Action Of External Load Research Articles

Experimental study of a viscous damped portal frame

The prototype analysed is based on the structure of a gantry made to scale for didactic purposes, relating its dimensions to large structures used in buildings. The present work contributes substantially in the vibrational analysis of structures, simulating in a practical way the behaviour of the portal against the action of external loads. Additionally, the contribution provided by the incorporation of a viscous damper in the structure is observed. The structure includes a mechanism that generates dynamic loads inducing horizontal movement in the system exactly as it happens during a telluric movement. The graphs that characterize the movement of the system are obtained, showing the notable reduction of the acceleration when including a viscous shock absorber. The behavior of a building that incorporates a viscous dampening system in its gantry presents ideal characteristics during a seismic movement reducing the damage generated to the structure during the event.

Mechanism of strain-induced magnetic signal change in ferromagnetic materials under weak magnetic environment

Weak magnetic detection based on force-magnetic coupling effect is widely used in nondestructive testing of ferromagnetic materials, but the weak magnetic signals caused by the deformation of ferromagnetic materials under the action of external load show nonlinear changes, and the existing theories can not make a unified conclusion on the mechanism of nonlinear changes of magnetic signals, which limits the further application of weak magnetic detection. In this paper, a microscopic model of ferromagnetic material is established with the strain of the material as the independent variable. Firstly, the reasonableness of the established model is verified by the stress–strain relationship, and the stress concentration phenomenon generated by the change of the microscopic structure of the model is studied in depth by using the XRD diffraction method, so as to put forward the idea of characterizing the macroscopic stress with microscopic dislocations; secondly, the mechanism of the change of the magnetic signals of the ferromagnetic material caused by strain is analyzed by using the atomic magnetic moments and the density of states. The model explains the mechanism of strain-induced magnetic signal change in ferromagnetic materials, and has a guiding role in the further application and promotion of the weak magnetic method.

Study on the microstructure and mechanical properties of W-wire/TiBe, ZrBe, and ZrTiBe alloy composites

The microstructure and mechanical performance of W wire/Ti70Be30, Zr65Be35, and Zr37.5Ti26Be36.5 alloy composites were investigated in this study using X-ray diffractometer, scanning electron microscopy, and mechanical universal testing machine. These composites were prepared through the melt impregnation method under optimized processing conditions. The results show that the compressive strength of the three composites is all above 2600 MPa. The Ti70Be30-W composites diffuse violently at the interface, the W-Ti phase is formed at the interface, and the cracks of the composites under the action of applied load show a stepped pattern. The Zr65Be35-W composite reacts violently at the interface, resulting in a W2Zr interfacial product, which adheres to the surface of the W filament and presents a continuous interfacial reaction layer. When subjected to external load, the crack will expand rapidly along the interfacial reactive layer. The addition of Ti in Zr37.5Ti26Be36.5-W composites effectively inhibited the W-Zr reaction, the interface reactant W2Zr disappeared, and the W-Ti interface product presented a discontinuous interfacial reaction layer on the surface of the W filament, and the material split under the action of external load, and the crack showed step-like propagation.

Оценка напряженнодеформированного состояния профильных соединений узлов машин

The article presents the results of studies of profile joints of mechanisms and machines for rigidity and strength. The device is based on the use of fixed and movable profile connections designed to transmit torque. Profile joints with a guaranteed gap are considered, made on the basis of an equiaxial contour of the P3, P5 type and a curved contour of the PC4 type, which have received the most widespread introduction in the nodes of metal-cutting machines and other machines manufactured in Russia, as well as Hungary, Germany and the DPRK. Using a well-known technique designed to assess the stress-strain state (VAT) of the parts of profile joints, calculations are performed according to the criteria of operability for strength and stiffness of hubs (bushings) with different wall thicknesses. The analysis of the results of the calculation of strength and stiffness is carried out using the example of the P3 profile. When stretching the hub from the action of spacer forces, the geometric shape, the nominal size of the covered part, the wall thickness of the covering part, as well as the magnitude of the external load transmitted by the connection in static are taken into account. The permissible values of the thickness of the walls of the hub (bushings) of the joint are determined to ensure the rigidity of the hub under tension from the action of external loads. As a result of the research, the influence of the thickness of the hub walls for the studied shapes of the joint parts on the values of the transmitted torque is established. For example, a change in the thickness of the hub wall from 15 to 3 mm for a normal range of shaft mounting diameters causes the sleeve to stretch radially up to 50 microns in the range of transmitted torques from 5 to 600 Nm.

Determination of the bone tissue mechanical properties by a numerical-digital method using CT data

Modeling of elements of inhomogeneous media is an actual direction in the study of composite materials and biomechanics objects. The need for research is determined by the insufficient development of methods for describing mechanical parameters, taking into account the anisotropy of materials. In this case, one of the directions is the use of digital prototyping and numerical modeling methods. In the field of biomechanics, the applicability of approaches to numerical modeling based on image data correlates with cases of clinical practice, which is due to the peculiarities of non-destructive testing methods and allows obtaining results that affect the quality of treatment. The paper considers a method for restoring effective mechanical properties of a material based on computational and field experiments. The simulation was based on the finite element method and assumed the use of data from a digital prototype obtained by computed tomography. The restoration of the calculated area was performed by filtering the initial grid relative to the proportion of the content of the material. The presented method makes it possible to restore the effective values of the elastic modulus and tangential modules based on the relationship established within the framework of the approach between the mechanical properties of the material and the loading parameters of the model sample. In the course of the work, the bone organs of pigs were modeled. Animal husbandry and experimental procedures were carried out in compliance with bioethical norms. Physical tests and numerical modeling were carried out under the conditions of bending action. Validation of the obtained distribution of values of the stress-strain state was performed according to the data of full-scale experiments. The presented solution showed a weak dependence of the results (less than 1 %) relative to the degree of discretization of the computational domain, which made it possible to perform calculations using fewer finite elements, avoiding the use of resource-intensive methods to restore the geometry of the sample. The results obtained in the framework of the work correspond to the literature data and determine the true values, the use of which in calculations makes it possible to assess the strength of the elements of an inhomogeneous structure under the action of external loads, taking into account the spatial distribution of the material.

Exact solutions for the symmetric elastoplastic response of functionally graded pressure vessels

With the development of functionally graded (FG) composite material technology, mechanical analyses of FG pressure vessels have attracted attention. Due to the non-uniform stress distributions inside such vessels, irreversible plastic deformation first occurs in some zones of the structure under the action of external loads. It is necessary to perform an elastoplastic analysis of FG structures to determine their load-bearing capacities. In this paper, exact solutions are obtained for the purely elastic, partially plastic, and fully plastic deformation of FG cylindrical and spherical shell pressure vessels under mechanical loads. The material properties (elastic modulus and yield strength) are assumed to vary nonlinearly in the radial direction of the vessel and the Poisson's ratio is assumed to be constant due to Poisson's ratio slight variations in the engineering materials. The novelty of the current work lies in the presentation of complete exact elastoplastic solutions for FG thick cylindrical and spherical shell pressure vessels, taking into account all deformation zones. Tresca's yield criterion is used to formulate four different deformation zones for an ideal plastic material. All of these states of deformation are studied in detail. It is shown that the elastoplastic response of the FG pressure vessels is notably affected by the radial variation of the material properties. With an increase in the FG parameter β, the first yielding position of the FG pressure vessels changes from the inner surface to the outer surface. The conclusions of this work should help with developing designs of FG pressure vessels to prevent yielding under excessive circumferential stresses.

Design and optimization study of a resistance structure for an industrial storage platform supporting injection molding tools for the automotive industry

The paper offers an optimized solution for an industrial storage platform supporting injection molding tools used to produce thermoplastic components in the automotive sector. After analyzing the current situation for storing the massive tools, a work platform was proposed in order to ensure the conditions imposed by the extension of the company’s implementation of LEAN methods to streamline the production flow. The design of the resistance structure was modeled in the program Autodesk Inventor Professional 2020, taking into account realistic loads and their statistical distribution in the construction of the static and loading scheme of the main beam. The analysis of stress and strain in the main beam under the action of external loads was performed using the finite element method of the program Autodesk Inventor Nastran. The optimized solution for the main beam has been found by analyzing the optimization possibilities in three steps: structural optimization, dimensional optimization and the validation of the proposed optimization options, by verifying the safety of the structure. This paper presents in detail the choice of optimization criteria, decision variables, constraints and objective function. Based on the numerical analysis of mechanical stress and safety coefficient in operation, an optimal variant was chosen from the analyzed models: recessed articulated structure simple and with intermediate support, using laminated profiles IPE 200 and IPE 140.

Product durability management using surface engineering technologies

The problem of managing the durability of products due to the creation of regions in materials with a given temporal and spatial non-locality is considered. A mathematical model of softening of materials under the action of external loads is proposed, allowing to take into account the special role in the formation of damaged places of exit of grain boundaries and their triple junctions on the outer surfaces of parts, as well as their interaction with stress concentrators formed after mechanical processing.
 The developed model representations are used to ensure the operational uniformity of structural elements with concentrators under stress by methods of surface engineering, in particular, when determining the role of changes in the quantitative parameters of the microstructure on the wear resistance of the surface layers of rolling stock parts of railway transport containing stressed concentrators. The optimal depth of the plasma hardening of the subsurface layers of the rims of wheel pairs of locomotives has been established, depending on the size, placement and geometric characteristics of the tension concentrators. It is shown that taking into account the dynamics of structural changes during the degradation of materials in the conditions of operation according to the proposed model ratios allows to achieve the specified life cycle of parts at minimal costs.
 Increasing the durability of products is achieved by optimizing technological modes of surface engineering, which ensure the formation of structures with a smaller gradient of properties.

Unbalanced vibration suppressing for aerostatic spindle using sliding mode control method and piezoelectric ceramics

The lubricating medium of the aerostatic spindle is gas, with relatively low rigidity, which is easy to cause rotor offset and additional vibration under the action of external load, thus affecting the processing accuracy of the spindle. To solve the problem of unbalanced vibration of the spindle, a new type of controllable radial aerostatic bearing is designed by combining piezoelectric ceramics, which use the inverse piezoelectric effect of piezoelectric ceramics to squeeze the air film to produce corresponding control force, and the radial unbalanced vibration of the spindle is suppressed. A bearing–rotor–piezoelectric ceramic coupling model was established, and the control method of feedforward combined with feedback was used to reduce the hysteresis characteristics of piezoelectric ceramics. On this basis, the sliding mode controller of the entire system, and through research, it is found that the sliding mode controller based on the extended observer has the best vibration suppression effect compared with other sliding mode controllers in the article; this research results can improve the rotation accuracy of the spindle system and the machining accuracy of ultra-precision machine tools.

The formation mechanism of modulation structures along three different crystallographic directions in pure hafnium

The microstructure of pure hafnium subjected to micro-hardness test was studied in detail by using transmission electron microscopy (TEM). Results indicated that the {101‾0}<112‾0> prismatic slip system was commonly activated and modulation structures along three modulation directions can be frequently observed. Based on the crystallographic characteristics of these modulation structures and the electronic structure theory, the formation mechanism of modulation structures in Hf was discussed. It was confirmed that the original Brillouin zone of α-Hf was shifted along three different directions, g1, g2 and g3, under the action of external load, which changed the relative locations of the Brillouin zone and the Fermi sphere of the α-Hf and stabilized the whole system, thereby causing the formation of the modulation structure along three different directions.

Analytical algorithm of longitudinal bending stiffness of shield tunnel considering longitudinal residual jacking force

Longitudinal bending stiffness is a fundamental parameter of shield tunnels, and its value directly affects the analysis of their longitudinal response. Existing studies have not considered the tensile stiffness of segment ring joints and longitudinal residual jacking force when determining the value of the longitudinal bending stiffness of an existing shield tunnel. Therefore, through theoretical analysis, this study considered the longitudinal bending deformation under an external load action as two parts, namely the longitudinal bending deformation of the homogeneous pipe and the longitudinal bending deformation induced by the opening of the segment ring joints. An analytical algorithm of the longitudinal bending stiffness of the shield tunnel was obtained, considering that this longitudinal bending stiffness was related to various factors such as the elastic modulus of the material of the segment ring, outer diameter of the shield tunnel, width of the segment ring, number of the segment ring joints and tensile stiffness of the connecting bolt. A scaled shield tunnel model that considered tensile stiffness of the segment ring joints and longitudinal residual jacking force was designed, and longitudinal bending stiffness tests of the model were conducted accordingly. The tests were designed to measure the longitudinal bending deformation and opening of the segment ring joints. The validation of the theoretical analysis result based on the test data demonstrates that the longitudinal residual jacking force could only reduce the longitudinal bending deformation and the opening of the segment ring joints at small loads, it had almost no effect under larger loads. The measured longitudinal bending stiffness of the shield tunnel model was generally consistent with that obtained using the theoretical algorithm. Thus, in the longitudinal response analysis of the shield tunnel, the effect of the longitudinal residual jacking force on the enhancement of the longitudinal bending stiffness need not be considered.

Safety assessment of massive buttress dams in the presence of thermal cracks in them

In the 1950s, the construction of hydropower facilities began in the regions of Siberia and the Far East, characterized by harsh climatic conditions, which should be taking into account to predict the stress state of dams. The aim of the study is an assessment of the conditions for the formation of temperature cracks in concrete dams and their influence on the further operation of the structure, as well as measures and technologies to combat cracking in massive concrete. Thermal stresses often exceed the stresses caused by the action of external loads and lead to the appearance of cracks in the concrete. Almost all modern concrete dams are subject to thermal cracking today. Appropriate design and technological measures must be provided for. When studying the thermally stressed state of lightweight concrete dams, the method of direct reproduction of thermal deformations on models made of brittle materials and computational methods oriented towards computer methods of solving problems are used. The results of modeling and computational studies of massive buttress dams are presented and the influence of the main influencing factors is considered, taking into account the effect of cracking on the operation of such dams.

Distribution development of pore/crack expansion and particle structure of cemented solid-waste composites based on CT and 3D reconstruction techniques

This work analyzes the effects of Industrial solid waste content and meso-microstructure on the mechanical and fracture behavior of cemented solid-waste composites (CSWC). The mechanical properties of CSWC were investigated using uniaxial compression tests. Quantitative analysis of pore and particle structure and cracks was performed using X-ray computed tomography (CT). In addition, the effects of solid waste content and porosity on the Uniaxial compressive strength (UCS) of CSWC were analyzed, and the effects of pore and steel slag (SS) particle distribution on crack expansion were investigated. The results show that the optimization of solid waste content can improve the pore structure of CSWC and promote the uniform distribution of SS particles within CSWC. SS content is 40 wt%, SS is the main factor affecting the strength of CSWC, SS content is less than 40 wt%, porosity and fly ash (FA) are the main factors affecting the strength of CSWC. Connected pores and microcracks are prone to develop as cracks under the action of external loads. Porosity is less than or equal to 0.10%, pore size is not related to crack development. SS content is greater than 10 wt%, particle structure affects crack development.

МЕТОДОЛОГИЧЕСКИЕ ОСНОВЫ И ПРАКТИЧЕСКИЕ АСПЕКТЫ РЕШЕНИЯ ЗАДАЧ ОПТИМИЗАЦИИ НЕСУЩИХ СИСТЕМ БЕСПЛАТФОРМЕННЫХ ИНЕРЦИАЛЬНЫХ НАВИГАЦИОННЫХ СИСТЕМ

This article describes approaches to solving problems of optimization of bearing structureof strapdown inertial navigation systems (SINS). A typical optimization problem in this case ismultiobjective parametric optimization of the bearing structure of the SINS accelerometer triad inorder to minimize the mass of the bearing structure and minimize deviation angles of the accelerometeraxes under the action of external loads. The ANSYS Mechanical and ANSYSDesignXplorer modules are used as a tool for numerical modeling and optimization, respectively.Practical issues related to parameterization of SINS bearing structure 3D-models, calculation ofaccelerometer axes deviation angles, possible variants of numerical experiment plans, estimationof response sensitivity to input parameters, generation and refinement of the response surface, andmultiobjective optimization are considered. For the rational parametrization of geometry, theSINS device assembly was decomposed, as a result of which the parts and structural elements that have the greatest influence on the considered objective functions were identified. To calculate thedeviation angles of the sensitive elements axes, special two-node finite elements and relations forthe Bryant angles were used, which describe the relative position in space of two coordinate systems.When planning a numerical experiment, at the first stage of optimization, a central compositionplan was used, and at subsequent stages, the parameter space was filled using the Latin hypercubemethod with the option of relations between parameters, which made it possible to avoiddegenerate design options. The response surface was built using the genetic aggregation methodand subsequently refined based on a set of optimal solutions. Optimization for conflicting goals ofmass minimization and stiffness maximization was carried out using a multiobjective genetic algorithm.The described set of approaches to solving optimization problems as a result of an exemplaryseries of calculations made it possible to reduce the mass of a serial SINS bearing structurepart by 23% with fixed stiffness.

Flexible and Robust Triboelectric Nanogenerators with Chemically Prepared Metal Electrodes and a Plastic Contact Interface Based on Low-Cost Pressure-Sensitive Adhesive.

Triboelectric nanogenerators (TENGs) are devices that can harvest energy from mechanical motions; such devices can be used to power wearable sensors and various low-power electronics. To increase the lifetime of the device, scientists mainly use the method of making TENG in a hard skeleton to simplify the complex possible relative movements between two triboelectric parts. However, the hard skeletons cannot be embedded in soft and lightweight clothing. To make matters worse, the materials used in the garments must be able to withstand high mechanical forces when worn, such as the pressure of more than 100 KPa exerted by body pressure or everyday knocks. Notably, the TENGs are usually made of fragile materials, such as vacuum-evaporated metal electrodes and nano-sized coatings, on the contact interface; these electrodes and coatings often chip or wear off under the action of external loads. In this work, we succeeded in creating a thin, light-weight, but extremely robust garment-integrated triboelectric nanogenerator (G-TENG) that can be embedded in clothing and pass the water wash test. First, we chemically deposited a durable electrode with flexible properties for G-TENG using a novel technique called polymer-assisted metal deposition (PAMD). The as-formed metal electrodes are firmly bonded to the plastic substrate by a sub-10 nm adhesive polymer brush and can withstand a pressure of 22.5 MPa and a tear force of 0.7 MPa. We then removed the traditionally used fragile nanoparticle materials and the non-durable poly-dimethylsiloxane (PDMS) layer at the triboelectric interface, and then used a cost-effective, durable and slightly flowable pressure-sensitive adhesive to form a plastic contact interface. Such a soft plastic interface can ensure full contact of the triboelectric materials, which is excellent in complex environments and ultimately improves the power generation efficiency of the devices. The as-formed low-cost energy harvesting device could become an industry standard for future smart clothing.

Long-term exploitation of reinforced concrete constructions of transport structures on a soil base under conditions of nonlinear rheological deformation with corrosion damage

The method of calculation of reinforced concrete constructions of transport structures on a soil base in an aggressive environment under rheological deformation conditions, taking into account corrosion damage, reflecting their real work under the combined action of load and aggressive environment on the basis of the modern phenomenological theory of deformation of elastic-creeping body, is proposed. The possibility of considering the processes of long-term deformation of reinforced concrete in conditions of long-term operation with a changing mode of action of external load is shown. An example of the calculation of a reinforced concrete flexible foundation on a soil base is given, taking into account the friction forces along its sole during the considered service life and the presence of corrosion damage.

Evaluation of Rock Burst Propensity and Rock Burst Mechanism in Deep Phosphate Mines: A Case Study of Sujiapo Phosphate Mine, Hubei Province, China

Rockburst is one of the major problems in rock underground engineering and mechanics. To make a risk assessment of rockburst and improve the mine safety index, some evaluation systems for rockburst propensity have been proposed and applied, and progress has been made in the study of high-value mines and single evaluation systems, but these evaluation systems are still immature for deep low and medium grade phosphate mines with more complex influencing factors. Therefore, to solve this problem, this study takes the phosphate mining area of the Sujiapo phosphate mine as the main research object, and combines the characteristics of the deep rockburst of the phosphate mine and its physical and mechanical properties; the evaluation system combines fuzzy mathematical method and multiple evaluation methods to determine the propensity of rockburst of deep mining of Sujiapo phosphate mine. The JSM-500LV SEM and acoustic emission results are used to analyze the microscopic mechanism of rockburst from the morphology and composition of the rocks, and the rationality of the evaluation system is further demonstrated. The study shows that dolomite and phosphorite in the study area are moderate rockburst, and shale has a weak rockburst tendency; because the roof dolomite and phosphorite crystallization degree are higher, the elastic modulus is large. Under the action of external load, the roof dolomite stored more elastic strain energy. Deformation damage consumes less energy. The energy released to the outside world after the damage is large, more likely to occur brittle damage, and the rockburst tendency is high. Therefore, the evaluation system combining multiple evaluation methods can comprehensively determine rockburst in phosphate mines.

Study on the automatic optimization design of the cross-sectional layout of an umbilical with layers based on the GA-GLM

Marine umbilical provides the remote control function for offshore oil and gas exploitation, which is usually integrated by different functional components that vary widely in their mechanical properties. Under the action of external load, unreasonable cross-sectional layouts may lead to large cross-sectional deformation and contact pressure between components thus affecting the service life of an umbilical. Therefore, how to design the cross-sectional layout is a very necessary research work in order to improve service life of the umbilical to withstand various loads during operation. At present, the research on the cross-sectional layout of an umbilical is not sufficient, and there is no standardized design method in the design specification. Considering the mechanical and geometrical properties as the quantitative design objectives, the mathematical optimization model of the cross-sectional layout of an umbilical is proposed. Meanwhile, the layering strategy is introduced because of the processing and manufacturing factors.Then, the genetic algorithm (GA) with good global search performance and the generalized Lagrange multiplier (GLM) with fast convergence speed are combined to solve the above model. Finally, taking an umbilical as an example, the optimal cross-sectional layout is obtained and the effectiveness of the algorithm is verified by the numerical simulation. The results show that the optimization method proposed in this paper can quickly obtain the optimal design cross-sectional layout, and supply a specific way for the fast design of an umbilical, which has the certain engineering application value.

Regulating the vibration of aerostatic journal spindle based on piezoelectric ceramics

The aerostatic spindle often occur offset and additional vibration under the action of external load due to the low stiffness, thus affecting the rotary accuracy of the spindle. In order to solve the problem of unbalanced vibration of the spindle, a new type of controllable radial aerostatic bearing is designed by combining piezoelectric ceramics. A bearing-rotor-piezoelectric ceramic coupling model was established, and the control method of variable structure sliding mode control was used to reduce the vibration amplitude due to the unbalance. From the results of simulation and experiment, it is found that when the disturbance is taken as a constant value, the vibration amplitude increases with the increase of force; when the disturbance force is an unknown random force, the control effect is slightly worse than that when the disturbance force is known, but the rotary accuracy can be improved by this suppression effect on the aerostatic spindle. Finally, the correctness and effectiveness of this control method are proved through experiments.

Study of mechanical behavior and cracking mechanism of prefabricated fracture cemented paste backfill under different loading rates from the perspective of energy evolution

Loading rate (LR) and initial defects are the vital factors influencing the mechanical properties of cemented paste backfill (CPB). Under the action of external load, the essence of the deformation and damage of the filling body is the evolutionary process of progressive damage driven by energy, which is the comprehensive performance of crack closure, development, expansion, and convergence. In this paper, uniaxial compressive strength (UCS) tests with different levels of LRs were conducted on 0°, 45°, 90° prefabricated fracture CPBs (PFCPB), and CPB. The results show that UCS and elastic modulus of the filling body were positively correlated with LR. The mechanical properties of the filling body were degraded by PF. During loading, the top and bottom surfaces of 0° and 45° PFs were closed, and the stress–strain curves showed stress drop phenomenon. The stress drop of the curve corresponded to the rapid release of elastic energy and the rapid increase of dissipated energy. The dissipation energy curve corresponded to crack opening and expansion, which could be divided into slowly growing, steadily growing, and rapidly growing stages. The steadily growing stage of the dissipative energy curve for higher LRs was beneath the other curves, and a decelerating rising period occurred in the rapidly growing stage. Meanwhile, the dissipation energy curves of 0° and 45° PFCPBs suffered from an accelerated rise, slow rise, and rapid rise periods in the rapidly growing stage. The cracks after the failure of PFCPB mainly included resistance to tensile cracks, wing cracks, coplanar and non-coplanar secondary cracks. The failure mode of PFCPB was the occurrence of mixed shear-tension failure, and CPB exhibited shear failure. The progressive damage law and cracking mechanism of the filled body were investigated with the help of AE energy rate (cumulative AE energy)-energy-time (strain) curves and microscopic morphology. The results could provide a theoretical basis for the stability assessment of the filling body.