A snake-bone flexible drill pipe was designed based on bionics to relieve the overlarge deflecting curvature radius of the sidetrack horizontal well. Specifically, flexible design is carried out for coiled tubing in combination with morphology and mechanism bionics. The ball head+external casing+torque pin structure was used to decompose the drill pipe, and the torque pin was used to transfer torque. Each section can reach a torsion angle of 4.1°, which can alleviate the buckling of the drill pipe in the casing pipe. A maximum bending angle of 5.12° can be generated between sections, and the deflection curvature radius is shortened to 1.8 m. To overcome the directional uncertainty between flexible drill pipe sections of small curvature radius during dispersion, a highly flexible pipe was added at the angle in the flexible drill pipe, which guaranteed a high discharging rate. Based on the multi-body dynamics finite element analysis software ADAMS and the statics simulation software ANSYS, the multi-body linkage dynamics and statics simulation analysis were carried out for the flexible drill pipe as a whole, which confirmed the effectiveness of the described deflecting method. Field experiments were carried out in Well PU 2-365, and the borehole trajectory was calculated based on the data derived from the inclinometer. The deflection section curvature radius could reach 1.8 m, which completed the design expectation.

The article investigates the structure, mechanical and electrical properties of spark plasma sintered metal-based Ti-Al-C system composite materials. The initial powder consisting of 85% titanium and 15% aluminum was treated in kerosene by high voltage electrical discharge. Such a powder treatment allowed the formation of carbides and MAX-phases that strengthened sintered composites by spark plasma sintering. The microstructure of Ti-Al-C samples was examined by optical and electron scanning microscopy. Vickers hardness measurement revealed high microhardness – approximately 500–550 HV and more, depending on the sintering temperature of the samples. X-ray diffraction was used to determine the phase composition of samples. The electrical properties of the Ti-Al-C composites were evaluated by measuring their resistivity.

The system for monitoring acoustic emission (AE) parameters in mechanical testing of materials built up from electronic equipment and corresponding software is described. The electronic equipment based on a high-speed data storage module with a USB interface provides conversion of AE signals, their amplification, filtering, and digital input to a personal computer. The AEMonitor software performs continuous analog-digital conversion of AE signals, evaluation of their spectral distribution (fast Fourier transform), online display, accumulation, and storage of experimental data with load parameters for their further analysis. The software features an online automatic display of the spectral distribution of signals and corresponding stresses against the number of AE pulses from tested materials. The functional potentials of the system were verified in bending tests of corundum refractory and glass fiber plastic specimens with recording AE parameters. The relations between major AE parameters, form, and spectral distribution of pulses under loading of those materials were greatly different due to varied fracture mechanisms.

Inverted modified Lindley distribution was developed without considering any special function or additional parameters in its formulation. This model provides better fit than exponential and Lindley distributions and it was suitable for modeling increasing, reverse bathtub (unimodal) and constant shaped hazard rate function. This article emphasize the estimation of a one-parameter inverted modified Lindley distribution by using order statistics. First, the explicit expressions for single and product moments of order statistics from this distribution are derived. We have also tabulated the first four inverse moments of order statistics for various values of the parameter. In the part of estimation, we first utilize the maximum likelihood (ML) estimator and approximate confidence interval to obtain the model parameter based on order statistics. Based on order statistics, a simulation study is carried out to check the efficiency of the estimator. Two real life data sets, have been analyzed for order statistics to demonstrate how the proposed methods may work in practice.

This paper provides a method to predict the long-term creep behavior of continuous glass fiber-reinforced polypropylene composites (CGFRPP). The finite element method was used in this study, which was based on short-term experiments. For these calculations, a viscoelastic constitutive equation named the Burgers model was introduced to describe the creep behavior of pure polypropylene (PP) resin. The suitability of the Burgers model for the PP resin was investigated by performing short-term creep experiments under various stress conditions. The stress-dependent Burgers model was, thereafter, proposed by the calibration of elastic stiffness and viscosity parameters in nonlinearity. This nonlinear model was finally incorporated into a representative volume elements (RVE) model to predict the long-term creep behavior of CGFRPP unidirectional (UD) tape. It was found that the simulation results agreed with experiments when using the nonlinear Burgers model. The creep mechanism of the UD tape was also analyzed microscopically with the RVE model, and the redistribution of stress in the fiber and matrix was discussed.

This work studied the ductile-brittle transition process of 15MnTi steel under different dynamic loading conditions. The strength of 15MnTi steel increased with strain rate because dislocation movement and element diffusion were inhibited. The fracture mode was different under different loading speeds. When the loading speed was lower than 0.025 m/s, the fracture mode was complete ductile fracture; when the loading speed was 0.1 –0.4 m/s, the fracture mode was ductile-brittle fracture; and when the loading speed was higher than 0.5 m/s, the fracture mode was a brittle fracture. In the three-point bending test, the dynamic brittle fracture rate of 15MnTi steel decreased with increasing crack tip constraint, and the brittle fracture resistance decreased with increasing loading rate. In the Charpy impact test, the fracture mode of the prefabricated crack specimens was a ductile fracture. In addition, when the loading rate was 0.1 m/s, the toughness characteristics were not obvious. The fracture had tear dimples at loading rates ranging from 1 to 3.5 m/s, showing certain ductile fracture characteristics. There were many dislocations in the matrix, and TiC was distributed in the matrix. Plenty of dislocations accumulated around the particles, which improved the strength by hindering the movement of the dislocations.

Aimed at the widespread concrete durability deterioration problem among old irrigation aqueducts in China, the main purpose of this study is to propose two dynamic elastic modulus (\({E}_{d}\)) targeted concrete quality evaluation methods as major supplements to the conventional inspection approaches mainly based on testing strength. First, with large pulse energy, the elastic impact wave can penetrate through the whole length of a large-dimension structural member to get the P-wave velocity and then \({E}_{d}\) in its entirety. Second, the in-situ dynamic testing combined with FE modal analysis can reasonably estimate the average \({E}_{d}\) of the whole structure. These two methods can be applied in coordination to improve the reliability of the test results.

The aim of this finite element stress analysis (FEA) study was to assess the effect of separated files (SF) that were broken at two levels (at apical 4 and 9 mm) on the biomechanics of premolars and to determine if removal techniques affect stresses. Six lower premolar teeth were screened on computerized microtomography (micro-CT), standard access cavities were prepared, working lengths were determined, and root canals were prepared (Protaper files, Protaper Universal, Dentsply, Switzerland). Notches were created on the final shaping-file F3 at points 4 and 9 mm from the file tips, inserted in the canals, and squeezed at the apical to break. The roots were rescreened, and SFs were removed by using a Masseran kit (MK; Micro Mega, France), ultrasonic tips (UT; Satelec, Acteon group, France), and the bypass (BP) technique. Final scans were obtained and converted into three-dimensional FEA models. The following conditions were then simulated: a) root-filled tooth with SF; b) root-filled tooth after removal of the SF by using MK, UT, or BP techniques. The models were loaded axially (from two directions) and vertically (300 N), and von Mises stresses were then analyzed. SFs increased the stresses within the root. Longer SFs cause higher stresses within the root and thus should be removed, while short SFs could be kept considering the other clinical factors. Removal via MK caused the highest stresses within the roots among the techniques used. Axial loading caused higher stresses at the cervical side, while the stresses moved toward the apical side under vertical loading. SFs increase the stresses within the root. Long SFs should be removed while short SFs can be left (considering other clinical factors that may affect the success of the treatment). Removing short SFs located at the apical side negatively affects the biomechanics of the teeth, and this effect is more dramatic with the MK technique.

The problem of the cylindrical cavity under axisymmetric constraint under plane strain conditions is analyzed. The soil is considered an elastoplastic material. The physical properties of soil are described. A proposed constitutive equation is adopted to describe the stress-strain relationship for soil. The soil strength characteristics are described by the united strength for spatial mobilized plane and Lade strength criteria. The analytical solution of critical plastic pressure in the cylindrical cavity can be obtained by solving the analytical elastic equilibrium equation. The stress ratio and the relation between the critical radial stress and the volume strain corresponding to the peak stress ratio are analyzed quantitatively. The results show that the critical value of the radial stress decreases with the increase of the peak stress ratio corresponding to the volume strain in the soil with a small amount of shear dilatancy. The critical value of the radial stress decreases first and then increases with the peak stress ratio of the corresponding volume strain in the soil with an intermediate amount of shear dilatancy of the volume strain. However, for soil with a large amount of dilatancy and shear strain, the critical value of radial stress increases monotonically with the peak stress ratio corresponding to the volume strain.

This study is focused on designing and manufacturing punches and dies of cylindrical and polygon shapes to produce a polygon shape with eight edges via two methods: drawing and redrawing operations. In the first method, a polygon cup was formed from the nondeformed circular blank of 1008-AISI low-carbon steel. In the second method, a polygon cup was redrawn from the cylindrical shape formed from the nondeformed circular blank. In addition, finite element method was utilized by adding ANSYS software for modeling and analysis of drawing and redrawing processes. The aim of this research is to produce polygon shapes from nondeformed circular blanks and cups of cylinder shapes and to draw a comparison between the experimental work results and the finite element analysis. The comparison revealed that in the drawing process, the maximum punch load required to produce a polygon shape was recorded as 40.250 and 35.165 kN with the redrawing process. The maximum effective strain recorded was 0.4185 with the polygon shape produced by the redrawing process. The redrawing process is a convenient process to form intricate shapes (polygons).

The paper presents the results of a computational assessment of the shape change of the WWER-1000 reactor core baffle using modern approaches to modeling the processes of radiation swelling, radiation creep, and subcritical damage of irradiated metal by the mechanism of ductile fracture. To simulate radiation effects, mathematical models are used that consider the influence of the stress state and accumulated irreversible deformation on the swelling and creep of austenitic steels exposed to neutron irradiation and elevated temperature. The increased volume concentration of ductile fracture pores in the irradiated metal is considered using the modified Huang equation and the proposed equation derived from Kachanov’s solution for a spherical cavity in an unbounded elastic-plastic medium. The determination of the stress-strain state of the WWER-1000 reactor cavity and the inner vessel shaft is based on solving a nonlinear boundary value problem of thermomechanics, which allows describing the kinetics of the coupled processes of elastic-plastic deformation, radiation swelling, radiation creep, contact interaction, and subcritical damage of irradiated metal depending on the accumulated dose of neutron irradiation. The computational analysis is based on a mixed finite element method scheme that provides a continuous approximation for both displacements and stresses and strains, which makes it possible to determine the shape change of the shielding with a high degree of accuracy. The calculation was performed in a two-dimensional formulation for the cross-section of the shielding with the maximum height of the damaging dose and irradiation temperature under the condition of generalized plane deformation. The calculation results were obtained using the median parameters of the temperature-dose dependence of free swelling of austenitic steel 08Kh18N10T. Based on the calculated data, the influence of radiation effects and metal damage according to the ductile fracture models on determining the shape change of the WWER-1000 reactor baffle under conditions of long-term operation was analyzed.

With semi-continuous casting AZ81 magnesium alloy as the carrier, the evolution of microstructure and properties in different deformation processes was analyzed and discussed by means of SEM, EBSD, XRD and metallographic microscope. The results show that the microstructure of as-cast AZ81 magnesium alloy is composed of α- Mg matrix, Mg32(Al, Zn)49 and MnAl6 phases, with coarse dendrite morphology. After die-forged net-final forming of the extrusion perform, the tensile strength, yield strength and elongation are increased by 95.8%, 138.8% and 353%, respectively, compared with that of as-cast AZ81 magnesium alloy. After solution treatment 400℃×0.5 h + 200℃×20 h, the internal stress was eliminated and the microstructure was more uniform. The tensile strength and yield strength were increased by 0.9% and 9.1% respectively compared with the untreated sample, but the elongation decreased by 48.5%. The fracture mechanism of as-cast AZ81 magnesium alloy is mainly brittle cleavage fracture, while the fracture characteristics of as-extruded and die-forged AZ81 magnesium alloy are the mixed fracture characteristics of cleavage and quasi cleavage fracture. After solution and aging treatment at 400℃×0.5 h + 200℃×20 h, the cleavage steps and cleavage patterns in the fracture surface increase, and the quasi-cleavage characteristics decrease, which makes the tensile strength and yield strength properties of the alloy slightly improve, but its plasticity decrease.

Recently, much attention has been paid to the study of the deformation and failure features of high-strength steels under extreme loads, under which they are mainly operated. One of the topical issues is the correct determination of the parameters of deformation models of materials. The use of tests for barrier penetration at high speeds of 100–1000 m/s is quite complicated and expensive, and also does not allow to obtain enough information. Therefore, alternative experimental methods have been developed recently, which include static and dynamic punching tests of thin sheet specimens at speeds of up to 10 m/s. Such tests are simpler and allow to obtain more information about the behavior of high-strength materials in conditions that simulate operational ones. This paper presents the results of static and dynamic punching tests on thin sheet specimens of 50×50 mm size and 1 mm thickness made of Armox 500T armor steel. The static punching tests were carried out on an Instron 8802 servohydraulic machine, for which special equipment was manufactured. The dynamic punching of thin-sheet specimens was carried out on an instrumented vertical impact tester equipped with a high-speed strain and force recording system. To conduct such tests, the experimental equipment was updated, and a design of special supports for the rigid fixing of thin-sheet specimens was developed. The loading speed was varied from 0.5 to 10 mm/min for static punching and from 3 to 5 m/s for dynamic punching. The tests were conducted using three types of punches: conical, flat and hemispherical. According to the test results, new data on the influence of strain rate on the features of deformation and failure of Armox 500T armor steel were obtained. The influence of the type of punches on the nature and mechanisms of failure of thin-sheet specimens under static and dynamic punching was investigated. It was found that an increase in loading speed leads to an increase in specimen failure force. Thus, the resistance to deformation increases by approximately 20% with an increase in the loading speed from 0.5 mm/min to 5 m/s.

The effect of engineering and process factors on the vibration stress of the cantilevered bladed disks of the 1st stage – low-pressure compressor and the shrouded blades of the 2nd stage – free power turbine for different types of aircraft gas turbine engines is investigated. The results of calculation-experimental studies on the frequency mistuning effect caused by the reduction of the cantilevered blade face length and its transition thinning to the shroud platform on the vibration stress of the intergroove ribs of the disk and blade rings, respectively, are presented. Three-dimensional finite element models of disks with the break of cyclic symmetry due to the vibration frequency mistuning of one blade, as the most dangerous case of the natural frequency scattering over the blade rings, were constructed. Calculation and experimental studies on the vibration stress of the intergroove ribs were carried out for two disk modifications with different rim thicknesses. The results of the complex calculation studies demonstrated that the resonant vibration amplitudes were localized in the vicinity of the frequency-mistuned blade. Thus, in the vicinity of the blades with the cross-section thinning of their face, the difference in the distribution of maximum equivalent stress zones is observed, which can lead to the localization of blade vibrations with their further failure. At the same time, the vibration stress of the intergroove ribs is established to depend on the vibration excitation harmonic, as well as the elastic bladed disk connection, which is determined by its stiffness. The results of computational experiments suggestive of reducing both the vibration stress and the localization level of resonant vibration amplitudes by analyzing and establishing those characteristics that effect the connection stiffness, which is of great practical importance for improving the vibration reliability of aircraft engine disks.

In this paper, the composite patch was prepared by wet spreading method, with which the damaged aluminum alloy specimen was repaired by bonding. The effects of different surface processing and curing modes on the fatigue properties of the specimens were studied. The results show that the surface coating coupling agent can significantly improve the fatigue properties of the repaired specimens; compared with unrepaired specimens, the fatigue life was increased by about 6.26 times and compared with uncoated specimens, the fatigue life was increased by 13.2–32.4%. Compared with unrepaired specimens, the fatigue life of repaired specimens can be increased by 6.20 times by heating and pressure curing. The fatigue life can be increased by 7.8–18.5% compared with normal temperature curing and repairing. Finally, the fatigue fracture of the specimen was observed and analyzed by SEM.

The creep test of T91/Super304H joint is carried out at 610°C and 180–150 MPa. OM and SEM were used to characterize the microscopic changes before and after the joint creep, and the finite element simulation was carried out according to the actual operating parameters, which are used to analyze failure reason of the T91/S304H joint. Finally, the creep life prediction is carried out. The results show that the creep deformation of T91/S304H welded joints with nickel-based filler metal is controlled by the part of martensite T91. Meanwhile, the T91 heat-affected zone is the weak location of the joint. When the stress decreases, the creep life gradually increases, and the creep rupture changes from ductile fracture to brittle fracture. The distribution of Nb-containing phases improves the creep strength of S304H steel. In the process of high-temperature creep, stress concentration occurs between the coarser M23C6, the precipitated Laves phase and the matrix interface, which leads to the formation of creep holes and then gradually connected into cracks. The fracture mechanism is a typical type IV cracking model. The revised \(\theta \) model can better predict the service life of T91/S304H welding.

The nickel content effects on the strength, plasticity, and low-cycle life of hardened and aged specimens of different modifications of austenitic iron-nickel steels and alloys in the initial state and after preliminary high-temperature hydrogenation in hydrogen at a pressure of 30 MPa and temperatures of 293, 773 and 973 K were studied. At 293 K, hydrogen embrittlement of hardened materials weakens with increasing nickel concentration from 10 to 23 wt.%; it is insignificant in the concentration range of 23–45 wt.% and significantly increases with higher nickel content. After aging, materials with a nickel content of 23 and 36 wt.% are insensitive to the action of the hydrogen environment; at higher hydrogen concentrations, embrittlement intensifies. The structural state of aged materials significantly affects the degree of hydrogen embrittlement of their various modifications during short-term tensile tests and slightly less during low-cycle fatigue tests. In the range of Ni concentrations of 23–73 wt.%, the effect of hydrogen on the relative transverse narrowing remains almost stable. The relative elongation of more hydrogen-resistant modifications of materials and low-cycle life increases with increasing nickel content. At 773 K, the effect of nickel content on the relative transverse narrowing in gaseous hydrogen at a pressure of 30 MPa is slightly smaller but qualitatively the same as at 293 K. At 973 K, more heat-resistant high-nickel alloys embrittle in a hydrogen environment much more strongly than hard dispersion steels. Thermomechanical treatment, according to the quenching scheme, tension at room temperature, and aging for 16 h at 973 K significantly increases the plasticity of materials in the presence of hydrogen at the same strength.

The alternate load path method for progressive collapse analysis ignores the cause and mechanism of member failure and its influence on the dynamic effect of the remaining structures. It must assume the location of member failure, which is unsuitable for grid structures with many members. In this paper, by using the double broken line follow-up strengthening model and the proposed VUMAT material constitutive model, taking the member instability and material failure as the member failure criteria and considering the geometric nonlinearity and material nonlinearity, the instantaneous member removal method for deleting the failure member in real time was proposed. On this basis, nonlinear dynamic analysis for a three-layer space truss was used to compare the effects of different member failure criteria on the structural responses, such as the member failure sequence and the occurrence time of the continuous structural collapse. The results show that when considering the instability of members, the initial member failure and the final progressive collapse occur earlier than when using the material failure criterion, which is more similar to the actual situation. Furthermore, the proposed VUMAT material constitutive model can apply to study the progressive collapse behavior of space truss structures.

The literature survey reveals the importance of determining the durability of materials before fatigue crack initiation. For this purpose, various criteria are used, including the most popular ones, featuring the microstructural characteristics of metal materials. However, incorporating these characteristics in the defining dependencies leads to complications associated with using specific values that are difficult to determine or find in the reference literature. In this regard, it is proposed to use the French line (FL) and the calculation-experimental method for its construction, considering the polycrystal's characteristic microstructural unit. The author has previously proposed such a method, substantiated by the experimental literature data on the FL accelerated construction. When applying this method to the new data on the experimental determination of the FL performed by the conventional, deviations in the calculated and experimental durabilities were obtained. The regularities of these deviations were established, their cause was identified, and a method for their elimination was proposed in this study. For this purpose, the concept of a variable endurance limit in the cyclic loading process was substantiated and accepted. The obtained dependencies were subdivided into two stages of a smooth specimen's fatigue damage: (i) from the beginning of loading to FL, and (ii) from FL to complete failure.

Calculations of the reliability of mine workings’ support usually imply multifactorial problems that can be solved using the risk theory in combination with the expert method of pairwise comparisons. The paper presents a methodology for such calculations on the example of the protection of sectional workings in coal mines. The necessity of improving the methodology for calculating the displacement of the mine workings contour in the area of influence of the cleaning operations by taking into account the coefficient of influence of the mine support equipment (MPE) on its stability is substantiated. This work aims to increase the reliability of mine workings’ support by risk-oriented substantiation of the choice of the type of protection means for sectional workings of coal mines during the development of an adjacent excavation column in various geological conditions. Technological schemes for the construction of modern types of MPE are proposed. Combining the risk theory with the matrix method of pairwise comparisons made it possible to calculate the risk Ri of deformation of the working faces and to obtain a qualitative assessment of the rating Ti of different types of MPE depending on the categories of roof collapse An and the strength of the floor rocks f. The criteria for comparing different types of MPE is their compliance with the utility function: at rational costs for the construction of MPE, the risks of roof and face displacements should be minimal. The proportion of negative consequences from failure to meet the initial requirements is as follows: the cost of MPE construction is 0.13, the risk of displacement of the working face roof is 0.53, and the risk of floor displacement is 0.33. A new formula for calculating the coefficient Ko of the influence of the type of underground protection on the displacement of the working faces is proposed, which takes into account the risk of deformation of the working face, the power and the inclination angle of the coal seam to the horizon, and the design parameters of the underground protection – its width and location relative to the working face.