Evgenia Yakushina - Academia.edu (original) (raw)
Papers by Evgenia Yakushina
Crystals
Within the framework of the formability limit assessment in sheet metal forming, testing of notch... more Within the framework of the formability limit assessment in sheet metal forming, testing of notched tensile samples coupled with digital image correlation (DIC) has been analysed as an alternative to overcome the implications of Nakajima testing in relation to times of test preparation, cost of the equipment, presence of friction, and amount of material required for the test. Additionally, the complications of the Nakajima testing at elevated temperatures need to also be considered. In this work, specific notched sample geometries have been investigated to accurately identify the forming limits of Aluminium alloy AA6016 in T4 condition. Once the notched geometry had been defined, experimental tensile testing of the samples coupled with DIC technology allowed us to identify the formability limits of interest. Finally, a comparison at room temperature with the conventional Nakajima testing was performed experimentally. Two different methodologies for strain limit evaluation in notched...
Materials
Typically, due to their limited formability, elevated temperatures are required in order to achie... more Typically, due to their limited formability, elevated temperatures are required in order to achieve complex shapes in titanium alloys. However, there are opportunities for forming such alloys at room temperature using incremental forming processes such as single-point incremental forming (SPIF). SPIF is an innovative metal forming technology which uses a single tool to form sheet parts in place of dedicated dies. SPIFs ability to increase the forming limits of difficult-to-form materials offers an alternative to high temperature processing of titanium. However, sheet thinning during SPIF may encourage the early onset of fracture, compromising in-service performance. An additive step prior to SPIF has been examined to tailor the initial sheet thickness to achieve a homogeneous thickness distribution in the final part. In the present research, laser metal deposition (LMD) was used to locally thicken a commercially pure titanium grade 2 (CP-Ti50A) sheet. Tensile testing was used to exa...
Journal of Manufacturing Processes
This paper presents the microstructure investigation results of linear friction welded joints of ... more This paper presents the microstructure investigation results of linear friction welded joints of Ti-6Al-4V samples with coarse-grained (CG) and ultrafine grained (UFG) structure. The features of phase and structural transformations in the weld and the thermo-mechanically affected areas, as well as the microhardness distribution across the width of the welded joint were demonstrated.
MATEC Web of Conferences
Titanium and its alloys are difficult to form, particularly at room temperature, due to their cry... more Titanium and its alloys are difficult to form, particularly at room temperature, due to their crystallographic structure and limited availability of slip systems. Such limited formability could be exacerbated by virtue of the technique used to cut the sheet. Forming limit diagrams will not necessarily recognize such effects, which can lead to failures during forming trials. An example of a situation where this could be demonstrated is in sheet with pre-fabricated holes. This work used a hemispherical punch to stretch in-plane a 20mm diameter hole prepared with laser, EDM and AWJ cutting techniques in order to quantify the edge formability of the material. It was identified that, the edge surface conditions have a major impact on the edge formability of the material. The edges of the material prepared with EDM showed very high formability tendencies compared with AWJ and laser cutting. The work proposed an alternative characterization method that could be adopted for edge formability...
Journal of Materials and Applications
Hole expansion ratio is a material parameter which defines the extent to which sheet metals are f... more Hole expansion ratio is a material parameter which defines the extent to which sheet metals are formed. Research has shown that, the stress state observed at the hole edge after hole expansion test is similar to those observed during conventional uniaxial tensile test. However, conventional tensile test methods are not efficient in evaluating material edge formability. This work utilised optical non-contact measuring techniques to examine failure behaviour during tensile test and hole expansion test of commercially pure titanium sheet, fabricated with either abrasive water jet cutting or electric discharge machining. The work found that, the deformation mode in conventional tensile testing are governed by localised necking and subsequently diffused necking prior to failure. Deformation mode observed in hole expansion test is characterised by localised necking with no visible occurrence of diffused necking prior to failure. The highest strains are concentrated at the hole edge during...
Materials Science and Engineering: A
The influence of ultra fine grained (UFG) and coarse grained (CG) microstructure of the titanium ... more The influence of ultra fine grained (UFG) and coarse grained (CG) microstructure of the titanium alloy Ti-6Al-4V on the strength of a diffusion bonded (DB) joint was studied using a laboratory DB fixture and a new shear test rig. The DB process was carried out at 725°C and 825°C during 2 and 4 h in a vacuum furnace. Coarsening of grain structure resulting from different DB cycles was quantified. The chain pores were observed at 725°C for both microstructure conditions bonded during 2 h. The increase of bonding time up to 4 h leads to subsequent elimination of the pores. The UFG samples bonded at 725°C showed a higher level of the shear strength than CG samples for both bonding times. The CG material demonstrated the highest shear strength after 4 h of DB bonding at 825°C. The increase of the creep deformation of UFG samples when compared to the CG condition was observed as a result of DB at of 725°C during 4 h.
IOP Conference Series: Materials Science and Engineering
The Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archiv... more The Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output.
A fully automated procedure for microstructural analysis is proposed. • Measurement accuracy is v... more A fully automated procedure for microstructural analysis is proposed. • Measurement accuracy is validated on Ti6Al4V microstructures. • Grain size measurements are consistent with results from existing procedures. • Much faster measurement times when compared with manual procedures.
Materials Science and Engineering A
Mechanical properties of AZ31B magnesium alloy were modified in this work by various processing r... more Mechanical properties of AZ31B magnesium alloy were modified in this work by various processing routes of incremental equal channel angular pressing (I-ECAP) followed by heat treatment. Possible strategies for improving ductility and strength of the alloy were investigated. Processing by routes A and BC showed that texture plays predominant role in controlling mechanical properties at room temperature. Four passes of I-ECAP by route C followed by annealing enhanced ductility up to 0.35 of true strain. It was found that tensile twinning was important in accommodating strain during tensile testing, which resulted in a very good hardening behaviour. The yield strength was improved to 300 MPa by refining grain size to 0.8 µm in I-ECAP at 150 °C. The obtained structure and properties were shown to be stable up to 150 °C. True strain at fracture was increased to 0.2 after annealing at 150 °C without lowering strength.
Materials & Design
A fully automated procedure for microstructural analysis is proposed. • Measurement accuracy is v... more A fully automated procedure for microstructural analysis is proposed. • Measurement accuracy is validated on Ti6Al4V microstructures. • Grain size measurements are consistent with results from existing procedures. • Much faster measurement times when compared with manual procedures.
Letters on Materials
Being very strong and of limited ductility, Ti alloys require special techniques to manufacture t... more Being very strong and of limited ductility, Ti alloys require special techniques to manufacture the parts with complex shapes. Many of these technologies are based on superplastic and near-to-superplastic deforming. In these processes the transformation of the microstructure of the material can be very significant and can lead to changes in the mechanical properties of the material during deformation. Because of this an appropriate description of the correlation between mechanical loading, changes in microstructure and mechanical behavior of material is required. A phenomenological scalar model with an internal variable based on a statistical description of microstructure is proposed and used for simulation of the high temperature deformation of Ti-6Al-4V alloy. The problems of obtaining the parameters of the model and sensitivity of the model to the accuracy of this process are discussed.
This paper presents the microstructure investigation results of linear friction welded joints of ... more This paper presents the microstructure investigation results of linear friction welded joints of Ti-6Al-4V samples with coarse-grained (CG) and ultrafine grained (UFG) structure. The features of phase and structural transformations in the weld and the thermo-mechanically affected areas, as well as the microhardness distribution across the width of the welded joint were demonstrated.
IOP Conference Series: Materials Science and Engineering, 2014
The majority of methods of severe plastic deformation (SPD) used for producing ultra-fine grained... more The majority of methods of severe plastic deformation (SPD) used for producing ultra-fine grained (UFG) and nano materials involve the non-uniform distribution of strains in the workpiece. To make the refinement of grains uniform, interlinked operations are used in which either the orientation of the workpiece or the type of SPD is changed in some sequence. Each operation has its own set of control parameters affecting the output result. As a result, the optimization of the total chain of operations becomes very difficult, especially taking into account that each stage of material processing comes from the previous one with a certain non-uniformity of the structure. To deal with such types of problems the capability of tracing the transformation of the microstructure and accounting for its effect on mechanical properties in finite element modeling (FEM) is required. There are a number of detailed physical models of grain refinement and texture formation, but very often they are too complicated for practical engineering simulations. The mechanics of SPD are also studied and simulated in many works, but normally it is assumed that material is uniform, isotropic and its properties don't change during deformation. In this paper a microstructurally-coupled FE model of the SPD process is proposed. The question of selection and verification of macroscopic and microscopic constitutive relations is discussed. The results of a simulation made in QForm are analyzed and compared with some initial experimental data.
Materials Science Forum, 2014
Diffusion bonding of Ti-6Al-4V titanium alloy in the coarse grained and ultrafine grained state w... more Diffusion bonding of Ti-6Al-4V titanium alloy in the coarse grained and ultrafine grained state was performed. The effect of initial structure and surface condition, as well as temperature and time, on the quality of joints was established. It is shown that, due to low-temperature superplasticity and high diffusion rate, samples with ultrafine grained structure demonstrate better bondability than coarse grained samples
Materials Science Forum, 2008
Nanostructured titanium (nTi) with essential enhanced strength and fatigue characteristics is an ... more Nanostructured titanium (nTi) with essential enhanced strength and fatigue characteristics is an advanced material for dental implant applications. Nano Ti is commercially pure titanium, that was nanostructured by a special technique of severe plastic deformation. It is bio inert, does not contain even potentially toxic or allergenetic additives and has significantly higher specific strength properties than any other titanium applied in dental implants. Cylindrical threaded screw implants Nanoimplant® sized 2.4 mm in diameter and 12 mm in length were made from nTi. It is the first application of nTi dental implant in the world reported. Recently more than 250 successful clinical applications dealing with surgery on the front teeth were carried out. No complications were noticed during the early postoperative period and early loading. Laboratory cytocompatibility tests undertaken so far on mice fibroblast cells have indicated that nanocrystalline Ti surface has a significantly better...
Key Engineering Materials, 2013
An AZ31B wrought magnesium alloy was processed by incremental equal channel angular pressing (I-E... more An AZ31B wrought magnesium alloy was processed by incremental equal channel angular pressing (I-ECAP) using routes A and B C. Despite the fact that the measured grain size for both routes was very similar, the mechanical properties were different. Tensile strength was improved using route A comparing to route B C , without ductility loss, while tension-compression anisotropy observed for route A was significantly suppressed when using route B C. Moreover, billet shape evolution resulting from subsequent passes of I-ECAP was studied. Significant distortion after processing using route B C and no occurrence of such effect for route A were observed. Results of a finite element analysis showed that nonuniform strain rate sensitivity might be responsible for different billet shapes. The conclusion is drawn that processing route has a strong influence on the billet shape and mechanical properties when processing magnesium alloys by I-ECAP.
Crystals
Within the framework of the formability limit assessment in sheet metal forming, testing of notch... more Within the framework of the formability limit assessment in sheet metal forming, testing of notched tensile samples coupled with digital image correlation (DIC) has been analysed as an alternative to overcome the implications of Nakajima testing in relation to times of test preparation, cost of the equipment, presence of friction, and amount of material required for the test. Additionally, the complications of the Nakajima testing at elevated temperatures need to also be considered. In this work, specific notched sample geometries have been investigated to accurately identify the forming limits of Aluminium alloy AA6016 in T4 condition. Once the notched geometry had been defined, experimental tensile testing of the samples coupled with DIC technology allowed us to identify the formability limits of interest. Finally, a comparison at room temperature with the conventional Nakajima testing was performed experimentally. Two different methodologies for strain limit evaluation in notched...
Materials
Typically, due to their limited formability, elevated temperatures are required in order to achie... more Typically, due to their limited formability, elevated temperatures are required in order to achieve complex shapes in titanium alloys. However, there are opportunities for forming such alloys at room temperature using incremental forming processes such as single-point incremental forming (SPIF). SPIF is an innovative metal forming technology which uses a single tool to form sheet parts in place of dedicated dies. SPIFs ability to increase the forming limits of difficult-to-form materials offers an alternative to high temperature processing of titanium. However, sheet thinning during SPIF may encourage the early onset of fracture, compromising in-service performance. An additive step prior to SPIF has been examined to tailor the initial sheet thickness to achieve a homogeneous thickness distribution in the final part. In the present research, laser metal deposition (LMD) was used to locally thicken a commercially pure titanium grade 2 (CP-Ti50A) sheet. Tensile testing was used to exa...
Journal of Manufacturing Processes
This paper presents the microstructure investigation results of linear friction welded joints of ... more This paper presents the microstructure investigation results of linear friction welded joints of Ti-6Al-4V samples with coarse-grained (CG) and ultrafine grained (UFG) structure. The features of phase and structural transformations in the weld and the thermo-mechanically affected areas, as well as the microhardness distribution across the width of the welded joint were demonstrated.
MATEC Web of Conferences
Titanium and its alloys are difficult to form, particularly at room temperature, due to their cry... more Titanium and its alloys are difficult to form, particularly at room temperature, due to their crystallographic structure and limited availability of slip systems. Such limited formability could be exacerbated by virtue of the technique used to cut the sheet. Forming limit diagrams will not necessarily recognize such effects, which can lead to failures during forming trials. An example of a situation where this could be demonstrated is in sheet with pre-fabricated holes. This work used a hemispherical punch to stretch in-plane a 20mm diameter hole prepared with laser, EDM and AWJ cutting techniques in order to quantify the edge formability of the material. It was identified that, the edge surface conditions have a major impact on the edge formability of the material. The edges of the material prepared with EDM showed very high formability tendencies compared with AWJ and laser cutting. The work proposed an alternative characterization method that could be adopted for edge formability...
Journal of Materials and Applications
Hole expansion ratio is a material parameter which defines the extent to which sheet metals are f... more Hole expansion ratio is a material parameter which defines the extent to which sheet metals are formed. Research has shown that, the stress state observed at the hole edge after hole expansion test is similar to those observed during conventional uniaxial tensile test. However, conventional tensile test methods are not efficient in evaluating material edge formability. This work utilised optical non-contact measuring techniques to examine failure behaviour during tensile test and hole expansion test of commercially pure titanium sheet, fabricated with either abrasive water jet cutting or electric discharge machining. The work found that, the deformation mode in conventional tensile testing are governed by localised necking and subsequently diffused necking prior to failure. Deformation mode observed in hole expansion test is characterised by localised necking with no visible occurrence of diffused necking prior to failure. The highest strains are concentrated at the hole edge during...
Materials Science and Engineering: A
The influence of ultra fine grained (UFG) and coarse grained (CG) microstructure of the titanium ... more The influence of ultra fine grained (UFG) and coarse grained (CG) microstructure of the titanium alloy Ti-6Al-4V on the strength of a diffusion bonded (DB) joint was studied using a laboratory DB fixture and a new shear test rig. The DB process was carried out at 725°C and 825°C during 2 and 4 h in a vacuum furnace. Coarsening of grain structure resulting from different DB cycles was quantified. The chain pores were observed at 725°C for both microstructure conditions bonded during 2 h. The increase of bonding time up to 4 h leads to subsequent elimination of the pores. The UFG samples bonded at 725°C showed a higher level of the shear strength than CG samples for both bonding times. The CG material demonstrated the highest shear strength after 4 h of DB bonding at 825°C. The increase of the creep deformation of UFG samples when compared to the CG condition was observed as a result of DB at of 725°C during 4 h.
IOP Conference Series: Materials Science and Engineering
The Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archiv... more The Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output.
A fully automated procedure for microstructural analysis is proposed. • Measurement accuracy is v... more A fully automated procedure for microstructural analysis is proposed. • Measurement accuracy is validated on Ti6Al4V microstructures. • Grain size measurements are consistent with results from existing procedures. • Much faster measurement times when compared with manual procedures.
Materials Science and Engineering A
Mechanical properties of AZ31B magnesium alloy were modified in this work by various processing r... more Mechanical properties of AZ31B magnesium alloy were modified in this work by various processing routes of incremental equal channel angular pressing (I-ECAP) followed by heat treatment. Possible strategies for improving ductility and strength of the alloy were investigated. Processing by routes A and BC showed that texture plays predominant role in controlling mechanical properties at room temperature. Four passes of I-ECAP by route C followed by annealing enhanced ductility up to 0.35 of true strain. It was found that tensile twinning was important in accommodating strain during tensile testing, which resulted in a very good hardening behaviour. The yield strength was improved to 300 MPa by refining grain size to 0.8 µm in I-ECAP at 150 °C. The obtained structure and properties were shown to be stable up to 150 °C. True strain at fracture was increased to 0.2 after annealing at 150 °C without lowering strength.
Materials & Design
A fully automated procedure for microstructural analysis is proposed. • Measurement accuracy is v... more A fully automated procedure for microstructural analysis is proposed. • Measurement accuracy is validated on Ti6Al4V microstructures. • Grain size measurements are consistent with results from existing procedures. • Much faster measurement times when compared with manual procedures.
Letters on Materials
Being very strong and of limited ductility, Ti alloys require special techniques to manufacture t... more Being very strong and of limited ductility, Ti alloys require special techniques to manufacture the parts with complex shapes. Many of these technologies are based on superplastic and near-to-superplastic deforming. In these processes the transformation of the microstructure of the material can be very significant and can lead to changes in the mechanical properties of the material during deformation. Because of this an appropriate description of the correlation between mechanical loading, changes in microstructure and mechanical behavior of material is required. A phenomenological scalar model with an internal variable based on a statistical description of microstructure is proposed and used for simulation of the high temperature deformation of Ti-6Al-4V alloy. The problems of obtaining the parameters of the model and sensitivity of the model to the accuracy of this process are discussed.
This paper presents the microstructure investigation results of linear friction welded joints of ... more This paper presents the microstructure investigation results of linear friction welded joints of Ti-6Al-4V samples with coarse-grained (CG) and ultrafine grained (UFG) structure. The features of phase and structural transformations in the weld and the thermo-mechanically affected areas, as well as the microhardness distribution across the width of the welded joint were demonstrated.
IOP Conference Series: Materials Science and Engineering, 2014
The majority of methods of severe plastic deformation (SPD) used for producing ultra-fine grained... more The majority of methods of severe plastic deformation (SPD) used for producing ultra-fine grained (UFG) and nano materials involve the non-uniform distribution of strains in the workpiece. To make the refinement of grains uniform, interlinked operations are used in which either the orientation of the workpiece or the type of SPD is changed in some sequence. Each operation has its own set of control parameters affecting the output result. As a result, the optimization of the total chain of operations becomes very difficult, especially taking into account that each stage of material processing comes from the previous one with a certain non-uniformity of the structure. To deal with such types of problems the capability of tracing the transformation of the microstructure and accounting for its effect on mechanical properties in finite element modeling (FEM) is required. There are a number of detailed physical models of grain refinement and texture formation, but very often they are too complicated for practical engineering simulations. The mechanics of SPD are also studied and simulated in many works, but normally it is assumed that material is uniform, isotropic and its properties don't change during deformation. In this paper a microstructurally-coupled FE model of the SPD process is proposed. The question of selection and verification of macroscopic and microscopic constitutive relations is discussed. The results of a simulation made in QForm are analyzed and compared with some initial experimental data.
Materials Science Forum, 2014
Diffusion bonding of Ti-6Al-4V titanium alloy in the coarse grained and ultrafine grained state w... more Diffusion bonding of Ti-6Al-4V titanium alloy in the coarse grained and ultrafine grained state was performed. The effect of initial structure and surface condition, as well as temperature and time, on the quality of joints was established. It is shown that, due to low-temperature superplasticity and high diffusion rate, samples with ultrafine grained structure demonstrate better bondability than coarse grained samples
Materials Science Forum, 2008
Nanostructured titanium (nTi) with essential enhanced strength and fatigue characteristics is an ... more Nanostructured titanium (nTi) with essential enhanced strength and fatigue characteristics is an advanced material for dental implant applications. Nano Ti is commercially pure titanium, that was nanostructured by a special technique of severe plastic deformation. It is bio inert, does not contain even potentially toxic or allergenetic additives and has significantly higher specific strength properties than any other titanium applied in dental implants. Cylindrical threaded screw implants Nanoimplant® sized 2.4 mm in diameter and 12 mm in length were made from nTi. It is the first application of nTi dental implant in the world reported. Recently more than 250 successful clinical applications dealing with surgery on the front teeth were carried out. No complications were noticed during the early postoperative period and early loading. Laboratory cytocompatibility tests undertaken so far on mice fibroblast cells have indicated that nanocrystalline Ti surface has a significantly better...
Key Engineering Materials, 2013
An AZ31B wrought magnesium alloy was processed by incremental equal channel angular pressing (I-E... more An AZ31B wrought magnesium alloy was processed by incremental equal channel angular pressing (I-ECAP) using routes A and B C. Despite the fact that the measured grain size for both routes was very similar, the mechanical properties were different. Tensile strength was improved using route A comparing to route B C , without ductility loss, while tension-compression anisotropy observed for route A was significantly suppressed when using route B C. Moreover, billet shape evolution resulting from subsequent passes of I-ECAP was studied. Significant distortion after processing using route B C and no occurrence of such effect for route A were observed. Results of a finite element analysis showed that nonuniform strain rate sensitivity might be responsible for different billet shapes. The conclusion is drawn that processing route has a strong influence on the billet shape and mechanical properties when processing magnesium alloys by I-ECAP.