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

metals

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

Shahan Mazlan 1 , Noorfaizal Yidris 1,* , Seyed Saeid Rahimian Koloor 1,2 and Michal Petr ˚u 2 1 Department of Aerospace Engineering, Universiti Putra Malaysia, Serdang 43400 UPM, Selangor, Malaysia; [email protected] (S.M.); [email protected] (S.S.R.K.) 2 Institute for Nanomaterials, Advanced Technologies and Innovation (CXI), Technical University of Liberec (TUL), Studentska 2, 461 17 Liberec, Czech Republic; [email protected] * Correspondence: [email protected]; Tel.: +603-9769-4413

Received: 31 October 2020; Accepted: 20 November 2020; Published: 26 November 2020

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 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.

Keywords: elevated temperature; aluminum Al 2024-T3; fatigue life; ANSYS Workbench

1. Introduction Aluminum alloy is one of the leading materials in aircraft, automotive and heavy industries due to its lightweight, high strength, good electrical conductivity, high elastic modulus and thermal resistance properties [1,2]. All these properties have an impact on the budgeting in terms of cost, performance and production. Furthermore, the designed components must meet the anticipated requirement and factor of safety of the parts for various working conditions. The study of fatigue is important because the components can experience catastrophic failure due to the condition of loading and unloading after a certain amount of time [3]. The fatigue behavior is quite important in order to estimate changes in the properties and cumulative damage of the material related to the life cycle [4,5]. Several coeﬃcients such as size, shape, surface ﬁnish and fatigue strength are important to determine the characteristics of the structural components. These characteristics are used in plotting the stress-life curve or strain-life curve [6]. In addition, the collection of data from experimental tests [7], and analytical or numerical models [8] is the common practice to determine the fatigue properties. A standard machine testing for axial loading can have frequency of up to 20 Hz and the commonly applied frequency is 10 Hz [9]. A study on the damage accumulation proposed an approach that takes the amplitude from below the fatigue limit [10]. Moreover, a fatigue prediction without material constant is also possible [11]

Metals 2020, 10, 1581; doi:10.3390/met10121581 www.mdpi.com/journal/metals Metals 2020, 10, 1581 2 of 14 and the calculation method for variable types of loading [12] with a combination of high and low cycle curves [13]. The effect of the mean stress in the surface crack growth [14] and multiple types of loading [15] related to fatigue prediction have also been studied. There are several standards and codes [16–18] to follow in order to ensure the reliability of the product under fatigue testing evaluation. Several studies on low cycle fatigue (LCF < 104) and high cycle fatigue (HCF < 107)[19–23] were conducted on aluminum alloy. In addition, fatigue life that is more than 107 is considered as a very high cycle fatigue (VHCF). The temperature during cruising speed at Mach 2.2 can reach up to 120 ◦C and 240 ◦C at most for frame generators [24]. Furthermore, some working conditions will require the components such as aircraft turbine, heat exchanger and steam turbine to be able to run under elevated temperatures [25]. The definition of elevated temperature is the temperature at which material can operate safely despite decreasing in strength and other properties [26]. Therefore, the low cycle fatigue (LCF) testing is important for designers to gain information and concern for the components that are working under this condition. Moreover, for aluminum alloy, as the temperature increases, the fatigue life and strength decreases under constant loading [27]. The strain deformation, crack growth and crack initiation are also influenced by an increase in temperature [28]. Numerous studies on damage accumulation [29–31] have been able to predict fatigue at elevated temperatures, but they are time consuming and require expensive setup and equipment. The unpolished surfaces or scratches contribute to faster crack initiation that starts from micro to macro scale [32]. Moreover, the crack initiation process is faster at elevated temperatures continued by rapid crack propagation rate than at room temperature [33]. The approach of using numerical software to solve problems of multiphysics solutions related to thermal, structural or fluid has been widely accomplished by other researchers. The advantage of using numerical software is that the strengths and weaknesses of the model are known before the final products manufactured. The commonly used numerical software programs for predicting fatigue life are ABAQUS, MSC NASTRAN, SolidWorks and ANSYS Workbench. Several studies were reported [34–38] predicting the fatigue life theoretically or by comparing with experimental results. ANSYS was used [39,40] in predicting the stress concentration areas. However, the design of the 3D model was by different computer aided design (CAD) software before being imported to the desired numerical software to run the fatigue analysis. This is due to experience in accustomed CAD software that reduces the time taken to design. This study presented the prediction of fatigue life of aluminum Al 2024-T351 at elevated temperatures of 100 ◦C and 200 ◦C under uniaxial loading using ANSYS Workbench. To the author’s knowledge, there is still no study conducted using this numerical software to predict the fatigue life at elevated temperatures. Several numerical software programs can predict fatigue life at room temperature. The author tried to implement the same procedure using the test data from the elevated temperature to the numerical software. The latest literature [34] showed the effectiveness of fatigue life prediction using ANSYS Workbench. The numerical software is user friendly that enables the author to complete the study. The fatigue life prediction of components that operate under elevated temperature can be conducted in the future using this study as a reference. The monotonic tensile and cyclic tests with different percentages of loadings were conducted to obtain the yield strength, ultimate strength, elastic modulus and life cycle as input to the numerical software. The results were also compared with a cyclic test at room temperature. It was expected that the results between experimental and numerical simulation be in good agreement to display the efficiency of the software in predicting fatigue life at elevated temperature.

2. Methodology

2.1. Experimental Procedures The material aluminum Al 2024-T351 was selected for the test due to good fatigue strength, corrosion resistance and lightweight properties. This material is widely used in transportation such as Metals 2020, 10, 1581x FOR PEER REVIEW 3 of 14 Metals 2020, 10, x FOR PEER REVIEW 3 of 14 as in the automotive and aerospace field. The lightweight properties require less force to move or fly asain vehicle in the the automotive automotive that leads and to and higher aerospace aerospace fuel field.efficiency field. The The lightweightand lightw lowereight manufacturing properties properties requirerequire cost. lessThisless forceforce strong to and move flexible or fly fly amaterial vehicle isthat ideal leads for to the higher design fuel of eefficiencyframes,fficiency aircra and ft lower fuselage, manufacturing wings and cost.other This component strong and structures. flexible flexible materialThe specimen is ideal was for cut the from design an aluminumof frames, aircra aircraftplate ftusing fuselage, water wings wingsjet technology and and other other with component component a dimension structures. structures. of 200 Themm specimen specimen× 20 mm ×was was3 mm cut cut renderingfrom from an an aluminum aluminumto ASTM plateE8M plate standard.using using water water The jet tensile jettechnology technology tests werewith with aconducted dimension a dimension at of room 200 of 200 mm 20 mm 3 mm rendering to ASTM E8M standard. The tensile tests were conducted at room mmand elevated× 20× mm temperatures—100× 3 mm× rendering to°C ASTMand 200 E8M °C, correspondingly.standard. The tensile tests were conducted at room and elevated A grip pressure temperatures—100 of 4.83 MPa ◦°C Cwas and applied 200 °C,◦C, to correspondingly. the test specimens at both ends. The alignment of grip Awas grip reset pressurepressure before ofof running 4.83 4.83 MPa MPa the was was test. applied applied The monoto to to the the testnic test specimens tensile specimens tests at bothwereat both ends. conducted ends. The The alignment at alignment a crosshead of grip of gripwasspeed resetwas of reset before1 mm/min before running usingrunning the test.100 the kN The test. MTS monotonic The 810 monoto servo tensilenic hydraulic teststensile were tests (MTS conducted were Systems conducted at a Corporation, crosshead at a crosshead speed Eden of speed1Prairie, mm/ minof MN, 1using mm/min USA) 100 at kN usingroom MTS 810100temperature servokN MTS hydraulic conditions,810 (MTSservo Systems hydraulicas shown Corporation, (MTSin Figure Systems Eden 1. For Prairie,Corporation, tests MN,at elevated USA) Eden at Prairie,temperature,room temperature MN, USA)the MTS conditions, at room810 was temperature as shownequipped in Figure conditions,with 1MTS. For tests653as shownhigh at elevated temperature in Figure temperature, 1. furnace For thetests (MTS MTS at elevated 810Systems was temperature,Corporation,equipped with theEden MTS MTS 653Prairie, 810 high wasMN, temperature equipped USA) as furnace with in FigureMTS (MTS 653 Systems2 withhigh Corporation,temperaturea capability Edenfurnaceto reach Prairie, (MTS a maximum MN, Systems USA) Corporation,temperatureas in Figure2 withofEden 1000 a capability Prairie,°C. The MN,entire to reach USA) gauge a maximum as area in ofFigure the temperature specimen 2 with of wasa 1000 capability covered◦C. The withto entire reach MTS gauge 653.a maximum area The of tests the temperaturewerespecimen performed was of covered 1000 to acquire °C. with The the MTSentire mechanical 653. gauge The area testsproperties of were the specimen performed such as yield was to acquire strengthcovered the andwith mechanical ultimate MTS 653. strength. properties The tests weresuch asperformed yield strength to acquire and ultimate the mechanical strength. properties such as yield strength and ultimate strength.

Figure 1. Monotonic tensile/cyclic test at room temperature using MTS 810 testing Figure 1.1.Monotonic Monotonic tensile tensile/cyclic/cyclic test test atmachine. room at room temperature temperature using MTSusing 810 MTS testing 810 machine. testing machine.

Figure 2. Monotonic/cyclicMonotonic/cyclic test at elevated temper temperatureature using MTS 810 equipped with MTS 653 high Figuretemperature 2. Monotonic/cyclic furnace. test at elevated temperature using MTS 810 equipped with MTS 653 high temperature furnace. The temperature was measured using digital thermometer TM902C (Reland Sung, Fujian, China).The Four temperature thermocouples, was measured T1, T2, T3 using and T4 digital were placedthermometer in the highTM902C temperature (Reland furnace.Sung, Fujian, Three China). Four thermocouples, T1, T2, T3 and T4 were placed in the high temperature furnace. Three Metals 2020, 10, 1581 4 of 14

Metals 2020, 10, x FOR PEER REVIEW 4 of 14 The temperature was measured using digital thermometer TM902C (Reland Sung, Fujian, China). Fourthermocouples, thermocouples, T1, T1, T2 T2, and T3 T3 and were T4 were attached placed to in th thee specimen high temperature and T4 furnace.hanging Threein the thermocouples, middle area, as T1,shown T2 and in T3 Figure were 3. attached to the specimen and T4 hanging in the middle area, as shown in Figure3.

FigureFigure 3. 3.Thermocouples Thermocouples placed placed in in the the high high temperature temperature furnace furnace at at di ﬀdifferenterent locations. locations.

TheThe cyclic cyclic tests tests were were performed performed according according to to ASTM ASTM E466 E466 standard standard at at a a frequency frequency of of 10 10 Hz, Hz, sinusoidalsinusoidal waveform waveform and and load load ratio ratio of 0.1. of 0.1. Each Each test wastest loadedwas loaded with awith specific a specific mean mean load and load for and tests for attests room at temperature, room temperature, the test started the test at thestarted maximum at the loadmaximum value ofload 90% value of the of yield 90% and of decrementedthe yield and bydecremented 5% for the next by tests5% for until the 70% next of tests the yield until strength. 70% of the Similarly, yield strength. the maximum Similarly, load the for 100maximum◦C started load fromfor 90%100 °C to 75%started of thefrom yield 90% strength; to 75% theof the maximum yield strength; load decreased the maximum by 5% inload each decreased test. For by tests 5% at in 200each◦C, test. the maximumFor tests at load 200 started °C, the from maximum 90% to 70%load ofstarted the yield from strength; 90% to the70% maximum of the yield load strength; decreased the bymaximum 10% in each load case. decreased The results by were10% in plotted each incase. the The form results of stress-life were plotted curves toin estimatethe form the of cyclesstress-life to failurecurves after to estimate definite loading.the cycles The to failure loads applied after defi werenite shownloading. in The Table loads1. applied were shown in Table 1. Table 1. The loads applied at a different percentage of the yield strength. Table 1. The loads applied at a different percentage of the yield strength. Condition Yield Strength (%) Mean Load (kN) Amplitude (kN) Condition Yield Strength90 (%) Mean 6.48 Load (kN) Amplitude 5.31 (kN) 8590 6.136.48 5.015.31 Room 8085 5.776.13 4.725.01 75 5.41 4.42 Room 7080 5.055.77 4.134.72 75 5.41 4.42 90 6.13 4.99 70 5.05 4.13 85 5.76 4.72 100 C ◦ 8090 5.436.13 4.444.99 7585 5.095.76 4.164.72 100 °C 9080 6.025.43 4.924.44 200 ◦C 8075 5.355.09 4.384.16 7090 4.686.02 3.834.92 200 °C 80 5.35 4.38 The cyclic test can only be conducted70 after certain inputs4.68 such as mean3.83 load, amplitude and frequency are known. The load ratio, Lr can be calculated by the given Equation (1) [41]. The cyclic test can only be conducted after certain inputs such as mean load, amplitude and frequency are known. The load ratio, Lr can be calculatedLmin by the given Equation (1) [41]. Lr = (1) Lmax L L = min (1) The range of load, LR can be calculated byr the difference between maximum load, Lmax and Lmax minimum load, Lmin in the following Equation (2). The range of load, LR can be calculated by the difference between maximum load, Lmax and minimum load, Lmin in the following EquationLR = L max(2). Lmin (2) − LR = Lmax − Lmin (2)

The amplitude load, La is half of range of load, LR is given by Equation (3). Metals 2020, 10, 1581 5 of 14 Metals 2020, 10, x FOR PEER REVIEW 5 of 14 Metals 2020, 10, x FOR PEER REVIEW 5 of 14

The amplitude load, La is half of range of load,LLL−R is given by Equation (3). L =LLmax− min (3) L a= max2 min (3) a Lmax Lmin La = 2− (3) Moreover, the mean load, Lm is important as higher2 load means the lower fatigue life of the Moreover, the mean load, Lm is important as higher load means the lower fatigue life of the tested components. The Equation (4) can be used to calculate the mean load. testedMoreover, components. the meanThe Equation load, Lm (4)is important can be used as higherto calculate load meansthe mean the load. lower fatigue life of the tested components. The Equation (4) can be used to calculateLL+ the mean load. L =LLmax+ min (4) L m = max2 min (4) m L + L L = max2 min (4) m 2 2.2. Numerical Procedures 2.2.2.2. Numerical Numerical Procedures Procedures The use of numerical software is to determine an approximate solution to the specific problem. The use of numerical software is to determine an approximate solution to the specific problem. WhenThe the use experimental of numerical results software are isavailable, to determine any annumerical approximate results solution can be to verified. the speciﬁc The problem.selected When the experimental results are available, any numerical results can be verified. The selected Whencomputer the aided experimental design (CAD) results software are available, to design any numericalthe 3D model results of the can specimen be veriﬁed. was The SolidWorks selected computer aided design (CAD) software to design the 3D model of the specimen was SolidWorks computer2012. The dimension aided design was (CAD) set to software200 mm toin designlength, the20 mm 3D modelwidth ofand the 3 mm specimen thickness was as SolidWorks shown in 2012. The dimension was set to 200 mm in length, 20 mm width and 3 mm thickness as shown in 2012.Figure The 4. A dimension top plane waswas setselected to 200 for mm the in sketch length,ing 20 of mm the widthmodel. and The 3 thickness mm thickness was generated as shown by in Figure 4. A top plane was selected for the sketching of the model. The thickness was generated by Figureusing a4 .boss-extrude A top plane feature was selected from the for thesketch. sketching The complete of the model. 3D model The is thickness as shown was in generatedFigure 5. The by using a boss-extrude feature from the sketch. The complete 3D model is as shown in Figure 5. The using3D model a boss-extrude was saved feature as IGES from format the sketch. for the The ea completese of importing 3D model from is as shownANSYS in Workbench Figure5. The 16.1 3D 3D model was saved as IGES format for the ease of importing from ANSYS Workbench 16.1 model(ANSYS was Inc., saved Canonsburg, as IGES format PA, USA). for the ease of importing from ANSYS Workbench 16.1 (ANSYS Inc., (ANSYSCanonsburg, Inc., Canonsburg, PA, USA). PA, USA).

Figure 4. Dimension of the flat ﬂat specimen (mm). Figure 4. Dimension of the flat specimen (mm).

Figure 5. TheThe 3D 3D model model by boss-extrude feature generated in SolidWorks. Figure 5. The 3D model by boss-extrude feature generated in SolidWorks. The mechanical properties such as yield strength, ultimate strength, mean stress, alternating The mechanical properties such as yield strength, ultimate strength, mean stress, alternating stress and fatigue life acquired from experimental tests were assigned in the engineering data of the stress and fatigue life acquired from experimental tests were assigned in the engineering data of the Metals 2020, 10, 1581 6 of 14

Metals 2020, 10, x FOR PEER REVIEW 6 of 14 The mechanical properties such as yield strength, ultimate strength, mean stress, alternating stress software.and Moreover, fatigue life acquireda fine frommesh experimental with SOLID tests were 187 assigned 10-noded in the engineeringelement was data ofselected the software. due to its suitabilityMoreover, in covering a fine meshthe uneven with SOLID surface 187 10-noded areas in element order was to selectedpredict due results to its suitabilitycloser to inthe covering experiments. The meshthe model uneven can surface be observed areas in order in toFigure predict 6a results with closer the togenerated the experiments. number The of mesh nodes model of can6181 be and the observed in Figure6a with the generated number of nodes of 6181 and the number of elements of number 1008.of elements The boundary of 1008. conditions The boundary shown in Figure conditio6b werens shown applied similarin Figure to the 6b experimental were applied setup. similar to the experimentalThe fixed support setup. A indicatesThe fixed the specimensupport endA indicates was clamped the with specimen all degrees end of freedom was fixedclamped and at with all degrees ofpoint freedom B the load fixed was and applied. at point In addition, B the stress-lifeload was was applied. selected In in addition, the fatigue stress-life tool option withwas theselected in the fatigueload tool ratio option set to 0.1. with the load ratio set to 0.1.

Figure 6. (a) Meshed model with SOLID 187 elements; (b) Boundary condition applied to the model. Figure 6. (a) Meshed model with SOLID 187 elements; (b) Boundary condition applied to the model. 3. Results and Discussion

3. Results3.1. and Fatigue Discussion Life of Aluminium Al 2024-T351 The working temperature changes the properties of the material, especially in terms of its 3.1. Fatigue Life of Aluminium Al 2024-T351 strength [42]. The yield strength at 100 ◦C had a decrease of 6%, and 7% at 200 ◦C when compared Theto working the controlled temperature room temperature. changes On the the properties other hand, theof averagethe material, ultimate especially strength had in a smallterms of its strength decrease[42]. The of 3.75%yield atstrength 100 ◦C and at 25%100 at°C 200 had◦C a when decrease compared of 6%, to the and controlled 7% at room200 °C temperature. when compared The data are shown in Table2. The ﬂat specimen under tensile loading experience shear rupture upon to the controlledfailure [43]. room The grains temperature. are aﬀected byOn the the level other of loading, hand, type the and average temperature. ultimate At room strength temperature, had a small decreasethe of visibilities3.75% at of100 the °C grains and were 25% not at clear 200 and°C therewhen was compared an increase to in the the lengthcontrolled as well. room In addition, temperature. The datathe are grain shown growth in atTable high temperature2. The flat caused specimen it to be under compressed tensile and loading elongated experience due to tensile shear load rupture upon failureapplied. [43]. The The length grains increases, are affected but the width by the decreases level [of44 ].loading, During teststype at and high temperature. temperature and At room temperature,loading, the the visibilities precipitates of from the the grains coarse were grain maynot notclear visibly and or there dissolve was completely. an increase in the length as well. In addition, the grain growth at high temperature caused it to be compressed and elongated due to tensile load applied. The length increases, but the width decreases [44]. During tests at high temperature and loading, the precipitates from the coarse grain may not visibly or dissolve completely.

Table 2. The results obtained from the monotonic tensile tests.

Condition Yield Strength (MPa) Ultimate Strength (MPa) Room 347.58 464.19 100 °C 326.12 446.78 200 °C 322.66 349.80 Metals 2020, 10, 1581 7 of 14

Table 2. The results obtained from the monotonic tensile tests.

Condition Yield Strength (MPa) Ultimate Strength (MPa) Room 347.58 464.19 Metals 2020, 10, x FOR PEER REVIEW 7 of 14 100 ◦C 326.12 446.78 200 C 322.66 349.80 The stress-life ◦curve for the aluminum at room and elevated temperatures is presented in Figure 7. As anticipated the number of cycles increases when the stress applied deceases. The averageThe fatigue stress-life life curve at 90% for was the aluminum45,343 cycles. at room As th ande load elevated decreased, temperatures the fatigue is presented life increased in Figure by7. 16%As anticipated to 85%. Moreover, the number the fatigue of cycles life increases at 80% whenwas 88,215 the stress cycles. applied There deceases. was about The a 49% average increase fatigue in thelife fatigue at 90% life was when 45,343 the cycles.difference As between the load the decreased, loading was the only fatigue 10%. life When increased the load by 16%was further to 85%. decreasedMoreover, by the 10%, fatigue the lifedifference at 80% increased was 88,215 to cycles.82% showing Therewas an average about a of 49% 252,827 increase cycles in theat 70% fatigue of thelife yield when strength. the difference The fatigue between life the at loading90% and was at 10 only0 °C 10%. was When21,679 the cycles. load There was further was an decreased increase of by 65%10%, when the difference the load increaseddecreased to to 82% 85% showing of the yield an average strength. of 252,827However, cycles there at 70%was ofonly the a yield 5% increase strength. inThe the fatigue fatigue life life at as 90% theand load at reduced 100 ◦C wasto 80%. 21,679 The cycles. fatigue There life at was 75% an increased increase ofby 65% 33% when compared the load to 80%decreased displaying to 85% an of average the yield of strength.96,688 cycles. However, there was only a 5% increase in the fatigue life as the load reduced to 80%. The fatigue life at 75% increased by 33% compared to 80% displaying an average of 96,688 cycles.

FigureFigure 7. 7. TheThe S-N S-N curve curve of of aluminum aluminum at at r roomoom and and elevated elevated temperatures. temperatures.

At 200 C, the fatigue life was 14,272 cycles. When the load was reduced by 10% the fatigue At 200 °C,◦ the fatigue life was 14,272 cycles. When the load was reduced by 10% the fatigue life life increased by 63% displaying 38,427 cycles. Further decrease in the percentage of loading by 10% increased by 63% displaying 38,427 cycles. Further decrease in the percentage of loading by 10% increased the fatigue life by 60%. The fatigue life at 70% has an increase of 85% compared to 90% of the increased the fatigue life by 60%. The fatigue life at 70% has an increase of 85% compared to 90% of yield strength. It can be observed that at 90% of the yield strength, the fatigue life was reduced by half the yield strength. It can be observed that at 90% of the yield strength, the fatigue life was reduced at 100 C and 69% at 200 C compared to the room temperature. Additionally, at 80%, the fatigue life by half◦ at 100 °C and 69%◦ at 200 °C compared to the room temperature. Additionally, at 80%, the difference was 27% and 56% at 100 C and 200 C, respectively. The difference at 70% for 200 C was fatigue life difference was 27% and 56%◦ at 100 °C◦ and 200 °C, respectively. The difference at 70%◦ for 62% and for 100 C the percentage was expected to be lower compared to the room temperature. 200 °C was 62% ◦and for 100 °C the percentage was expected to be lower compared to the room When a material is subjected to a repeated loading and unloading, formation of micro-crack temperature. arises in the stress concentration area. The surface area is the most common place that the crack When a material is subjected to a repeated loading and unloading, formation of micro-crack initiation starts [45,46]. Next, the crack propagates until reaching the critical length that causes failure arises in the stress concentration area. The surface area is the most common place that the crack of the material. The letter A represents the stable region and letter B the unstable region. The surface initiation starts [45,46]. Next, the crack propagates until reaching the critical length that causes failure of aluminum at room temperature can be observed in Figure8 with di fferent percentages of failure of the material. The letter A represents the stable region and letter B the unstable region. The loading. The visibility of the fracture areas with smooth and shiny plus uneven appearance [47] can be surface failure of aluminum at room temperature can be observed in Figure 8 with different observed as well. In addition, the size of cavities in the unstable region is larger than the stable region. percentages of loading. The visibility of the fracture areas with smooth and shiny plus uneven The bigger particle size in the cavities means shorter fatigue life. The formation of void is a sign that appearance [47] can be observed as well. In addition, the size of cavities in the unstable region is damage is experienced by the specimen and contributed by separation of grain boundaries or particle larger than the stable region. The bigger particle size in the cavities means shorter fatigue life. The formation of void is a sign that damage is experienced by the specimen and contributed by separation of grain boundaries or particle fracture [48]. Moreover, the crack growth pattern is not consistence due to different orientation of the grains. The fatigue life can also be estimated using the striation length [49]. Metals 2020, 10, 1581 8 of 14

Metals 2020, 10, x FOR PEER REVIEW 8 of 14 fracture [48]. Moreover, the crack growth pattern is not consistence due to diﬀerent orientation of the Metalsgrains. 2020, 10 The, x FOR fatigue PEER life REVIEW can also be estimated using the striation length [49]. 8 of 14

Figure 8. Surface failure of the specimens at room temperature; (a) 90%; (b) 85%; (c) 80%; (d) 75%; (e) 70%. FigureFigure 8. Surface 8. Surface failure failure of the of the specim specimensens at at room room temperature; temperature; (a(a)) 90%; 90%; (b ()b 85%;) 85%; (c) ( 80%;c) 80%; (d) 75%;(d) 75%; (e) 70%. (Thee) 70%. surface failure at 100 °C can be observed in Figure 9 ranging from 90% to 75% of the yield strength. TheThe surface visibility failure of atthe 100 stableC can crack be observed growth inregion Figure is9 rangingvery small from due 90% to to 75%catastrophic of the yield failure The surface failure at 100 °C◦ can be observed in Figure 9 ranging from 90% to 75% of the yield duringstrength. loading. The Meanwhile, visibility of in the Figure stable 10, crack surface growth failures region from is very 90% small to 70% due toof catastrophicthe yield strength failure can strength. The visibility of the stable crack growth region is very small due to catastrophic failure be seen.during The loading. stable Meanwhile, region insu Figurerfaces 10 ,are surface smaller failures compared from 90% toto 70% those of the at yield room strength temperature. can be during loading. Meanwhile, in Figure 10, surface failures from 90% to 70% of the yield strength can Consequently,seen. The stable at elevated region surfacestemperature, are smaller the elasti comparedc modulus to those and at room surface temperature. energy are Consequently, lower, causing be seen. The stable region surfaces are smaller compared to those at room temperature. fasterat crack elevated initiation temperature, and the crack elastic propagation modulus and surface[50]. The energy increased are lower, grain causing size faster causes crack initiationthe particle Consequently, at elevated temperature, the elastic modulus and surface energy are lower, causing densityand to crack decrease. propagation As a [result,50]. The the increased fatigue grainlife decreases size causes as the temperature particle density increases to decrease. [51]. Similarly, As a fasterresult, crack the initiation fatigue life and decreases crack as propagation temperature increases[50]. The [51 increased]. Similarly, grain the fracture size ofcauses particles the leads particle the fracture of particles leads to formation of voids [52]. In addition, the increase in rate of oxidation densityto formation to decrease. of voids As [a52 result,]. In addition, the fatigue the increase life decreases in rate of oxidationas temperature also contributes increases to the[51]. decrease Similarly, also contributes to the decrease in fatigue life and affects the mechanical properties as well [53]. the fracturein fatigue of lifeparticles and aﬀ leadsects the to mechanicalformation of properties voids [52]. as well In addition, [53]. Therefore, the increase the total in fatiguerate of lifeoxidation at Therefore, the total fatigue life at elevated temperature is affected by mechanical and also elevatedcontributes temperature to the decrease is aﬀected in by fatigue mechanical life and and micro-structural affects the mechanical behavior that properties contributes as to well crack [53]. micro-structural behavior that contributes to crack initiation and crack propagation [54]. The plastic Therefore,initiation the and total crack propagationfatigue life [ 54at]. Theelevated plastic crackingtemperature mechanism is affected happened by when mechanical exposed to and crackingelevated mechanism temperature. happened The plastic when zone exposed in the micro to andelevated macro temperature. cracks during loadingThe plastic leads tozone plastic in the micro-structural behavior that contributes to crack initiation and crack propagation [54]. The plastic microdeformation and macro at cracks the elevated during temperature. loading leads to plastic deformation at the elevated temperature. cracking mechanism happened when exposed to elevated temperature. The plastic zone in the micro and macro cracks during loading leads to plastic deformation at the elevated temperature.

Figure 9. Surface failure at 100 C; (a) 90%; (b) 85%; (c) 80%; (d) 75%. Figure 9. Surface failure at 100 °C;◦ (a) 90%; (b) 85%; (c) 80%; (d) 75%. Figure 9. Surface failure at 100 °C; (a) 90%; (b) 85%; (c) 80%; (d) 75%.

Figure 10. Surface failure at 200 °C; (a) 90%; (b) 80%; (c) 70%.

3.2. Numerical Results Figure 10. Surface failure at 200 °C; (a) 90%; (b) 80%; (c) 70%.

3.2. Numerical Results Metals 2020, 10, x FOR PEER REVIEW 8 of 14

Figure 8. Surface failure of the specimens at room temperature; (a) 90%; (b) 85%; (c) 80%; (d) 75%; (e) 70%.

The surface failure at 100 °C can be observed in Figure 9 ranging from 90% to 75% of the yield strength. The visibility of the stable crack growth region is very small due to catastrophic failure during loading. Meanwhile, in Figure 10, surface failures from 90% to 70% of the yield strength can be seen. The stable region surfaces are smaller compared to those at room temperature. Consequently, at elevated temperature, the elastic modulus and surface energy are lower, causing faster crack initiation and crack propagation [50]. The increased grain size causes the particle density to decrease. As a result, the fatigue life decreases as temperature increases [51]. Similarly, the fracture of particles leads to formation of voids [52]. In addition, the increase in rate of oxidation also contributes to the decrease in fatigue life and affects the mechanical properties as well [53]. Therefore, the total fatigue life at elevated temperature is affected by mechanical and micro-structural behavior that contributes to crack initiation and crack propagation [54]. The plastic cracking mechanism happened when exposed to elevated temperature. The plastic zone in the micro and macro cracks during loading leads to plastic deformation at the elevated temperature.

Metals 2020, 10, 1581 9 of 14 Figure 9. Surface failure at 100 °C; (a) 90%; (b) 85%; (c) 80%; (d) 75%.

FigureFigure 10. 10. SurfaceSurface failure failure at at 200 200 °C;◦C; (aa)) 90%;90%; ( b(b)) 80%; 80%; (c )(c 70%.) 70%.

3.2. Numerical Results 3.2.Metals Numerical 2020, 10, x ResultsFOR PEER REVIEW 9 of 14 Figure 11 shows the example of numerical results from the software ANSYS. The maximum stressFigure is 11 located shows at thethe center example of the of specimen. numerical At re thissults area, from the the failure software occurs andANSYS. the fatigue The maximum life is stressthe is minimum.located at the center of the specimen. At this area, the failure occurs and the fatigue life is the minimum.

FigureFigure 11. Examples 11. Examples of numerical of numerical results results for for aluminum aluminum atatroom room temperature, temperature, from from the the percentage percentage of of the stressthe stress of the of theyield yield strength; strength; (a ()a )90%; 90%; ( (bb)) 80%; 80%; (c)) 70%.70%.

Figure 12 shows the comparison of the stress-life curve for the aluminum at room temperature. The increase in stress decreases fatigue life as expected. At 90% of the yield strength, the experimental fatigue life was 45,343 cycles and the numerical value was 47,213 cycles. There was only a small difference of about 4%. At 85%, the difference increased to 13.5%. The experimental life at 80% was 88,125 cycles and numerical life was 100,172 cycles. The difference was 14%. Moreover, the difference between experimental and numerical results decreased by 1% at 75% of the yield strength. At 70%, the difference was reduced to 9%. The highest difference between experimental and numerical results was at 80% and the lowest was at 90%.

Metals 2020, 10, 1581 10 of 14

Figure 12 shows the comparison of the stress-life curve for the aluminum at room temperature. The increase in stress decreases fatigue life as expected. At 90% of the yield strength, the experimental fatigue life was 45,343 cycles and the numerical value was 47,213 cycles. There was only a small difference of about 4%. At 85%, the difference increased to 13.5%. The experimental life at 80% was Metals88,125 2020, 10 cycles, x FOR and PEER numerical REVIEW life was 100,172 cycles. The difference was 14%. Moreover, the difference10 of 14 between experimental and numerical results decreased by 1% at 75% of the yield strength. At 70%, the difference was reduced to 9%. The highest difference between experimental and numerical results Metalswas 2020 at, 10 80%, x FOR and PEER the lowestREVIEW was at 90%. 10 of 14

Figure 12. Comparison of results between experimental and simulation at room temperature.

The stress-life in Figure 13 shows the comparison of experimental and numerical results at 100 °C. TheFigure highestFigure 12. Comparison 12.differenceComparison ofwas results of results27% between betweenat 90% experimental experimental of the yield andandsimulation simulationstrength. at at roomIn room terms temperature. temperature. of numbers, the experiment displayed 21,679 cycles and numerical 29,548 cycles. The lowest difference was at 85% The stress-life in Figure 13 shows the comparison of experimental and numerical results at 100 ◦C. The stress-life in Figure 13 shows the comparison of experimental and numerical results at 100 withThe only highest a 1% difference. difference was The 27% difference at 90% ofat the80% yield and strength. 75% were In at terms 10% of and numbers, 4%, respectively. the experiment °C. Thedisplayed highest 21,679 difference cycles and was numerical 27% 29,548at 90% cycles. of th Thee yield lowest strength. difference wasIn terms at 85% withof numbers, only a 1% the experimentdifference. displayed The diff erence21,679 at cycles 80% and and 75% numerical were at 10% 29,548 and 4%,cycles. respectively. The lowest difference was at 85% with only a 1% difference. The difference at 80% and 75% were at 10% and 4%, respectively.

FigureFigure 13. 13.ComparisonComparison of of results results between between experimentalexperimental and and simulation simulation at 100 at 100◦C. °C.

The comparison of experimental and numerical results at 200 °C is presented by the stress-life curve in FigureFigure 14. 13. The Comparison results showed of results the between fatigue expe liferimental of 14,272 and simulationcycles and at 16,620100 °C. cycles for the experimental and numerical work, respectively, at 90% of the yield strength. The difference betweenThe comparisonthe two methods of experimental was 14%. Atand 80%, numerical the difference results decreasedat 200 °C is by presented 2%. The lowestby the stress-lifedifference curvewas at in 70% Figure with 14. only The a differenceresults showed of 3%. theNeverthe fatigueless, life the of gap14,272 decreased cycles andbetween 16,620 the cycles trend forlines the at experimental100 °C and 200 and °C numericalusing ANSYS work, as therespectively, stress decrea at sed.90% Theof thedifference yield strength.of experimental The difference results is betweendue to theseveral two methodsfactors such was 14%.as scratches, At 80%, theunpolished difference surfaces decreased and by micro-structural2%. The lowest differencebehavior. wasTherefore, at 70% allwith the only results a difference show a good of 3%. trend Neverthe line comparisonless, the gap which decreased proves between a good agreement.the trend lines at 100 °C and 200 °C using ANSYS as the stress decreased. The difference of experimental results is due to several factors such as scratches, unpolished surfaces and micro-structural behavior. Therefore, all the results show a good trend line comparison which proves a good agreement.

Metals 2020, 10, 1581 11 of 14

The comparison of experimental and numerical results at 200 ◦C is presented by the stress-life curve in Figure 14. The results showed the fatigue life of 14,272 cycles and 16,620 cycles for the experimental and numerical work, respectively, at 90% of the yield strength. The difference between the two methods was 14%. At 80%, the difference decreased by 2%. The lowest difference was at 70% with only a difference of 3%. Nevertheless, the gap decreased between the trend lines at 100 ◦C and 200 ◦C using ANSYS as the stress decreased. The difference of experimental results is due to several factors such as scratches, unpolished surfaces and micro-structural behavior. Therefore, all the results Metalsshow 2020, a10 good, x FOR trend PEER line REVIEW comparison which proves a good agreement. 11 of 14

FigureFigure 14. 14.ComparisonComparison of of results results between between experimentalexperimental and and simulation simulation at 200 at 200◦C. °C. 4. Conclusions 4. Conclusions The fatigue testing of aluminum has been conducted at elevated temperatures with a frequency of 10The Hz fatigue and load testing ratio of 0.1.aluminum The influence has been of this conduc temperatureted at elevated has caused temperatures a decrease inwith fatigue a frequency life, of 10yield Hz and strength load andratio ultimate of 0.1. The strength. influence The yieldof this and temperature ultimate strength has caused decrease a decrease as the temperature in fatigue life, yieldincreases. strength Theand increaseultimate in strength. the crack The growth yield rate and and ultimate grain size strength has caused decrease the particle as the density temperature to increases.decrease. The The increase surface in failure the crack was separated growth intorate a and stable grain and unstablesize has region. caused The the stable particle region density was to decrease.smaller The when surface the load failure applied was wasseparated higher. into Factors a st suchable asand grain unstable size, particle region. density, The stable loading region and was smallertemperature when the have load influence applied in was the higher. fatigue lifeFactors of the such material. as grain The size, fatigue particle life at density, 90% of theloading yield and strength decreased by 50% when exposed to a temperature of 100 C compared to the results at room temperature have influence in the fatigue life of the material. ◦The fatigue life at 90% of the yield temperature. A further decrease in fatigue life was observed when the temperature was increased to strength decreased by 50% when exposed to a temperature of 100 °C compared to the results at room 200 ◦C. The comparison of experimental and numerical results at room temperature showed that the temperature. A further decrease in fatigue life was observed when the temperature was increased to highest difference was 14% and the lowest was 4%. The comparison at 100 ◦C showed that the highest 200 °C. The comparison of experimental and numerical results at room temperature showed that the difference was 27% and the lowest was 1%. The lowest difference at 200 ◦C was 3% and the highest highestwas difference 14%. A good was agreement 14% and between the lowest experimental was 4% and. The numerical comparison results at was 100 observed °C showed for all that the the higheststress-life difference curves. was The 27% numerical and the software, lowest ANSYSwas 1%. Workbench The lowest successfully difference proved at 200 its °C eff ectivenesswas 3% and in the highestpredicting was 14%. the fatigueA good life agreement at room and between elevated experi temperatures.mental and numerical results was observed for all the stress-life curves. The numerical software, ANSYS Workbench successfully proved its Author Contributions: Conceptualization, N.Y.; methodology,S.M.; software, N.Y.; validation, S.M.; formal analysis, effectivenessS.M.; investigation, in predicting N.Y. and the S.M.; fatigue resources, life N.Y.,at room S.S.R.K. and and elevated M.P.; data temperatures. curation, S.M.; writing—original draft preparation, S.M.; writing—review and editing, N.Y. and S.S.R.K.; visualization, S.M., S.S.R.K. and M.P.; supervision, AuthorN.Y.; Contributions: project administration, Conceptualization, N.Y., S.S.R.K. and N.Y.; M.P.; methodology, funding acquisition, S.M.; N.Y.,software, S.S.R.K. N.Y.; and M.P.validation, All authors S.M.; have formal read and agreed to the published version of the manuscript. analysis, S.M.; investigation, N.Y. and S.M.; resources, N.Y., S.S.R.K. and M.P.; data curation, S.M.; writing—originalFunding: The Ministrydraft preparation, of Higher Education S.M.; writing—review (MOHE) funded this and work editing, to Universiti N.Y., and Putra S.S. MalaysiaR.K.; visualization, (UPM) through S.M., FGRS/1/2015/TK09/UPM/02/1. This work was supported by the Ministry of Education, Youth, and Sports of the S.S.R.K.Czech and Republic M.P.; supervision, and the European N.Y.; Union project (European administrati Structuralon, and N.Y., Investment S.S.R.K. Funds and OperationalM.P.; funding Program acquisition, Research, N.Y., S.S.R.K. and M.P. All authors have read and agreed to the published version of the manuscript.

Funding: The Ministry of Higher Education (MOHE) funded this work to Universiti Putra Malaysia (UPM) through FGRS/1/2015/TK09/UPM/02/1. This work was supported by the Ministry of Education, Youth, and Sports of the Czech Republic and the European Union (European Structural and Investment Funds Operational Program Research, Development, and Education) in the framework of the project “Modular platform for autonomous chassis of specialized electric vehicles for freight and equipment transportation”, Reg. No. CZ.02.1.01/0.0/0.0/16_025/0007293, as well as financial support from internal grants in the Institute for Nanomaterials, Advanced Technologies and Innovations (CXI), Technical University of Liberec (TUL).

Conflicts of Interest: The authors declare no conflict of interest.

References

Development, and Education) in the framework of the project “Modular platform for autonomous chassis of specialized electric vehicles for freight and equipment transportation”, Reg. No. CZ.02.1.01/0.0/0.0/16_025/0007293, as well as financial support from internal grants in the Institute for Nanomaterials, Advanced Technologies and Innovations (CXI), Technical University of Liberec (TUL). Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. Heinz, A.; Haszler, A.; Keidel, C.; Moldenhauer, S.; Benedictus, R.; Miller, W. Recent development in aluminium alloys for aerospace applications. Mater. Sci. Eng. A 2000, 280, 102–107. [CrossRef] 2. Dursun, T.; Soutis, C. Recent developments in advanced aircraft aluminium alloys. Mater. Des. 2014, 56, 862–871. [CrossRef] 3. Wachowski, M.; Sniezek, L.; Szachogluchowicz, I.; Kosturek, R.; Płociński,T. Microstructure and Fatigue life of Cp-Ti/316L Bimetallic Joints Obtained by Means of Explosive Welding. Bull. Pol. Acad. Sci. Tech. Sci. 2018, 66, 925–933. 4. Badaruddin, M.; Zulhanif; Supriadi, H. Low Cycle Fatigue Properties of Extruded 6061-T6 Aluminum Alloy. J. Phys. Conf. Ser. 2019, 1198, 032002. [CrossRef] 5. Zhao, X.; Li, H.; Chen, T.; Cao, B.; Li, X. Mechanical Properties of Aluminum Alloys under Low-Cycle Fatigue Loading. Materials 2019, 12, 2064. [CrossRef][PubMed] 6. Kurek, A.; Kurek, M.; Łagoda, T. Stress-life curve for high and low cycle fatigue. J. Theor. Appl. Mech. 2019, 57, 677–684. [CrossRef] 7. Pereira, A.B.; Fernandes, F.A.; De Morais, A.; Carvalhoso, P.; Morais, D. Development of a Delamination Fatigue Testing Machine for Composite Materials. Machines 2019, 7, 27. [CrossRef] 8. Ai, Y.; Zhu, S.-P.; Liao, D.; Correia, J.A.; De Jesus, A.M.; Keshtegar, B. Probabilistic modelling of notch fatigue and size effect of components using highly stressed volume approach. Int. J. Fatigue 2019, 127, 110–119. [CrossRef] 9. Ohnistova, P.; Piska, M.; Petrenec, M.; Dluhos, J.; Hornikova, J.; Šandera, P. Fatigue Life of 7475-T7351 Aluminum After Local Severe Plastic Deformation Caused by Machining. Materials 2019, 12, 3605. [CrossRef] 10. Zhang, J.; Fu, X.; Lin, J.; Liu, Z.; Liu, N.; Wu, B. Study on Damage Accumulation and Life Prediction with Loads below Fatigue Limit Based on a Modified Nonlinear Model. Materials 2018, 11, 2298. [CrossRef] 11. Yu, Z.-Y.; Zhu, S.-P.; Liu, Q.; Liu, Y. Multiaxial Fatigue Damage Parameter and Life Prediction without Any Additional Material Constants. Materials 2017, 10, 923. [CrossRef][PubMed] 12. Xue, L.; Shang, D.-G.; Li, L.J. Online fatigue damage evaluation method based on real-time cycle counting under multiaxial variable amplitude loading. IOP Conf. Ser. Mater. Sci. Eng. 2020, 784, 012014. [CrossRef] 13. Zhu, S.-P.; Yue, P.; Yu, Z.-Y.; Wang, Q. A Combined High and Low Cycle Fatigue Model for Life Prediction of Turbine Blades. Materials 2017, 10, 698. [CrossRef][PubMed] 14. Rozumek, D.; Faszynka, S. Surface cracks growth in aluminum alloy AW-2017A-T4 under combined loadings. Eng. Fract. Mech. 2020, 226, 106896. [CrossRef] 15. Pec, M.; Zapletal, J.; Šebek, F.; Petruska, J. Low-Cycle Fatigue, Fractography and Life Assessment of EN AW 2024-T351 under Various Loadings. Exp. Tech. 2018, 43, 41–56. [CrossRef] 16. ASTM E739-80. Standard practice for statistical analysis of linearized stress-life (S-N) and strain-life (E-N) fatigue data. In Annual Book of ASTM Standards; ASTM International: Philadelphia, PA, USA, 1989; Volume 32, pp. 667–673. 17. ASTM E8/E8M. ASTM E8/E8M Standard TestMethods for TensionTestingof Metallic Materials; ASTM International: West Conshohocken, PA, USA, 2010; Volume 1, pp. 1–27. [CrossRef] 18. ASTM E466-15. American Society for Testing and Materials. In Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials; ASTM: West Conshohocken, PA, USA, 2015; pp. 1–6. [CrossRef] 19. Hockauf, M.; Wagner, M.-X.; Halle, T.; Niendorf, T.; Lampke, T. Influence of precipitates on low-cycle fatigue and crack growth behavior in an ultrafine-grained aluminum alloy. Acta Mater. 2014, 80, 250–263. [CrossRef] 20. DelBove, M.; Vogt, J.-B.; Bouquerel, J.; Soreau, T.; François, N.; Primaux, F. Microstructure Evolution of a Precipitation Hardened Cu-Ni-Si Alloy during Low Cycle Fatigue. Solid State Phenom. 2016, 258, 546–549. [CrossRef] Metals 2020, 10, 1581 13 of 14

21. Ziaja, W.; Motyka, M.; Dybiec, H.; Sieniawski, J. High cycle bending fatigue life of submicrocrystalline aluminum alloy. Mech. Mater. 2013, 67, 33–37. [CrossRef] 22. Takahashi, Y.; Shikama, T.; Yoshihara, S.; Aiura, T.; Noguchi, H. Study on dominant mechanism of high-cycle fatigue life in 6061-T6 aluminum alloy through microanalyses of microstructurally small cracks. Acta Mater. 2012, 60, 2554–2567. [CrossRef] 23. Rozumek, D.; Marciniak, Z. Fatigue crack growth in AlCu4Mg1 under nonproportional bending-with-torsion loading. Mater. Sci. 2011, 46, 685–694. [CrossRef] 24. Chakherlou, T.; Aghdam, A.; Akbari, A.; Saeedi, K. Analysis of cold expanded fastener holes subjected to short time creep: Finite element modelling and fatigue tests. Mater. Des. 2010, 31, 2858–2866. [CrossRef] 25. Mannan, S.; Valsan, M. High-temperature low cycle fatigue, creep–fatigue and thermomechanical fatigue of steels and their welds. Int. J. Mech. Sci. 2006, 48, 160–175. [CrossRef] 26. Szusta, J.; Seweryn, A. Experimental study of the low-cycle fatigue life under multiaxial loading of aluminum alloy EN AW-2024-T3 at elevated temperatures. Int. J. Fatigue 2017, 96, 28–42. [CrossRef] 27. Lee, Y.-L.; Taylor, D. Stress-Based Fatigue Analysis and Design. Fatigue Test. Anal. 2005, 103–180. [CrossRef] 28. Karaka¸s,Ö.; Szusta, J. Monotonic and low cycle fatigue behaviour of 2024-T3 aluminium alloy between

room temperature and 300 ◦C for designing VAWT components. Fatigue Fract. Eng. Mater. Struct. 2015, 39, 95–109. [CrossRef] 29. Lee, K.-O.; Bae, K.-H.; Lee, S.-B. Comparison of prediction methods for low-cycle fatigue life of HIP superalloys at elevated temperatures for turbopump reliability. Mater. Sci. Eng. A 2009, 519, 112–120. [CrossRef] 30. Li, H.; Nishimura, A.; Nagasaka, T.; Muroga, T. Stress–strain behavior on tensile and low cycle fatigue tests of JLF-1 steel at elevated temperature in vacuum. Fusion Eng. Des. 2006, 81, 2907–2912. [CrossRef] 31. Nagode, M. An online algorithm for temperature influenced fatigue–life estimation: Strain–life approach. Int. J. Fatigue 2004, 26, 155–161. [CrossRef] 32. Weiss, M.P.; Lavi, E. Fatigue of metals—What the designer needs? Int. J. Fatigue 2016, 84, 80–90. [CrossRef] 33. Uematsu, Y.; Akita, M.; Nakajima, M.; Tokaji, K. Effect of temperature on high cycle fatigue behaviour in 18Cr–2Mo ferritic stainless steel. Int. J. Fatigue 2008, 30, 642–648. [CrossRef] 34. Gurubaran, P.; Afendi, M.; Fareisha, M.A.N.; Majid, M.A.; Haftirman, I.; A Rahman, M.T. Fatigue life investigation of UIC 54 rail profile for high speed rail. J. Phys. Conf. Ser. 2017, 908, 12026. [CrossRef] 35. Ergenc, A.F.; Ergenc, A.T.; Kale, S.; Sahin, I.G.; Dagdelen, K.; Pestelli, V.; Yontem, O.; Kuday,B. Reduced Weight Automotive Brake Pedal Test & Analysis. Int. J. Automot. Sci. Technol. 2017, 1, 8–13. 36. Singh, P.K.; Gautam, M.G.; Lal, S.B. Stress Analysis Spur Gear Design by Using Ansys Workbench. Int. J. Mech. Eng. Robot. Res. 2014, 3, 64–68. 37. Adigio, E.M.; Nangi, E.O. Computer Aided Design and Simulation of Radial Fatigue Test of Automobile Rim Using ANSYS. IOSR J. Mech. Civ. Eng. 2014, 11, 68–73. [CrossRef] 38. Lesiuk, G.; Szata, M.; Rozumek, D.; Marciniak, Z.; Correia, J.; De Jesus, A. Energy response of S355 and 41Cr4 steel during fatigue crack growth process. J. Strain Anal. Eng. Des. 2018, 53, 663–675. [CrossRef] 39. Jain, N. The reduction of stress concentration in a uni-axially loaded infinite width rectangular isotropic/ orthotropic plate with central circular hole by coaxial auxiliary holes. IIUM Eng. J. 2012, 12.[CrossRef] 40. Jain, N.; Banerjee, M.; Sanyal, S. Three Dimensional Parametric Analyses on Effect of Fibre Orientation for Stress Concentration Factor in Fibrous Composite Cantilever Plate with Central Circular Hole under Transverse Loading. IIUM Eng. J. 2012, 13.[CrossRef] 41. Fuchs, H.O.; Stephens, R.I.; Saunders, H. Metal Fatigue in Engineering; Wiley: New York, NY, USA, 2001. 42. Lipski, A.; Mroziński,S. The Effects of Temperature on the Strength Properties of Aluminium Alloy 2024-T3. Acta Mech. Autom. 2012, 6, 62–66. 43. Khan, S.; Kintzel, O.; Mosler, J. Experimental and numerical lifetime assessment of Al 2024 sheet. Int. J. Fatigue 2012, 37, 112–122. [CrossRef] 44. Tomczyk, A.; Seweryn, A. Fatigue life of EN AW-2024 alloy accounting for creep pre-deformation at elevated temperature. Int. J. Fatigue 2017, 103, 488–507. [CrossRef] 45. Man, J.; Obrtlík, K.; Polak, J. Study of surface relief evolution in fatigued 316L austenitic stainless steel by AFM. Mater. Sci. Eng. A 2003, 351, 123–132. [CrossRef] 46. Cao, X.; Xu, L.; Xu, X.-L.; Wang, Q. Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification. Metals 2018, 8, 77. [CrossRef] Metals 2020, 10, 1581 14 of 14

47. Khan, S.; Vyshnevskyy, A.; Mosler, J. Low cycle lifetime assessment of Al2024 alloy. Int. J. Fatigue 2010, 32, 1270–1277. [CrossRef] 48. Wisner, B.; Kontsos, A. Investigation of particle fracture during fatigue of aluminum 2024. Int. J. Fatigue 2018, 111, 33–43. [CrossRef] 49. Caton, M.; John, R.; Porter, W.; Burba, M. Stress ratio effects on small fatigue crack growth in Ti–6Al–4V. Int. J. Fatigue 2012, 38, 36–45. [CrossRef] 50. François, D. The Influence of the Microstructure on Fatigue. Adv. Fatigue Sci. Technol. 1989, 23–76. [CrossRef] 51. Hussain, F.; Abdullah, S.; Nuawi, M. Effect of temperature on fatigue life behaviour of aluminium alloy AA6061 using analytical approach. J. Mech. Eng. Sci. 2016, 10, 2324–2335. [CrossRef] 52. Marno, M.; Ismail, A.F.; Marini, B.A. Torsional Deformation and Fatigue Behaviour of 6061 Aluminium Alloy. IIUM Eng. J. 2012, 12.[CrossRef] 53. Zakaria, K.; Abdullah, S.; Ghazali, M.J. Comparative study of fatigue life behaviour of AA6061 and AA7075 alloys under spectrum loadings. Mater. Des. 2013, 49, 48–57. [CrossRef] 54. Liu, Y.; Yu, J.; Xu, Y.; Sun, Y.; Guan, H.; Hu, Z. High cycle fatigue behavior of a single crystal superalloy at elevated temperatures. Mater. Sci. Eng. A 2007, 454, 357–366. [CrossRef]

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional aﬃliations.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).