Papers by Keyword: Fatigue

Abstract: The mechanical and fatigue behavior of a reactively modified Inconel 625 alloy (IN625-RAM2) produced by Laser Powder Bed Fusion (PBF-LB) was investigated. The alloy achieved near-full density (≈8.30 g/cm³) and exhibited a refined, irregular grain structure with localized equiaxed regions from ceramic-induced nucleation and Zener pinning. It showed high tensile strength (YS 680–770 MPa, UTS 1170–1250 MPa) with modest anisotropy. Under fully reversed loading (R = –1), fatigue limits at 2×10⁶ cycles were 110–122 MPa in the as-built condition and 180–187 MPa after electropolishing, improving fatigue efficiency from ~10% to ~15% of UTS. Compared with reference alloys (AISI 316L, Ti6Al4V, IN718), IN625-RAM2 combined high strength with moderate fatigue resistance, emphasizing the critical role of surface quality in optimizing PBF-LB nickel alloys.

Abstract: Fatigue damage is one of the key degradation mechanisms affecting the service life and reliability of aluminum alloys in a wide range of technical applications. The present study focuses on the fracture mechanisms of aluminum alloys under cyclic loading, with a view to the initiation and analysis of fatigue crack propagation in the context of the microstructural characteristics of the material. Special attention was paid to the influence of grain morphology, distribution and type of intermetallic phases, as well as the presence of casting defects on the initiation and development of cracks. Fatigue experiments were performed on a selected Al-Mg alloy of the EN AC 51200 type for the use of three-point bending loading. The results show that the key factors affecting the fatigue behavior are the size and distribution of precipitates, the nature of the interfaces between the phases and the occurrence of microcracks initiated mainly in areas of stress concentration. The knowledge gained contributes to a deeper understanding of fatigue mechanisms in aluminum alloys and provides a basis for their optimization in terms of composition and technological processing in order to increase their resistance to fatigue failures.

Abstract: Titanium scaffolds produced by additive manufacturing were studied using the scanning electron microscopy (SEM) and the confocal optical microscopy (COM). The previous research has shown that the titanium scaffolds with porous filaments (14 % porosity) exhibited markedly better fatigue resistance than those with compact filaments (6 % porosity). This article is devoted to macroscopic and microscopic images of fracture surfaces of both types of scaffolds after cyclic compression (CC) tests and after cyclic three-point bending tests (CTPB). A high density of cracks and broken filaments was indicated particularly in scaffolds with porous filaments. The fatigue crack growth was highly affected by the microporosity. Fracture facets were smaller and rougher for the porous filaments compared to the compact ones. Values of roughness parameters S_a and S_v for porous filaments were significantly higher than those for compound fibres. Both SEM and COM studies confirmed an important role of crack-pore interactions especially in the porous filaments.

Abstract: This paper presents the relationship between crack width and acoustic emission (AE) energy in reinforced concrete (RC) beams subjected to cyclic loading. Two types of RC beams were tested, each reinforced with different tensile bar diameters: 12 mm (Y12) and 16 mm (Y16). The average ultimate loads (P_ult) for beams with Y12 and Y16 were 31 kN and 51 kN respectively. Beams tested under cyclic loading using Y12 and Y16 were labelled FT12 and FT16. Cyclic loading was applied at 80% of the P_ult and tests were continued until failure. A three-point bending test was performed under a sinusoidal load frequency of 1 Hz. AE monitoring was performed with six sensors installed at selected locations on the beams. The results showed that the crack width increased with the number of cycles, with correlation coefficients (R²) of 0.95 for FT12 and 0.93 for FT16, indicating a stronger linear relationship for both beams. Based on the trends in AE energy and crack width, three crack propagation stages were identified, with high AE energy found in both the initial microcrack formation and the final unstable failure stage. The results confirm that AE is an effective tool for early damage detection and fatigue monitoring in RC structures.

Abstract: The aim of the work was to assess the nature and causes of defects – cracks in the welds of membrane wall panel tubes (MW) of a thermal power plant boiler made of T24 steel. This steel is intended to produce MW evaporators and superheaters for power plant units operating in the area of supercritical steam conditions. Its advantage, compared to the originally used materials, is higher creep resistance. The main expected advantage of the steel was to obtain optimal properties of welded joints without subsequent post-weld heat treatment (PWHT).

Abstract: This paper deals with results of detailed investigations on a failed cast upper ram (63 tons) of a die-forging hammer. Subsurface cast defects primarily represented the “weak areas” responsible for the initiation of fatigue cracks during industrial exploitation. These defects mostly corresponded to gas bubbles. The occurrence of Ti (C,N) particles on the surface of these bubbles indicated that these defects were probably a consequence of release of gas products from the casting mould and/or mould's painting during the pouring of liquid metal. The evidence of fatigue initiation on repair welds was obtained only in one case. It was revealed that in this case the cast defects on the surface of the guiding radius were not completely cut off before repair welding. The remnants of the cast defects in the interface weld/base material initiated the fatigue crack. Basic mechanical properties of the subsurface layer of the upper ram complied with the design requirements.

Abstract: The development of structural changes at the nanoscale in the austenitic chromium-nickel steels used in the nuclear power industry is studied after Low-Cycle Fatigue (LCF) deformation. The reasons and mechanism of the nanocracks formation due to the structural relaxation in the regions of localized residual internal stresses in slip bands and grain boundaries are discussed. It showed that the locations and distribution of LCF slip bands in the process of microplastic deformation depend on the material’s microstructure.

Abstract: The purpose of this study is to investigate the effectiveness of laser peening (LP) and shot peening (SP) on the fatigue strength and harmless crack size ( of 3D additively manufactured maraging steel. LP and SP was performed under random condition and pre-optimal condition, respectively. Compressive residual stresses of 510MPa and 1650MPa could be introduced on the surface by LP and SP, respectively. Bending fatigue tests were conducted using base metal (BM) specimen, LP specimen and SP specimen. The fatigue strength of the LP and SP specimens were about 57 and 47% higher than that of BM specimen, respectively. Fatigue fracture was initiated from internal by LP and SP. The semicircular cracks less than 0.3mm and 0.1mm in the depth could be rendered harmless by LP and SP, respectively. The estimated based on fracture mechanics were similar to experimental result. The fatigue strength and was affected by the distribution of the compressive residual stress induced by LP and SP. Thus, the LP and SP process can contribute to improving the reliability of 3D additively manufactured maraging steel. Compressive residual stress is the dominant factor in improving fatigue strength and rendering surface defects harmless.

Abstract: Adhesive joints are essential in modern engineering, offering lightweight, durable and efficient solutions for bonding in industries such as aerospace, automotive, and renewable energy. However, their fatigue performance under cyclic loading remains a critical challenge, shaped by a complex interplay of geometrical, material, environmental, and loading factors. This review explores the mechanisms of fatigue failure, highlighting the importance of joint design, material optimization, and surface preparation in mitigating stress concentrations and enhancing durability. Advances in toughened adhesives, surface treatments, and environmental protection methods are highlighted, along with predictive models ranging from empirical S-N curves to advanced finite element simulations and probabilistic approaches. Despite significant progress, challenges remain in integrating these techniques for real-world applications, particularly under variable loading and harsh environmental conditions. Future research must focus on hybrid methodologies, adaptive materials, and standardized protocols to bridge the gap between laboratory insights and practical implementations. This comprehensive review provides a foundation for improving the fatigue performance of adhesive joints, ensuring their reliability and effectiveness in critical engineering systems.

Abstract: Increasing usage of the high-strength steels in structural design requires deeper understanding of the residual manufacturing stresses effect on the product service fatigue life. The bending forming process is being examined in this work. High cycle fatigue testing of the specimens before and after the bend shaping is performed by means of the vibrational fatigue method. The manufacturing residual and the fatigue tests stress fields are estimated by means of finite element analysis. The similarity principle is used to compare the fatigue curves constructed for the specimens with different geometries based on their local stress field concentration. A comparison with reference work is provided to support the similarity premise. The implementation of the mean stress correction for the residual stress is evaluated. The goal of this work is to demonstrate a methodological integration of the finite element analysis throughout manufacturing and fatigue testing for accurizing design life estimations. It may also serve as an end-to-end review and provide an outline for similar projects.