion. The difference between the calculated increase of the endurance limit stress of cylindrical specimens with cuts under the bend for the symmetrical cycle of loading and the experimental data is not more then 11 %.

Исследуется поведение углеродного композита (УКМ) в процессе механических испытаний на растяжение и сжатие. Образцы для испытаний изготавливались из углеродных заготовок с разных технологических этапов производства углерод-углеродного композита. В качестве армирующего компонента материала использовались два типа наполнителя, один из которых подвергался дополнительной высокотемпературной обработке. Механические испытания проводились на универсальной электромеханической системе Instron 5882 с использованием бесконтактного видеоэкстензометра AVE Instron для записи продольных деформаций в образце. В процессе испытаний проводилась непрерывная запись сигналов акустической эмиссии (АЭ) системой AMSY-6 с использованием высокочастотных преобразователей с рабочим диапазоном частот 450-1150 кГц. Во избежание записи шумов, возникающих от рабочих частей испытательной машины, проводилась фильтрация сигналов по низкочастотной компоненте. Также проводилась синхронизация системы записи сигналов АЭ с видеоэкстензометром и установкой для механических испытаний. По полученным результатам строились графики зависимостей нагрузки и параметров сигналов АЭ (пиковая амплитуда, энергетический параметр) от перемещений, а также распределения пиковых амплитуд от количества сигналов. На основании значений параметров выделялись основные механизмы разрушения композита. В зависимости от технологического этапа и типа используемого наполнителя у образцов выявлены различия в процессе накопления повреждений. Сделано предположение, что у материала на основе наполнителя, подвергаемого дополнительной высокотемпературной обработке, наблюдается худшая адгезия компонентов, чем у материала без дополнительной обработки наполнителя. Также выявлено, что изучение прочностных свойств и механизмов разрушения заготовок УКМ с начальных этапов изготовления позволяет спрогнозировать поведение готового материала, без прохождения дорогостоящего и длительного процесса производства.

The present paper deals with analysis of local indentation and their energies in point loading of sandwich panel with thin orthotropic composite faces and honeycomb core as an introduction for low velocity impact loading and energy absorbing in sandwich structures. Energy is consumed in two stages: local indentation of sandwich panel skin and bending of sandwich panel. If the impact is located near support or clamping only first stage (indentation of sandwich panel) will be presented. Here the analytical model has been used assuming a rigid-perfectly plastic compressive behaviour of the honeycomb core and membrane behaviour of orthotropic skin for large indentation of sandwich panel. In experimental work were investigated two types of sandwich panels, which consisted of different laminated skins: cross-ply of unidirectional CFRP and AFRP (aramid fabric reinforced plastic) and core honeycomb materials (impregnated paper like Nomex and one layer of glass fabric reinforced plastic). Length of cell side is 2.5 mm. Skins were made with symmetrical lay-ups [0/90]s and [45/-45]s. For indentation test we used steel balls with radius 5-30 mm, speed of loading was 2 mm/min. The experimental results are in good agreement with the analysis. These results can be used in impact loading and energy absorption studies of laminated structures by integrating of “local load vs deflection” curve.