The fact that standard specimens made of high-strength bearing steel undergo spall fracture during quasi-static tension is experimentally proved. The uniqueness of this fracture consists in the fact that it proceeds due to the elastic energy of the specimen, in contrast to the classical spallation during high-speed collision or a high-energy pulsed external action. High-speed video filming is used to demonstrate that the mode I fracture of a specimen and its subsequent spall fracture are spaced in time.

The mechanical properties of square section (up to 350 mm) forgings made of domestic steel VKS-9M (obtained by the duplex process of vacuum induction melting plus vacuum arc remelting) are studied. The mechanical properties of steel VKS-9M and American high-strength structural steel 300M are compared in terms of the calculated characteristics of materials. We extend the concept of «design characteristics of materials» to all the mechanical properties of materials used in determination of the strength and durability of structures. The design characteristics of materials include the strength characteristics under quasi-static tension, compression, crushing and shearing, as well as the strength under variable loads and the crack resistance of the material. The correctness of comparing the calculated values of the static strength of steels VKS-9M and 300M is based on the identity of test methods and the equivalence of processing and presentation of test results. The determination of the strength characteristics was carried out according to domestic standards, which are basically harmonized with the American standards. A difficult situation arises when determining the strength indicators of a newly developed material. Nowel material, as a rule, is developed in laboratory conditions, produced on experimental equipment in small volumes, and, therefore, the statistical assessment of the general population at the development stage is unreliable. In conditions of the full-scale manufacture of industrial semi-finished products, a statistical assessment of their strength characteristics becomes necessary. In the aviation industry, a statistical assessment of the calculated values of the strength characteristics of the material is prescribed by the law. The airworthiness standards set the levels of the calculated values of strength characteristics with a certain probability of non-destruction. For parts, the destruction of which can lead to an accident, the calculated values of the strength characteristics of materials should be selected in such a way that the strength of the material is to be ensured with a probability of 99% — with a 95% confidence interval (basis «A»). Statistical evaluation of the static strength characteristics of two heats of VKS-9M steel on the basis of «A» revealed their insignificant excess in comparison with steel 300M. The data obtained allow us to believe that the calculated values of the static strength characteristics of VKS-9M steel will not be lower than the calculated values for 300M steel. Large-scale fatigue tests of VKS-9M steel were carried out, which proved that the fatigue characteristics of VKS-9M and 300M steels practically coincide, as well as the arrays of their determinations. The equivalence of the strength characteristics of the VKS-9M and 300M steels allows replacement of the American 300M steel by the domestic VKS-9M steel.

The article deals with the features of deformation and destruction of samples that have undergone chemical-thermal treatment, using the example of testing nitrided samples of steels 38H2MYuA and 30H3MA. It is established that the mechanical properties determined during the tensile testing of samples with a highly rigid brittle layer cannot serve as design characteristics when evaluating the bearing capacity of parts that have undergone chemical-thermal treatment. Testing of nitrided samples of 38H2MYuA and 30H3MA steels demonstrated a complex process of their deformation and destruction, and the test result showed that this steel treated to the «hardened + high tempering» mode sensitivity to the most dangerous concentration the crack is absent.

The paper considers the issue of durability of hinged-bolt joints under the influence of a corrosive environment. There has been performed the analysis of the stress-strain state of the eyes’ material in the preloaded joints. Possibility of corrosion cracking of the eyes in case of exposure to a corrosive medium has been determined. Experimental confirmation of The destruction of the eyes’ material in a preloaded joint has been confirmed experimentally. The article proposes the development of the testing methodology of structural materials under the prolonged exposure to constant stress and corrosive medium under the conditions of a given deformation.

The phenomenon of spall fracture of high-strength steel specimens with the formation of two fracture surfaces during standard tensile tests is discussed. The fracture along two planes is shown to occur not simultaneously: first, fracture induced by a tensile load is observed, and then a second fracture plane forms, presumably, according to the spallation mechanism. The sequence proposed for the two fractures is confirmed by the results of fractographic analysis. The spallation during tension of standard specimens is found to differ from the classical spallation under an intense external action in the scheme of deformation wave formation and the source of spallation energy.

Earlier, we proposed a technique to estimate the fracture toughness of a metallic material. It differs from standard techniques in the determination of the operating stresses in an improved compact specimen with an edge crack. Using this technique, we determine the corrosion damage resistance of martensitic 30KhGSA (σ u ≈ 1080 MPa) and VKS-9n (σ u ≈ 2010 MPa) steels under full-scale and laboratory conditions and analyze their corrosion fracture kinetics. The corrosion fractures of the steels with different strength levels are found to have different characters: the 30KhGSA steel is likely to undergo anodic dissolution at the crack tip, and the high-strength VKS-9 steel undergoes hydrogen embrittlement.

Critical analysis of the methods of testing for fracture toughness in corrosive media under long-term load is presented. Bearing in mind the shortcomings of the known methods, we develop a technique for estimating the fracture toughness of structural materials in corrosive media under the impact of a long-term static load which is set with a high accuracy on a testing machine, which is then fixed with a spacer bolt. The method makes it possible to determine the effective load in the sample at any given time and study the kinetics of corrosion attack and change in the fracture toughness under conditions of long static loading.

A technique is suggested to determine the stress relaxation at the crack tip during tests of a specimen of a new type at a constant crack opening fixed by a stay bolt. The shape and geometry of the specimen make it possible to set the load and to determine the crack closure force after long-term exposure using the force transducer of a tensile-testing machine. The stress relaxation at the crack tip is determined in a V95pchT2 alloy specimen at elevated temperatures.

A new type of specimens is proposed to study the fracture kinetics of the metallic materials subjected to a long-term simultaneous action of a tensile load and a corrosive medium. The new design of specimens makes it possible to determine the stress intensity factor at the crack opening fixed by a wedging bolt, to perform investigations in any aggressive medium, and to measure the tensile load on a specimen at any stage of tests. Standard apparatus is used for this purpose. Plate specimens made of structural aluminum alloys 1163T and V95pchT2 are tested. A paradoxical fact of increasing the conventional stress intensity factor of the V95pchT2 alloy during the development of a corrosion crack is revealed.

Приведены результаты усталостных испытаний высокопрочной стали ВКС-9, разработанной для применения в шасси самолетов и других высоконагруженных деталях летательных аппаратов. Проиллюстрирована основная сложность разработки высокопрочных сталей, обусловленная тем, что несущая способность конструкции с концентратором напряжений оказывается существенно ниже предела прочности, определенного на стандартном образце. Наряду с оценкой сопротивления материала хрупкому разрушению критерий усталостного разрушения также является основой определения несущей способности. Исходя из аппаратурного оснащения, отечественная практика испытаний на усталость базировалась на нагружении по схеме «изгиб с вращением». Американские справочники предоставляют данные по усталости, полученные при испытаниях по схеме нагружения «растяжение–сжатие». Для корректного сравнения данных по усталости проведены сравнительные испытания высокопрочной стали ВКС-9 по различным схемам нагружения. Установлено, что пределы ограниченной выносливости на базах 10 4 –10 6 циклов при испытании по схеме нагружения «изгиб с вращением» превышают пределы выносливости, определенные при испытаниях по варианту «растяжение–сжатие». Ключевые слова: высокопрочная сталь, усталостные испытания, хрупкое разрушение, пределы выносливости, циклическое нагружение, чистый изгиб с вращением.