The role of defects and critical pore size analysis in the fatigue response of additively manufactured IN718 via crystal plasticity

Prithivirajan, Veerappan; Sangid, Michael D.

doi:10.1016/j.matdes.2018.04.022

Cited by 124 publications

(47 citation statements)

References 64 publications

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“…In contrast, under asymmetric strain controlled loadings, depending on the applied strain amplitude, 425 experiments usually exhibit a non-zero cyclic mean stress. For Inconel 718, this has been demonstrated experimentally by Prithivirajan and Sangid (2018); Gribbin et al (2016) whereas for steels Wehner and Fatemi (1991); Nikulin et al (2019) have reported such behaviour. In addition, asymmetric strain controlled experiments show that the mean stress relaxes to progressively lower values with an increasing strain amplitude as found for Inconel 718 by Chaboche et al (2012) and aluminum by Hao et al (2015).…”

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confidence: 88%

“…On the other hand, experimental observations indicate levels of mean stress for which there is very low ratcheting and the mechanical state of the material converges 20 towards plastic shakedown (Pellissier-Tanon et al, 1982). Similarly, for asymmetric strain controlled loading conditions, a cyclic mean stress is observed, and several experimental studies (Wehner and Fatemi, 1991;Nikulin et al, 2019;Prithivirajan and Sangid, 2018) have deciphered the corresponding physical mechanisms. These observations show that for a given positive mean strain, and a low strain amplitude, the mean stress does not completely relax to zero.…”

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confidence: 99%

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Crystal plasticity modeling of the cyclic behavior of polycrystalline aggregates under non-symmetric uniaxial loading: Global and local analyses

Farooq

Cailletaud

Forest

et al. 2020

International Journal of Plasticity

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When a sample is cyclically loaded under a mean stress or strain, incremental strain ratcheting or mean stress relaxation phenomena are usually observed. Experiments show that for metallic materials there is generally no full mean stress relaxation as well as saturation of macroscopic strain ratcheting. In contrast, most macroscopic constitutive models produce both quantities in excess, and complex sets of additional internal variables must be introduced to improve the modeling. Little attention has been paid to model such phenomena using polycrystal aggregates especially going up to the regime of cyclic mechanical stability. In this work based on an elementary crystal plasticity model for FCC crystals and large scale finite element, it is be shown that the interaction between different grains is sufficient to cater for such complex phenomena. Light is shed on how different regions of the polycrystal accommodate each other and how the classical definition of constant rate strain ratcheting or a zero mean stress is nearly impossible to apply to a polycrystalline aggregate. In addition, it is shown that even if a macroscopic stable hysteresis stress strain loop is observed, ratcheting phenomena can still be observed at the local scale. The distributions of different constitutive quantities within a polycrystal are also analyzed which gives a new insight into what is happening inside a polycrystal in terms of stress and strain redistribution. In particular, the existence of evolving bimodal distributions of stress and accumulated plastic strain is evidenced and related to the occurrence of plastic shakedown and incomplete mean stress relaxation. Two numerical criteria to detect strain ratcheting are finally proposed and discussed. Kang et al., 2010). Mean stress in this article is defined as (Σ max + Σ min )/2 where Σ max and Σ min are the 15 maximum and minimum applied stresses in a cyclically loaded component. The stress amplitude is defined as Σ max −Σ min /2. With regards to asymetric strain controlled cyclic loadings, it is also known that under a given stress amplitude, increasing the mean stress, or increasing the applied mean stress under constant amplitude, both increase the rate of ratcheting (Goodman, 1984). On the other hand, experimental observations indicate levels of mean stress for which there is very low ratcheting and the mechanical state of the material converges 20 towards plastic shakedown (Pellissier-Tanon et al., 1982). Similarly, for asymmetric strain controlled loading conditions, a cyclic mean stress is observed, and several experimental studies (Wehner and Fatemi, 1991;Nikulin et al., 2019;Prithivirajan and Sangid, 2018) have deciphered the corresponding physical mechanisms. These observations show that for a given positive mean strain, and a low strain amplitude, the mean stress does not completely relax to zero. Also, increasing the strain amplitude leads to a nonlinear decrease of the 25

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confidence: 88%

mentioning

confidence: 99%

Crystal plasticity modeling of the cyclic behavior of polycrystalline aggregates under non-symmetric uniaxial loading: Global and local analyses

Farooq

Cailletaud

Forest

et al. 2020

International Journal of Plasticity

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“…where the constants for the single-crystal elastic tensor C ijkl in Voigt's notation with cubic symmetry are C 11 = 225.7 GPa, C 12 = 151.2 GPa, and C 44 = 112.3 GPa. 34…”

Section: High-energy X-ray Characterizationmentioning

confidence: 99%

“…First, crystal plasticity simulations 32 are used to identify the stress state around a pore, in the regime in which the pore size is similar to the microstructural features. 12,33,34 These grain-level stress fields are used to identify the critical pore size, in which the stress concentrations around a pore are greater than those around other microstructural features (especially grain boundaries). Next, a pair of synchrotron-based x-ray characterization techniques are used during in situ loading 35 to produce a data-rich means to identify the role of pores in the fatigue behavior, and to inform and validate the model's predictions.…”

Section: Introductionmentioning

confidence: 99%

ICME Approach to Determining Critical Pore Size of IN718 Produced by Selective Laser Melting

Sangid

Ravi

Prithivirajan

et al. 2019

JOM

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A degree of porosity is expected in additively manufactured (AM) materials. To aid in the qualification of AM materials, the smallest pore size that results in a debit in the fatigue performance is quantified. In the work presented herein, crystal plasticity simulations are used to identify the stress concentration around pores of various sizes, revealing that a single 20-lm pore or two 10-lm pores (with centers spaced 15 lm apart) localize stress at the pore, as opposed to elsewhere in the microstructure. In situ microtomography and far-field high-energy x-ray diffraction microscopy were used to identify crack formation and the evolution of the grain-level micromechanical fields during cyclic loading. Eighteen cracks were observed (15 at pores, 3 at the surface) at highly stressed grains in a sample, although most did not propagate. The dominant crack was seen to originate from the free surface, which is rationalized by fracture mechanics.

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“…Additive manufacturing (AM) has recently attained much popularity both in research and application fields such as aerospace, automobile, maritime, biomedical, and other industrial sectors [1][2][3]. Among different additive manufacturing process available, laser powder bed fusion (LPBF) also known as selective laser melting (SLM) is a widely accepted method to fabricate metals and alloys [4][5][6][7][8]. LPBF is capable of depositing near-net-shape internal and external complex geometries but the major drawbacks of the AM materials are the surface irregularities, residual stress, and defects such as porosity, microcracks, inclusions, dislocations, and others.…”

Section: Introductionmentioning

confidence: 99%

High Cycle Fatigue Performance of LPBF 304L Stainless Steel at Nominal and Optimized Parameters

et al. 2020

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In additive manufacturing, the variation of the fabrication process parameters influences the mechanical properties of a material such as tensile strength, impact toughness, hardness, fatigue strength, and so forth, but fatigue testing of metals fabricated with all different sets of process parameters is a very expensive and time-consuming process. Therefore, the nominal process parameters by means of minimum energy input were first identified for a dense part and then the optimized process parameters were determined based on the tensile and impact toughness test results obtained for 304L stainless steel deposited in laser powder bed fusion (LPBF) process. Later, the high cycle fatigue performance was investigated for the material built with these two sets of parameters at horizontal, vertical, and inclined orientation. In this paper, displacement controlled fully reversed (R = −1) bending type fatigue tests at different levels of displacement amplitude were performed on Krouse type miniature specimens. The test results were compared and analyzed by applying the control signal monitoring (CSM) method. The analysis shows that specimen built-in horizontal direction for optimized parameters demonstrates the highest fatigue strength while the vertical specimen built with nominal parameters exhibits the lowest strength.

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The role of defects and critical pore size analysis in the fatigue response of additively manufactured IN718 via crystal plasticity

Cited by 124 publications

References 64 publications

Crystal plasticity modeling of the cyclic behavior of polycrystalline aggregates under non-symmetric uniaxial loading: Global and local analyses

Crystal plasticity modeling of the cyclic behavior of polycrystalline aggregates under non-symmetric uniaxial loading: Global and local analyses

ICME Approach to Determining Critical Pore Size of IN718 Produced by Selective Laser Melting

High Cycle Fatigue Performance of LPBF 304L Stainless Steel at Nominal and Optimized Parameters

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