We took up the rental: the new model will calculate the strength of train wheels and aircraft landing gear

Russian scientists have developed a model describing the behavior of steel products under cyclic loads. It shows how parts deform at the initial stage of operation, and then switch to a stable mode of operation, while maintaining the ability to restore their original shape after each subsequent impact. Understanding these processes will allow engineers to more accurately calculate the required safety margin, which will make it possible to reduce the cost of parts for aviation, automotive, railway and other equipment without loss of quality. However, for the practical implementation of the technology, it will be necessary to accumulate a sufficient amount of experimental data, experts noted.

How predicting the behavior of steel will help reduce the weight of machinery

Scientists from St. Petersburg State University and the Institute of Problems of Mechanical Engineering of the Russian Academy of Sciences have developed a mathematical model that makes it possible to predict the behavior of steel under multiple loads. The object of the study was steel 20, an alloy of iron and carbon with a carbon content of about 0.2%. This material is characterized by good weldability, ductility and fracture resistance.

Experts drew attention to the peculiarity of the behavior of parts made of such steel under cyclic loads. At the initial stage of operation, they gradually accumulate deformations, but then they become stable and cease to change shape after regular impacts. The developed mathematical model allows predicting the moment of the onset of this regime with high accuracy.

— When designing any equipment, it is important for engineers to predict in advance how the metal will react to cyclic loads. However, until now, there has not been a reliable model that could mathematically describe this. Therefore, specialists put an additional safety margin in the parts, which makes them heavier and requires more material to manufacture," Nina Selyutina, senior researcher at the Department of Elasticity Theory named after N.F. Morozov and the Laboratory Dynamics and Extreme Characteristics of Promising Nanostructured Materials at St. Petersburg State University, told Izvestia.

During the study, the specialists conducted a series of experiments, subjecting the samples to cyclic loads of varying intensity and frequency. It turned out that at the initial stage — during the first hundreds of cycles — the material undergoes plastic deformation. In other words, after each exposure, its shape changes, albeit slightly, but irreversibly. However, after 800-5000 cycles, depending on the loading mode, this process stops: the steel becomes stable and begins to behave elastically, each time returning to its original shape after the load is removed.

— For engineers, this means that after passing the so-called stabilization threshold, the part goes into a predictable mode of operation. Its further operation becomes more reliable and safer, and the service life begins to be determined mainly by fatigue processes, which develop much more slowly," the scientist explained.

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How will the model tell you the terms of repair and replacement of parts

The created mathematical model reflects how sensitive the material is to different loads, and shows how stresses are redistributed in it due to the movement of microdefects. The technology will help to calculate the characteristics of structures more accurately and avoid their excessive weighting in cars, airplanes and railway equipment, which will reduce production and operation costs without compromising the reliability of products.

— This means fewer accidents and sudden breakdowns of machinery, saving materials and ultimately saving the health and lives of people who work on transport or near industrial equipment. In the future, we plan to develop the model so that it takes into account the mutual influence of plasticity and crack growth over the entire life of the part, as well as expand the range of loads," Nina Selyutina added.

At the same time, the expert emphasized, the stable state of the material does not persist indefinitely. Over time, the accumulation of microcracks still leads to the destruction of the structure. However, the new model gives engineers the opportunity to predict this moment in advance and replace parts in a timely manner. The ultimate goal of the project is to create simple and versatile tools for calculating the life cycle of steel products, applicable to various operating conditions.

— In mechanical engineering, models have long been used to describe the behavior of materials under fatigue loading. The advantage of the development is the ability to take into account the speed and frequency of impacts. Similar work was carried out in the 1960s and 1980s, but many of the data are either lost or outdated. It is important that scientists have started researching common and sought—after steels," Konstantin Shramko, head of the strength laboratory at the Moscow Aviation Institute, explained to Izvestia.

According to him, the safety margin is created due to the wide range of experimental data. Therefore, in order to put the development into practice, it is necessary to accumulate significant statistics on testing materials.

— The model clarifies the theory of metal destruction. It will help you choose the right processing modes for products so that they do not deform, for example, at the beginning of operation, when the parts are just rubbing against each other," commented Denis Simisinov, Vice—rector for Research, Head of the Department of Mining Equipment Operation at Ural State Mining University.

According to the model, to achieve stable operation, the parts must undergo multiple load cycles, he noted. If they are carried out artificially, the cost of products will increase. The developers believe that stabilization comes naturally. Understanding these processes will allow you to accurately plan the cycles of major repairs and replacement of parts.