Detachable Joints Research Articles

RESEARCH, DEVELOPMENT AND IMPLEMENTATION OF METHODS AND TECHNOLOGIES OF ACOUSTIC STRAIN GAUGING OF SPLIT JOINTS OF LIQUID ROCKET ENGINES FOR SPACE LAUNCH VEHICLES

A review of the results of research, development and implementation of methods and technologies of acoustic strain measurement of split joints of liquid rocket engines for space launch vehicles is presented. A brief description of methods for measuring the incremental time of propagation of ultrasonic longitudinal waves and the ratio of longitudinal and shear wave velocities is given. The description of the developed and enacted GOST R 52889‒2007 “Non-destructive testing. Acoustic method of control of tightening force of threaded joints. General requirements”. Acoustic strain gauges, including those in regular operation at NPO Energomash, are described. A brief description of the specialized program “Acoustic Tensometer” is given, as well as a set of standard samples for performance control and preliminary adjustment of devices and calibration bench. The method of acoustic tensometry based on the ratio of longitudinal and shear wave velocities proposed by the specialists of NPO “Energomash” is described. The application of the method of acoustic strain gauge tightening of detachable joints, along with the improvement of the LPRD production technology, made it possible to completely eliminate leakage and leakage failure.

Effect of Core Hole Diameter on Tensile and Fatigue Properties of the Helically Formed Internal Thread in AlSi10MnMg Cast Alloys

The manufacturing of internal thread using the helical thread forming process (Punch Tap) as a novel high-performance manufacturing technology provides high productivity by reducing the tool path, which can save manufacturing time up to 75% compared to the conventional thread forming process. For instance, cast gearboxes in the transport sector consisting of numerous internal threads can benefit from this manufacturing method to realize detachable joints. While the required core hole diameter for conventional (cut) tapping depends on the thread dimension, this diameter depends either on the material properties for the thread forming process. The proper core hole diameter according to material flow possibility enables forming of complete thread profiles, which can consequently enhance the mechanical properties of the thread. This study aims to analyze the effect of the core hole diameter on the quality of the formed threads in AlSi10MnMg cast profiles. M6 threads were formed into the pre-drilled core holes with two different diameters. CT-scan analysis indicated that reducing the core hole diameter decreases the inner volume of the formed internal thread, which is justified by better material flow and complete forming of the thread profiles. Adaptation of the manufacturing parameters according to the material properties enhanced the geometry of the formed thread profiles. This enhancement increased the tensile and fatigue strengths of the detachable joints by subjecting the four initially formed threads at the top of manufactured nuts to the static and cyclic loads.

Possibilities for Efficient Furniture Construction Made of Thin and Ultra-Thin Materials by Using Mitre Joints.

One of the biggest challenges for designers and manufacturers of furniture is to reduce the thickness of conventional furniture materials such as particleboard (PB), medium-density fibreboard (MDF) and plywood. Designing furniture based on thin (less than 16 mm) and ultra-thin materials (less than 10 mm) is desirable for aesthetic reasons and because of the substantial material savings. However, the use of thin and ultra-thin materials reduces the strength of the furniture, especially the strength and deformation resistance of the joints. This study aimed to establish the possibilities for efficient furniture construction made of thin and ultra-thin materials using mitre joints. For this purpose, 14 types of L-type joints were tested: 12 glued and 2 detachable. The joints were made of eight wood-based panels and one non-wood panel. The bending moments and the stiffness coefficient under compression were determined. The obtained results show that the mitre joints made of laminated material with high-pressure laminate (HPL), 8 mm thick, MDF achieved the highest bending moment, and the highest stiffness coefficient was achieved by joints made of 10 mm thick compact HPL. Compact HPL joints were significantly affected by the type of adhesive used. Detachable joints had a relatively high bending strength but very low stiffness.

Fatigue crack initiation life prediction using different plasticity models in cold expanded AL-alloy plates utilized in double shear lap joints

Cold expansion of fastener holes is a recognized technique for enhancing the fatigue life of holed plates utilized in detachable joints. This method involves introducing compressive residual stress around the holes, which has proven to be effective in improving the structural integrity and longevity of such components. In this research, the role of using different plasticity models in finite-element simulations of cold expansion (CE) in determining residual stress distribution and predicting the fatigue life of lap joints was investigated. Finite-element simulations were conducted to analyze the distribution of residual stress in cold-expanded Al-alloy 2024-T3 plates utilized in double-shear lap joints. Three time-independent plasticity models, specifically multilinear kinematic hardening, multilinear isotropic hardening (M.L.I.H) based on monotonic tensile tests, and nonlinear combined hardening models derived from saturated hysteresis stress and strain loops, were employed in the simulations. These models allowed for an accurate determination of the residual stress distribution in the plates. In finite-element simulations, two CE sizes of 1.5% and 4.7% were employed to create residual stresses. In the simulations, after creating residual stress by CE, remote sinusoidal loads are applied to the joints corresponding to the previously conducted fatigue tests in order to obtain stress and mechanical strain distributions. In order to predict the fatigue life, four different multiaxial fatigue criteria (Smith–Watson–Topper, Glinka, Kandil–Brown–Miller, and Fatemi–Socie) were employed, using the stress and strain distributions obtained from the finite element simulations with the different plasticity models. The simulations yielded varying stress and strain distribution results for the multilinear kinematic and M.L.I.H models, while the results of the nonlinear combined hardening model fell between the other two models. Notably, the fatigue life prediction based on the nonlinear combined hardening plasticity model closely matched the experimentally observed fatigue lives, with an absolute percentage deviation of 24.8%.

Flange connections of chemical technology equipment and pipelines

The subject of the research is the most common type of detachable joints in chemical, petrochemical, oil refining, food and energy machine and apparatus construction, namely flanged joints of technological and auxiliary equipment, as well as pipelines.
 The study of the state of the issue and trends in the development of structural and technological design of flanged joints is based on a critical analysis of scientific and technical sources of information and, above all, patent information of the leading countries of the world, since it is in the patent documentation that information is given about innovative developments in the relevant field of engineering and technology.
 With the help of methods of analysis and synthesis, flange connections that affect the efficiency of operation of equipment and pipelines in the chemical and related fields of technology have been systematized. A thorough classification has been developed for each type of device, based on which the most interesting designs proposed by scientists, designers and inventors of the world's leading countries have been examined in detail. A critical assessment of most of the above constructions is provided, their advantages and disadvantages are discussed. Preference is given to sources of information from the end of the second and beginning of the third millennium.
 The constructions of flanged joints were analyzed depending on the degree of assembly, the degree of mobility of their structural elements, the possibility of removing the flanges without dismantling the entire joint, the mechanism of compression of the sealing gasket, the presence of additional functions, as well as the material of the flanges.
 It is shown that, despite the considerable variety of developed designs of flanged connections, the most demanded by the industry are flat welded and butt-welded flanges, as well as free flanges on a welded ring. However, thanks to the advances in materials science and computer modelling, the search for new flange connection designs continues.
 The developed detailed classification of flange connections can be useful to the developers of new equipment for the creation of highly efficient technological equipment of various industries.

ИССЛЕДОВАНИЕ КОЭФФИЦИЕНТА ТРЕНИЯ ПОЛИМЕРНЫХ МАТЕРИАЛОВ ДЛЯ 3D-ПЕЧАТИ ЭЛЕМЕНТОВ КОНСТРУКЦИИ ПОДВИЖНОГО СОСТАВА

Additive technologies are represented by various methods of 3D printing and are increasingly being used in various industries around the world. For example, printing with metal powders is used for the production of such structural elements as various arm supports in the aircraft industry or the manufacture of spacecraft hulls. The use of 3D printing with the use of polymer materials makes it possible to manufacture, for example, various gears for non-principle mechanisms. The use of such technology in pneumatics is also relevant. However, at the same time, the possibility of using these technologies for the manufacture of various pneumatic devices has not been widely studied up to now. In the course of studying this issue, a pneumatic gearbox was made. However, it was found out that one of the problems that does not allow to design and manufacture a normally functioning pneumatic device is an unknown value of friction factor of the materials of which its elements are made.
 The study objective is to find out the static friction factor of products made of polymer materials using 3D printing technologies. The necessity of this study is explained by the problems that arose as a result of testing a high-performance pneumatic gearbox manufactured using additive technologies applying various polymer materials. The main problem of this device is the density violation of fixed detachable joints of gearbox case parts and covers. Since the medium to be used is compressed air under a pressure of 0.9 MPa, any density violation can lead to the gearbox destruction or to air losses from the braking system of a freight train due to an increase in the number of leaks in the pipeline for additional power supply to the spare reserve.
 The paper presents the results of experimental studies on finding the friction factor of various types of materials used in 3D printing. The obtained friction factors are required for the design of seals of pneumatic devices according to generally accepted methods.

A novel ultrasonic-assisted staking process for mechanical fasteners

Increasing material variety in car body engineering causes new challenges regarding the joining processes and therefore, leads to an enhanced usage of mechanical joining technologies. Mechanical fasteners, as self-piercing nuts, can be staked cost-efficiently without a pre-punching operation to create detachable joints. Nevertheless, elevated workpiece strengths lead to high forming forces and a limited application range. One promising approach to reduce tool and workpiece loads in forming operations is superimposing a high-frequency oscillation to the tool movement. The so-called ultrasonic assistance enables an immediate and considerable reduction of the material's flow stress. This beneficial softening effect has been confirmed for several materials and processes. Since the process management and monitoring are highly affected by the frequency-dependent dynamic behavior of the whole test setup, the application of ultrasonic assistance is already challenging for basic forming operations. Hence, only a few studies have been investigating ultrasonic-assisted joining processes. In particular, joining processes with auxiliary elements have been hardly considered. Within the scope of this work, a novel ultrasonic-assisted staking process for mechanical fasteners is proposed. Therefore, the punch movement for the installation of a self-piercing nut into an aluminum sheet is superimposed with a 20 kHz oscillation of 10 µm, 15 µm, and 20 µm amplitude. Ultrasonic assistance in the initial staking phase, characterized by moderate loads, causes irregular tool–specimen contact. Since the effect is promoted by increasing amplitudes, a correlation with the elastic tool deflection is presumed. Additionally, the transferability of the ultrasonic-based force reduction to mechanical joining with auxiliary element is confirmed and a beneficial influence on the joint formation is identified. Thus, ultrasonic assistance is proven as a promising approach for the extension of existing process limits.

Dimension-based failure analysis of formed internal threads in AlSi10Mg cast profiles using coupled DT/NDT testing methods

The production of detachable joints in lightweight components using friction drilling and internal thread forming processes could be considered as a lightweight design strategy, which can reduce material and time consumption and enhance the thread strength by imposing a further work-hardening into the subsurface of the formed threads. Pre-study indicated that oversizing the friction drilled bores as a pilot bore can hinder the complete deformation of the thread profiles during the thread forming process. This work investigates the effect of process parameters in the friction drilling process (friction drill speeds and diameter) on the quality of the drilled bores and following formed threads. Computed tomography was chosen to measure the dimension deviation of manufactured bores and threads. Comparing the deviation with the measured static and dynamic strengths declared that increasing the tool diameter by 0.1 mm increased the inner volume of the friction drilled bore, which led to an incomplete deformation of the thread profiles and decreased static and cyclic strength accordingly. Although the friction drilling with an adaptive speed reduced the oversizing of the created bore in comparison to the friction drilled bores with a constant speed, measuring the volume of the formed threads into mentioned bores indicated an opposite trend. While the formed M6-threads into the friction drilled bores with constant speed showed a better strength by subjecting to a quasi-static load, manufactured threads with an adaptive speed indicated a higher dynamic strength. The fatigue tests were monitored through NDT methods by measuring the change in deformation-induced temperature and ACPD potential. The measured results were correlated to plastic strain up to failure corresponding to occurring softening, hardening, or possible crack initiation and propagation in thread profiles.

INNOVATIVE THREAD METHOD THROUGH CYLINDRICAL HOLES

Innovative activity in the field of engineering and technology, based on the use of best practices, contributes to scientific and technological progress in production. The latest projects in the field of technology significantly increase the technical and economic performance of enterprises. Innovative technical solutions of production nature significantly improve the structure and quality of production. Given the level of the proposed technological changes in the manufacture of threads in through holes, these innovations cover the field of combinatorial and partial. Today mechanical engineering is characterized by mechanization and automation of technological processes, a wide range of products of various parts. Among the non-detachable and detachable joints of parts, the threaded connection is the most common. Simplicity, reliability, the ability to adjust the force with which the conjugate surfaces come into contact, the possibility of repeated cycles of disassembly and assembly, etc., make this type of connection the most commonly used in mechanisms and machines of modern engineering. With the simplicity of the contact pair of threaded joints, where one of them contains the outer and the other the inner screw surface, during their manufacture there are problems that significantly inhibit production. The subject of research of this article is the solution of difficulties of manufacturing of an internal cut in through openings of small diameter by means of a tap. According to various sources, up to 80% of marriage is due to breaking taps. Studies by a group of scientists has found that more than 75% of taps break when the reverse (reverse) stroke of the tap, when the torque reaches its maximum value. The reverse scheme of production of a screw profile of a cutting surface by means of the mechanized devices and their alternative analogs, and also machines of drilling group, is offered.

Experimental and Numerical Study of Pressure Intensity in Detachable Joints of D Series Pumps

The object of study is a single-stage double-suction axially split volute casing centrifugal pump.
 Background. In the design process of pumps, the problems associated with ensuring the tightness of the axial joint of a pump casing being under the effect of mechanical and temperature loads, are being solved. During the study of axial joint tightness, numerical calculation methods are used to estimate the pressure intensity on the contacting surfaces. A detachable joint under the external load satisfies the criterions of the tightness if the pressure intensity on the sealing surfaces is higher than values of the specific pressure prescribed by regulations. However, inability to experimentally determine the pressure intensity on the contacting surfaces has so far prevented to assess the accuracy of results obtained by the numerical calculation methods.
 Objective. In order to verify the numerical results obtained by mathematical models, an experiment was carried out using a special Prescale film that registers the magnitude of the contact pressure on the joint of the specimen model of the flange fragment. Based on the experimental results, an analysis of the pressure intensity distribution was conducted.
 Methods. To conduct the experiment, there was developed a method for determining the pressure intensity on the contacting surfaces according to the proposed scheme of the specimen of the flange fragment.
 Results. A comparative analysis of the solving results obtained for the contact problem on the finite-element models of the flange fragment and the zone of the pump casing joint in the discharge chamber area showed a good coincidence of the results. Analysis of results obtained experimentally on the specimen of flange fragment and results of the numerical calculation on the flange fragment model also showed a good agreement.
 Conclusions. Therefore, results of the calculation of the pressure intensity in the detachable joints on mathematical models have been experimentally confirmed.

Adapted Process Strategies in Front Face Flow Drilling and Thread Forming of Lightweight Casting Materials

By using modern technologies to produce detachable joints in lightweight components, it is possible to reduce material consumption and manufacturing times. By front face flow drilling of lightweight cast materials, expanded bore walls are formed into thin-walled profiles, which are used as core holes for internal threads. The flow drilling process has to be adapted to the specific properties of the regarded materials AZ91 and AlSi10Mg. Thus, enhanced adjustments make it possible to increase the bore qualities significantly. Particularly in order to improve the roundness of the holes, the influence of decreased feed rates on the shape of the flow-drilled holes is analysed. Furthermore, this paper deals with the influence of the process temperature during flow drilling. By varying the predrilling diameter as well as the peripheral speed, the friction between the tool and the workpiece can be significantly influenced. This directly affects the thermally induced formability of the lightweight alloys. In order to produce high strength threads, cold forming is used instead of conventional tapping. In particular, in the context of the adapted flow drilling strategies, the surface qualities and the threads profiles are investigated in detail. Finally, continuous load increase tests were conducted to evaluate the fatigue properties of the formed internal threads using various strategies.

АНАЛИЗ УСЛОВИЙ ДОПУСТИМОЙ УТЕЧКИ ИЗ РАЗЪЕМНЫХ СОЕДИНЕНИЙ ТЕХНОЛОГИЧЕСКОГО ОБОРУДОВАНИЯ НА ОСНОВЕ РОССИЙСКИХ И ЗАРУБЕЖНЫХ СТАНДАРТОВ

In the petrochemical, nuclear and gas industries, high technological parameters are used, and first of all, they include temperature and pressure. Technological processes, as a rule, are carried out in capacitive equipment, the reliability of which is determined by the tightness of its detachable joints. In the period of integration of the development, manufacture and use of equipment for chemical, petrochemical and other industries, there is a need for common regulatory documents for their calculations and manufacture. In different areas, there are already many common European standards applied in individual countries. Recently, the issue of creating uniform standards in the field of tightness of detachable joints has arisen. The analysis of literary sources and, first of all, the existing standards of leading industrial countries for the calculation of detachable joints for strength and tightness is given.

Influence of Temperature of Working Medium on Airtightness of a Detachable Joint

The airtightness of a detachable joint depends on the load on its sealing surfaces and is determined by the magnitude of the leakage of the sealing medium or its viscosity, where the value of the latter depends on temperature. When a gas is heated, leakage decreases, while when a liquid is heated, leakage increases. An analysis of the influence of temperature on the airtightness of detachable joints is presented and recommendations are given for reducing this effect.

Main reasons of leaktightness failure of detachable flanged joints with lens seal ring

The main indicator of the performance of any design of detachable joints is its tightness, which is ensured by pressing the sealing surfaces of its parts to each other with a certain force. The frequent depressurization of detachable joints arising in practice is explained by the difficulty of determining the force that takes into account the influence of the design features of the parts of detachable joints and the intensity of their change from external conditions and the time of operation. Work on the definition of tightness carried out by the authors is different in that they take into account changes in the contact characteristics and the mutual influence of irregularities of the contacting surfaces. Considering the results of previous studies on the relationship between the tightness of the sealing device and technological factors, it can be said that the role of these factors is very significant, but it is rather difficult to assess the joint influence of technological factors on the tightness of any one design. Development and operation of new detachable connections with a lens sealing ring should be carried out taking into account the analysis carried out in this study and the established reasons for their depressurization.

On Unification of Used Materials and Processes at the Enterprise

The unification is one of possible ways to reduce costs and labor intensity. When unique technologies are used, the unification of technological processes can not be massive, but it can greatly simplify the manufacture of assemblies and units by reducing the amount of plating coating and finding the best coating to provide reliable material prevention. A liquid rocket engine is a subject to enormous loads during its operation, and the loss of tightness in the fuel and oxidizer channels can lead to irreversible consequences. The unification of the materials of the sealing elements is one of the necessary directions to ensure the safety of the engine. Thus, by unifying the engineering process of plating coating a stable tightness of detachable joints can be achieved, the production cycle may be optimized by reducing the number of toolings. By the end the unique technologies ensuring the tightness of components and assemblies will not be lost.

Capabilities of acoustic methods in testing of interference-fit joints

Tightness of joints on railway wheelsets is controlled by instruments based on a shrink fit method. To date, the shrink fit method has been replaced by an interference fit method. As a result, standard values of tightness have doubled. Therefore, there is an urgent need to upgrade and develop new methods for testing interference-fit joints. A promising solution is to use acoustic methods based on influence of material properties on propagation patterns of elastic waves. The purpose of this study is to evaluate the possibility to test fixed detachable joints by acoustic methods. Reference samples of interference-fit joints with known interference fits (29, 72 and 126 μm) were designed and produced. Experimental tests of samples and wheelset axles with inner bearing rings were conducted by a pulse-echo method and a method of free oscillations. The authors developed a procedure for determining the equivalent thickness of oil clearance using the proportionality factor of echo amplitude and sequence number of echo signals. When testing reference samples and loose bearing rings, frequency responses of the signals were obtained.

Магнитный метод контроля для оценки равномерности затяжки болтов фланцевых соединений

Flange joints refer to the most widespread detachable joints used in various industries. Such joints should be strong, durable and leak proof. Compliance with these requirements depends largely on the uniformity of bolt tightening. In flange joints it is necessary to provide that all bolts (pins) are tightened with equal force. Nonuniformity of bolt tightening could lead to different negative consequences, for example, to the lack of parts alignment, irregular gasket compression and as a result leaking of the product, disalignment of connected details, origination of fastening details plastic deformations and even breakage of bolts or pins. That is why control of steel pins and bolts tightening force is very important for the provision of joint reliability and not only during assembly and installation of units and details of any other equipment but also during its operation. The present article is devoted to studying and testing of one of modern and universal methods of bolt (pin) tightening force control – magnetic inspection based on structure-sensitive magnetic parameter control–remaining magnetic induction of the metal. The aim of the present studies is to test the metal mechanical stress indicator ИН-01м of scanning type used at real facilities for measuring pin tightening force during operation

Novel Process Approach for in-situ Insertion of Functional Elements in RTM-Applications

Lightweight design in vehicles leads to an increasing use of fibre-reinforced-plastics (FRP). To ensure the possibility of detachable joints in those constructions specific joining technologies have to be developed. Available technologies are not suitable for mass production or are leading to damage in the FRP. The aim of this paper is to show the possibilities and the general feasibility of a new process approach for the application of functional elements in FRP or hybrid materials during resin transfer moulding (RTM) processes. Therefore the movement of the RTM-tool-punch is utilised to produce an interlock between the splay stud and the fibres of the non-consolidated preform. This enables the application of the elements during the RTM-process. The resin infusion leads to the consolidation of the CFRP and a further fixation of the splay stud. Pull-out-tests as well as torsion tests are showing the mechanical performance of the joints.

Loading analysis of detachable joints by the acoustic method

The use of the acoustic method for measuring stresses in detachable joints is considered. It is characterized by improved accuracy, can be applied in an automated mode, and allows measurements in large parts in the sonic test area. The data on the instrumental facilities of the method are given and cases of their use in real designs are described.

Combined Detachable Joints for Textile Reinforced Thermoplastic Composites with Embedded Sensor Networks

In regard to the realization of innovative lightweight constructions, textile reinforced composites show outstanding mechanical properties, e. g. adjustable high specific stiffness and strengths. Furthermore, these materials enable a process immanent integration of functional elements (f. e. conductors, sensors, actuators or electronic components) directly into the composite structure due to their layered built up. Currently, no joining technologies for such function integrative composite parts exists, which enable a simultaneous mechanical and electrical load transfer from part to part by only one joining element type. Therefore, the paper focuses on detachable functional interfaces, which enable the mechanical connection of two join partners and the transfer of electrical signals by contacting the composite embedded conductors. Investigations in regard to the selection of suitable joining elements and their behavior under mechanical and thermal loads are performed. The investigations show that the electrical resistances are low and not affected significantly by rising tensile loads or repetitive joining operations. Tensile tests using both single lap shear and double lap shear specimens show that the electrical contact almost exists until the mechanical failure of the joints occurs.