The Effects of Grain Size and Strain Amplitude on Persistent Slip Band Formation and Fatigue Crack Initiation

Ou, Chun-Yu; Liu, C. Richard

doi:10.1007/s11661-019-05423-6

Cited by 6 publications

(8 citation statements)

References 22 publications

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“…where a is the crack radius, ν is Poisson's ratio, σ is the normal load applied, and E is the elastic modulus. The cracks tend to be initiated from stress-concentrated areas such as gas pores [14], slip bands [16], and areas lacking diffusion [14,17,18] for AM-fabricated materials. The plastic energy stored at the potential crack-initiated areas can be modeled based on Fine [19] as in Equation 3:…”

Section: Fatigue Crack Initiation Modelmentioning

confidence: 99%

“…In contrast, the dislocation model [21] did not consider the anisotropic nature of the microstructure, which led to poor accuracy. The dislocation model is as shown in Equation (16):…”

Section: Fatigue Crack Initiation Life Estimationmentioning

confidence: 99%

“…In addition, by considering the effect of microstructure on the critical resolved shear stress (g 0 ) and the strain hardening modulus (h 0 ), the localized dislocation slip and plastic slip per cycle ( ∆γ p 2 ), as shown in Equation (17), can be precisely calculated. As discussed in previous papers [16,[22][23][24][25], the energy efficiency coefficient (ρ), and the maximum persistent slip band width (t m ) are also coefficients related to microstructure. However, due to limited experimental data, we assumed they were a constant value in this study.…”

Section: Fatigue Crack Initiation Life Estimationmentioning

confidence: 99%

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Fatigue Crack Initiation of Metals Fabricated by Additive Manufacturing—A Crystal Plasticity Energy-Based Approach to IN718 Life Prediction

Voothaluru

Liu

2020

Crystals

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There has been a long-standing need in the marketplace for the economic production of small lots of components that have complex geometry. A potential solution is additive manufacturing (AM). AM is a manufacturing process that adds material from the bottom up. It has the distinct advantages of low preparation costs and a high geometric creation capability. However, the wide range of industrial processing conditions results in large variations in the fatigue lives of metal components fabricated using AM. One of the main reasons for this variation of fatigue lives is differences in microstructure. Our methodology incorporated a crystal plasticity finite element model (CPFEM) that was able to simulate a stress–strain response based on a set of randomly generated representative volume elements. The main advantage of this approach was that the model determined the elastic constants (C11, C12, and C44), the critical resolved shear stress (g0), and the strain hardening modulus (h0) as a function of microstructure. These coefficients were determined based on the stress–strain relationships derived from the tensile test results. By incorporating the effect of microstructure on the elastic constants (C), the shear stress amplitude (Δτ2) can be computed more accurately. In addition, by considering the effect of microstructure on the critical resolved shear stress (g0) and the strain hardening modulus (h0), the localized dislocation slip and plastic slip per cycle (Δγp2) can be precisely calculated by CPFEM. This study represents a major advance in fatigue research by modeling the crack initiation life of materials fabricated by AM with different microstructures. It is also a tool for designing laser AM processes that can fabricate components that meet the fatigue requirements of specific applications.

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Section: Fatigue Crack Initiation Modelmentioning

confidence: 99%

“…In contrast, the dislocation model [21] did not consider the anisotropic nature of the microstructure, which led to poor accuracy. The dislocation model is as shown in Equation (16):…”

Section: Fatigue Crack Initiation Life Estimationmentioning

confidence: 99%

Section: Fatigue Crack Initiation Life Estimationmentioning

confidence: 99%

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Fatigue Crack Initiation of Metals Fabricated by Additive Manufacturing—A Crystal Plasticity Energy-Based Approach to IN718 Life Prediction

Voothaluru

Liu

2020

Crystals

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“…An electrolytic tough pitch (ETP) sheet of Grade 110 polycrystalline copper sheet was used in this study. The sample preparation methods were based on a previous study [26]. The copper bar was cut into a dog-bone shape for fatigue and tensile tests by an end mill.…”

Section: Microstructure Characterization and Sample Designmentioning

confidence: 99%

“…The surface energy was 1.7 J/m 2 for copper, obtained from Kwon [46]. The maximum persistent slip band width (t m ) was based on a previous experimental study [26] and the crack initiation life (N i ) was described in Section 2.3. The resolved shear stress ∆τ 2 and plastic slip per cycle…”

Section: Effect Of Grain Size On the Energy Efficiency Coefficient (ρ)mentioning

confidence: 99%

A Methodology for Incorporating the Effect of Grain Size on the Energy Efficiency Coefficient for Fatigue Crack Initiation Estimation in Polycrystalline Metal

Voothaluru

Liu

2020

Metals

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Estimating fatigue crack initiation of applied loading is challenging due to the large number of individual entities within a microstructure that could affect the accumulation of dislocations. In order to improve the prediction accuracy of fatigue crack initiation models, it is essential to accurately compute the energy dissipated into the microstructure per fatigue loading cycle. The extent of the energy dissipated within the microstructure as a fraction of the overall energy imparted by loading has previously been defined as the ‘energy efficiency coefficient’. This work studied the energy efficiency coefficient as a factor in the measurement of accumulated plastic strain energy stored at the crack initiation site during cyclic loading. In particular, the crystal plasticity constitutive formulation was known as ’length scale independent’ previously. As a result, a semi-empirical approach was presented whereby the potential effect of grain size can be accounted for without the use of a strain gradient plasticity approach. The randomized representative volume elements were created based on the experimental analysis of grain size distribution. The work was aimed at capturing some of the effects of grain size and utilizing them to complete a semi-empirical estimation of crack initiation in polycrystalline materials. The computational methodology ensured the representative of microstructural properties, including the elastic constant and critical resolved shear stress via appreciable fit achieved with the empirical tensile test results. Crystal plasticity finite element modeling was incorporated into a finite element code to estimate the potential for crack initiation. The energy efficiency coefficient was computed for a class of material with grain size to C11000 electrolytic tough pitch (ETP) copper. This methodology can improve fatigue crack initiation life estimation and advance the fundamental study of energy efficiency coefficient during fatigue crack initiation.

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Interfacial Interactions in Particle‐Induced Abnormal Grain Growth

2023

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The presence of secondary particles to polycrystalline alloys results in kinetic stabilization of the grain boundaries, which maintains desirable fine microstructures. In some instances, secondary particles trigger abnormal grain growth. The mechanisms influencing abnormal grain growth are still a subject of conjecture. As dispersed fine particles can contribute to abnormal grain growth, it is necessary to clarify the governing mechanism by which this occurs. The current work employs a multiphase field modeling approach to shed light onto abnormal grain growth. Particular attention is placed on understanding the role of grain boundary–particle interactions on abnormal grain growth. The results show that, in the presence of particles, normal grain growth occurs until a pinned state is achieved. In the pinned state, some grains overcome the pinning pressure exerted by some particles by piercing through the particles, which results in abnormal grain growth. The piercing events appear to be entirely random and not related to the size of the interacting particles. None‐the‐less, a bimodal particle size distribution is observed to lead to abnormal grain growth. A pinning parameter is introduced as a metric to identify the transition from normal to abnormal grain growth.

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The Effects of Grain Size and Strain Amplitude on Persistent Slip Band Formation and Fatigue Crack Initiation

Cited by 6 publications

References 22 publications

Fatigue Crack Initiation of Metals Fabricated by Additive Manufacturing—A Crystal Plasticity Energy-Based Approach to IN718 Life Prediction

Fatigue Crack Initiation of Metals Fabricated by Additive Manufacturing—A Crystal Plasticity Energy-Based Approach to IN718 Life Prediction

A Methodology for Incorporating the Effect of Grain Size on the Energy Efficiency Coefficient for Fatigue Crack Initiation Estimation in Polycrystalline Metal

Interfacial Interactions in Particle‐Induced Abnormal Grain Growth

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