arXiv subjects

Fionn P. E. Dunne

Publications and source records attributed to Fionn P. E. Dunne.

7 recordsLinked to original sources

arXiv2023

Slip intermittency and dwell fatigue in titanium alloys: a discrete dislocation plasticity analysis

Slip intermittency and stress oscillations in titanium alloy Ti-7Al-O that were observed using in-situ far-field high energy X-ray diffraction microscopy (ff-HEDM) are investigated using a discrete dislocation plasticity (DDP) model. The mechanistic foundation of slip intermittency and stress oscillations are shown to be dislocation escape from obstacles during stress holds, governed by a thermal activation constitutive law. The stress drop events due to -basal slip are larger in magnitude than those along -prism, which is a consequence of their differing rate sensitivities, previously found from micropillar testing. It is suggested that interstitial oxygen suppresses stress oscillations by inhibiting the thermal activation process. Understanding of these mechanisms is of benefit to the design and safety assessment of jet engine titanium alloys subjected to dwell fatigue.

cond-mat.mtrl-sci↗

arXiv2023

An FFT-based crystal plasticity phase-field model for micromechanical fatigue cracking based on the stored energy density

A novel FFT-based phase-field fracture framework for modelling fatigue crack initiation and propagation at the microscale is presented. A damage driving force is defined based on the stored energy and dislocation density, relating phase-field fracture with microstructural fatigue damage. The formulation is numerically implemented using FFT methods to enable modelling of sufficiently large, representative 3D microstructural regions. The early stages of fatigue cracking are simulated, predicting crack paths, growth rates and sensitivity to relevant microstructural features. Crack propagation through crystallographic planes is shown in single crystals, while the analysis of polycrystalline solids reveals transgranular crack initiation and crystallographic crack growth.

cs.CE↗

arXiv2022

Multi-scale plasticity homogenization of Sn-3Ag-0.5Cu: from β-Sn micropillars to polycrystals with intermetallics

The mechanical properties of $β$-Sn single crystals have been systematically investigated using a combined methodology of micropillar tests and rate-dependent crystal plasticity modelling. The slip strength and rate sensitivity of several key slip systems within $β$-Sn single crystals have been determined. Consistency between the numerically predicted and experimentally observed slip traces has been shown for pillars oriented to activate single and double slip. Subsequently, the temperature-dependent, intermetallic-size-governing behaviour of a polycrystal $β$-Sn-rich alloy SAC305 (96.5Sn-3Ag-0.5Cu wt%) is predicted through a multi-scale homogenization approach, and the predicted temperature- and rate-sensitivity reproduce independent experimental results. The integrated experimental and numerical approaches provide mechanistic understanding and fundamental material properties of microstructure-sensitive behaviour of electronic solders subject to thermomechanical loading, including thermal fatigue.

cond-mat.mtrl-sci↗

arXiv2022

A multi-scale approach to microstructure-sensitive thermal fatigue in solder joints

This paper presents a multi-scale modelling approach to investigate the underpinning mechanisms of microstructure-sensitive damage of single crystal Sn-3Ag-0.5Cu (wt%, SAC305) solder joints of a Ball Grid Array (BGA) board assembly subject to thermal cycling. The multi-scale scheme couples board-scale modelling at the continuum macro-scale and individual solder modelling at the crystal micro-scale. Systematic studies of tin crystal orientation and its role in fatigue damage have been compared to experimental observations. Crystallographic orientation is examined with respect to damage development, providing evidence-based optimal solder microstructural design for in-service thermomechanical fatigue.

cond-mat.mtrl-sci↗

arXiv2021

Characterisation of microstructural creep, strain rate and temperature sensitivity and computational crystal plasticity in Zircaloy-4

Crystal-level strain rate sensitivity and temperature sensitivity are investigated in Zircaloy-4 using combined of bending creep test, digital image correlation, electron backscatter detection and thermo-mechanical tensile tests with crystal plasticity modelling. Crystal rate-sensitive properties are extracted from room temperature microscale creep, and temperature sensitivity from thermal polycrystalline responses. Crystal plasticity results show that large microscale creep strain is observed near notch tip increased up to 50% due to cross-slip activation. Grain-level microscale SRS is highly heterogeneous, and its crystallographic sensitivity is dependent on plastic deformation rate and underlying grain-based dislocation slip activation. Pyramidal slip and total dislocation pileups contribute to temperature-sensitive texture effect on yielding and strength hardening. A faithful reconstruction of polycrystal and accurate rate-sensitive single-crystal properties are the key to capture multi-scale SRSs.

cond-mat.mtrl-sci↗

arXiv2021

Slip band interactions and GND latent hardening in a galling resistant stainless steel

Slip activation, slip band interactions, and GND densities in iron-base, galling resistant alloy Nitronic 60 have been characterised at the grain length scale using small-scale mechanical testing with high resolution digital image correlation and high-angular resolution electron backscatter diffraction. By correlating the two measurement techniques, new insight into slip band interactions, the generation of lattice curvature and the corresponding accumulation of geometrically necessary dislocations (GNDs) is provided. Multiple discrete slip bands are typically active within single grains, resulting in significant slip band interactions. Crossing slip bands were found to generate accumulations of GNDs. Regions where slip bands block other slip bands were associated with the highest GND densities, in excess of three time the densities of crossing slip bands. Representative crystal plasticity modelling investigations have demonstrated that discrete slip blocking events are responsible for locally elevated GND density. This behaviour is rationalised in terms of lattice curvature associated with the differing levels of constraint provided by the crossing or blocking-type behaviours. Ferrite grains are also found to contribute to the generation of GNDs. Together, these two effects provide significant work hardening mechanisms, likely to be key to the development of future iron-base hard facing alloys.

cond-mat.mtrl-sci↗

arXiv2019

Crystal plasticity analysis of deformation anisotropy of lamellar TiAl alloy: 3D microstructure-based modelling and in-situ micro-compression

Detailed microstructure characterisation and in-situ micropillar compression were coupled with crystal plasticity-based finite element modelling (CP-FEM) to study the micro-mechanisms of plastic anisotropy in lamellar TiAl alloys. The consideration of microstructure in both simulation and in-situ experiments enables in-depth understanding of micro-mechanisms responsible for the highly anisotropic deformation response of TiAl on the intra-lamella and inter-lamella scales. This study focuses on two specific configurations of γ/α_2 lamellar microstructure with the γ/α_2 interfaces being aligned {25}^o and {55}^o to the loading direction. Microstructure-based CP-FEM shows that longituginal slip of super and ordinary dislocations are most responsible for the plastic anisotropy in the {25}^o micropillar while the anisotropy of the {55}^o micropillar is due to longitudinal superdislocations and longitudinal twins. In addition, transversal superdislocations were more active, making the deformation in the {25}^o micropillar less localised than that in the {55}^o micropillar. Moreover, the CP-FEM model successfully predicted substantial build-up of internal stresses at γ/α_2 interfaces, which is believed to be detrimental to the ductility in TiAl. However, as evidenced by the model, the detrimental internal stresses can be significantly relieved by the activation of transverse deformation twinning, suggesting that the ductility of TiAl can be improved by promoting transverse twins.

cond-mat.mtrl-sci↗