Decoupling Strain-Rate Sensitivity and Deformation Length Scale Effects in Neutron-Irradiated Tungsten: A Coupled Nano-Indentation, HR-EBSD and Crystal Plasticity Study
Abstract
Strain-rate-dependent deformation in spherical nanoindentation couples material rate sensitivity effects with the evolving contact radius, penetration depth and plastic-zone size. A rate-sensitive model where loading rate and indentation depth are prescribed independently allows their contributions to be disentangled. We study this in unirradiated and neutron-irradiated single-crystal tungsten, indented to the same final indentation strain at nominal strain-rates of 3.2e-5 to 3.2e-3 per second and reaching different final depths. Surface pile-up, residual lattice strain and dislocation distributions were measured by AFM and HR-EBSD. A rate-sensitive, strain-gradient crystal plasticity framework, incorporating thermally activated slip and irradiation hardening derived from measured defect populations, was calibrated at the highest strain rate and reproduced all these observables at the two lower strain rates without further parameter adjustment. The framework was then used to vary strain rate and depth independently. At fixed depth, strain rate over the experimental range changes the predicted peak load by < 1% and the pile-up by < 2 nm. At fixed strain rate, the experimental depth differences alone produce pile-up increases of ~ 90% and 130%, comparable to the measured 66% and 150% for unirradiated and irradiated tungsten. The measured differences between strain rate conditions therefore predominantly reflect the different depths reached; a 10% difference in final depth mimics more than an order of magnitude change in strain rate. Irradiation is seen to promote localisation, with its effect on pile-up increasing with depth up to ~ 500 nm, while remaining consistent with a common thermally activated deformation mechanism.
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BibTeX
@misc{joshi2026decoupling,
title = {{Decoupling Strain-Rate Sensitivity and Deformation Length Scale Effects in Neutron-Irradiated Tungsten: A Coupled Nano-Indentation, HR-EBSD and Crystal Plasticity Study}},
author = {Prashil S. Joshi and Bethany Jim and Chris Hardie and Angus Wilkinson and David EJ Armstrong and Suchandrima Das},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2607.12960},
eprint = {2607.12960},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.12960},
}
RIS
TY - UNPB
TI - Decoupling Strain-Rate Sensitivity and Deformation Length Scale Effects in Neutron-Irradiated Tungsten: A Coupled Nano-Indentation, HR-EBSD and Crystal Plasticity Study
AU - Prashil S. Joshi
AU - Bethany Jim
AU - Chris Hardie
AU - Angus Wilkinson
AU - David EJ Armstrong
AU - Suchandrima Das
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2607.12960
UR - https://arxiv.org/abs/2607.12960
AB - Strain-rate-dependent deformation in spherical nanoindentation couples material rate sensitivity effects with the evolving contact radius, penetration depth and plastic-zone size. A rate-sensitive model where loading rate and indentation depth are prescribed independently allows their contributions to be disentangled. We study this in unirradiated and neutron-irradiated single-crystal tungsten, indented to the same final indentation strain at nominal strain-rates of 3.2e-5 to 3.2e-3 per second and reaching different final depths. Surface pile-up, residual lattice strain and dislocation distributions were measured by AFM and HR-EBSD. A rate-sensitive, strain-gradient crystal plasticity framework, incorporating thermally activated slip and irradiation hardening derived from measured defect populations, was calibrated at the highest strain rate and reproduced all these observables at the two lower strain rates without further parameter adjustment. The framework was then used to vary strain rate and depth independently. At fixed depth, strain rate over the experimental range changes the predicted peak load by < 1% and the pile-up by < 2 nm. At fixed strain rate, the experimental depth differences alone produce pile-up increases of ~ 90% and 130%, comparable to the measured 66% and 150% for unirradiated and irradiated tungsten. The measured differences between strain rate conditions therefore predominantly reflect the different depths reached; a 10% difference in final depth mimics more than an order of magnitude change in strain rate. Irradiation is seen to promote localisation, with its effect on pile-up increasing with depth up to ~ 500 nm, while remaining consistent with a common thermally activated deformation mechanism.
ER -