Mechanical Lock Joint for Effective In-Plane Application of Concentrated Loads to Thin Polymer Matrix Laminates

Means of in-plane loading of thin laminates with concentrated loads are of high practical importance. The purpose of this work was to investigate experimentally and numerically the mechanism of load transfer, load capacity, damage and associated failure modes of a specific, mechanical lock joint intended for in-plane loading of thin laminate plates with concentrated loads. The experimental investigations were carried out with the digital image corelation (DIC) and computed tomography (CT), and numerical ones with the help of a non-linear FE modelling, accounting for progressive damage. For this purpose, a special algorithm was developed accounting for a continuous degradation of the stiffness moduli of the laminate with strains according to the custom defined degradation law. Due to the specific design, the joint loaded a laminate plate with its front and rear parts, unlike a typical bolt joint transferring a load only by contact pressure developed at the front side of a bolt. Due to this feature, the load capacity of the joint was almost two times higher than that of a typical bolt joint of the same relevant dimensions.

Stress-Strain State of Steam Turbine Lock Joint Under Plastic Deformation

The stress-strain state problem for the lock joint of the rotor blades of the first stage of the medium-pressure cylinder under plastic deformation is solved. When solving the problem, the theory of elastic-plastic deformations is used. The problem is solved using two different approaches to specifying plastic deformation curves. The applicability of using a simpler bilinear approximation instead of the classical multilinear one is estimated. Based on the example of solving this problem, the time required to perform the calculation with the use of the bilinear and multilinear approximations is shown. Comparison of the results obtained in the form of the distribution of plastic deformations, equivalent stresses, and contact stresses over support pads made it possible to assess the difference when the two types of approximation are used. The obtained result error value when using the bilinear approximation made it possible to draw conclusions about the applicability of this approach to the processing of plastic deformation curves for solving problems of this kind. The problem is solved using the finite element method. To objectively assess the effect of plastic deformation on the redistribution of loads in the lock joint, a finite element model is used, obtained when solving the problem of the thermally stressed state of the rotor blade lock joint. The distribution of contact stresses in the lock joint is shown. The results are compared with those obtained earlier when solving the problem of thermoelasticity. Significant differences in the level of contact stresses are noted. Results of the computational assessment of the stress-strain state of the lock joint of the rotor blades of the first stage of the medium-pressure cylinder of a steam turbine are presented, which allow characterizing the degree of relaxation and redistribution of stresses in the structure in comparison with the results obtained earlier when solving the problem of thermoelasticity. Conclusions are made about the economic viability of using the calculation methods presented.

Insulation Sheath Materials for Cold Preservation

The article studies one of the aspects of the heat-insulating multifunctional shells use - the cold preservation. Such task is relevant for cold storages, workshops and warehouses, in which low temperatures constant maintenance is necessary, for sports facilities (for example, ice rinks and ski facilities). In all cases of application, the main goal is to achieve the economic efficiency, which is expressed in functional results (preservation of the material that breaks down at positive temperatures) and in energy savings. The use of polyethylene-based shells, which are connected by a lock joint, is substantiated. The experimental studies results of the material given in the article shows that in terms of resistance to low and alternating temperatures, operational durability, tensile strength and water absorption, this material and insulating shells based on it are quite applicable for insulation of cold-saving objects. The experience of using heat, vapor and moisture insulating shells based on polyethylene foam with the equipment of frameless and frame structures, sports facilities, as well as for the preservation of snow at ski resorts is also provided in the article.

The Determination of Rational Parameters of Lock Joints of Ceramic Blades with a Metal Disk in Advanced Aircraft Gas Turbine Engines. Part II. Testing of the Rotor Model

The limited thermal stability of commonly used nickel alloys is an obstacle to further increases in operating temperatures in aircraft gas turbine engines. Alternative solutions that overcome the limitations of the operating temperatures of the gas in front of the turbine can be achieved using ceramic materials, including ceramic composites used for manufacturing blades and rotor. Due to a number of design and technological limitations associated with the production of fully ceramic parts of gas turbine engines, the option of connecting metal impellers with blades made of monolithic ceramic material deserves attention. A design of a model steel impeller with blades made of silicon carbide ceramics with reinforcing diamond particles is proposed. To determine the bearing capacity of the ‘dovetail’ type lock joint, bench tests were carried out. A computer program for probabilistic evaluation of the strength of ceramic parts is developed. A conclusion is made about the required characteristics of ceramic materials for the use in turbine impellers.

Insulation systems for buildings and structures based on expanded polyethylene

Insulation systems for buildings and structures imply the use of efficient thermal insulation products based on mineral wool, expanded polystyrene, expanded polyurethane, etc. For a long time, products from non-cross-linked expanded polyethylene were used as insulation for pipelines, reflective insulation, protection against air infiltration, etc. Modern technologies and engineering solutions allowed widening the field of application of non-cross-linked expanded polyethylene (NXLPE) as a construction insulation material. In particular, we can consider a complex of insulation systems for walls, floors and a pitched roof, which allows to form a fully insulating shell of a low-rise building, e.g. a cottage. The novelty of the patented technology Tepofol® and that of the material concerned in comparison with the known solutions is the development of a rolled material based on NXLPE (20 to 150 mm thick) with a lock joint, as well as the technology of seamless connection of individual heat-insulating cloths. The rolls of NXLPE are mechanically fixed to the frame and connected with the lock. One of the advantages of expanded polyethylene, which only few insulating materials possess, is the possibility of forming seamless insulating shells. The article considers a number of insulation systems based on the use of products from expanded polyethylene. In particular, these are the systems of insulation of the walls of frame buildings, the insulation of floors, as well as the insulation of logistics facilities and hangars.