Research

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13 pages, 5732 KiB

Open AccessArticle

Proposal of Fatigue Limit Design Curves for Additively Manufactured Ti-6Al-4V in a VHCF Regime Using Specimens with Artificial Defects

by Yoshihiko Uematsu, Toshifumi Kakiuchi, Yaodong Han and Masaki Nakajima

Metals 2021, 11(6), 964; https://doi.org/10.3390/met11060964 - 15 Jun 2021

Cited by 5 | Viewed by 2252

Abstract

Cantilever-type rotating bending fatigue tests were conducted under a very high cycle fatigue regime using conventionally manufactured Ti-6Al-4V specimens having drilled artificial defects with different sizes. The relationship between fatigue limit and defect size was defined as a fatigue limit design curve considering [...] Read more.

Cantilever-type rotating bending fatigue tests were conducted under a very high cycle fatigue regime using conventionally manufactured Ti-6Al-4V specimens having drilled artificial defects with different sizes. The relationship between fatigue limit and defect size was defined as a fatigue limit design curve considering the transition from the fracture-mechanics dominating area to the fatigue-limit dominating area. A conventional Murakami’s equation was applicable as a design curve of additively manufactured Ti-6Al-4V with defects at 10⁷ cycles. However, conventional equation gave un-conservative predictions for the fatigue limit at 10⁸ cycles. Therefore, two kinds of modified Murakami’s equation were proposed as fatigue limit design curves for the very high cycle fatigue regime. Simple parallel shift of Murakami’s equation gave a conservative fatigue limit, whilst better result was obtained by changing the slope of Murakami’s equation. The proposed design curve was valid for the defect sizes ranging from 10 to 500 μm. Full article

(This article belongs to the Special Issue Microstructure, Deformation, and Fatigue Behavior in Metals)

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13 pages, 16301 KiB

Open AccessArticle

Remanufacturing the AA5052 GTAW Welds Using Friction Stir Processing

by Ghasem Azimi Roeen, Sajjad Ghatei Yousefi, Rahmatollah Emadi, Mohsen Shooshtari and Saeid Lotfian

Metals 2021, 11(5), 749; https://doi.org/10.3390/met11050749 - 01 May 2021

Cited by 11 | Viewed by 2007

Abstract

Progress in sustainable manufacturing is a crucial element to minimise negative environmental impacts. The conventional fusion weld process used to join aluminium alloys resulted in coarse grain structure, inevitable defects, and severe joint softening. Friction stir processing (FSP) has the potential to modify [...] Read more.

Progress in sustainable manufacturing is a crucial element to minimise negative environmental impacts. The conventional fusion weld process used to join aluminium alloys resulted in coarse grain structure, inevitable defects, and severe joint softening. Friction stir processing (FSP) has the potential to modify the microstructure of materials in joint structure and improve the mechanical properties. In this investigation, the effect of friction stir post–processing was evaluated to study the microstructural characteristics and mechanical properties of GTAW (gas tungsten arc welding) welds in the aluminium 5052 alloy. During FSP, the grains’ dendritic microstructure was destroyed, and the dynamic recrystallisation resulted in a very fine and equiaxed grains structure in the fusion zone. The hardness of the friction-stir-processed welds significantly improved because of microstructure grain refinement. The processed joint demonstrated higher ultimate tensile and yield strength (~275 MPa and 221 MPa, respectively) and superior elongation (31.1%) compared to the unprocessed weld; at the same time, the mechanical strength (yield and ultimate tensile) is similar to that of the base metal. Full article

(This article belongs to the Special Issue Microstructure, Deformation, and Fatigue Behavior in Metals)

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14 pages, 3022 KiB

Open AccessArticle

Experimental and Numerical Analysis of Fatigue Life of Aluminum Al 2024-T351 at Elevated Temperature

by Shahan Mazlan, Noorfaizal Yidris, Seyed Saeid Rahimian Koloor and Michal Petrů

Metals 2020, 10(12), 1581; https://doi.org/10.3390/met10121581 - 26 Nov 2020

Cited by 16 | Viewed by 3281

Abstract

This paper presents the prediction of the fatigue life of aluminum Al 2024-T351 at room and elevated temperatures under uniaxial loading using finite element simulation. Structural parts such as fuselage, wings, aircraft turbines and heat exchangers are required to work safely at this [...] Read more.

This paper presents the prediction of the fatigue life of aluminum Al 2024-T351 at room and elevated temperatures under uniaxial loading using finite element simulation. Structural parts such as fuselage, wings, aircraft turbines and heat exchangers are required to work safely at this working condition even with decreasing fatigue strength and other properties. The monotonic tensile and cyclic tests at 100 °C and 200 °C were conducted using MTS 810 servo hydraulic equipped with MTS 653 high temperature furnace at a frequency of 10 Hz and load ratio of 0.1. There was an 8% increase in the yield strength and a 2.32 MPa difference in the ultimate strength at 100 °C. However, the yield strength had a 1.61 MPa difference and 25% decrease in the ultimate strength at 200 °C compared to the room temperature. The mechanical and micro-structural behavior at elevated temperatures caused an increase in the crack initiation and crack propagation which reduced the total fatigue life. The yield strength, ultimate strength, alternating stress, mean stress and fatigue life were taken as the input in finite element commercial software, ANSYS. Comparison of results between experimental and finite element methods showed a good agreement. Hence, the suggested method using the numerical software can be used for predicting the fatigue life at elevated temperature. Full article

(This article belongs to the Special Issue Microstructure, Deformation, and Fatigue Behavior in Metals)

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14 pages, 7510 KiB

Open AccessArticle

Experimental Characterization of Tool Wear Morphology and Cutting Force Profile in Dry and Wet Turning of Titanium Metal Matrix Composites (Ti-MMCs)

by Masoomeh Safavi, Marek Balazinski, Hedayeh Mehmanparast and Seyed Ali Niknam

Metals 2020, 10(11), 1459; https://doi.org/10.3390/met10111459 - 31 Oct 2020

Cited by 5 | Viewed by 1958

Abstract

Metal-matrix composites (MMCs) are made of non-metallic reinforcements in metal matrixes, which have excellent hardness, corrosion, and wear resistance. They are also lightweight and may pose a higher strength-to-weight ratio as compared to commercial titanium alloys. One of the MMCs with remarkable mechanical [...] Read more.

Metal-matrix composites (MMCs) are made of non-metallic reinforcements in metal matrixes, which have excellent hardness, corrosion, and wear resistance. They are also lightweight and may pose a higher strength-to-weight ratio as compared to commercial titanium alloys. One of the MMCs with remarkable mechanical properties are titanium metal matrix composites (Ti-MMCs), which are considered a replacement for super-alloys in many industrial products and industries. Limited machining and machinability studies of Ti-MMCs were reported under different cutting and lubrication conditions. Tool wear morphology and life are among the main machinability attributes with limited attention. Therefore, this study presents the effects of cutting and lubrication conditions on wear morphology in carbide inserts when turning Ti-MMCs. To that end, maximum flank wear (VB) and cutting forces were recorded, and the wear morphologies within the initial period of the cut, as well as the worn condition, were studied under dry and wet conditions. Experimental results denoted that despite the lubrication mode used, abrasion, diffusion, and adhesion mechanisms were the main wear modes observed. Moreover, built-up layer (BUL) and built-up edge (BUE) were the main phenomena observed that increase the tendency of adhesion at higher cutting times. Full article

(This article belongs to the Special Issue Microstructure, Deformation, and Fatigue Behavior in Metals)

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19 pages, 9318 KiB

Open AccessArticle

Effect of Strain Rate on the Deformation Behaviour of A356-T7 Cast Aluminium Alloys at Elevated Temperatures

by Elanghovan Natesan, Johan Ahlström, Swathi K. Manchili, Stefan Eriksson and Christer Persson

Metals 2020, 10(9), 1239; https://doi.org/10.3390/met10091239 - 15 Sep 2020

Cited by 5 | Viewed by 2641

Abstract

Internal combustion engine downsizing and powertrain electrification trends in recent years have led to higher thermal loads on the cylinder head materials with an increased number of engine start–stop thermal load cycles. This requires designing cylinder heads that are resilient against thermomechanical fatigue [...] Read more.

Internal combustion engine downsizing and powertrain electrification trends in recent years have led to higher thermal loads on the cylinder head materials with an increased number of engine start–stop thermal load cycles. This requires designing cylinder heads that are resilient against thermomechanical fatigue damage. To reduce the developmental costs, reliable numerical models for use in computer-aided design approaches are required. Thus, a comprehensive understanding of the material deformation behaviour under loads mimicking in-service conditions is desired to make better engineering decisions. This study examines the effect of strain rate on the cyclic deformation behaviour of the A356-T7 + 0.5% Cu aluminium alloy commonly used in modern internal combustion engine cylinder heads. Samples extracted from the valve bridge areas of the cylinder heads are tested in strain-controlled fatigue tests. Samples are tested at strain rates of 1% s⁻¹ and 10% s⁻¹ at room temperature, 150 and 200 °C. The material exhibits increased isotropic hardening and softening rates and an increased number of cycles to failure at 10% s⁻¹. The strain rate has a dramatic influence on the mean stress development at room temperature. The role of silicon particles in the fracture mechanism is investigated using electron microscopy techniques. Full article

(This article belongs to the Special Issue Microstructure, Deformation, and Fatigue Behavior in Metals)

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14 pages, 5466 KiB

Open AccessFeature PaperArticle

Numerical Analysis of Stress Distribution in Offshore Wind Turbine M72 Bolted Connections

by Raquel Redondo and Ali Mehmanparast

Metals 2020, 10(5), 689; https://doi.org/10.3390/met10050689 - 24 May 2020

Cited by 10 | Viewed by 5163

Abstract

The use of bolted joints to connect the transition piece and monopile is nowadays widely applied in the offshore wind industry. Traditionally, grouted connections were used in the early generation of offshore wind turbines, but the experienced failures in such connections led to [...] Read more.

The use of bolted joints to connect the transition piece and monopile is nowadays widely applied in the offshore wind industry. Traditionally, grouted connections were used in the early generation of offshore wind turbines, but the experienced failures in such connections led to an increased tendency towards bolted flange connections to join the transition piece and monopile in the new generation of offshore wind turbines. The bolts used for this purpose have high strength and huge sizes, and are subjected to a preload that is applied during the tightening process. The present study is focused on the analysis of preload effects on stress distribution in M72 bolted connections by considering different friction coefficients between the bolt and nut threads. The bolt is considered to be made of grade 10.9 steel, whereas the nut is assumed to be made of grade 8.8 steel, which is a softer material. Using the finite element commercial software package Abaqus, numerical models were developed and analysed to establish trends for stress distribution and plastic strains during the bolt tightening process, and to quantify stress concentration factors in individual engaged threads. Full article

(This article belongs to the Special Issue Microstructure, Deformation, and Fatigue Behavior in Metals)

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Review

Jump to: Research

37 pages, 2174 KiB

Open AccessReview

A Systematic Review of Structural Reliability Methods for Deformation and Fatigue Analysis of Offshore Jacket Structures

by Abdulhakim Adeoye Shittu, Athanasios Kolios and Ali Mehmanparast

Metals 2021, 11(1), 50; https://doi.org/10.3390/met11010050 - 28 Dec 2020

Cited by 30 | Viewed by 3927

Abstract

This paper presents the state of the art in Structural Reliability Analysis (SRA) methods with a view of identifying key applications of each method and its proposed variations, qualifying characteristics, advantages, and limitations. Due to the increasing complexity and scale of modern offshore [...] Read more.

This paper presents the state of the art in Structural Reliability Analysis (SRA) methods with a view of identifying key applications of each method and its proposed variations, qualifying characteristics, advantages, and limitations. Due to the increasing complexity and scale of modern offshore jacket structures, it becomes increasingly necessary to propose an accurate and efficient approach for the assessment of uncertainties in their material properties, geometric dimensions, and operating environments. SRA, as a form of uncertainty analysis, has been demonstrated to be a useful tool in the design of structures because it can directly quantify how uncertainty about input parameters can affect structural performance. Herein, attention was focused specifically on the probabilistic fracture mechanics approach because this accounts accurately for fatigue reliability mostly encountered as being dominant in the design of such structures. The well-established analytical/approximate methods such as the First- and Second-Order Reliability Methods (FORM/SORM) are widely used as they offer a good balance between accuracy and efficiency for realistic problems. They are, however, inaccurate in cases of highly non-linear systems. As a result, they have been modified using methods such as conjugate search direction approach, saddle point approximation, subset simulation, evidence theory, etc. in order to improve accuracy. Initially, direct simulations methods such as the Monte Carlo Simulation Method (MCS) with its various variance reduction techniques such as the Importance Sampling (IS), Latin Hypercube Sampling (LHS), etc. are ideal for structures having non-linear limit states but perform poorly for problems that calculate very low probabilities of failure. Overall, each method has its own merits and limitation, with FORM/SORM being the most commonly used, but recently, simulation methods have increasingly been used due to continuous advances in computation powers. Other relevant methods include the Response Surface Methods (RSM) and the Surrogate Models/Meta-models (SM/MM), which are advanced approximation methods and are ideal for structures with implicit limit state functions and high-reliability indices. Combinations of advanced approximation methods and reliability analysis methods are also found in literature as they can be suitable for complex, highly non-linear problems. Full article

(This article belongs to the Special Issue Microstructure, Deformation, and Fatigue Behavior in Metals)

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19 pages, 2748 KiB

Open AccessReview

A Review of Challenges and Opportunities Associated with Bolted Flange Connections in the Offshore Wind Industry

by Ali Mehmanparast, Saeid Lotfian and Sukumara Pillai Vipin

Metals 2020, 10(6), 732; https://doi.org/10.3390/met10060732 - 01 Jun 2020

Cited by 25 | Viewed by 7130

Abstract

The use of bolted flange connections in the offshore wind industry has steeply risen in the last few years. This trend is because of failings observed in other modes of joints such as grouted joints, coupled with enormous economic losses associated with such [...] Read more.

The use of bolted flange connections in the offshore wind industry has steeply risen in the last few years. This trend is because of failings observed in other modes of joints such as grouted joints, coupled with enormous economic losses associated with such failures. As many aspects of bolted flange connections for the offshore wind industry are yet to be understood in full, the current study undertakes a comprehensive review of the lessons learned about bolted connections from a range of industries such as nuclear, aerospace, and onshore wind for application in offshore wind industry. Subsequently, the collected information could be used to effectively address and investigate ways to improve bolted flange connections in the offshore wind industry. As monopiles constitute an overwhelming majority of foundation types used in the current offshore wind market, this work focusses on large diameter flanges in the primary load path of a wind turbine foundation, such as those typically found at the base of turbine towers, or at monopile to transition piece connections. Finally, a summary of issues associated with flanges as well as bolted connections is provided, and insights are recommended on the direction to be followed to address these concerns. Full article

(This article belongs to the Special Issue Microstructure, Deformation, and Fatigue Behavior in Metals)

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