Papers by Keyword: Fatigue Failure

Abstract: Actuality. The accumulation of damage due to fatigue, plastic deformation, and wear significantly reduces the service life of railway rolled metal products. The development of a fatigue crack to its critical length (main cracks) leads to failure at stress levels much lower than the material's strength limit. In industrial-grade steels, there may be chemical micro-inhomogeneity of the main element—carbon. Objective of the study: To determine the effect of chemical micro-inhomogeneity (carbon content variation of 0.02%) on fatigue failure characteristics (crack growth rate, threshold stress intensity factor, fatigue life, and critical defect size) of railway wheel steels of grades ER7 and ER8 according to EN 13262. Results. Segments of the fatigue crack growth rate (FCGR) diagram were constructed to characterize the development of fatigue cracks. The crack growth rate on the second linear section of the diagram and the critical value of the stress intensity factor at which failure occurs were determined. It was found that on the linear portion, which describes the crack growth process, the indicator values vary slightly (up to 10%), indicating that the crack growth rate differs minimally between these steels. Fatigue life—the number of loading cycles until failure—was also determined, and the critical size of the fatigue crack was calculated. A carbon content fluctuation within 0.02% by mass leads to a reduction in fatigue life by approximately 10% for ER7 steel and about 20% for ER8 steel, and a reduction in the critical crack size by around 8% for ER7 and 18% for ER8. Conclusion. Chemical micro-inhomogeneity with carbon content variation in the range of 0.02% in ER7 and ER8 railway wheel steels leads to a decrease in fatigue life (as determined from specimens with cracks) and in the critical size of the fatigue crack (up to 20%). However, it has only a minor effect (about 10%) on the stable fatigue crack growth rate.

Abstract: Fatigue crack generation and propagation processes in oxygen-free copper for power equipment were investigated in a time series to search for new parameters that indicate the fatigue damage degree. The damage behavior of crystal grains was observed by optical microscopy, electron backscattered diffraction (EBSD) analysis and elastic strain analysis. The obtained results suggest that the change in grain orientation spread (GOS) and grain average misorientation (GAM) values is possible to detect the fatigue crack generation. Moreover, it was found that the change in the plastic strain range is also possible to detect it.

Abstract: Magnetic abrasive finishing (MAF) is an advanced surface finishing technology that utilizes magnetic fields to control abrasive particles, enabling precise material removal and superior surface integrity. This review paper comprehensively analyzes MAF research from 2015 to 2024, focusing on key developments, process optimizations, and industrial applications. The study looks at how MAF affects different materials like titanium alloys, stainless steels, and 3D-printed parts, showing how it improves surface smoothness, leftover stress, and resistance to wear and tear. This review paper expands on the experimental investigation of MAF’s efficacy in removing crack fatigue layers for a high-cost product to give it a high performance and longer life, a critical aspect in enhancing the functional performance of components. It is synthesizing various studies that explore the principles of MAF, the preparation of magnetic abrasives, tool design, and the process’s modeling and simulation. It also examines the force measurement and material removal mechanisms, providing a comprehensive understanding of the process parameters and their optimization. It is highlighting the challenges faced ‎in the field and suggests future directions for research, aiming to contribute to the development of more efficient and precise finishing techniques in manufacturing industries. The findings of this study are expected to benefit researchers and practitioners in MAF-related fields, paving the way for innovations in surface finishing technologies.

Abstract: The consumption of steel for fasteners in China is about 9 million tons annually, accounting for approximately one-fifth of worldwide usage. High strengthening is the main development trend of high performance of fasteners. As strength increase, the sensitivity of both fatigue failure and delayed fracture increases, and the processing technology varies. These are the main problems need to be addressed. Fasteners of property classes 8.8-12.9 are currently the most widely used high-strength fasteners. The match between fatigue life with strength is commonly the paramount consideration. We have developed a series of steels involving (i) SCM435 steel wire for key fasteners of engine with ultra-narrow composition (ΔC≤0.01%), slight hardness variation (ΔHRC≤ 2) and a qualified fatigue performance of 1×10⁷ cycles; (ii) 10.9 and 12.9 fastener steels with large size, low cost and high hardenability for wind tower; (iii) A286 alloy wire with desirable 650 °C durability. In addition, we developed ML35 wire free of spheroidizing and microalloyed steels for slender bolts free of quenching & tempering process. The use of ultra-high strength fasteners ≥13.9 is necessary to achieve equipment light weighting. We have developed steels for 13.9 and 15.9 fasteners with an excellent resistance to delayed fracture. An austempering process was applied to 14.8-17.8 fasteners, which enables the reduction of the alloy content. A novel strengthening method needs to be introduced to develop fasteners in excess of class 19.8 fastener. We have developed 19.8 fastener steel with good fatigue and delayed fracture resistance. Secondary hardening plays a key role in the improvement of strength.

Abstract: The main goal of this work was to conduct metallographic and fractographic studies, the purpose of which was to determine the cause of electric locomotive axle failure. The padding weld with a depth about 3 mm in the surface of the axle during fractographic observations was revealed. In addition, several sharp cracks inside of this weld were noticed. According to the fractographic analysis these cracks were the direct cause of the gradual spread of fatigue failure.

Abstract: Based on ultrasonic vibration-assisted mode, high-frequency impacting tests with diamond indenter at different amplitudes on AlTiN coating of cutting tool are carried out. The microstructure and morphology are obtained by scanning electron microscopy (SEM) and 3D profiler. The failure mechanism of coating under impact is analyzed. The high frequency fatigue property of the coating is analyzed. The results show that: lateral crack could be seen under impact test; the maximum tensile stress occurs close the edge of the contact zone of impact center; AlTiN coating is easy to emerge the fatigue damage under the high-frequency impact loading, and the adhesion strength of the coating and substrate interface affects the impact fatigue strength of cutting tool coating.

Abstract: The downtime problem of wind turbine increases due to fatigue damage of wind turbine blades, which is even more crucial in the larger blades. One of the critical failure modes is the blade trailing edge failure, which can result in the trailing edge joint cracked. In this paper, we experienced that abnormal sound was happened in the trailing edge at the cross-section in the max chord during fatigue testing of a 2 MW full-scale wind turbine blade according to IEC61400-23. Through the conditional monitoring of the trailing edge, the delamination between GFRP and balsa wood is caused by stress concentration. The abnormal sound is happened due to GFRP beat the balsa wood when the blade vibrates in the edgewise direction. Moreover, the sound is amplified because the introduction of air due to the delamination. The local stress distribution and stability factors are computed through FEM methods, the program that increasing the core materials in the trailing edge is proposed. Therefore the structure reliability in the trailing edge is improved.

Abstract: Material fatigue of different technical systems parts belongs to the most frequent causes of boundary states occurrence and relating operation breakdowns. An extraordinary attention is dedicated to the prediction of fatigue damage processes in structures elements all over the world because breakdowns, caused by a fatigue failure, have often a character of catastrophe. There should be a dominant effort to bring conditions of calculation or experimental measures near to the working conditions in which the investigated system is exploited. A modern way of calculation of any technical systems (e.g. large mechanical or civil structures) therefore demands to respect dynamic and stochastic nature of all influencing working factors and related working loads. The main reason for it is prevention from their working breakdowns. The objective of the paper is general formulation of reliability of technical systems assessment, brief characteristic of basic areas to be taken into account as input into calculated prediction of technical systems fatigue damage level and analysis of risk items by its practical application in real operating conditions.

Abstract: This review looks into the state of gigacycle fatigue behavior of some structural materials used in engineering works. Particular attention is given to the use of ultrasonic fatigue testing machine (USF-2000) due to its important role in conducting gigacycle fatigue tests. Gigacycle fatigue behavior of most materials used for very long life engineering applications is reviewed.Gigacycle fatigue behavior of magnesium alloys, aluminum alloys, titanium alloys, spheroid graphite cast iron, steels and nickel alloys are reviewed together with the examination of the most common material defects that initiate gigacycle fatigue failures in these materials. In addition, the stage-by-stage fatigue crack developments in the gigacycle regime are reviewed. This review is concluded by suggesting the directions for future works in gigacycle fatigue.

Abstract: With the increase of design fatigue life of many critical mechanical components and engineering structures, research on very high cycle fatigue (VHCF) has become a new topic for engineering components failure. This paper summarizes works of VHCF of high strength steel, such as the observations on fish-eye, which is one of the typical characteristics in VHCF regime; Characteristics of crack initiation and crack propagation are analyzed based on fracture surface; The present work also analyzes the fatigue mechanism and related models. Loading frequency effect on the VHCF behavior is also discussed. Some prospective aspects of future researches are proposed.