Comparison of the low‐cycle and medium‐cycle fatigue behaviour of ferritic, pearlitic, isothermed and austempered ductile irons

Meneghetti, G.; Ricotta, Mauro; Masaggia, Stefano; Atzori, B.

doi:10.1111/ffe.12041

Cited by 19 publications

(19 citation statements)

References 20 publications

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“…The hardness and strength values are higher at low austempering temperatures, which produces a lower ausferritic microstructure, which is ideal for improvements in hardness, strength, fatigue [31][32][33] and specific wear. This could be due to lesser development of carbon-enriched austenite.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

Austempered Ductile Iron (ADI): Influence of Austempering Temperature on Microstructure, Mechanical and Wear Properties and Energy Consumption

Sellamuthu

Samuel

Dinakaran

et al. 2018

Metals

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Alloyed Ductile iron, austenitized at 840 • C for 30 min in a special sealed austempering furnace, was austempered for 30 min in molten salt mixture at 4 trial temperatures of 300 • C, 320 • C, 340 • C and 360 • C. Tensile strength, yield strength, percentage elongation and impact energy were evaluated for the as-cast and austempered samples. Microstructures were investigated using microscopy, coupled with analyzing software and a scanning electron microscopy. The specific wear of samples was tested using pin-on-disc wear testing machine. X-ray diffraction was performed to calculate the amount of retained austenite present in the ausferrite matrix. As-cast microstructure consists of ferrite and pearlite, whereas austempered ductile iron (ADI) contains a mixture of acicular ferrite and carbon enriched austenite, called "ausferrite". Hardness and strength decreased, whereas ductility and impact strength improved with an increase in the austempering temperature. XRD analysis revealed that the increase in austempering temperature increased the retained austenite content. A decrease in wear resistance with austempering temperature was observed. Modified Quality Index (MQI) values were envisaged, incorporating tensile strength, elongation and wear resistance. MQI for samples austempered at 340 • C and 360 • C showed a better combination of properties. About an 8% reduction in energy consumption was gained when the heat treatment parameters were optimized.

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Section: Mechanical Propertiesmentioning

confidence: 99%

Austempered Ductile Iron (ADI): Influence of Austempering Temperature on Microstructure, Mechanical and Wear Properties and Energy Consumption

Sellamuthu

Samuel

Dinakaran

et al. 2018

Metals

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“…), Δ K 1 and Δ K 2 are the ranges of the relevant NSIFs, E is the Young's modulus while e 1 and e 2 are known parameters depending on the notch opening angle 2 α and the Poisson's ratio ν ; see Tables and . An experimental, energy‐based approach to notch fatigue was also proposed by one of the authors, taking the heat energy dissipated in a unit volume of material per cycle as a fatigue damage indicator …”

Section: Introductionmentioning

confidence: 99%

“…4,6 An experimental, energy-based approach to notch fatigue was also proposed by one of the authors, taking the heat energy dissipated in a unit volume of material per cycle as a fatigue damage indicator. 7,8 In the case of stress-relieved welded joints, it is possible to take into account the influence of the nominal load ratio, R (defined as the ratio between the minimum and the maximum applied load), by using the following expression:…”

Section: Introductionmentioning

confidence: 99%

Fatigue strength assessment of partial and full‐penetration steel and aluminium butt‐welded joints according to the peak stress method

Meneghetti

Campagnolo

Berto

2015

Fatigue Fract Eng Mat Struct

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A B S T R A C T In fatigue design of welded joints, the local approach based on the notch stress intensity factors (NSIFs) assumes that the weld toe profile is a sharp V-notch having a tip radius equal to zero, while the root side is a pre-crack in the structure. The peak stress method (PSM) is an engineering, FE-oriented application of the NSIF approach to fatigue design of welded joints, which takes advantage of the elastic peak stresses from FE analyses carried out by using a given mesh pattern, where the element type is kept constant and the average element size can be chosen arbitrarily within a given range. The meshes required for the PSM application are rather coarse if compared with those necessary to evaluate the NSIFs from the local stress distributions. In this paper, the PSM is extended for the first time to butt-welded joints in steel as well as in aluminium alloys, by comparing a number of experimental data taken from the literature with the design scatter bands previously calibrated on results relevant only to fillet-welded joints. A major problem in the case of butt-welded joints is to define the weld bead geometry with reasonable accuracy. Only in few cases such geometrical data were available, and this fact made the application of the local approaches more difficult. Provided the local geometry is defined, the PSM can be easily applied: a properly defined design stress, that is, the equivalent peak stress, is shown (i) to single out the crack initiation point in cases where competition between root and toe failure exists and (ii) to correlate with good approximation all analysed experimental data.Keywords butt-welded joints; fatigue design; local approaches; peak stress method (PSM); strain energy density (SED). N O M E N C L A T U R E2a = length of the lack of penetration c w = parameter which accounts the influence of the nominal load ratio d = mean size of a finite element e 1 , e 2 = parameters for the determination of the strain energy density (SED) f w1 , f w2 = weight parameters of the peak stresses h = bead height k = inverse slope of the design scatter band r,θ = polar coordinates t = thickness of the welded plate w toe = bead width BC = Boundary conditions E = elastic modulus EBM = Electron beam welding FE = Finite element FEM = Finite element method K 1 , K 2 = mode I and II notch stress intensity factors (NSIFs) K Ã FE = normalised K 1 in the application of the peak stress method K ÃÃ FE = normalised K 2 in the application of the peak stress method

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“…In short, because hysteresis is one of the key factors in fatigue characterization of various materials, many studies have been conducted to evaluate fatigue characteristics of materials using hysteresis. Recently, stress–strain curves have been utilized to compare the low‐cycle and medium‐cycle fatigue behaviour of ductile irons . Moreover, many researchers investigated the relationship between the hysteresis energy and surface temperature increment related to fatigue tests, as already quoted.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, stress-strain curves have been utilized to compare the low-cycle and medium-cycle fatigue behaviour of ductile irons. 7 Moreover, many researchers investigated the relationship between the hysteresis energy and surface temperature increment related to fatigue tests, as already quoted.…”

mentioning

confidence: 99%

Mechanical and thermal parameters for high‐cycle fatigue characterization in commercial steels

Curá

Sesana

2014

Fatigue Fract Eng Mat Struct

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A B S T R A C T In the present paper, the fatigue behaviour of two commercial steels has been investigated by means of thermal and mechanical measurements on specimens during fatigue testing.In particular, the investigated parameters are the surface thermal increment of the specimen and the hysteresis loop area along with the corresponding integrals of the two parameters for a number of cycles. An analytical description was firstly presented, focusing on the relations between surface temperature and hysteresis area. To both verify the theoretical relationships and emphasize the fatigue damage behaviour, an experimental procedure has been set up for mechanical and thermal parameters monitoring. Results have been finally compared in terms of fatigue limit estimation and fatigue parameters evolution.A h = subtended area by the hysteresis loops evolution to a specified number of cycles, MPa A shl = hysteresis loop area when loops evolution stabilizes, MPa A ΔT = area subtended by the thermal increment profile to a specified number of cycles for each loading block, K s or°C c = steel specimen specific heat, J (K kg) À1 dE = differential value of macroscopic alternate strain d 1 = intrinsic dissipation heat source, J (s m 3 ) À1 e d 1 = mean intrinsic dissipation heat source during a load cycle, J (s m 3 ) À1 E = Young's modulus, MPa E 0 = macroscopic alternate strain component f r = fatigue test frequency, Hz N b = number of cycles per loading block N f = number of cycles to failure for a fatigue tested specimen R m = ultimate tensile stress, MPa R p02 = elastic limit, MPa s = fatigue limit scatter, MPa t = time, s T l = oscillation period during fatigue test, s α = hysteresis cycle area, J m À3 ΔT stab = superficial thermal increment in the stabilization zone, respectively K or°C Δσ = stress amplitude increment in step loading fatigue tests, MPa Δ(∑ 0 ) = global dissipated energy density in a cycle due to microplasticization activation, J m À3 ε(t) = instant strain value ρ = steel density, kg m À3 σ aCAL = stress amplitude in constant amplitude loading fatigue tests, MPa σ ai = first loading block stress amplitude in step loading fatigue tests, MPa

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Comparison of the low‐cycle and medium‐cycle fatigue behaviour of ferritic, pearlitic, isothermed and austempered ductile irons

Cited by 19 publications

References 20 publications

Austempered Ductile Iron (ADI): Influence of Austempering Temperature on Microstructure, Mechanical and Wear Properties and Energy Consumption

Austempered Ductile Iron (ADI): Influence of Austempering Temperature on Microstructure, Mechanical and Wear Properties and Energy Consumption

Fatigue strength assessment of partial and full‐penetration steel and aluminium butt‐welded joints according to the peak stress method

Mechanical and thermal parameters for high‐cycle fatigue characterization in commercial steels

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