Validation of a cyclic plasticity computational method using fatigue full‐field deformation measurements

Abstract

The evolution of crack tip displacement and strain fields during uniaxial, room temperature, low‐cycle fatigue experiments of Nickel superalloy compact tension specimens was measured by a digital image correlation approach and was further used to validate a cyclic plasticity model and corresponding deformation calculations made by a finite elements methodology. The experimental results provided data trends for the opening displacements and near crack tip strains as function of cycles. A finite element model was developed to capture test conditions for a measured crack size. The model captures crack tip plasticity by using a constitutive model calibrated against stress‐strain measurements performed on a round bar. Similar quantities were extracted from the model predictions to compare with the digital image correlation measurements for model validation purposes. This type of direct comparison demonstrated that the computational model was capable to adequately capture the crack opening displacements at various stages of the specimen's fatigue life, providing in this way a tool for quantitative cyclic plasticity model validation. In addition, this integrated experimental‐computational approach provides a framework to accelerate our understanding related to interactions of fatigue test data and models, as well as ways to inform one another.

The use of nondestructive evaluation methods in fatigue: A review

“…Similar applications have F I G U R E 1 Typical digital image correlation (DIC) setups for A, the microscale using a scanning electron microscope 67 and B, the laboratory scale using stereo (3D) DIC for crack growth investigations 33 [Colour figure can be viewed at wileyonlinelibrary.com] succeeded to relate local measurements with globally observed data trends, which have been additionally leveraged to validate various fatigue models. 13,14,59,[70][71][72] In the same context of using optical metrology in fatigue investigations, Zhang and Liu used the DIC to estimate the plastic zone size both during unloading and reloading, 34 which contributes to the understanding of fatigue driving forces that have frequently been explored by the use of various experimental and characterization methods. 73,74 Zhang and Liu's experimental observations showed differences in the estimated plastic zone size compared with theoretical predictions that do not account for crack closing behaviour.…”

“…The data points shown were used to investigate the effect of the resulting plastic fields on the crack growth behaviour and to provide estimations of crack growth rates. Similar applications have succeeded to relate local measurements with globally observed data trends, which have been additionally leveraged to validate various fatigue models …”

Local strain accumulation in fatigue crack propagation process of Ti‐6Al‐4V alloy

“…19 Through the use of in situ DIC measurements, the evolution of strain field at crack tips in stainless steel 316 L and nickel-based superalloy were also tracked. 20,21 Fatigue life prediction and crack propagation behaviour of Ti-6Al-4V alloy under different loading conditions have been widely investigated. [22][23][24] Some studies focused on the effect of microstructures and processing method of specimen on fatigue properties of Ti-6Al-4V.…”

“…The variation of crack tip plastic zone within a single cycle was also identified by DIC . Through the use of in situ DIC measurements, the evolution of strain field at crack tips in stainless steel 316 L and nickel‐based superalloy were also tracked …”

Uncertainty quantification and sensitivity analysis of material parameters in crystal plasticity finite element models

“…In the last decade, advances in both computational methods and experimental techniques have made it possible to create very detailed and precise finite element (FE) models of real polycrystals and directly compare their simulated responses to experimental observations. Due to current computational limitations, the polycrystals studied are usually either very small [1][2][3][4][5][6][7], or their constituent grains are very big and few in number [8][9][10][11][12][13][14]. The small number of grains allows measuring and comparing the local strain fields on the surfaces of the specimens to the simulation results.…”