Tyutin, Marat Ravilevich

Botvina L.R., Tyutin M.R., Alexandrov A.P.

The goal of the study is to elucidate the reasons for early fracture of the gear wheel teeth of a Cameron TA9000 turbocharger (1820 kW) after an operational load up to 1.3 × 109 cycles. The chemical composition and the microstructure of the tooth metal were studied using the methods of metallography, microhardness and optical microscopy. The microrelief of fracture surfaces of operational fractures was studied using electron scanning microscopy. Analysis of the chemical composition proved the steel grade of the tooth metal (DIN 31CrMoV9) declared by the manufacturer. Visual analysis of the fragments under study revealed numerous cracks present on the tooth contact surfaces. The origins of fatigue fracture detected on the fracture surfaces are typical of high cycle and gigacycle fatigue fracture. In the latter case, the detected fracture looks like a “fisheye” exhibiting an area of structural heterogeneity with inclusions and pores in the center. The fracture probably developed from the first tooth fragment to the fifth one, being accompanied by an increase in the number of origins of fatigue fracture known to be attributed to an increase in the stress amplitude. Metallographic study showed the presence of a subsurface hardened layer with a thickness of 120–200 μm with a defect-containing structure associated with grain-boundary precipitates (presumably, carbides (Fe, Cr)3C), which could have resulted from violation of the modes of heat treatment of the gear wheel. Formation of brittle intergranular cracks on the contact surface and their subsequent development in the entire depth of the subsurface hardened layer appeared to be the reason for a decrease in the strength and bearing capacity of the gear teeth. The interaction of the resulting cracks with longitudinal microcracks that originated from defects due to poor-quality mechanical processing of the gear led to the formation of centers of fatigue cracks, the development of which caused the final destruction of several teeth.

Botvina L.R., Beletsky E.N., Tyutin M.R., Demina Y.A., Sinev I.O., Bolotnikov A.I.

Notched 30CrMnSiA steel specimens were exposed to rupture load (mode I) at an angle of 90° between their fracture surface and load direction and to shear load (mode II) at an angle of 45° and 15°. For shear loading, Richard’s grips were used allowing one to vary the load from pure tension to pure shear by varying the notch orientation angle to the tensile load direction. Assessed under loading were the parameters of acoustic emission (AE) and strain fields (by the digital image correlation (DIC) method), and after failure, the damage parameters and microhardness on the polished lateral surface of the specimens, and the macro- and microreliefs of fracture surfaces. It is shown that increasing the shear component under tension changes the mechanical and the acoustic parameters of the specimens (total number of AE signals, their activity, bAE-value), and the critical temperature of brittleness, changing the fracture surface morphology from ductile to brittle at a load orientation of 45°. Simultaneously, a nonlinear dependence of the damage parameters (relative area of microcracks S*, their average length lav, orientation to the loading axis) on the load angle is observed, showing a correlation with principal strains estimated by the DIC method.

Botvina L.R., Tyutin M.R., Sinev I.O., Bolotnikov A.I., Levin V.P., Beletsky E.N., Perminova Y.S., Rybalchenko O.V., Dobatkin S.V.

The kinetics of microcracks accumulation and fracture at various stages of tension of grade 20 steel samples with coarse-grained and ultrafine-grained (UFG) structure obtained by equal-channel angular pressing (ECAP) has been studied. To research the effect of mechanical degradation, a part of the samples were subjected to preliminary cycling to a relative lifetime of 50%, followed by tensile tests, during which the parameters of acoustic emission and deformation fields obtained by digital image correlation were evaluated, and the intensity of the residual magnetic field was measured. The length and density of surface microcracks were measured by optical microscopy using computer image analysis. It is established that pre-cycling causes hardening of the material and a decrease in its plasticity. The fracture stages were revealed, and the origins of fatigue cracks were found on the internal delaminations of samples with a UFG structure after preliminary cyclic loading. It is shown that the formation of the UFG structure after the ECAP of samples made of grade 20 steel leads to hardening and reduction of the fracture work, the area of the plastic zone, maximum major deformations and damage, as well as to an increase in the number of AE signals and the intensity of the residual magnetic field.

Tyutin M.R., Botvina L.R., Shuvalov A.N., Petersen T.B., Levin V.P., Sineev A.A., Solov’ev V.G.

Abstract—The influence of reinforcement with basalt fibers in an amount of 0.6 vol % on the size effect in concrete made of Portland cement TsEM II/A-K(Sh-I) 42.5N (GOST 31108–2016) is investigated. For this purpose, geometrically similar specimens of length L = 1075, 465, and 215 mm and width D = 40, 93, and 215 mm, respectively, having a central notch of length a0 are subjected to three-point bending tests; the conditions L/D = 5 and a0/D ≈ 0.3 are met for all specimens. The mechanical properties, the acoustic emission parameters, the characteristics of a local deformed state estimated by the digital image correlation method, and the fracture zone size at the notch tip determined by ultrasonic flaw detection are investigated. The stages of fracture are analyzed using the changes in the acoustic emission parameters and the principal strains at the notch tip. The nominal strength decreases with increasing specimen size. In addition, the specimen size is found to affect the acoustic emission parameters, the principal strains, and the fracture zone size. The introduction of basalt fibers into the composition of concrete is shown to decrease its nominal strength, to increase the fracture energy, and to weaken the size effect.

Tyutin M.R., Botvina L.R., Shuvalov A.N., Petersen T.B., Levin V.P., Sineev A.A., Soloviev V.G.

Botvina L.R., Tyutin M.R., Alexandrov A.R.

   The goal of the study is to elucidate the reasons for early fracture of the gear wheel teeth of a Cameron TA9000 turbocharger (1820 kW) after an operational load up to 1. 3 x 109 cycles.   The chemical composi­tion and the microstracture of the tooth metal were studied using the methods of metallography, microhardness and optical microscopy. The microrelief of fracture surfaces of operational fractures was studied using electron scanning microscopy. Analysis of chemical composition proved the steel grade of the tooth metal (DIN 31CrMoV9) declared by the manufacturer. Visual analysis of the fragments under study re­vealed numerous cracks present on the tooth contact surfaces. The fatigue fracture origins detected on the fracture surfaces are typical of high cycle and gigacycle fatigue fracture. In the latter case, the detected fracture looks like a "fish eye" exhibiting an area of?? structural heterogeneity with inclusions and pores in the center. The fracture probably developed from the first tooth fragment to the fifth one being accom­ panied by an increase in the number of fatigue fracture origins known to be attributed to an increase in the stress amplitude. Metallographic study showed the presence of a subsurface hardened layer with a thickness of 120 - 200 pm with a defect-containing structure associated with grain-boundary precipitates (presumably, carbides (Fe, Cr)3C), which can result from violation of the modes of heat treatment of the gear wheel. Formation of brittle intergranular cracks on the contact surface and their subsequent develop­ment in the entire depth of the subsurface hardened layer appeared to be the reason for a decrease in the strength and bearing capacity of the gear teeth.

Botvina L.R., Bolotnikov A.I., Sinev I.O., Tyutin M.R., Beletskii E.N.

Abstract—The mechanical and physical properties of a D16ch alloy, which is used as the fuselage skin of the IL-62M aircraft with a service life of more than 28 years, has been studied. The influence of the service life and preliminary cyclic loading on the acoustic emission (AE) characteristics, the strain characteristics during tension obtained by the digital image correlation (DIC) method, and the real damage determined using optical microscopy are estimated. The mechanical properties of the material during operation are found to remain almost unchanged as compared to the initial state. However, the AE study demonstrates a significant increase in the AE activity $${{\dot {N}}_{{{\text{AE}}}}}$$ and the accumulated number of AE signals ΣNAE, and the DIC investigation reveals an increase in the plastic zone area in specimens after operation. Preliminary cyclic loading of specimens both in the initial state and after operation leads to an increase in the relative damaged surface area. The results obtained indicate that the research methods used in this work give important information to estimate the degradation of the material and the effect of preliminary cyclic loading on it.

Tyutin M.R., Botvina L.R., Levin V.P., Beletskii E.N., Petersen T.B., Sinev I.O.

The kinetics of damage accumulation in a D16ch sheet aluminum alloy (Al–Cu–Mg system) at various stages of static loading is investigated using a combined technique, which includes the detection of acoustic emission (AE) signals, structural studies, and the determination of electrical resistance and an eddy-current parameter. The dependences of these characteristics on the relative strain demonstrate the presence of four stages of specimen fracture. Correlation exponential dependences of the electrical resistance and the eddy-current parameter on damage are obtained, and they can be used to diagnose the state of the material.

Demina Y.A., Tyutin M.R., Marchenkov A.Y., Levin V.P., Botvina L.R.

The mechanical and physical properties of X70 pipeline steels produced in France and Japan are comprehensively studied using tensile and impact bending tests, analysis of the fracture reliefs of specimens, and the estimation of acoustic emission parameters, the attenuation coefficient of longitudinal ultrasonic waves, and the residual magnetic field intensity. A correlation between the mechanical and physical characteristics during tensile tests is revealed. After long-term operation, the yield strength and the ultimate tensile strength are shown to decrease and the plasticity and impact characteristics are shown to increase in comparison with the initial values from pipelines sertificates for both studied steels. The predominant mechanism of these changes is associated with the presence of a large number of delaminations, which cause fracture energy dissipation and hide the true picture of changes in the estimated strength characteristics.

Tyutin M.R., Botvina L.R., Ioffe A.V.

Mechanical and physical properties of bainitic steel 15Cr2MnMoV used as a material of oil pump rods were studied in three states: as received, after operation in hydrogen sulfide-containing environment, and after hydrogen charging in H2S-containing media for 1 week. In addition, the austenitic corrosion-resistant steel 12Cr18Ni10Ti has been studied in two states: as received and after operation for 6 years. No degradation of the standard mechanical properties of the investigated steels after operation was revealed, although a decrease in the fatigue properties of the austenitic steel 12Cr18Ni10Ti was observed. Mechanical properties were most affected by hydrogen charging of bainitic steel, after which a decrease in ductility, fracture energy, and fatigue life is observed. Four stages of fracture development of the investigated steels under tension are distinguished. It is shown that acoustic emission is the most sensitive method for assessing the degree of structural degradation after operation or hydrogen charging. It is established that the magnetic methods of nondestructive testing show the greatest sensitivity at the elastic stage and at the stage of deformation localization before fracture.

Tyutin M.R., Botvina L.R., Levin V.P., Beletskii E.N., Petersen T.B., Sinev I.O.

Botvina L.R., Tyutin M.R., Perminova Y.S., Utkin A.V.

High-strength martensitic–austenitic 5KhN3MA steel is subjected to static and impact bending tests. The crack initiation and propagation energies, the dynamic fracture toughness, the critical ductile–brittle transition temperature, and the fracture microrelief parameters are estimated. The influence of a preliminary shock-wave action on the strength and the dynamic fracture toughness of the steel is studied. The high-rate shock-wave action is shown to increase the fracture toughness of the steel and to shift the brittleness threshold toward lower temperatures. The estimation of acoustic emission characteristics during static bending tests shows that a preliminary dynamic action significantly decreases the total number and the accumulation rate of acoustic emission signals considerably and shifts the final stage of fracture toward large deformation.

Botvina L.R., Tyutin M.R., Levin V.P., Ioffe A.V., Perminova Y.S., Prosvirnin D.V.

The mechanical properties of 15Kh2GMF steel are estimated, and the fracture stages and mechanisms in this steel are studied during static, cyclic, and impact loading in the temperature range from –100°C to 20°C. A direct method is used to measure the real damage of the steel and to determine its physical properties, namely, the velocity and the attenuation coefficient of longitudinal ultrasonic waves, the coercive force, the eddy current parameter, and the self-magnetic field, at various stages of static and cyclic loading. The influence of preliminary cyclic loading on the residual strength and the acoustic emission parameters measured during tensile tests of cyclically deformed specimens and the fracture mechanisms are studied. The stages of damage accumulation characterized by changes in the damage parameters and the physical properties of the steel are distinguished, and informative criteria for the diagnostics of a construction in the initial and late stages of operation are proposed.

Botvina L.R., Kushnarenko V.M., Tyutin M.R., Levin V.P., Morozov A.E., Bolotnikov A.I.

The paper investigates the mechanical and physical properties of low-carbon pipe steel (analog of steel 20 corresponding to TU-28-FR-73) after 39 years of service life in a crude gas pipeline at the Orenburg oil and gas condensate field. It is shown that the standard mechanical properties of the gas pipeline steel after long-term operation correspond to the TU-28-FR-73 standard. The effect of preliminary cyclic loading on the residual tensile strength of steel, the acoustic emission characteristics, and the residual magnetic field intensity estimated by the metal magnetic memory method is studied. After preliminary cycling, the steel was hardened and the acoustic regime changed due to damage accumulation. Four stages of damage evolution in the tensile steel are identified both before and after preliminary cyclic loading, and informative diagnostic criteria for the stages are proposed. Relationships are derived to relate the relative number of preloading cycles with the cumulative acoustic count, acoustic activity, slope of cumulative count-strain curves, acoustic gap duration, and residual magnetic field intensity. The listed characteristics are shown to be promising as diagnostic criteria for the state of the material.

Botvina L.R., Tyutin M.R., Bolotnikov A.I., Petersen T.B.

The stages of changing the acoustic emission characteristics of 15Kh2GMF steel used for manufacturing oil-pump sucker rods is studied during tension before and after preliminary cyclic loading to various values of relative life. The revealed stages are shown to agree with the data of estimating the development of real damage by optical and digital microscopy. The acoustic parameters that can be diagnostic criteria characterizing a change in the steel state after preliminary cyclic loading have been determined, and their dependence on the relative number of cycles has been found. The changes in the form, spectrum, and median frequency of acoustic signals in steel samples are studied in the initial state and after preliminary cycling.

Garkushin G.V., Savinykh A.S., Razorenov S.V., Brodova I.G., Rasposienko D.Y., Devyaterikov D.I., Panfilov P.E.

Zinc single crystals have been shocked by planar impact along the [101¯0] axis as well as in the off-axis direction. The evolution of compression waves has been analyzed from the free surface velocity profiles of zinc single crystal samples. A slip on the primary system is activated by impact loading in directions making angles of θ = 17°–64° with respect to the [101¯0] axis. The phenomenon of the formation of two plastic compression waves propagating at different velocities is observed in samples oriented at angles of 53° and 64°. The spall fracture of single crystal zinc samples oriented in different directions has been measured. It is shown that the highest value of spall strength is recorded along the highly symmetric axis of the crystal. The experimental results presented are consistent with the data published in the scientific literature on beryllium and magnesium and confirm the important role of crystalline anisotropy in the process of inelastic deformation of single crystals.

Kositski R., Miller T.

Plate impact experiments are widely used to study materials under high strain rates and pressures. However, discrepancies often arise when attempting to simulate the free surface velocity at the back of the target, even with modern and advanced material models. This work focuses on two key experimental features: the smooth rise in the elastic precursor wave and the smooth decay of the elastic release wave. We show, through mesoscopic simulations, that these features can be accurately reproduced when material strength heterogeneity is considered. To validate our model, we simulate polycrystalline metals—tantalum and copper—as well as a heterogeneous metallic composite, tungsten heavy alloy. Our results demonstrate that by incorporating mesoscopic strength variations, either due to grain orientation or a composite phase, the smoothed velocity profiles observed experimentally can be simulated while maintaining consistency with uniaxial stress compression tests.

Zhang Y., Ji Y., Zhao Y., Deng Q., Wang C.

A comprehensive understanding of shale's bedding anisotropy is crucial for shale-related engineering activities, such as hydraulic fracturing, drilling and underground excavation. In this study, seven Brazilian tests were conducted on shale samples at different bedding orientations with respect to the loading direction (0°, 45° and 90°) and the disc end face (0°, 45° and 90°). An acoustic emission (AE) system was employed to capture the evolution of damage and the temporal-spatial distribution of microcracks under splitting-tensile stress. The results show that the Brazilian tensile strength decreases with increasing bedding inclination with respect to the disc end face, while it increases with the angle between bedding and loading directions. Increasing the bedding inclination with respect to the end face facilitates the reduction in b value and enhances the shale's resistance to microcrack growth during the loading process. Misalignment between the bedding orientation and the end face suppresses the growth of mixed tensile-shear microcracks, while reducing the bedding angle relative to the loading direction is beneficial for creating mixed tensile-shear and tensile cracks. The observed microscopic failure characteristics are attributed to the competing effects of bedding activation and breakage of shale matrix at different bedding inclinations. The temporal-spatial distribution of microcracks, characterized by ·AE statistics including the correlation dimension and spatial correlation length, illustrates that the fractal evolution of microcracks is independent of bedding anisotropy, whereas the spatial distribution shows a stronger correlation. The evolution features of correlation dimension and spatial correlation length could be potentially used as precursors for shale splitting failure. These findings may be useful for predicting rock mass instability and analyzing the causes of catastrophic rupture.

Gatões D., Rodrigues P.F., Cacho L.M., Alves B., Fernandes F.M., Vieira M.T.

Additive manufacturing (AM) technologies are revolutionising the production of complex and customised components. Despite these geometric innovations, the microstructure of these ‘new’ materials has posed a major obstacle to the widespread adoption of these technologies in novel applications. However, understanding the microstructural evolution during mechanical loading is necessary to elucidate the mechanisms and implications of using AM 3D objects in critical applications. This study uses in-situ synchrotron X-ray diffraction (XRD) during tensile testing to clarify the deformation mechanisms and microstructural transformations in additively manufactured 17 − 4 PH stainless steel (AISI 630). Controlled tensile loading was applied to the tensile specimens, enabling the simultaneous capture of XRD, thereby providing real-time insights into material response. The analysis highlighted the structural evolution and phase transformations occurring during deformation, providing a deeper understanding of the underlying mechanisms that influence the unique mechanical properties resulting from Laser Powder Bed Fusion (LPBF). The results demonstrate a clear correlation between microstructural attributes and mechanical performance, contributing to optimising the design vs. properties.

Shilo D., Faran E.

Zhou P., Xie H., Wang J., Zou B., Hu J., Li C.

Brown N.P., Ruggles T.J., Johnson C.R., Valdez N.R., Rodriguez M.A., Specht P.E.

We studied the orientation-dependent dynamic properties and plastic deformation mechanisms in single-crystal austenitic FeCr18Ni12.5 stainless steel shocked to peak stresses ranging 3.8-12.0 GPa. The 〈110〉 and 〈111〉 principal Hugoniots generally match that of polycrystalline 304L stainless steel, but the 〈100〉 Hugoniot exhibits lower shock velocities and comprises two distinct regions. The Hugoniot elastic limits (HELs) and spallation strengths range 0.5-1.2 GPa and 2.2-3.8 GPa, respectively, and exhibit trends previously observed in polycrystalline steels. We generally observed the largest HELs along 〈100〉 and the largest spallation strengths along 〈111〉. Microscopy revealed larger twin and martensite fractions in the 〈100〉 samples, correlations in twinning and martensite prevalence with dynamic response, and orientation-dependent differences in dislocation behavior near the spallation plane.

Lomov S.V., Morkovkin A.I.

A mechanical digital twin (a mechanical finite-element model) of an asphalt concrete sample has been developed in the framework of a project for recycling polymer composite materials with fibrous reinforcement (fiberglass) as an alternative for crushed stone in the asphalt concrete production. A methodology of using X-ray computed tomography (XCT) for analysis of the asphalt concrete microstructure and calculation of the mechanical properties is developed. The data processing chain for developing a digital twin of the asphalt concrete microstructure, based on X-ray micro-computed tomography (XCT) image includes the following steps: 1) image enhancement; 2) image segmentation; 3) analysis of the morphology of pores and solid particles; 4) transformation of the segmented image into a voxels-based finite element (FE) model. It is demonstrated that the XCT resolution of 40 μm is sufficient for a reliable identification of microstructural parameters, i.e., volume fractions of the components, distributions of voids (pores) in size, shape and spatial position, as well as distributions of the crushed brittle additives (fiberglass chips) in size. The FE model constitutes a digital twin of the material, and, after specifying the characteristics of the material components, can be used for simulation of the thermomechanical and functional properties of the material. The developed procedure is exemplified in the calculation of statistics of the compression and shear moduli of the asphalt concrete with addition of crushed fiberglass particles. The dependence of the calculated elastic properties on the size of the digital twin is studied. It is shown that a model size of 10 mm and more is sufficient for the microstructural representativity and calculation of the homogenization characteristics. The results can be used for analysis of the microstructure and structure-dependent thermomechanical properties of asphalt concrete. The developed finite element model can be used for modelling of the visco-elastic response of asphalt concrete and its behavior under cyclic loading.

Shiverskii A.V., Kukharskii A.V., Abaimov S.G.

An epoxy resin is an important modifier in the production of polymer asphalt concretes; adding epoxy resins to bitumen increases the crack resistance, shear resistance, and the long-term strength of the final product. However, polymer asphalt concrete production is chargeable compared to that of traditional asphalt concrete due to high fraction of epoxy introduced. Hyperbranched polymers (HBP) with epoxy end groups form a highly branched spatial network at curing, their application as an active modifier in bitumen composition leads to the formation of additional spatial reinforcement architectures in asphalt concrete, which allows to strengthen the effects achieved by epoxy resins, as well as to increase impact toughness, moisture resistance, fuel resistance, and temperature stability of asphalt concrete at low fraction of the modifier. We present an experimental study of the mechanical properties of asphalt concrete with a bitumen modified by a hyperbranched polymer. The bitumen was modified with relatively low fractions (3, 5, and 8 wt.%) of the hyperbranched epoxy resin. The mechanical properties of asphalt concrete were characterized with the modulus of elasticity, compressive strength, tensile strength at break, shear strength, residual compressive strength after low-cycle loading, coefficient of residual compressive strength, and the ultimate percent compression. The results demonstrated that asphalt concrete with modified bitumen has improved characteristics compared to the original asphalt concrete, even at low fractions of the modifier. The elastic modulus and compressive strength are closely bound and, during the formation of the architecture of links in bitumen, increase almost linearly with an increase of hyperbranched modifier fraction, achieving an improvement of 9.0 and 17.7%, respectively, for samples with 8 wt.% of epoxy modifier. At the same time, asphalt concrete becomes more ductile; the ultimate percent compression increases from 2.75 to 3.5% and does not depend significantly on the amount of hyperbranched polymer. The tensile strength at break decreases as the fraction of an epoxy modifier increases, which is consistent with the literature data. However, the ductility of asphalt concrete is significantly improved, reaching the ultimate percent deformation of 1.8% at 5 wt.% of the modifier. At the same fraction of the modifier, the highest shear strength of 0.48 MPa is achieved. With an increase in the mass fraction of the epoxy modifier, the compaction under low-cycle loading decreases; the residual strength coefficient, as the ratio of the residual compressive strength after low-cycle fatigue to the static compressive strength, tends to unity for asphalt concrete, also modified with 5 wt.% of hyperbranched polymer. Thus, the best result, as a compromise of all factors under study, is achieved when 5 wt.% of epoxy hyperbranched modifier is introduced into the bitumen.

Latypov F.T., Fomin E.V., Krasnikov V.S., Mayer A.E.

Lipski A., Witek M., Abdelghani M., Swacha P.

The aim of this work is an experimental evaluation of a specific heat capacity as a function of plastic strain for thermo-mechanically rolled pipe material, with application of an infrared thermographic camera. The tensile load tests of samples prepared of L485ME (X70M) steel grade were performed with the use of a strength machine. Based on other known material thermophysical properties, the determination of heat source parameters was conducted with the use of an infrared thermography and with an optimization task solution. A linear regression equation describing the specific heat capacity as a function of plastic percentage elongation for L485ME steel grade was determined. The experimental results of the present study showed a linear increase in the specific heat capacity in the range of the analyzed tensile deformation up to 16%. The presented methodology is suitable for assessment of the material specific heat capacity as a function of strain up to the occurrence of the sample narrowing in a direction perpendicular to the tensile force.

Euser V.K., Mangan A.S., Jones D.R., Martinez D.T., Steckley T.E., Agrawal A.K., Thoma D.J., Fensin S.J.

The dynamic spall properties of an additively manufactured (AM), CoCrFeMnNi high-entropy alloy (HEA) were investigated as a function of processing defects. Laser Powder Bed Fusion (LPBF) was used to additively manufacture HEA samples that were subsequently subjected to shock loading through plate impact experiments. Seven different combinations of laser power and scan speeds were explored, ranging from 180-280 W and 925-1350 mm/s, respectively. All samples were considered within the bounds of lack-of-fusion and keyholing defects based on initial experiments, but exhibited varying degrees of solidification cracking and microstructural changes. Grain size and grain aspect ratio were found to modestly decrease with faster scan speeds and lower laser powers, while cracking associated with the AM process increased with faster scan speeds and higher laser powers. Spall strength and spall damage did not systematically trend with microstructural characteristics such as grain size, but did exhibit a relationship with pre-existing crack density. Spall properties were found to generally degrade with increasing crack density. Evidence of defect compaction was not observed in soft recovered spall samples, thus pre-existing cracks were proposed to degrade spall properties by acting as stress concentrators and preferred damage nucleation sites during tensile impact loading. Here, the presence of manufacturing-related defects, such as cracks, dominated the dynamic response; however, in the absence of these defects, microstructural changes like grain size and texture would be expected to control dynamic behavior.

Solanki K., Williams C.L., Darling K.A.

A material’s ability to withstand high deformation rates without failure has a profound effect on many applications. Indeed, in modern industrial society, e.g., alternative energy sources (fusion reactors), automobile crashes, projectile impact, and deep-space exploration (meteoroid impact), structural metals often experience deformation rates of 103–104 s−1 or higher, which can lead to catastrophic failures due to loss in ductility. However, the effects of stress state combined with high strain-rate behavior on deformation mechanisms are still not fully explored. Therefore, this paper attempts to lay out a perspective of anomalous dynamic behavior observed in low-melting-temperature materials such as magnesium (Mg)-based alloys. In other words, the paper reviews research conducted on time-dependent dynamic behavior along with the multiaxial state of stress in Mg alloys.

Vinod, Krishna A., Vijayan N., Yadav S., Kiran, Kaphi, Saini S.K., Yadav R., Varshney U., Satapathy S., Gupta G.

The utilization of shock waves plays a pivotal role in the advancement of multiple scientific domains like aerospace, defense, geology, environment, medicine and many more. They serve as essential tools in scientific investigations, enabling the exploration of material behavior under extreme conditions, viz. elevated pressure and temperature. The present study is specifically dedicated to scrutinizing the repercussions of shock waves on an L-ascorbic acid single crystal, to which they were intentionally applied to assess their influence on structural, optical and third-order nonlinearity properties. Powder X-ray diffraction analysis unveiled a discernible overall enhancement in the crystalline quality of the grown crystal following exposure to shock waves. This observation was consistently corroborated by high-resolution X-ray diffraction data, particularly on the (200) crystallographic planes. Furthermore, the optical transmittance of the crystal exhibited a notable increase upon the application of shock waves, while the material's band gap remained unaffected. In parallel, the third-order nonlinearity of the crystal was found to undergo a significant augmentation as a consequence of the shock treatment, as confirmed through Z-scan measurements. These empirical findings unequivocally demonstrate the substantial enhancement in the structural, optical and nonlinear properties of the grown crystal when subjected to shock waves, rendering it well suited for nonlinear optical applications.

Wang X., Xu J., Yue Q., Liu X.

The application of advanced acoustic emission signal analysis techniques can facilitate the identification of fracture damage modes in ductile materials and enable the provision of fracture precursor warnings. Given the vast array of acoustic emission signal characteristic parameters, there must be a systematic and comprehensive basis for selection and a deep comparison among different fracture warning indicators. This study uses G20Mn5QT cast steel material fracture acoustic emission monitoring tests under different in-plane constraints as an example. We adopted principal component analysis and k-means++ to select acoustic emission feature parameters and cluster damage modes. Additionally, we conducted a comparative analysis of several fracture precursor warning indicators and influencing factors, including fractal dimensions, b/Ib values, and natural time analysis. Our findings show that shear and tensile fracture damage modes are present in type-I fracture tests when applying the k-means++ cluster to the rise angle-average frequency-energy parameter, but tensile fracture modes dominate. Fractal dimensions, b-values, and Ib-values show a strong trend correlation with the fracture damage evolution process. Natural time analysis can quantitatively provide the moment of fracture precursor warnings, but the sliding window length inversely affects the absolute value sizes. Through acoustic emission signal analysis, our research provides a reference for identifying and examining the evolution of fracture damage in ductile materials and engineering components.

Li Y., Zhang J., He Y., Huang G., Li J., Niu Z., Gao B.

In order to further broaden the application scope of basalt fiber reinforced concrete (BFRC), prolong service life in complex environment, master development status and sort out development needs, the durability of BFRC in complex environment was systematically summarized. First of all, the reason and damage mechanism of concrete deterioration in a variety of harsh environment are analyzed and grasped. Secondly, the strengthening mechanism of basalt fiber (BF) structure in permeability, carbonization, sulfate erosion, alkali environment, freeze-thaw cycle and high temperature is reviewed in detail, and the strengthening effect and performance of BFRC are discussed from the perspective of macroscopic properties and microscopic pore structure. The addition of BF reduces the generation and development of early microcracks in concrete structures, promotes the densification of structures on a microscopic scale. What's more, the permeability, carbonation resistance, acid and alkali corrosion resistance, frost resistance and high temperature resistance of concrete structures can be significantly improved. Finally, the problems in the current research are summarized and research ideas to cope with the environmental complexity are proposed to provide a research basis for BFRC to maintain excellent performance in the actual complex application scenarios. This paper focuses on the strengthening effect of basalt fiber on cement-based materials, and mainly introduces its strengthening effect and action mechanism from several aspects in the figure.

Yan H., Wei P., Zhou P., Chen L., Liu H., Zhu C.

Tooth bending fatigue remains as a fundamental bottleneck restricting the safety and reliability of modern high-performance gear. In this study, a serial of bending fatigue tests on case carburized and shot peening treated gears is conducted. The fatigue crack propagation behaviors during bending fatigue test were analyzed. The alternations of macroscopic mechanical properties and microstructure features of gear samples subjected to bending fatigue are experimentally examined and analyzed in detail. It is found that the measured tooth root crack trajectories basically conform to the dangerous section of the tooth root determined by the 30° tangent method with a slight variation of about 1°. The phenomena of residual stress relaxation in gear bending fatigue is observed with the maximum residual compressive stress decreasing from −698 MPa of intact state to −572 MPa of failure state. Furthermore, the content of retained austenite of tooth root surface decreases by about 3.8 % after the gear bending fatigue failure, and the grain size of the tooth root core region illustrates a certain tendency of coarsening.

Böhme S.A., Szanti G., Keski-Rahkonen J., Komssi T., Santaella J.G., Vinogradov A.

• Application of developed material, stress and multiaxial fatigue model to a set of bevel gear tests. • Accurate failure prediction of the majority of wheel-initiated tooth flank fractures. • Methodology capable of differentiating and predicting surface and subsurface fatigue in gears. • Fractographic analysis of subsurface failures, revealing elongated MgO-Al 2 O 3 cluster in initiation site. • Proposal of a reiterated lifetime factor based on the Maximum Likelihood Method. A material model for carburized CrNiMo steel and an advanced shear stress intensity, multiaxial fatigue criterion against surface and subsurface fatigue in bevel gears have been developed and presented in earlier publications. This study assesses the accuracy of the proposed methodology by comparing it to load-controlled bevel gear tests at varying hardening layer thicknesses. The dominant failure mode was wheel-initiated tooth flank fracture. Fractographic analysis by means of scanning electron microscopy revealed a severely elongated MgO-Al 2 O 3 cluster in the only pinion-initiated tooth flank fracture. By correlating the calculated material utilizations and the number of cycles to failure, a reiterated lifetime factor is presented. The refined methodology is shown to be capable to differentiate between and accurately predict pitting and subsurface fatigue under well-defined test conditions.

Qin S., Zhang C., Zhang B., Ma H., Zhao M.

Carburizing heat treatment is widely used in the fabrication of gears to improve their fatigue performance. The effects of carburizing process on the material properties surface hardness, residual stresses, retained austenite of case-hardened 18CrNiMo7-6 and the consequential fatigue strength have not been studied in detail. In this research, the high-cycle fatigue performance of uncarburized and carburized 18CrNiMo7-6 gear steel were studied. In addition, the evolution processes of hardness, microstructure and residual stress of carburized specimens during the fatigue test were observed quasi-in situ. The initiation of fatigue cracks was also analyzed by SEM and the transformation of retained austenite during the fatigue test was observed by TEM. The results showed that the fatigue strength of carburized specimens has an increase-decrease trend with the increase of effective case depth. Besides, the fatigue failure mode of steel changes from surface failure to internal failure after being carburized, during which retained austenite plays an important part. In addition, if a large amount of retained austenite exists in the specimen with internal failure, the high-density twin martensite region formed by the retained austenite transformation can act as the crack initiation site, which is harmful to fatigue performance.

Cai S., Sun J., He Q., Shi T., Wang D., Si J., Yang J., Li F., Xie K., Li M.

• The surface hardness of carburizing quenching hardening layer is low. • Non-martensite microstructure is formed after heat treatment. • The presence of inclusions reduces the mechanical and fatigue properties of the steel. • The gear shaft is ductile fracture. Gear shaft of 16MnCr5 steel is an important moving part to transfer torque in truck steering, which fatigue design life is 50,000 times. However, the lifetime of the test results is only about half in two design life. The microstructure, slag inclusion, phase composition and microhardness profiles of failure gear shaft were characterized by the optical microscope, scanning electron microscope and microhardness tester, respectively. The results show that cracks appeared at the fillet of the top, pitch circle and root of the gear. The size and distribution of slag inclusions in16MnCr5 steel also have a certain effect on the initiation of surface cracks of gears. The surface hardness of carburizing quenching hardening layer is low. After the heat treatment, a non-martensitic microstructure is formed, and machining hardening occurs on the right tooth surface, which seriously affects the contact fatigue degree of the gear.

Botvina L.R., Tyutin M.R., Levin V.P., Ioffe A.V., Perminova Y.S., Prosvirnin D.V.

The mechanical properties of 15Kh2GMF steel are estimated, and the fracture stages and mechanisms in this steel are studied during static, cyclic, and impact loading in the temperature range from –100°C to 20°C. A direct method is used to measure the real damage of the steel and to determine its physical properties, namely, the velocity and the attenuation coefficient of longitudinal ultrasonic waves, the coercive force, the eddy current parameter, and the self-magnetic field, at various stages of static and cyclic loading. The influence of preliminary cyclic loading on the residual strength and the acoustic emission parameters measured during tensile tests of cyclically deformed specimens and the fracture mechanisms are studied. The stages of damage accumulation characterized by changes in the damage parameters and the physical properties of the steel are distinguished, and informative criteria for the diagnostics of a construction in the initial and late stages of operation are proposed.

Böhme S.A., Vinogradov A., Papuga J., Berto F.

This publication focuses on the numerical stress prediction in case-carburized bevel gears and on their fatigue assessment. Four gear sets are analyzed for the common fatigue failure modes of pitting, tooth root breakage, and subsurface fatigue. The proposed algorithm, enabling the prediction of the dominant failure type and region, relies on the previously published material model for carburized CrNiMo steels. It utilizes a 2D plane strain simplification as only the mean cross-section is analyzed and evaluates the shear mean and amplitude stresses through the maximum rectangular hull method. A novel multiaxial fatigue criterion is presented and validated.

Vityaz P.A., Moiseenko V.I., Sidorenko A.G., Sotnikov M.V., Shkatulo N.D., Haritonchik D.I.

The experience of using known and new steels to improve the manufacturability and strength of the main parts of machines, hardened by nitriding, is generalized. New approaches to manufacture of gear wheels hardened by nitriding, both when using aluminum-containing steels and a new material, steel 40ХМФА, are considered. To improve the efficiency and man ufacturability of parts production from aluminum-containing steel 38Х2МЮА, widely used in mechanical engineering, a fundamentally new technology of preliminary heat treatment of workpieces of parts – “incomplete hardening” has been developed, which provides both an increase in the machinability and accuracy of large-sized gear wheels, and an increase in strength due to the elimination of the brittleness of nitrided layer. The high hardness of the nitrided surface of the parts – up to 900 HV – also ensures high wear resistance of the parts. Gear wheels made of new aluminum-containing steel 20ХН4МФЮА solidified at the nitriding stage, have strength characteristics equal to cemented parts, which allows not only increasing the bearing capacity of a number of products, but significant simplification of the technology of manufacturing precise parts that are complex in shape, replacing carburizing with nitriding, thereby eliminating the necessary after-carburizing finishing operation – grinding. Steel 40ХМФА, which does not contain aluminum, has increased heat resistance, hardenability and machinability of parts, as well as the characteristics of their hardened layer. The nitrided layer of gears 0.5–0.7 mm thick does not contain brittle components, which, with a core hardness of 300–320 HB, excludes its “flaking” and subsequent destruction of parts. The use of 40ХМФА steel makes it possible to solve the problems of reliability and service life of large-sized nitrided gears, but it is also promising for the entire range of gears with internal gearing, as well as parts of movable spline gearings. These characteristics also in some cases allow replacing the carburizing of gears (modulus less than 4 mm) by nitriding when using 40ХМФА steel.

Pluvinage G.

Hydrogen economy considers hydrogen as a substantial fraction of a nation's energy and services. This could happen in the future if hydrogen can be produced from domestic energy sources economically and in an environmental-friendly manner. Hydrogen can also be used as fuel in stationary fuel cell systems for buildings, emergency power or distributed generation. Hydrogen transport is generally made by pipelines. This solution is preferable than transport on road by truck for security reasons. The addition of hydrogen in natural gas could have an impact on the materials degradation over time especially those used for the storage, transport and distribution of natural gas. The compatibility of these materials with natural gas including of hydrogen is dependent on the proportion of hydrogen added into the gas and is assessed with regard to several criteria: - permeation of hydrogen through metallic materials; - loss of integrity of these materials and adaptation of follow-up actions in service, surveillance and maintenance of equipment. This paper is devoted to the effect of hydrogen embrittlement (HE) caused by adding hydrogen into natural gas network on its design, maintenance, supervision and maximum allowable service pressure (MAOP) for smooth and damaged pipes. •Effect of hydrogen embrittlement (HE) on pipe steels. •Influence on maximum allowable service pressure. •Influence on defect assessment. •Influence on surveillance and maintenance.

Botvina L.R., Kushnarenko V.M., Tyutin M.R., Levin V.P., Morozov A.E., Bolotnikov A.I.

The paper investigates the mechanical and physical properties of low-carbon pipe steel (analog of steel 20 corresponding to TU-28-FR-73) after 39 years of service life in a crude gas pipeline at the Orenburg oil and gas condensate field. It is shown that the standard mechanical properties of the gas pipeline steel after long-term operation correspond to the TU-28-FR-73 standard. The effect of preliminary cyclic loading on the residual tensile strength of steel, the acoustic emission characteristics, and the residual magnetic field intensity estimated by the metal magnetic memory method is studied. After preliminary cycling, the steel was hardened and the acoustic regime changed due to damage accumulation. Four stages of damage evolution in the tensile steel are identified both before and after preliminary cyclic loading, and informative diagnostic criteria for the stages are proposed. Relationships are derived to relate the relative number of preloading cycles with the cumulative acoustic count, acoustic activity, slope of cumulative count-strain curves, acoustic gap duration, and residual magnetic field intensity. The listed characteristics are shown to be promising as diagnostic criteria for the state of the material.

Zhao Y., Gu Y., Guo Y.

The conventional engineering stress-strain curve could not accurately describe the true stress-strain and local deformability of the necking part of tensile specimens, as it calculates the strain by using the whole gauge length, assuming the tensile specimen was deformed uniformly. In this study, we employed 3D optical measuring digital image correlation (DIC) to systematically measure the full strain field and local strain during the whole tensile process, and calculate the real-time strain and actual flow stress in the necking region of ultrafine-grained (UFG) Ti. The post-necking elongation and strain hardening exponent of the UFG Ti necking part were then measured as 36% and 0.101, slightly smaller than those of the coarse grained Ti (52% and 0.167), suggesting the high plastic deformability in the necking part of the UFG Ti. Finite elemental modeling (FEM) indicates that when necking occurs, strain is concentrated in the necking region. The stress state of the necking part was transformed from uniaxial in the uniform elongation stage to a triaxial stress state. A scanning electron microscopic (SEM) study revealed the shear and ductile fracture, as well as numerous micro shear bands in the UFG Ti, which are controlled by cooperative grain boundary sliding. Our work revealed the large plastic deformability of UFG metals in the necking region under a complex stress state.

Botvina L.R., Tyutin M.R., Bolotnikov A.I., Petersen T.B.

The stages of changing the acoustic emission characteristics of 15Kh2GMF steel used for manufacturing oil-pump sucker rods is studied during tension before and after preliminary cyclic loading to various values of relative life. The revealed stages are shown to agree with the data of estimating the development of real damage by optical and digital microscopy. The acoustic parameters that can be diagnostic criteria characterizing a change in the steel state after preliminary cyclic loading have been determined, and their dependence on the relative number of cycles has been found. The changes in the form, spectrum, and median frequency of acoustic signals in steel samples are studied in the initial state and after preliminary cycling.

Sinev I.O., Beletsky E.N., Tyutin M.R., Botvina L.R., Rybalchenko O.V., Dobatkin S.V.

Beletsky E.N., Levin V.P., Sinev I.O., Botvina L.R., Tyutin M.R., Kulemin A.V.

This paper studies damage accumulation at different stages of static and cyclic loading of the D16ChATV aluminum alloy. The damage is assessed using optical microscopy. The dependences of the eddy current parameter and electrical resistance on relative deformation (under static loading) and on relative durability (under cyclic loading) are obtained.

Botvina L.R., Tyutin M.R., Sinev I.O., Bolotnikov A.I.

Preliminary cyclic loading of structural low-carbon and 15Cr2MnMoV steels specimens to a relative lifetime of 0.3, 0.5 and 0.7 were conducted. After preloading, tensile tests with the acoustic emission (AE) registration were performed and the effects of preliminary cyclic loading on the intensity (dNAE/dt), the cumulated number (ΣNAE) and energy (ΣEAE)of acoustic emission signals, and the bAE-value (the slope coefficient of cumulative distributions of the AE signals amplitudes) were investigated. According to the test results, the dependencies of the AE parameters on the relative deformation were plotted. An analysis of these dependencies made it possible to distinguish the stages of changes in AE characteristics that correlate with the stages of changes in mechanical properties and material damage. New relations connecting acoustic emission parameters to the relative number of cycles before fracture of steels studied were obtained.