Papers by Alexander Korsunsky
Marine Biological Journal, 2020
The topic of interactions between plastic and natural communities is now more relevant than ever ... more The topic of interactions between plastic and natural communities is now more relevant than ever before. Gradual accumulation of artificial polymer products and their fragments in the natural environment has reached a level at which it is already impossible to ignore the affect of these materials on living organisms. First and foremost, microorganism colonies inhabiting different biotopes, both aquatic and terrestrial, have been affected. These species are at the front-end of interaction with plastic, including those present in marine ecosystems. Nevertheless, in order to understand these processes, it is necessary to take into account several aspects of such interactions: the impact of different types of plastic on microbial community through the release of their decomposed products into the environment, the forms of plastic usage by microorganisms themselves, including mechanisms for surface colonization, as well as possible biodegradation processes of polymers due to the actions ...
Materials & Design, Nov 1, 2016
Journal of the Royal Society Interface, Jun 6, 2014
situ X-ray scattering evaluation of heat-induced ultrastructural changes in dental tissues and sy... more situ X-ray scattering evaluation of heat-induced ultrastructural changes in dental tissues and synthetic hydroxyapatite.
<i>In </i> <i>Si</i><i>tu</i> X-Ray Diffraction Measurements of the Apparent Modulus of Human Dental Tissue in the Vicinity of the Dentine-Enamel Junction (DEJ)
Applied Mechanics and Materials, Oct 1, 2015
The dentine-enamel junction (DEJ) is an important biological interface between the highly mineral... more The dentine-enamel junction (DEJ) is an important biological interface between the highly mineralized hard out layer (enamel) and the comparatively softer tooth core (dentine) of teeth. The remarkable performance of this interface provides the motivation for investigation into the detailed structure and function of the DEJ. In this study, synchrotron X-ray diffraction measurements of the DEJ subjected to the in situ uniaxial loading were carried out to capture the structure-property relationship between the DEJ architecture and its response to the applied force. The knowledge of the architecture and properties of the natural DEJ will hopefully help in biomimetic engineering of superior dental restorations and prostheses, and the development of novel materials to emulate the DEJ.
Coupled Damage-Plasticity Modelling of Ductile Failure in an Aluminium Alloy
Applied Mechanics and Materials, Aug 1, 2015
The ductile failure of metallic alloys is characterized by the long plateau of the stress-strain ... more The ductile failure of metallic alloys is characterized by the long plateau of the stress-strain response during plastic deformation. In aluminium alloys this complex process is principally mediated by crystal slip associated with dislocation nucleation, motion, interaction, and locking. This results in hardening, i.e. the increase in the flow stress and progressive exhaustion of ductility, eventually leading to damage. Therefore, in the advanced stages of deformation the strength increase at the material level competes with overall stiffness and strength decrease due to effective cross-section reduction by decohesion and voiding. Capturing the complex hierarchical failure of these materials requires developing sophisticated concurrent constitutive descriptions of both plastic deformation and damage at different stages of failure. In the present study the modelling of aluminium alloy failure is accomplished using a plasticity-based model with nonlinear hardening coupled with isotropic damage in a thermodynamically consistent framework. The model developed in this way is enhanced with nonlocal regularization to deal with material instabilities issues due to softening. Emphasis is placed on the correspondence between experimental measurements of the essential work of fracture and the non-essential work of fracture, and both local and spatial sets of model parameters. This approach is the key to assuring a constitutive response consistent with experimental observations, an issue usually overlooked in nonlocal constitutive modelling. Numerical examples are used to demonstrate the features of the new approach.
Analysis and control of residual stresses in advanced engineering materials are important issues ... more Analysis and control of residual stresses in advanced engineering materials are important issues for reliability assessment at small scales, e.g. for micro-electromechanical systems (MEMS) and nano-crystalline and amorphous bulk and thin film materials. This presentation gives an overview of the recent advances in the field of sub-micron scale residual stress assessment by the use of focused ion beam (FIB)-controlled material removal techniques. Materials and The two step method consists of incremental FIB ring-core milling combined with high-resolution in-situ SEMFEG imaging of the relaxing surface and a full field strain analysis by digital image correlation (DIC). The through-thickness profile of the residual stress can be also obtained by comparison of the experimentally measured surface strain with finite element modelling using Schajer’s integral method. In this presentation, we will review the most recent advances in the field of FIB-DIC methods for residual stress assessment...
A good practice guide for measuring residual stresses using FIB-DIC
This focused ion beam-digital image correlation (FIB-DIC) Good Practice Guide (GPG) is one of the... more This focused ion beam-digital image correlation (FIB-DIC) Good Practice Guide (GPG) is one of the key outputs from the iSTRESS project, aimed at providing users with practical advice for making reliable residual stress measurements on their own systems and materials using this technique. It brings together the expertise and experience of the project partners in a single document, and is being used to promote the transfer and uptake of the newly developed methodologies to a wider industry. Led by NPL and RomaTre and Oxford Universities, it is based largely on input and technical expertise of the project partners involved in Work Packages 2-5, and the results and findings from the various round robin exercises and studies carried out within the project. The GPG covers all aspects of the measurement process and residual stress analyses for the range of materials and sample geometries examined within the iSTRESS project. It is designed to be a practical guide, with advice, supporting in...
Materials & Design, 2021
Multi-axial residual stress distributions across a notched CrN-Cr clamped micro-cantilever were d... more Multi-axial residual stress distributions across a notched CrN-Cr clamped micro-cantilever were determined experimentally. • Residual stresses in Cr introduce an effective stress intensity of −5.9 ± 0.4 MPa m ½ , forming a plastic zone around the notch. • Upon crack growth through Cr to the adjacent CrN-Cr interface, the crack is arrested there and its stress fields disappears.
Materials & Design, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Surface and Coatings Technology, 2019
Residual stresses in thin films and multi-layered coatings fabricated by physical vapour depositi... more Residual stresses in thin films and multi-layered coatings fabricated by physical vapour deposition largely affect their mechanical and thermal reliability during operation in numerous fields of applications. By changing the argon working pressure in between each multilayer planar DC magnetron sputter deposition step, it is possible to control the residual stress distribution within coatings. A combination of FIB-DIC ring-core strain analysis, synchrotron XRD analysis based on the sin 2 (Y) method and micro-cantilever deflection analysis is used to reconstruct the in-plane stress state of multilayer coatings at different deposition pressures, with a residual stress depth profile resolution of 50 nm. A clear transition from compressive to tensile residual stresses is observed with an increase of working pressure, with pronounced stress peaks near the substrate-coating interface. These peak stresses resolved by FIB-DIC ring-core analysis exceed the average XRD stress measurements significantly, thus providing a reasonable explanation for multilayer failure. Experimental results are presented and comprehensively discussed in the context of deposition conditions for different thin film applications.
Procedia Structural Integrity, 2016
Peer-review under responsibility of the Scientific Committee of ECF21.
Dental Materials, 2019
Highlights Residual stress and phase analysis at the microscale at interface and coping edge ... more Highlights Residual stress and phase analysis at the microscale at interface and coping edge X-ray diffraction and Raman spectroscopy show comparable results Cross validation using ring-core focused ion beam and digital image correlation Monoclinic and highly stressed regions identified close to interface Phase transformation volumetric expansion is the origin of porcelain failure Abstract 1 Objectives: Yttria Partially Stabilised Zirconia (YPSZ) is a high strength ceramic which has become widely used in porcelain veneered dental copings due to its exceptional toughness. Within these components the residual stress and crystallographic phase of YPSZ close to the interface are highly influential in the primary failure mode; near interface porcelain chipping. In order to improve present understanding of this behaviour, characterisation of these parameters is needed at an improved spatial resolution. Methods: In this study transmission micro-focus X-ray Diffraction, Raman spectroscopy, and focused ion beam milling residual stress analysis techniques have, for the first time, been used to quantify and cross-validate the microscale spatial variation of phase and residual stress of YPSZ in a prosthesis cross-section. Results: The results of all techniques were found to be comparable and complementary. Monoclinic YPSZ was observed within the first 10 μm of the YPSZ-porcelain interface with a maximum volume fraction of 60%. Tensile stresses were observed within the first 150 μm of the interface with a maximum value of ≈ 300 MPa at 50 μm from the interface. The remainder of the coping was in mild compression at ≈ −30 MPa, with shear stresses of a similar magnitude also being induced by the YPSZ phase transformation. Significance: The analysis indicates that the interaction between phase transformation, residual stress and porcelain creep at YPSZ-porcelain interface results in a localised porcelain fracture toughness reduction. This explains the increased propensity of failure at this location, and can be used as a basis for improving prosthesis design.
Fatigue & Fracture of Engineering Materials & Structures, 2019
Friction stir welding (FSW) since its invention has been attracting relevant interest for joining... more Friction stir welding (FSW) since its invention has been attracting relevant interest for joining aluminium alloys. Due to the nature of this process, the materials can be joint without melting. Thanks to this peculiar characteristic, the issues associated with the cooling from liquid phase are avoided or considerably reduced, such as cracking, porosity, and defects.However, as well as other well‐established welding techniques, the FSW process gives rise to formation of residual stress in the welding region and surrounding volume: heat and thermo‐mechanical affected zones. Presence of residual stress in a mechanical component is well‐known to affect its performance, particularly regarding fatigue at high number of cycles. Another aspect that influences the fatigue life is the underlying microstructure.In this work, we firstly study the residual stress field and the underlying microstructural features arising in FSW butt joints and their effect on the fatigue performance of this type...
Journal of the Mechanics and Physics of Solids, 2019
The study of Residual Stress is gaining more and more attention due to its importance in design f... more The study of Residual Stress is gaining more and more attention due to its importance in design for structural integrity. At present a lot of emphasis is placed on understanding the origins of mechanical failure that lie at the nano-/micron-scale. This leads to the evident need for evaluating residual stress distributions at increasingly smaller scales, and the search for modern tools capable of accomplishing this task. Prior state-of-the-art methodologies mostly required expensive and time-consuming sample preparation and examination processes to evaluate residual stress, e.g. the study of thin TEM lamellae. The recent advent of Focused Ion Beam methods opened up methods suitable for direct application at sample surface, yet allowing the observation and quantification of stress relief phenomena at the nano-scale. In the last decade, technical aspects of FIB-based method(s) have seen significant development. On the other hand, the calculation framework employed to analyse the experimental outcome remained largely conventional, in most inconvenient for high precision analysis of challenging problems. In the present paper, the eigenstrain-based method previously presented by the authors for the depthresolved evaluation of equi-biaxial residual stress, is generalised to non-equi-biaxial distributions of residual stress. This extends the applicability of the method to a much wider class of problems. The use of cylindrical ring-core shape in FIB-DIC analysis allows reconstructing the full in-plane residual stress tensor as a function of milling depth. We report formulae for calibrated influence functions that have very broad applicability, and can be used in the overwhelming majority of cases. Their derivation is based on an extensive set of FEM simulations that allowed reliable identification of the limitations of this approach, and highlight the importance of making appropriate selection of ring-core diameter(s). Finally, experimental validation of the method is presented that involves the reconstruction a known non-equibiaxial residual stress depth profile, confirming the validity and reliability of the present approach.
Surface and Coatings Technology, 2017
Probing the deformation and fracture properties of Cu/W nano-multilayers by in situ SEM and synch... more Probing the deformation and fracture properties of Cu/W nano-multilayers by in situ SEM and synchrotron XRD strain microscopy
Engineering Fracture Mechanics, 2016
Abrupt increase in the maximum load during fatigue cycling modifies the deformation conditions at... more Abrupt increase in the maximum load during fatigue cycling modifies the deformation conditions at the crack tip, causing plastic flow that may lead to crack closure, introducing residual stress and hardening. The net consequence of these effects is notable crack growth retardation. Despite decades of research in the field, controversy persists regarding the role of each specific mechanism and their interaction. Resolving these issues with the help of experimental observation is related to the difficulty of obtaining local residual stress information at appropriate resolution. The present study examines the effect of overload on fatigue crack grown in a Compact Tension (CT) specimen of aluminium alloy AA6082 (BS HE30). Fatigue crack was grown in the sample under cyclic tension (R=0.1). After the application of a single overload cycle, fatigue loading was recommenced under previous cycling conditions. The crack morphology was investigated using Scanning Electron Microscopy (SEM). Electron Backscattered Diffraction (EBSD) was used to map grain orientation and crystal lattice distortion (pattern quality) in the vicinity of the crack. EBSD analysis of intra-granular misorientation allowed the qualitative analysis of the region around the crack tip location at the time of the overload application. Observations are discussed with a view to identify the roles of crack closure and residual stress effects. Residual stress was evaluated at salient locations around the crack retardation site using the FIB-DIC method which combines the use of Focused Ion Beam (FIB) and Digital Image Correlation (DIC) for residual stress measurement at the (sub)micron-scale. The residual stress field due to overload occurrence was also simulated using Finite Element Method (FEM), and the results compared with experimental observations.
International Journal of Solids and Structures, 2016
Elastic anisotropy can have a significant effect on the reliability and precision of residual str... more Elastic anisotropy can have a significant effect on the reliability and precision of residual stress evaluation, due to the uncertainty in the elastic constants multiplied by the measured strains. For the focused ion beam-digital image correlation (FIB-DIC) ring-core method taken as an example, a Mathematica package was developed to evaluate the complete in-plane residual stress state from the measured strain relief values using known material orientation and anisotropic elastic properties for materials displaying cubic symmetry. However, in many practical situations the underlying material orientation is unknown, and nominal isotropic continuum elastic constants are used. This leads to a systematic error in the stress calculation. The present analysis focuses on the statistical evaluation of the uncertainty in stress evaluation due to the unknown material orientation as a function of its degree of anisotropy. We demonstrate an experimental application of this procedure to a real case of micron scale residual stress analysis in a nickel-base superalloy.
Quantifying eigenstrain distributions induced by focused ion beam damage in silicon
Materials Letters, 2016
Abstract Eigenstrain offers a versatile generic framework for the description of inelastic deform... more Abstract Eigenstrain offers a versatile generic framework for the description of inelastic deformation that acts as the source of residual stresses. Focused ion beam (FIB) milling used for nanoscale machining is accompanied by target material modification by ion beam damage having residual stress consequences that can be described in terms of eigenstrain. Due to the lack of direct means of experimental determination of residual stress or eigenstrain at the nanoscale we adopt a hybrid approach that consists of eigenstrain abstraction from molecular dynamics simulation, its application within a finite element simulation of a flexible silicon cantilever, and satisfactory comparison of the prediction with experimental observation. Directions for further enquiry are briefly discussed.
Mechanics of Materials, 2017
This paper presents a characterisation of surface damage, more specifically dents, caused by low ... more This paper presents a characterisation of surface damage, more specifically dents, caused by low velocity impacts of blunt objects on RR1000 Nickel superalloys. These are representative of damage that may occur during handling and service of components during manufacturing or maintenance. The characterisation of dents produced in laboratory tests is carried out both in terms of their geometry and the residual stresses the damage. A finite element model is presented and the results are validated in terms of dent geometry produced for different impact velocities. The stress distribution predicted by the numerical model is also compared with experimentally measured stresses via X-ray diffraction for validation of the model. The residual stresses obtained from the finite element (FE) model and their implications to fatigue and crack propagation lives are also discussed here.
International Journal of Plasticity, 2017
An analysis of macro-and micro-scale residual stresses of Type I, II and III using FIB-DIC micro-... more An analysis of macro-and micro-scale residual stresses of Type I, II and III using FIB-DIC micro-ring-core milling and crystal plasticity FE modelling,
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Papers by Alexander Korsunsky