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In this study, monolayer TiN and multilayer TiN/Ti coatings involving different modulation ratios were deposited on Ti–6Al–4V substrate. Ti interlayers in the multilayer TiN/Ti coatings were prepar...

Based on analysis of mechanical test the results a search is completed for the optimum content of the main alloying elements of maraging steels (MS) based on Fe–Cr–Ni–Mo that provides a combination of increased strength properties, impact strength, and static crack resistance. A multiple regression model that determines the dependence of the mechanical properties of steel on the alloying elements contained within them is proposed. It is shown that the optimization task is multi-factorial with conflicting criteria and can be effectively resolved using an “ideal point” method.

In this work, we use heat treatment to vary the size of nanoscale droplets in a phase-separated B2O3-SiO2-Al2O3-P2O5 glass without traditional modifiers and explore the effect of phase separation on the mechanical properties. The melt-quenched version of this glass already exhibits phase separation with a droplet phase rich in B2O3. The glass transition temperature (Tg) of the droplet phase is lower than that of silica-rich glass matrix. Upon heat treatment at a temperature below the Tg of the droplet phase, the size of droplets decreases but the fraction of the droplet phase increases. Consequently, the crack initiation resistance more than doubles. Upon heat treatment at the Tg of the matrix phase, the fracture toughness increases from 0.61 to 0.73 MPa·m0.5, which is primarily due to the aggregation of individual droplets. Upon the different heat treatments, the phase-separated glasses retain their optical transparency, while the hardness increases slightly.

The article provides information about the stress state protective and decorative coatings during aging. The influence of the discrete nature of the substrate on the change in the stress state of the coatings from the action of the wind load is considered. It was revealed that for each type of coating there is its own critical value of the pore size (unfilled paint), the excess of which leads to cracking of the coatings. A method is proposed for selecting the optimal coating thickness.

Information on the stress state of protective and decorative coatings during the curing process, in particular on the cohesive state of destruction, is given. The influence of the type of substrate on the change in internal stresses in the coating is considered. It was revealed that the greatest value of shear stresses is observed in coatings on a heavyweight concrete substrate. The subsequent increase in temperature after curing to 50°C leads to an increase in the value of the normal stresses. The probability of cracking of coatings during thermal aging is estimated. It was revealed that during aging there is an exponential decrease in the cohesive strength of coatings and an increase in internal stresses. Aging tends to increase the likelihood of cracking of coatings. The change in stresses in coatings as a result of seasonal fluctuations in air temperature is considered.

Specimens of armco iron and steels 09GS and 37G2S possessing strongly different load-extension diagrams are studied. The σ = f (δ) curves are divided into regularly alternating periods, i.e., linear, power within the uniform stage, and I, II, III in the lumped stage. Each period is characterized by the yielding parameter (YP), plasticity components (elongation δi), initial stress σi, and rate of growth/decrease of the stress (∆σ/δ∆)i. Analysis of the YP is used to compare the periods in differently hardened specimens. It is shown that the combination of these periods is responsible for the standard mechanical properties of the specimens. The values of the YP are used to trace the relation between the ductility and the crack resistance and to show that the stress σII and the elongation $$ {\updelta}_{\mathrm{l}}^{\mathrm{IIs}} $$ at the start of period II of the concentrated stage may be treated as criteria of crack resistance.

In this paper, the brittleness coefficient, elastic modulus-to-strength ratio, drying shrinkage and autogenous shrinkage and cracking sensitivity were used to investigate the effect of styrene-acrylic emulsion (SAE) on crack resistance of cement-based materials under ultralow water binder ratio (0.22). Then the pore structures, hydration products and surface morphology were also studied to explore the mechanism of SAE on improving the crack resistance of cement-based materials. Results show that, the addition of SAE significantly reduces the elastic modulus, brittleness coefficient, elastic strength ratio, drying shrinkage and autogenous shrinkage of the specimen. The cracking susceptibility is also decreased by the incorporation of SAE and when the dosage of SAE was 5%, the initial cracking time would be extended by 43 hours. In addition, incorporation of SAE can reduce the amount of pores that have an adverse effect on shrinkage, refine the microstructure and decrease the calcium hydroxide formation and microcracks of cement-based materials. Such results would be expected to provide guidance on enhancing the anti-cracking ability of high-performance cementitious materials by the dosage of SAE under low water-binder ratio in practical engineering.

In order to solve the problem of workability and durability of concrete caused by poor particle shape and morphology of manufactured sand and high content of stone powder, which leads to crack problems of concrete, the tensile strength, elastic modulus, shrinkage performance and adiabatic temperature rise performance of manufactured sand concrete were studied in this paper. And the cracking risk factor (the reciprocal of the anti cracking safety factor) of the concrete with the special admixtures and the crack resistant functional materials was calculated by according to GB 50496-2018. The experimental results show that the elastic modulus and tensile strength at the age of 28 d of the test concrete are increased from 31.0 GPa to 34.6 GPA and 2.91 MPa to 4.23 MPa, respectively. The shrinkage performance and adiabatic temperature rise of the concrete are reduced from 98 με to 65 με and 38.9°C to 38.4°C, respectively. The risk factors of surface and center crack resistance of mass concrete floor are 0.52 and 0.75, so the concrete under inspection will not crack.

Mechanical properties as well as crack resistance and stress corrosion cracking (SCC) resistance parameters of ultralow-carbon martensite steels (ULMS) type 05H2G2B and HSLA pipe steel 10G2FB with a different structures depending on processing are investigated. It is shown that despite a higher strength level, SCC resistance of ULMS steel is 25–30% higher than for HSLA steel with ferrite-perlite structure and close to that for this steel subjected to quenching and tempering.

In order to restore worn parts during repair work, it is often used to press the repair bushings. While assembling joints, cracks may form in the spanning part (bushing), as it may have surface and structure defects. Therefore, an urgent task is to increase the crack resistance of joints with tension during its assembly. The paper examines the influence of the geometry of the spanning part on the process of cracking. To assess the effect of defects on the crack formation, the method of modeling defects with a surface crack of a semi elliptical shape was used. The crack resistance is estimated using the force criterion of fracture mechanics – the stress intensity coefficient. As a result, it was found that the ratio between the wall thickness of the enclosing sleeve and its outer diameter has a significant effect on the crack resistance of the joint with tension, which allows reducing the origin probability and crack development during its pressing by varying these parameters. While assembling joints, the following methods are often used: mechanical-using a press and thermal with heating of the covering part. When the method of joint with cooling of the covered part, the greatest strength of the joint is achieved, but the probability of cracking increases. This is because when the temperature of the enclosing sleeve decreases in contact with the cooled shaft, the critical stress intensity coefficient (fracture toughness), which is a mechanical characteristic of crack resistance, decreases. To reduce the effect of cooling the sleeve, you can use a combined method of assembling the joint, in which the covered part is cooled and the covering part is heated. It is shown that to assess the fracture resistance at low temperatures, it is optimal to conduct full-scale tests, where the cooling and heating temperatures of the press joint parts are the experimental factors.

Among the various polymer fibers available, polypropylene (PP) fibers are often used to improve the impermeability, impact resistance, anti-wear and crack resistance of concrete. In order to improv...

We analyze the influence of model stratal water with low acidity on the cyclic crack resistance of 20N2M steel of a pump rod after operation for 5.5 yr. The state of the metal of a pump rod head is conventionally regarded as the reference state. We revealed insignificant differences between the basic mechanical properties and the characteristics of cyclic crack-growth resistance of steel in air for different states of the material. However, under the action of corrosive media, the fatigue crack-growth rate for the exploited steel is much higher than for steel in the reference state. This means that the in-service degradation of the rod steel manifests itself mainly in its sensitivity to the action of corrosive media.

The influence of microstructure parameters and chemical composition on the fracture toughness of steel is investigated. It is shown that the crack resistance of steel can not be reliably estimated only by a single parameter of the microstructure or only by chemical composition. A generalized parameter of microstructure and chemical composition, which correlates well with crack resistance, is proposed.

The authors present the experience of applying their methodology for calculating the residual life of metal structures of reloading machines by the criterion of the development of fatigue cracks to a critical size. The methodology is based on the well-known calculated dependencies of fracture mechanics, refined and supplemented with elements that take into account the specifics of the operation of transshipment machines in difficult weather conditions. Particular attention was paid to the accuracy of determining the stresses in the metalwork element when performing working operations because of the ever changing of the load acting on the metalwork, depending on the weight of the lifted load and the position of the machine in space. To confirm the high sensitivity to the accuracy of the determination of stresses, the dependence of the influence of the resource element metal with a crack from the amplitude of stress is graphically presented. The methodology for assessing the residual resource has been successfully tested on a number of complex metal.

The structure, the dynamic crack resistance, and the characteristics of mechanical properties of quenched and tempered structural steel 09G2S are studied. Special features of structure in the zones of plastic strain (ZPS) under fracture surfaces are considered after a single dynamic test. The structural features of bands of adiabatic shear formed in the starting region of the zone of plastic strain and in the region of the force action of the hammer are studied. The influence of formation of bands of adiabatic shear on the level of dynamic crack resistance is assessed. The temperatures arising in the material in the process of three-point dynamic bending are calculated.

The doping of amorphous carbon is one way of specifically modifying its properties. The present work is a contribution to understand the effect of dopant selection on structure, mechanical properties and crack resistance of hydrogen-free tetrahedral amorphous carbon (ta-C) coatings. For this purpose, nonmetallic (B, Si) and metallic (Mo, Fe, Cu) dopants were selected. The coatings were produced by the Laser-Arc technique and investigated by Raman spectroscopy, transmission electron microscopy, nanoindentation, bending, and scratch tests. It was found that doping generally affected the sp2 content and cluster size of the sp2 carbon phase, and thus hardness, Young's modulus, and intrinsic compressive stresses, but also the defect content and the crack resistance. The addition of metallic dopants led to an increase and clustering of the sp2-bonded carbon and, consequently, to a significant reduction in hardness and Young's modulus. This effect was much less pronounced when doping with non-metallic elements. The failure behavior changed toward higher ductility and crack resistance when metals were added. The crack resistance was found to be directly dependent on the H3/E2 value, with H3/E2 > 0.2 leading to a more brittle behavior with unstable crack propagation, while at H3/E2 < 0.2 the material was more ductile and exhibited stable crack propagation and thus higher crack resistance.

The high water demand of finishing compositions obtained using expanded perlite and vermiculite sand reduces the crack resistance of the resulting thermal insulation coatings. The use of microspheres as fillers should make it possible to increase the crack resistance of the resulting coatings. The crack resistance of lime heat-insulating coatings for the finishing of aerated concrete obtained using ash microspheres of aluminosilicate and expanded vermiculite sand has been determined. It is established, that coatings obtained using aluminosilicate ash microspheres, are characterized by good crack resistance due to low shrinkage deformations, high ultimate tensile properties and uniform distribution of moisture content in the process of moistening.

In order to research on the influence of the height of the fiber reinforcement zone on the normal sections crack resistance, we produced and tested rubcon beams of rectangular cross section with mixed reinforcement; our studies showed that the height of the fiber reinforcement zone has a similar effect on the normal sections crack resistance with the percentage of longitudinal reinforcement. It is important to note that the arrangement of fiber reinforcement at 3/4 of the section height greatly complicates the process of manufacturing the beam while not increasing the strength of the tensile zone compared to the beams with the location of the fiber over the entire height of the section.

The article discusses the methodology for the reinforced concrete structures’ probabilistic deformation calculation. The uniform deformation criteria for assessing the reliability of reinforced concrete structures in the operation stage for strength, stiffness and crack opening are proposed. Taking into consideration the relatively high degree of heterogeneity of reinforced concrete as a building material, each criterion is determined with a predetermined provision.

K2NiXCo(1−X) (SO4)2·6H2O (KCNSH) mixed crystal is a promising material for solar blind optical filters, combining high transparency in the ultraviolet range with effective suppression of the visible spectral region. Increasing the mechanical strength of these crystals is important to enable them to be machined in the manufacture of optical elements. A comprehensive study of the inhomogeneities and crack resistance of KCNSH crystal as a function of the growth conditions was carried out. The influence of the radial and mosaic inhomogeneity, as well as other structural defects, on the crack resistance of the crystals was analyzed. To assess the crack resistance of crystals, the parameters ca (crack length), c/a (the ratio of crack length to the size of the indentation), and KC (fracture toughness) were used. The correctness of the obtained results was analyzed. The conditions for growing KCNSH crystals with the best crack resistance were determined on the basis of the results of the study. It is shown that growing the mixed crystals using the temperature difference technique with a peripheral solution supply into the shaper provides the best crystal quality.

GRC-PC wall is a new type of integrated composite exterior wall with decorative and structural functions. It is formed by superimposing GRC surface layer on the outer leaf of prefabricated PC wall. Due to the complexity of indoor and outdoor environment and the difference of shrinkage performance between concrete and GRC materials, GRC surface layer in GRC-PC wall is prone to shrinkage and cracking, among which, the connection modes between GRC layer and PC layer and change of temperature and humidity have the greatest influence. Therefore, GRC material formula was adjusted, and seven experimental panels were produced. In view of the temperature and the humidity changes in different indoor and outdoor environments, the influences of different connection modes between GRC layer and PC layer on the material shrinkage performance were studied, and a one year material shrinkage performance experiment was conducted. The results show that, in indoor environment, the shrinkage of GRC layer and PC layer is relatively gentle due to the small range of temperature and humidity change. Compared with the indoor environment, the changes of outdoor temperature and humidity are more drastic. The shrinkage changes of GRC layer and PC layer show great fluctuations, but the overall strain value is still within a reasonable range, and there is no crack. At the same time, this suggests that smooth interface is more conducive to crack resistance of GRC surface layer compared with different interface types between GRC layer and PC layer. The research provides an experimental basis for the large-scale application of the wall panel, and it has great advantages in improving the efficiency of prefabricated building construction.

Significance of assessing the characteristics of crack resistance of centrifugal-cast (CFC) tubes made of steel 15KhlMlF is substantiated. The characteristic features of the metal under study are considered along with the methodology of crack resistance tests. Three modifications of the metal of the CFC pipes in the initial state, that differ in the degree of developed segregational heterogeneity, and two modifications of the metal with almost the same degree of structural heterogeneity, which differ in the running time as a part of the operating equipment are studied. It is shown that a decrease in the intensity of the segregational damage of the metal structure has almost no effect on the level of the strength characteristics, but is accompanied by an increase in the plastic properties and toughness of the metal. We present the results of studying crack resistance of centrifugal-cast pipes (steel 15KhlMlF) under static, cyclic and prolonged static loading in conditions of high-temperature creep. It is shown that an increase in the degree of structural heterogeneity of the CFC steel adversely affects the characteristics of static crack resistance and cyclic crack resistance as well, but to a far lesser extent and has little if any effect on the crack resistance of the CFC steel at creep. Cyclic crack resistance slightly decreases with increase of the operating time of the metal in functioning pipelines, whereas the characteristics of the prolonged static crack resistance get worse significantly. It is shown that welded joints of the CFC pipelines have a substantially lower crack resistance under creep conditions compared to the base metal. Statistical processing of the experimental data is used to get kinetic diagrams of cyclic and prolonged static crack resistance of 15X1M1F CFC-steel in creep conditions. The results of practical applications of the obtained crack resistance characteristics of the metal of the CFC pipes are demonstrated with a focus on the problems of ensuring the reliable operation of the steam pipelines of thermal power plants at the end of their service lifetime.

Results are provided for assimilation under casting and rolling complex conditions of pipe rolled product of the V–N microalloying system that is characterized not only by high strength (up to K60) and ductility, but also quite good cold resistance and crack resistance in a hydrogen sulfide medium.

The research performed in China on cement-based composites reinforced with randomly 3D distributed basalt fibers is analyzed and summarized, and six possible directions of further investigations into this field are proposed.

In this article is described a problem of increasing crack resistance of aerated cement concrete. Authors, having a model of concrete’s structure, made a disclosure of ratios for calculation of parameters the aerated concrete with disperse reinforcement. These ratios show data about change of structure parameters of aerated concretes with disperse reinforcement such as different density by variation of factors water-cement ratio, percent of reinforcement, ratio between dosing of cement and sand. Concrete’s cracking resistance was evaluated by compressive strength and parameter KIc. As result of experimental data processing authors got regression’s equations, which adequately describe changes of fracture toughness and compressive strength of aerated cement concrete (foam concrete) with density 1200 kg/m3 and 1400 kg/m3 in limits of factor area. There was shown a possibility of two-time increasing of fracture toughness and strength of aerated cement concrete with disperse reinforcement its structure by rough basalt fiber.

Special features of structure formation in steel 40Kh2N2MA are studied after a high-temperature thermomechanical treatment with martensitic-bainitic transformation of austenite. It is shown that the treatment produces a mixed structure represented by alternating extended regions of tempered martensite and lower bainite. The treatment raises substantially the impact toughness and the crack resistance of the steel. The process is the most effective for hardening alloy steels with enhanced stability of supercooled austenite.

The results of comprehensive studies of multifactor processes, mechanisms and criteria for fracture at a variation of the crack-like defect state, loading conditions and mechanical properties of structural materials carried out in the 20th - 21st centuries are presented on the basis of monographic publications and articles published in the journal “Zavodskaya Laboratoriya. Diagnostika Materialov.” Crack resistance of materials and structures has become a key problem of the material science, technology, design, manufacture and service of structures. Fracture mechanics including estimation of the stress-strain and limiting states in a cracks tip formed a scientific basis of the crack resistance analysis Stress intensity factors (linear fracture mechanics) and strain intensity factors (nonlinear fracture mechanics) are accepted as the basic criteria of those states. The basic computational relations for construction of the fracture diagrammes which link the cracks growth with conditions of a static, cyclic, long-term, dynamic loading are presented. Parameters of computational relations are put into correspondence with the features of fracture processes on nano-, micro-, meso- and macrolevels. Prospects of the research and guidelines of further studing crack resistance are discussed.

The resistances of glasses to crack initiation and crack growth are both important parameters for evaluating their mechanical performance. However, it is important to distinguish them as they refer to different mechanical phenomena. In this work, we study the difference in resistance to crack initiation and growth by determining the load required to induce indentation cracking (named crack resistance, CR) and the fracture toughness (KIc), respectively, for six oxide glasses with a wide range of CR values from as low as 0.05 N to above 100 N. These new data as well as existing literature data suggest that there is no systematic relation between CR and KIc, and as such, we conclude that these two terms should not be used interchangeably. We discuss the origin of the lacking relation by considering the competing effects of glass structure, rigidity, and atmospheric humidity on crack initiation and growth.

Accurately assessing fatigue crack growth resistance of structural materials is critical for service safety. We developed a theoretical model to describe the fatigue crack growth rate (FCGR) in an elastoplastic solid with fatigue-mediated random secondary microcracks. The model is applied to twinned materials. A special crack-microstructure interaction is examined which considers microcrack initiation occurs inside and outside twin ahead of the crack tip. The variations in spatial position and size characteristic of microcrack are considered using an extension of distributed dislocation technique. It is demonstrated that the FCGR exhibits significant dependence on fatigue-mediated microcrack for both the microcrack-inside and microcrack-outside cases. By solving the stress response near the crack tip, the combined effect of microcrack and twin lamella characteristics on FCGR is revealed. In parallel, we elucidate the competitive mechanism of the shielding and accelerating effects caused by microcrack. Besides, the effect of angle between the loading axial and the twin lamella is discussed. As the angle increases, the effects caused by secondary microcrack are weakening. This work expects to arouse new interest in the aspect of material crack resistance design concerning the influence of interaction between fatigue crack and fatigue-mediated microstructure.

Ensuring effective operation of structures in zones of aggressive media is associated with the task of studying, obtaining and developing composites of increased chemical resistance, strength and crack resistance. Structures based on corrosion-resistant materials (particularly polymer concretes) play a large role in solving these problems. One of these polymer concretes is rubber concrete or abbreviated as rubcon. This article is devoted to the study of the resistance of the external load to rubber concrete beams of a T-section. As a result of the experiments carried out on three series of rubber concrete T-beams with a different amount of longitudinal reinforcement, quantitative characteristics of the strength and crack resistance of their normal sections were obtained.

The investigations carried out in the field of creation of large-size crack-resistant structures and cellular concrete products have shown that this problem is multifaceted and it must be solved in a complex manner, and one of the ways to increase the crack resistance and durability of such structures and products is prestressed reinforcement.

The article describes experimental research of bending rubber fiber concrete elements with favorable deformation-strength characteristics. The use of such a material as fiberrubcon in load-bearing structures due to its high strength leads to a decrease in material consumption and weight of structures.

The problem of limit equilibrium of an elastoplastic body weakened by a crack is considered in the case of simultaneous realization of three macromechanisms of fracture. On the basis of the energy approach and some hypotheses, the criterion equations are proposed for the case of mixed fracture. The comparison of the theoretical and experimental values is presented.

Crack resistance of welded joints is one of the most important indices of service reliability of critical designation structures. The purpose of the research is the establishment of the influence of technological modes, hybrid laser-arc welding of high strength steel NA-XTRA-70 on the formation of structure in the metal welded joints, as well as analysis of the influence of this structure on their crack resistances. For the experiments the laboratory setup has been developed on which the experiments were carried out in the technological scheme that provides the location of the consumable electrode arc at a certain distance in front of the laser beam in the welding direction. Nd: YAG-laser DY 044 of company ROFIN (Germany) was a laser radiation source. Power for consumable electrode arc was carried out by welding generator PSG-500. Investigations of structural-phase changes in weld metal and HAZ were carried out by means of optical microscopy (optical microscope Versamet-2 and Neophot-32), microhardness was measured using M-400 gage of Leco company at 0.98N loading. Fractographic investigations were carried out by scanning electron microscopy (scanning electron microscope SEM-515 of PHILIPS company, Netherlands) on fractured specimens of welded joints, made as a result of impact bend tests. An analysis of crack resistance of the welded joints was carried out under different conditions of test temperatures. It was based on experimental data, received by a quantitative fractography method. It is shown that metal of a welded joint produced by hybrid laser-arc welding at Vw = 72m/h rate has mainly failure of ductile nature after external loading. This indicates sufficient level of crack resistance and further working capacity under operation conditions.

The prospect of introducing natural biological secrets to improve the crack resistance of gray cast iron is presented. We demonstrated that the mechanism of resisting crack owned by plant leaf can be referred to fabricate an alternating structure of hard and soft with low cost, high strength, and an exceptional ability to resist crack growth. Laser alloying was introduced to fabricate the hard phase which associated with the original matrix constituted the alternating structure. A homogeneous microstructure and a uniform distribution of chemical composites were achieved in hard phase. Nanoindentation test showed the resistance to plastic deformation of hard phase was improved. Crack propagation tests verified the crack resistance was enhanced by the alternating structure which could change and prolong crack path, and the effectiveness of resisting crack propagation was proportional to the size of hard phase.

The crack resistance of welded joints of pipe steels of strength class K60 and different alloying systems is studied. The parameter of the crack tip opening displacement (CTOD) is shown to be dependent on the size of the austenite grains and on the morphology of bainite in the superheated region of the heat-affected zone of the weld. The crack resistance is shown to be controllable due to optimization of the alloying system.

Fiber reinforced polymer (FRP) bars are widely used in building structures, especially that are exposed to the aggressive environment influence and other special conditions. Nevertheless, due to the low FRP (e.g. glass, basalt, aramid fibers reinforced polymers) bars modulus of elasticity, exceeding crack opening width, as well as deflections can be observed. FRP bars pretensioning is considered as an effective method of its structural performance increasing. Physico-chemical method of the FRP bars pretensioning based on the self-stressing concrete utilizing is an alternative to the mechanical method and in its turn doesn’t need for special devices and anchorage systems as well as qualified personnel. Assessment of the initial stress-strain state obtained during self-stressing concrete expansion stage in the reinforced self-stressed members is presented. Diagram method of the self-stressing parameters verification based on the static loading tests results is presented. Comparison of the initial stress-strain state obtained during concrete expansion stage and predicted by the proposed model, as well as assessment of its influence on the behavior at the static loading stage in cases of the self-stressed reinforced with FRP bars members and traditionally reinforced with steel bars self-stressed members was performed.

Иванов Михаил Александрович, канд. техн. наук, заведующий кафедрой оборудования и технологии сварочного производства, Южно-Уральский государственный университет, г. Челябинск; ivanovma@susu.ru. M.A. Ivanov, ivanovma@susu.ru South Ural State University, Chelyabinsk, Russian Federation

This paper presents new experimental data concerning the effect of the complex combined loading mode on changes in the mechanical properties of titanium alloys of different classes subjected to static stretching. The complex combined loading mode consists in the application of additional pulse loads for given degrees of static pre-loading followed by quenching of titanium alloys at a temperature of liquid nitrogen under a pre-set scheme. The authors used a new method for studying the material fracture kinetics, the so-called method of complete stress-strain diagrams, to explore a full range of mechanical properties of titanium alloys subjected to the combined loading mode, including the crack resistance.

The crack resistance of railroad rails with transverse internal and external cracks in the head formed in operation is determined. The ultimate crack resistance Ic, the values of which coincide with the critical values of the stress intensity factor KIc under the brittle fracture typical for rails, is determined.

This paper studies the fracture characteristics of wood in the longitudinal direction by combining KR curves and GR curve for fracture resistance ability analysis. Three-point-bending fracture test is carried out on the notched specimens. Digital image correlation (DIC) technique is applied to obtain the crack opening displacement and then calculate the equivalent crack length according to the double K fracture criterion. The KR and GR curves are constructed based on the experiment. The results show that the fracture toughness becomes larger but the fracture energy gets smaller with the increase of notch-to-depth ratio. Both the two curves show that the crack resistance ability is approximately improved when the notch-to-depth ratio increases. Through comparing KR and GR curves of the same specimen, it is seen that although these two kinds of fracture resistance curves have different evolution shapes, they both have three stages with the same dividing points, and they both can be used to analyze the quasi-brittle fracture process of wood.

This study is to pinpoint the effect of B doping and Ti-B co-doping on the crack resistance of CrN coating via nanoindentation. X-ray photoelectron spectroscopy (XPS) indicated that, besides Cr-N bond, B-N bond formed in CrBN coating while B-N and Ti-N bonds formed in CrTiBN coating. Owing to the stronger B-N, Ti-N bonds and nano-composite structure, CrBN and CrTiBN coatings presented a much higher hardness of 25.2 and 27.4 GPa than CrN coating (15.2 GPa). More importantly, the improved mechanical properties ( H / E ≥ 0.083, W e ≥ 78.6%) and high compressive stress (σ ≥ 3.53 GPa) of CrBN and CrTiBN coatings prevented them from encountering radial cracks under 700 mN. In contrast, CrN coating suffered radial cracks even under 400 mN. However, circumferential cracks emerged on CrBN and CrTiBN coatings under a combination effect of high compressive stress, poor plasticity ( R p ) and low hardness ratio between substrate and coatings ( H s / H ). It was indicated that B doping and Ti-B co-doping could improve the resistance of CrN coating to radial crack, but weaken its resistance to circumferential crack. In addition, more circumferential cracks found on CrTiBN coating demonstrated that an extra Ti doping would further deteriorate the crack resistance of CrBN coating.

The characteristics of strength, static crack resistance, rate of growth of fatigue cracks and cyclic endurance of annealed sheets from weldable alloys of the Al – Mg – Sc system are studied as compared to annealed sheets from alloy AMg6. The compositions of aluminum alloys with scandium (01545 and 1570S) with characteristics substantially superior to those of AMg6 and level of properties comparable to that of the base aircraft not weldable alloy 1163 in state T6 are determined.

The crack resistance of the 38CrNi3MoV (34NiCrMoV14—5. 35NiCrMoV12—5) tempered steel (at various tempering temperatures) has been estimated based on a comprehensive study of the steel fractures, microstructure, physical, and mechanical properties. Stress-intensity factor K 1C at the apex of the crack is growing continuously with an increase in the tempering temperature from 200 to 620°C. This indicates that K 1C is a structural-sensitive parameter, which depends on the steel microstructure and submicrostructure, the fracture mechanism that occurs under these structural conditions, the internal stress level, and the existence of microdefects and microcracks. The linear correlation dependence is found between the coefficient K 1C and the transverse velocity V transv. The obtained results reveal that the acoustic method can be used to quickly and efficiently estimate the crack resistance of the thermostrengthened steel without the recourse to labor-consuming mechanical tests and computations of the K 1C value.

The structure and the dynamic crack resistance of steel 09G2S tubular billets are compared after a heat treatment and different versions of deformation and heat treatment, including cold plastic deformation by radial forging and subsequent annealing. Radial forging followed by annealing has a favorable effect on strength and dynamic crack resistance, which confirms the possibility of industrial use of tubular billets from steel 09G2S after cold radial forging.

Steel slag is a kind of industrial waste generated during steelmaking. It has been widely used in asphalt mixtures as aggregate in previous research. The utilisation of steel slag in asphalt mixtures as filler is rarely reported. The primary objective of this research was to evaluate the effect of steel slag powder (SSP) on the crack resistance of asphalt mixtures. Two types of fillers – namely, SSP and limestone powder (LP) – were used, and LP functioned as the control group. The characteristics of SSP and LP, including surface texture, chemical composition and particle size gradation, were first investigated. Then, asphalt mixtures containing SSP and LP were designed by the Superpave procedure. Finally, the indirect tensile strength (ITS) and fracture energy of asphalt mixtures were determined to evaluate the crack resistance of asphalt mixtures. Results suggest that the particles in SSP and LP both possess obvious edges and corners and coarse surface textures. The average chemical compositions indicate that SSP is a high-alkalinity slag filler. Determining the crack resistance of asphalt mixtures by ITS value is not sufficient because of the similar results caused by SSP and LP. The fracture energy parameter suggests that SSP improves the crack resistance of asphalt mixtures.