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16 pages, 21816 KiB

Open AccessArticle

The High-Cycle Tensile–Shear Fatigue Properties and Failure Mechanism of Resistance Spot-Welded Advanced High-Strength Steel with a Zn Coating

by Yu Sun, Jiayi Zhou, Rongxun Hu, Hua Pan, Kai Ding, Ming Lei and Yulai Gao

Materials 2024, 17(18), 4463; https://doi.org/10.3390/ma17184463 - 11 Sep 2024

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Abstract

Advanced high-strength steels (AHSSs) with Zn coatings are commonly joined by the resistance spot welding (RSW) technique. However, Zn coatings could possibly cause the formation of liquid metal embrittlement (LME) cracks during the RSW process. The role of a Zn coating in the [...] Read more.

Advanced high-strength steels (AHSSs) with Zn coatings are commonly joined by the resistance spot welding (RSW) technique. However, Zn coatings could possibly cause the formation of liquid metal embrittlement (LME) cracks during the RSW process. The role of a Zn coating in the tensile–shear fatigue properties of a welding joint has not been systematically explored. In this study, the fatigue properties of tensile–shear RSW joints for bare and Zn-coated advanced high-strength steel (AHSS) specimens were comparatively studied. In particular, more severe LME cracks were triggered by employing a tilted welding electrode because much more stress was caused in the joint. LME cracks had clearly occurred in the Zn-coated steel RSW joints, as observed via optical microscopy. On the contrary, no LME cracks could be found in the RSW joints prepared with the bare steel sheets. The fatigue test results showed that the tensile–shear fatigue properties remained nearly unchanged, regardless of whether bare or Zn-coated steel was used for the RSW joints. Furthermore, Zn mapping adjacent to the crack initiation source was obtained by an electron probe micro-analyzer (EPMA), and it showed no segregation of the Zn element. Thus, the failure of the RSW joints with the Zn coating had not initiated from the LME cracks. It was concluded that the fatigue cracks were initiated by the stress concentration in the notch position between the two bonded steel sheets. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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19 pages, 11603 KiB

Open AccessFeature PaperArticle

Inverse Method to Determine Parameters for Time-Dependent and Cyclic Plastic Material Behavior from Instrumented Indentation Tests

by Hafiz Muhammad Sajjad, Thomas Chudoba and Alexander Hartmaier

Materials 2024, 17(16), 3938; https://doi.org/10.3390/ma17163938 - 8 Aug 2024

Viewed by 584

Abstract

Indentation is a versatile method to assess the hardness of different materials along with their elastic properties. Recently, powerful approaches have been developed to determine further material properties, like yield strength, ultimate tensile strength, work-hardening rate, and even cyclic plastic properties, by a [...] Read more.

Indentation is a versatile method to assess the hardness of different materials along with their elastic properties. Recently, powerful approaches have been developed to determine further material properties, like yield strength, ultimate tensile strength, work-hardening rate, and even cyclic plastic properties, by a combination of indentation testing and computer simulations. The basic idea of these approaches is to simulate the indentation with known process parameters and to iteratively optimize the initially unknown material properties until just a minimum error between numerical and experimental results is achieved. In this work, we have developed a protocol for instrumented indentation tests and a procedure for the inverse analysis of the experimental data to obtain material parameters for time-dependent viscoplastic material behavior and kinematic and isotropic work-hardening. We assume the elastic material properties and the initial yield strength to be known because these values can be determined independently from indentation tests. Two optimization strategies were performed and compared for identification of the material parameters. The new inverse method for spherical indentation has been successfully applied to martensitic steel. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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14 pages, 1493 KiB

Open AccessArticle

Crystal Plasticity Parameter Optimization in Cyclically Deformed Electrodeposited Copper—A Machine Learning Approach

by Karol Frydrych, Maciej Tomczak and Stefanos Papanikolaou

Materials 2024, 17(14), 3397; https://doi.org/10.3390/ma17143397 - 9 Jul 2024

Viewed by 553

Abstract

This paper describes an application of a machine learning approach for parameter optimization. The method is demonstrated for the elasto-viscoplastic model with both isotropic and kinematic hardening. It is shown that the proposed method based on long short-term memory networks allowed a reasonable [...] Read more.

This paper describes an application of a machine learning approach for parameter optimization. The method is demonstrated for the elasto-viscoplastic model with both isotropic and kinematic hardening. It is shown that the proposed method based on long short-term memory networks allowed a reasonable agreement of stress–strain curves to be obtained for cyclic deformation in a low-cycle fatigue regime. The main advantage of the proposed approach over traditional optimization schemes lies in the possibility of obtaining parameters for a new material without the necessity of conducting any further optimizations. As the power and robustness of the developed method was demonstrated for very challenging problems (cyclic deformation, crystal plasticity, self-consistent model and isotropic and kinematic hardening), it is directly applicable to other experiments and models. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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20 pages, 10400 KiB

Open AccessArticle

Interpretation of Frequency Effect for High-Strength Steels with Three Different Strength Levels via Crystal Plasticity Finite Element Method

by Yingxin Zhao, Xiaoya Wang, Like Pan, Jun Wang, Liming Chen, Tong Xing, Junchen Zhu and Aiguo Zhao

Materials 2024, 17(10), 2350; https://doi.org/10.3390/ma17102350 - 15 May 2024

Viewed by 635

Abstract

The fatigue behavior of a high-strength bearing steel tempered under three different temperatures was investigated with ultrasonic frequency and conventional frequency loading. Three kinds of specimens with various yield strengths exhibited obvious higher fatigue strengths under ultrasonic frequency loading. Then, a 2D crystal [...] Read more.

The fatigue behavior of a high-strength bearing steel tempered under three different temperatures was investigated with ultrasonic frequency and conventional frequency loading. Three kinds of specimens with various yield strengths exhibited obvious higher fatigue strengths under ultrasonic frequency loading. Then, a 2D crystal plasticity finite element method was adopted to simulate the local stress distribution under different applied loads and loading frequencies. Simulations showed that the maximum residual local stress was much smaller under ultrasonic frequency loading in contrast to that under conventional frequency at the same applied load. It was also revealed that the maximum local stress increases with the applied load under both loading frequencies. The accumulated plastic strain was adopted as a fatigue indicator parameter to characterize the frequency effect, which was several orders smaller than that obtained under conventional loading frequencies when the applied load was fixed. The increment of accumulated plastic strain and the load stress amplitude exhibited a linear relationship in the double logarithmic coordinate system, and an improved fatigue life prediction model was established. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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13 pages, 13083 KiB

Open AccessArticle

Experimental Study on the Fatigue Crack Propagation Rate of 925A Steel for a Ship Rudder System

by Li Yu, Wenyong Guo, Chenghao Cao, Min Li, Zhe Wu, Te Wang, Hantao Chen and Xinglong Pan

Materials 2024, 17(8), 1808; https://doi.org/10.3390/ma17081808 - 15 Apr 2024

Cited by 1 | Viewed by 756

Abstract

The low-temperature fatigue crack propagation rate of 925A steel, as a rudder steel for polar special ships, has a crucial impact on the evaluation of the fatigue strength of polar ships. The purpose of this article is to study the fatigue crack propagation [...] Read more.

The low-temperature fatigue crack propagation rate of 925A steel, as a rudder steel for polar special ships, has a crucial impact on the evaluation of the fatigue strength of polar ships. The purpose of this article is to study the fatigue crack propagation rate of 925A steel under different low-temperature conditions from room temperature (RT) to −60 °C. The material was subjected to fatigue crack propagation tests and stress intensity factor tests. The experimental tests were conducted according to the Chinese Standard of GB/T6398-2017. The results show that as the temperature decreases, the lifespan of 925A increases. Within a certain stress intensity factor, as the temperature decreases, the fatigue crack propagation rate decreases. At −60 °C, it exhibits ductile fracture; within normal polar temperatures, it can be determined that 925A meets the requirements for low-temperature fatigue crack propagation rates in polar regions. However, in some extreme polar temperatures below −60 °C, preventing brittle failure becomes a key focus of fatigue design. Finally, the fatigue crack propagation behavior at the microscale of 925A steel at low temperatures was described using fracture morphology. The experimental data can provide reference for the design of polar ships to further resist low-temperature fatigue and cold brittle fracture. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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24 pages, 33744 KiB

Open AccessArticle

Experimental and Simulation Investigation on Fatigue Performance of H13 Steel Tools in Friction Stir Welding of Aluminum Alloys

by Ling Long, Xiaohong Zhang, Song Gu, Xiuxin Li, Xuefeng Cheng and Gaoqiang Chen

Materials 2024, 17(7), 1535; https://doi.org/10.3390/ma17071535 - 28 Mar 2024

Cited by 1 | Viewed by 781

Abstract

As the central component in friction stir welding, the design and manufacture of welding tools for aluminum alloys have garnered substantial attention. However, the understanding of tool reliability during the welding process, especially in terms of fatigue performance, remains unclear. This paper focuses [...] Read more.

As the central component in friction stir welding, the design and manufacture of welding tools for aluminum alloys have garnered substantial attention. However, the understanding of tool reliability during the welding process, especially in terms of fatigue performance, remains unclear. This paper focuses on the welding of AA2219-T4 as a case study to elucidate the predominant failure mode of the tool during the friction stir welding (FSW) of aluminum alloys. Experimental methods, including FSW welding and fracture morphology analysis of the failed tool, coupled with numerical simulation, confirm that high-cycle mechanical fatigue fracture is the primary mode of the tool failure. Failures predominantly occur at the tool pin’s root and the shoulder end face with scroll concave grooves. The experimental and simulation results exhibit a noteworthy agreement, validating the reliability of the simulation model. The FSW Arbitrary Lagrangian–Eulerian (ALE) model developed in this study analyzes stress distribution and variation under the thermo-mechanical coupling effect of the tool. It reveals that stress concentration resulting from structural changes in the tool is the primary driver of fatigue crack initiation. This is attributed to exposure to alternating cyclic stresses such as bending, tension, and torsion at the tool pin’s root, manifesting as multiaxial composite mechanical fatigue. Among these stresses, bending alternating cyclic stress exerts the most significant influence. The paper employs the Tool Life module in DEFORM software to predict the fatigue life of the tool. Results indicate that reducing welding speed or increasing rotation speed can enhance the tool’s fatigue life to some extent. The methodology proposed in this paper serves as a valuable reference for optimizing FSW structures or processes to enhance the fatigue performance of welding tools. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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12 pages, 5795 KiB

Open AccessArticle

Effect of Strain Rate on Hydrogen Embrittlement of Ti6Al4V Alloy

by Tien-Dung Nguyen, Nooruddin Ansari, Keun Hyung Lee, Dong-Hyun Lee, Jun Hyun Han and Soo Yeol Lee

Materials 2024, 17(5), 1100; https://doi.org/10.3390/ma17051100 - 28 Feb 2024

Viewed by 1115

Abstract

The phenomenon of hydrogen embrittlement (HE) in metals and alloys, which determines the performance of components in hydrogen environments, has recently been drawing considerable attention. This study explores the interplay between strain rates and solute hydrogen in inducing HE of Ti6Al4V alloy. For [...] Read more.

The phenomenon of hydrogen embrittlement (HE) in metals and alloys, which determines the performance of components in hydrogen environments, has recently been drawing considerable attention. This study explores the interplay between strain rates and solute hydrogen in inducing HE of Ti6Al4V alloy. For the hydrogen-charged sample, as the strain rate was decreased from 10⁻²/s to 10⁻⁵/s, the ductility decreased significantly, but the HE effect on mechanical strength was negligible. The low strain rate (LSR) conditions facilitated the development of high-angle grain boundaries, providing more pathways for hydrogen diffusion and accumulation. The presence of solute hydrogen intensified the formation of nano/micro-voids and intergranular cracking tendencies, with micro-crack occurrences observed exclusively in the LSR conditions. These factors expanded the brittle hydrogen-damaged region more deeply into the interior of the lattice. This, in turn, accelerated both crack initiation and intergranular crack propagation, finally resulting in a considerable HE effect and a reduction in ductility at the LSR. The current study underscores the influence of strain rate on HE, enhancing the predictability of longevity and improving the reliability of components operating in hydrogen-rich environments under various loading conditions. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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17 pages, 6618 KiB

Open AccessArticle

Damage-Accumulation-Induced Crack Propagation and Fatigue Life Analysis of a Porous LY12 Aluminum Alloy Plate

by Cheng Lv, Kejie Wang, Xiang Zhao and Fenghui Wang

Materials 2024, 17(1), 192; https://doi.org/10.3390/ma17010192 - 29 Dec 2023

Cited by 2 | Viewed by 910

Abstract

Rivets are usually used to connect the skin of an aircraft with joints such as frames and stringers, so the skin of the connection part is a porous structure. During the service of the aircraft, cracks appear in some difficult-to-detect parts of the [...] Read more.

Rivets are usually used to connect the skin of an aircraft with joints such as frames and stringers, so the skin of the connection part is a porous structure. During the service of the aircraft, cracks appear in some difficult-to-detect parts of the skin porous structure, which causes great difficulties in the service life prediction and health monitoring of the aircraft. In this paper, a secondary development subroutine in PYTHON based on ABAQUS-XFEM is compiled to analyze the cracks that are difficult to monitor in the porous structure of aircraft skin joints. The program can automatically analyze the stress intensity factor of the crack tip with different lengths in the porous structure, and then the residual fatigue life can be deduced. For the sake of safety, the program adopts a more conservative algorithm. In comparison with the physical fatigue test results, the fatigue life of the simulation results is 16% smaller. This project provides a feasible simulation method for fatigue life prediction of porous structures. It lays a foundation for the subsequent establishment of digital twins for damage monitoring of aircraft porous structures. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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Review

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23 pages, 17686 KiB

Open AccessReview

An Overview on Fatigue of High-Entropy Alloys

by Junchao Hu, Xue Li, Qiuchen Zhao, Yangrui Chen, Kun Yang and Qingyuan Wang

Materials 2023, 16(24), 7552; https://doi.org/10.3390/ma16247552 - 7 Dec 2023

Cited by 2 | Viewed by 1353

Abstract

Due to their distinct physical, chemical, and mechanical features, high-entropy alloys have significantly broadened the possibilities of designing metal materials, and are anticipated to hold a crucial position in key engineering domains such as aviation and aerospace. The fatigue performance of high-entropy alloys [...] Read more.

Due to their distinct physical, chemical, and mechanical features, high-entropy alloys have significantly broadened the possibilities of designing metal materials, and are anticipated to hold a crucial position in key engineering domains such as aviation and aerospace. The fatigue performance of high-entropy alloys is a crucial aspect in assessing their applicability as a structural material with immense potential. This paper provides an overview of fatigue experiments conducted on high-entropy alloys in the past two decades, focusing on crack initiation behavior, crack propagation modes, and fatigue life prediction models. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Metals and Alloys: Numerical and Experimental Study (3rd Edition))

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