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24 pages, 18169 KiB

Open AccessArticle

Failure Mechanism and Control Mechanism of Intermittent Jointed Rock Bridge Based on Acoustic Emission (AE) and Digital Image Correlation (DIC)

by Hang Lin, Xing Zhang and Su Li

Materials 2024, 17(13), 3190; https://doi.org/10.3390/ma17133190 - 29 Jun 2024

Viewed by 982

Abstract

Deep foundation pit excavation is an important way to develop underground space in congested urban areas. Rock bridges prevent the interconnection of joints and control the deformation and failure of the rock mass caused by excavation for foundation pits. However, few studies have [...] Read more.

Deep foundation pit excavation is an important way to develop underground space in congested urban areas. Rock bridges prevent the interconnection of joints and control the deformation and failure of the rock mass caused by excavation for foundation pits. However, few studies have considered the acoustic properties and strain field evolution of rock bridges. To investigate the control mechanisms of rock bridges in intermittent joints, jointed specimens with varying rock bridge length and angle were prepared and subjected to laboratory uniaxial compression tests, employing acoustic emission (AE) and digital image correlation (DIC) techniques. The results indicated a linear and positive correlation between uniaxial compressive strength and length, and a non-linear and negative correlation with angle. Moreover, AE counts and cumulative AE counts increased with loading, suggesting surges due to the propagation and coalescence of wing and macroscopic cracks. Analysis of RA-AF values revealed that shear microcracks dominated the failure, with the ratio of shear microcracks increasing as length decreased and angle increased. Notably, angle exerted a more significant impact on the damage form. As length diminished, the failure plane’s transition across the rock bridge shifted from a complex coalescence of shear cracks to a direct merger of only coplanar shear cracks, reducing the number of tensile cracks required for failure initiation. The larger the angle, the higher the degree of coalescence of the rock bridge and, consequently, the fewer tensile cracks required for failure. The decrease of length and the increase of angle make rock mass more fragile. The more inclined the failure mode is to shear failure, the smaller the damage required for failure, and the more prone the areas is to rock mass disaster. These findings can provide theoretical guidance for the deformation and control of deep foundation pits. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials – 2nd Edition)

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15 pages, 13798 KiB

Open AccessArticle

Studies on the Evolution of Fatigue Strength of Aluminium Wires for Overhead Line Conductors

by Bartosz Jurkiewicz and Beata Smyrak

Materials 2024, 17(11), 2537; https://doi.org/10.3390/ma17112537 - 24 May 2024

Cited by 3 | Viewed by 1038

Abstract

Traditional ACSR overhead wires, which consist of a high-strength steel core and several layers of aluminium wires, are currently the most popular overhead line conductor (OHL) design globally. Operating conditions, particularly operating under varying stresses from Karman vortices, lead to the fatigue cracking [...] Read more.

Traditional ACSR overhead wires, which consist of a high-strength steel core and several layers of aluminium wires, are currently the most popular overhead line conductor (OHL) design globally. Operating conditions, particularly operating under varying stresses from Karman vortices, lead to the fatigue cracking of wires of the outer layer, followed by wires of the inner layers. Karman vortices are formed by the detachment of a laminar wind stream flowing around the conductor, which causes vibrations in the conductor called wind or aeolian oscillations. Aluminium wires are manufactured using standard batch material drawing technology. Although the fatigue strength of such wires is not standardised, there are various criteria for evaluating this characteristic, as well as established limits on the number of cycles needed to break the first wires of the outer layer. Fatigue strength also strongly depends on the geometric structure of the wire and its operating conditions. The article analyses the influence of the mechanical condition of aluminium wires used in ACSR cables on their fatigue strength. We then present results from aluminium wire fatigue tests conducted on a specially constructed test rig. In addition, fatigue cracks were interpreted using scanning microscopy. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials – 2nd Edition)

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32 pages, 14336 KiB

Open AccessArticle

Eigenvibrations of Kirchhoff Rectangular Random Plates on Time-Fractional Viscoelastic Supports via the Stochastic Finite Element Method

by Marcin Kamiński, Michał Guminiak, Agnieszka Lenartowicz, Magdalena Łasecka-Plura, Maciej Przychodzki and Wojciech Sumelka

Materials 2023, 16(24), 7527; https://doi.org/10.3390/ma16247527 - 6 Dec 2023

Cited by 3 | Viewed by 1311

Abstract

The present work’s main objective is to investigate the natural vibrations of the thin (Kirchhoff–Love) plate resting on time-fractional viscoelastic supports in terms of the Stochastic Finite Element Method (SFEM). The behavior of the supports is described by the fractional order derivatives of [...] Read more.

The present work’s main objective is to investigate the natural vibrations of the thin (Kirchhoff–Love) plate resting on time-fractional viscoelastic supports in terms of the Stochastic Finite Element Method (SFEM). The behavior of the supports is described by the fractional order derivatives of the Riemann–Liouville type. The subspace iteration method, in conjunction with the continuation method, is used as a tool to solve the non-linear eigenproblem. A deterministic core for solving structural eigenvibrations is the Finite Element Method. The probabilistic analysis includes the Monte-Carlo simulation and the semi-analytical approach, as well as the iterative generalized stochastic perturbation method. Probabilistic structural response in the form of up to the second-order characteristics is investigated numerically in addition to the input uncertainty level. Finally, the probabilistic relative entropy and the safety measure are estimated. The presented investigations can be applied to the dynamics of foundation plates resting on viscoelastic soil. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials – 2nd Edition)

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18 pages, 10628 KiB

Open AccessArticle

Research of the Ball Burnishing Impact over Cold-Rolled Sheets of AISI 304 Steel Fatigue Life Considering Their Anisotropy

by Stoyan Slavov, Diyan Dimitrov, Mariya Konsulova-Bakalova and Lyubomir Si Bao Van

Materials 2023, 16(10), 3684; https://doi.org/10.3390/ma16103684 - 11 May 2023

Cited by 3 | Viewed by 1925

Abstract

The present work focusses on the research of the plastic deformation accumulated effect obtained after two different plastic deformation treatments, over the fatigue life of AISI 304 austenitic stainless steel. The research is focused on ball burnishing as a finishing process to form [...] Read more.

The present work focusses on the research of the plastic deformation accumulated effect obtained after two different plastic deformation treatments, over the fatigue life of AISI 304 austenitic stainless steel. The research is focused on ball burnishing as a finishing process to form specific, so-called “regular micro-reliefs” (RMRs) on a pre-rolled stainless-steel sheet. RMRs are formed using a CNC (Computerized Numerically Controlled) milling machine and toolpaths with the shortest unfolded length, generated by an improved algorithm, based on the Euclidean Distance calculation. The effect of the predominant tool trajectory direction during the ball burnishing process (which can be coinciding or transverse with the rolling direction), the magnitude of applied deforming force, and feed-rate is subjected to evaluation using Bayesian rule analyses of experimentally obtained results for the fatigue life of AISI 304 steel. The obtained results give us reason to conclude that the fatigue life of researched steel is increased when directions of pre-rolled plastic deformation and the tool movement during ball burnishing are coincident. It also been found that the magnitude of deforming force has a stronger impact over the fatigue life, than the feed-rate of the ball tool. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials – 2nd Edition)

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10 pages, 8475 KiB

Open AccessArticle

Strength and Cyclic Properties of Additive vs. Conventionally Produced Material AlSi₁₀Mg

by Vladimír Chmelko, Miroslav Šulko, Jaroslava Škriniarová, Matúš Margetin, Marek Gašparík, Tomáš Koščo and Marián Semeš

Materials 2023, 16(7), 2598; https://doi.org/10.3390/ma16072598 - 24 Mar 2023

Cited by 8 | Viewed by 1697

Abstract

Additive metals are practically identical in strength to the properties of conventionally produced materials. This article experimentally analyses strength properties and fatigue properties in the tensile–pressure mode for two different directions of 3D printing of AlSi₁₀Mg material. The resulting fatigue parameters [...] Read more.

Additive metals are practically identical in strength to the properties of conventionally produced materials. This article experimentally analyses strength properties and fatigue properties in the tensile–pressure mode for two different directions of 3D printing of AlSi₁₀Mg material. The resulting fatigue parameters of the Basquin curve are confronted with a conventionally produced alloy of the same composition. The microstructure analysis explains the different fatigue properties obtained by these two material production technologies. Phenomena such as strength enhancement in additive manufacturing material, anisotropy of cyclic properties, and cyclic hardening are discussed. The limits of current additive manufacturing are clarified, and the future direction of research in this field is outlined. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials – 2nd Edition)

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15 pages, 8524 KiB

Open AccessArticle

Influence of Pre-Strain on Static and Fatigue Properties of S420M Steel

by Stanisław Mroziński, Adam Lipski, Michał Piotrowski and Halina Egner

Materials 2023, 16(2), 590; https://doi.org/10.3390/ma16020590 - 7 Jan 2023

Cited by 5 | Viewed by 1632

Abstract

This paper reports the results of static tensile and low-cycle fatigue tests on S420M steel specimens. As-received (unstrained) and pre-strained specimens were used during the tests. Based on the static tensile tests carried out, no effect of pre-strain on the basic strength parameters [...] Read more.

This paper reports the results of static tensile and low-cycle fatigue tests on S420M steel specimens. As-received (unstrained) and pre-strained specimens were used during the tests. Based on the static tensile tests carried out, no effect of pre-strain on the basic strength parameters of the S420M steel was found. Low-cycle fatigue tests showed that the pre-strain of the specimens causes a change in the cyclic properties of the steel and a slight increase in fatigue life compared to that of the as-received specimens. The greatest increase in durability was observed at the lowest strain levels. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials – 2nd Edition)

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14 pages, 2196 KiB

Open AccessArticle

Using the Fourier Methods for Cycle Counting of Bimodal Stress Histories with Variable in Time Amplitudes of Components

by Marek S. Kozień

Materials 2023, 16(1), 254; https://doi.org/10.3390/ma16010254 - 27 Dec 2022

Cited by 2 | Viewed by 1441

Abstract

The application of the Fourier methods to perform cycle identification and description for different cases of bimodal stress histories are presented and discussed in the paper. The direct spectral method and the modified direct spectral method, previously co-proposed by the author, together with [...] Read more.

The application of the Fourier methods to perform cycle identification and description for different cases of bimodal stress histories are presented and discussed in the paper. The direct spectral method and the modified direct spectral method, previously co-proposed by the author, together with the aspects of the use of Fourier methods discussed in this article, offer a unique alternative to the methods known in the literature for identifying and counting various types of bimodal stress variations in time (with constant or variable amplitudes; completely reversed, reversal, or pulsed type). The application of the Fast Fourier Transform (FFT) and the Short-Time Fourier Transform (STFT) is discussed. The method is useful, especially in cases when it is known that due to the form of work of the mechanical system the two existing components of vibrations with various frequencies can be identified, of which the one with higher frequency has a vibration amplitude lower than a component with a lower frequency and, above all, a variable in time. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials – 2nd Edition)

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Review

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28 pages, 50735 KiB

Open AccessReview

The Main Failure Modes of Hot-Work Die Steel and the Development Status of Traditional Strengthening Methods and Nano-Strengthening Technology

by Hong-Yu Cui, Ze-Ju Bao, Qin Gong, Shi-Zhe Bao, Yun-Zhi Zou, Ai-Min Li, Hong-Yu Yang, Cheng-Gang Wang, Zhi-Gang Li, Fang Chang, Shi-Li Shu, Jie Kang, Ming Zhu, Feng Qiu and Qi-Chuan Jiang

Materials 2024, 17(14), 3455; https://doi.org/10.3390/ma17143455 - 12 Jul 2024

Viewed by 1625

Abstract

As an important part of die steels, hot-work die steels are mainly used to manufacture molds made of solid metal or high-temperature liquid metal from heating to recrystallization temperature. In view of the requirements for mechanical properties and service life for hot-work die [...] Read more.

As an important part of die steels, hot-work die steels are mainly used to manufacture molds made of solid metal or high-temperature liquid metal from heating to recrystallization temperature. In view of the requirements for mechanical properties and service life for hot-work die steel, it is conducive to improve the thermal fatigue resistance, wear resistance, and oxidation resistance of hot work die steel. In this review, the main failure modes of hot-work die steel were analyzed. Four traditional methods of strengthening and toughening die steel were summarized, including optimizing alloying elements, electroslag remelting, increasing the forging ratio, and heat treatment process enhancement. A new nano-strengthening method was introduced that aimed to refine the microstructure of hot-work abrasive steel and improve its service performance by adding nanoparticles into molten steel to achieve uniform dispersion. This review provides an overview to improve the service performance and service life of hot work die steel. Full article

(This article belongs to the Special Issue Study on Cyclic Mechanical Behaviors of Materials – 2nd Edition)

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