Experimental damage tolerance evaluation of thick fabric carbon/epoxy laminates under low-velocity and high-velocity impact and compression-after-impact

Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are conducted at distinct energy levels and thicknesses to characterise the damage process. These specimens and loading conditions are representative of a new generation of critical structural components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly being made entirely from composites. The tests address the need to better understand the damage process for specimens with a small thickness ratio since existing experimental impact data for large thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric layups and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed cameras were processed in a novel way, providing the force during impact. C-scans and micrographs were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences in damage size for the thickness range analysed. The influence of layup on the global impact response is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly with the impact energy and the delaminated area linearly with the impact velocity. There is no clear correlation between the compression-after-impact failure mechanisms and the residual strength. Impact damage, at the current energy levels, showed a minimal reduction of residual strength.

Behavior of solution of the elasticity problem for a radial inhomogeneous cylinder with small thickness

A non-axisymmetric problem of the theory of elasticity for a radial inhomogeneous cylinder of small thickness is studied. It is assumed that the elastic moduli are arbitrary positive piecewise continuous functions of a variable along the radius. Using the method of asymptotic integration of the equations of the theory of elasticity, based on three iterative processes, a qualitative analysis of the stress-strain state of a radial inhomogeneous cylinder is carried out. On the basis of the first iterative process of the method of asymptotic integration of the equations of the theory of elasticity, particular solutions of the equilibrium equations are constructed in the case when a smooth load is specified on the lateral surface of the cylinder. An algorithm for constructing partial solutions of the equilibrium equations for special types of loads, the lateral surface of which is loaded by forces polynomially dependent on the axial coordinate, is carried out. Homogeneous solutions are constructed, i.e., any solutions of the equilibrium equations that satisfy the condition of the absence of stresses on the lateral surfaces. It is shown that homogeneous solutions are composed of three types: penetrating solutions, solutions of the simple edge effect type, and boundary layer solutions. The nature of the stress-strain state is established. It is found that the penetrating solution and solutions having the character of the edge effect determine the internal stress-strain state of a radial inhomogeneous cylinder. Solutions that have the character of a boundary layer are localized at the ends of the cylinder and exponentially decrease with distance from the ends. These solutions are absent in applied shell theories. Based on the obtained asymptotic expansions of homogeneous solutions, it is possible to carry out estimates to determine the range of applicability of existing applied theories for cylindrical shells. Based on the constructed solutions, it is possible to propose a new refined applied theory.

The Effect of a Rubber Sheet on the Dynamic Response of a Machine Foundation Located over a Small Thickness of Soil Layer

Placing a machine footing over a small thickness of soil layer, which is located over a bedrock, could encounter many challenges due to the bed’s notable stiffness in comparison to the soil. The advantages of using rubbers to protect facilities (structures, machine foundations, nearby footings and equipment, etc.) from vibration and control its consequences are well known nowadays. In this study, the benefits of employing a small thickness of rubber sheet (2 mm) on the dynamic response of a machine foundation which is located over four thicknesses of soil (210, 420, 630, and 840 mm) has been investigated. The soil layer is located over an artificial bedrock that is consisted of a thick concrete layer. The tests have been conducted in a vast test pit of size 2500×2500 mm and a depth of 840 mm by using a semi large-scale machine foundation model with a square concrete foundation of width 400×400×100 mm. It was observed that, by increasing the soil layer thickness, the resonant frequency and amplitude of the vibrating system decreases. Moreover, by employing a rubber sheet beneath the machine footing, the resonant frequency of the vibrating system significantly decreases especially for a small thickness of the soil layer. Although, using a rubber sheet could slightly increase the resonant amplitude, but the benefit of the resonant frequency-changing capability of the rubber sheet is too impressive by taking the resonant frequency of the system far enough from the unchangeable working frequency of the machine and preventing the resonant phenomenon to happen.

Effect of Temperature Field and Stress Field of Different Crack Behavior on Twins and Dislocations under Mg Alloy Rolling

Aiming at the problem of the poor plasticity of magnesium alloy leading to serious edge cracks in the rolling process, this paper conducts a systematic study on the crack suppression mechanism of rolling under different thickness reductions. Using restricted rolling and conventional rolling, comparing the microstructure evolution of the plate after rolling, and combining the information of the simulated temperature field and stress field of the plates, the behavior of twins and dislocations under different thickness reductions is explained, and the influence of serious damage caused by single-pass hot rolling of magnesium alloy is explored. The compressive stress fields along with the transverse and normal directions under restricted rolling cause the compression twins to mature into secondary twins under rolling with small thickness reduction and induce a large number of tensile twins when the thickness reduction amount is increased. The multiple slips activated by the higher temperature field at the edge of the small thickness reduction amount cause dislocations to be distributed inside and outside the twins, while the edge with large thickness reduction can activate more slip due to the high-temperature field resulting from friction, resulting in the twin be destroyed.

THE EARLY HORIZON OF THE KUSHMANSKOE (UCHKAKAR) FORTIFIED SETTLEMENT, IX-XII CENTURIES

The article considers the early chronological horizon of one of the key archaeological sites of the Chepetskaya archaeological culture - the Kushmanskoe (Uchkakar) fortified settlement. The paper highlights the issues of the features of the occupation layer of the early settlement, its dating, the characteristics of the identified structures and the material culture are given. The early medieval settlement on the territory of the Kushmanskoe (Uchkakar) fortified settlement was limited by defensive structures consisting of a wood-earth bank and a ditch. They defended a settlement with an area of 6-10 thousand sq. m. The occupation layer of the early settlement had a small thickness of 0.2 m. Several structures were identified in it and investigated by excavation, two of which are the remains of ground buildings, another is a stone laying of an unclear purpose. The material culture of the early horizon allows us to determine the time of the existence of an early settlement within the IX-X centuries. It ceased to exist after the destruction of defensive structures, the ruins of which partially blocked the occupation layer of the early settlement. The cultural layer of the late chronological horizon on this site of the settlement was formed already on the surface of the ruins of defensive structures of the early period. A small area of the early settlement, defensive structures, features of its occupation layer allow us to hypothesize: it was a refuge for people of another nearby fortified settlement - Kushmanskoe III settlement.

The selection of the main axis and the forming plane in automatic profiling and stamping lines

The article defines the main axis and the profiling plane in automatic profiling and stamping lines. Specific recommendations are given for choosing the position of the main axis and the profiling plane, depending on the configuration of the manufactured parts of the roll-formed section. Under the general name of profiling in the practice of stamping works, it is meant to obtain rigid and light profiles of large length and various configurations from sheet blanks. Profiling is carried out in four ways: in dies on crank presses, in dies on special bending presses, on universal bending machines (edging machines), on profiling roller machines. The first method, profiling on crank presses, is used for complex semi-closed and open profiles of relatively small length, if there are no special bending presses or profiling machines. The second method, profiling on special bending presses, is used for open and semiclosed profiles up to 5 mm long. The advantage of such presses is the possibility of using simple, and therefore cheap, tools in the manufacture. The third method, profiling on universal bending machines (edging machines), is used for bending parts (profiles of a simple shape in straight lines with different coupling radii determined by the radius of the machine ruler, for which the latter has a set of rulers). Bending machines allow bending materials of small thickness. Low productivity and the need for physical labor costs limit the use of these machines. The fourth method, profiling on roller machines, is used for open, semi-closed and closed profiles. The essence of the profiling process is to gradually change the profile drawing of a flat belt to a given profile when it is moved sequentially through several pairs of shaped rollers arranged sequentially one after the other in the same plane and rotating at the same speed. The article describes in detail the fourth method; the advantages and disadvantages are noted.

Initiation Parameters of Granulated Synthetic Polymers

Polymeric materials, which are currently very often used in various industries, are often transported and stored in the form of granules before processing. This method has several advantages, but in most studies the test samples are modified to different shapes and dimensions. This paper is therefore focused on the initiation of selected granular plastics. Samples of five polymeric materials were exposed to an external heat flux from 20 kW.m−2 to 40 kW.m−2. A spark initiator was used to ignite the released gaseous products of thermal decomposition of the polymer sample. FTP (flow-time product) method was applied to the obtained parameter - time to ignition, from which other initiation parameters were determined. The critical heat flux was determined in the range of 5.0 kW.m−2 - 11.8 kW.m−2. Despite the relatively small thickness (4 mm), the samples behaved as thermally thick. During the measurement, thin surface layer melted, and the rest of the polymer remained in its original granulated form. Ignition temperatures were calculated according to the Stefan-Boltzmann’s law between 273 °C - 402 °C.

Radiative Surface Waves in Layered Plasma–Dielectric Structures and Prospects of Their Application in Plasma Microwave Electronics

Surface waves in layered systems consisting of material media with different frequency dispersions are considered: dielectric–plasma–vacuum, vacuum–plasma–plasma, and dielectric–vacuum–plasma. It is shown that in such systems, one of the surface waves can be radiative into a medium that does not form an interface for the surface wave under consideration, in view of which the wave becomes decaying. In the dielectric–vacuum–plasma system, there is only one surface wave localized at the vacuum–plasma interface, which is radiative into the dielectric in a certain region of wavenumbers with a not too small thickness of the vacuum layer. For all cases, the possibilities of exciting surface waves of a layered structure by an electron beam are analyzed. It is indicated which surface waves will be excited most efficiently. The prospects of using such waves in plasma microwave electronics in the development of sub-terahertz and possibly terahertz frequency ranges are shown.

Numerical investigation of the 2d–1d structure interaction model

In this article, we explore the possibility of modeling the interaction of a 2d elastic body with a thin 2d elastic body of possibly higher thickness using a 1d model for the thin body. We use the asymptotic analysis with respect to the small thickness of the 2d interaction model and formulate five different limit models depending on the order of stiffness of the thin body with respect to the thickness. Then we formulate a 2d–1d model which has the same asymptotics as the 2d–thin 2d model with respect to thickness. Finally, we numerically test the approximation of the 2d–thin 2d model by the 2d–1d model on two problems, one with an analytical solution and one more realistic problem.

Design and Properties of Magnetically Controlled Sorbents

In this work, the main parameters and advantages of magnetically controlled sorbents are considered. A large surface of nanodispersed magnetically controlled sorbents adsorbs large amounts of toxins, therefore, the consumption of magnetically controlled sorbents in each operation is insignificant. The ability to quickly replace the spent magnetically controlled sorbents in the detoxification apparatus with a new portion of magnetically controlled sorbents increases the reliability, simplicity and ease of use of the method under consideration. The small thickness of the sorbent layer and the availability of the sorbent surface provide almost instantaneous establishment of equilibrium concentrations, which significantly reduces the required processing time for the biofluid and increases the productivity of the purification process.