Toward Predictive Understanding of Fatigue Crack Nucleation in Ni-Based Superalloys

Abstract

Predicting when and where materials fail is a holy grail for structural materials engineering. Development of a predictive capability in this domain will optimize the employment of existing materials, as well as rapidly enhance the uptake of new materials, especially in high-risk, high-value applications, such as aeroengines. In this article, we review and outline recent efforts within our research groups that focus on utilizing full-field measurement and calculation of micromechanical deformation in Ni-based superalloys. In paticular, we employ high spatial resolution digital image correlation (HR-DIC) to measure surface strains and a high-angular resolution electron backscatter diffraction technique (HR-EBSD) to measure elastic distortion, and we combine these with crystal plasticity finite element (CPFE) modeling. We target our studies within a system of samples that includes single, oligo, and polycrystals where the boundary conditions, microstructure, and loading configuration are precisely controlled. Coupling of experiment and simulation in this manner enables enhanced understanding of crystal plasticity, as demonstrated with case studies in deformation compatibility; spatial distributions of slip evolution; deformation patterning around microstructural defects; and ultimately development of predictive capability that probes the location of microstructurally sensitive fatigue cracks. We believe that these studies present a careful calibration and validation of our experimental and simulation-based approaches and pave the way toward new understanding of crack formation in engineering alloys.

Experimental and crystal plasticity study on deformation bands in single crystal and multi-crystal pure aluminium

“…al. [30,31,37,38], the effect of neighbouring grains, complex strain path and strain levels can be simulated in mesoscale, to obtain the eventuated plastic strain distribution and the peak value of slip field.…”

Does Drying Affect Gel Networks?

“…On top of this, there is also the issue that any microscopy technique will only capture a tiny fraction of the sample. It has been calculated for example that it would take a billion years to study the volume of material contained within a little finger by TEM [11]. By default, this means one is likely to miss important details, or know whether the image presented is representative of the sample for example.…”

“…Dave J. Adams thanks the EPSRC for a Fellowship (EP/L021978/1). Dave J. Adams also thanks Ben Britton for providing the details of reference [11] via Twitter.…”

Fatigue Behavior of Additively Manufactured IN718 with Columnar Grains

“…This provides the possibility of predicting crack nucleation, using a combination of a damage evolution rule and a criteria based on the stress/strain of components and microstructural length scale associated with the storage of dislocations. The SED criterion has been used various studies [33,34] to predict fatigue crack nucleation. It has been revealed that the stored energy is a good indicator of fatigue crack initiation.…”