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Achilles Vairis
Mechanical Engineering Department, Hellenic Mediterranean University, 71410 Heraklion Crete, Greece

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Journal article
Published: 15 March 2021 in International Journal of Environmental Research and Public Health
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Enhancing gait stability in people who use crutches is paramount for their health. With the significant difference in gait compared to users who do not require an assistive device, the use of standard gait analysis tools to measure movement for temporary crush users and physically disabled people proves to be more challenging. In this paper, a novel approach based on video analysis is proposed as non-contact low-cost solution to the more expensive alternative with the data collected from processed videos, two values are calculated: the Signal to Noise Ratio (SNR) of acceleration, and the Signal to Noise Ratio of the jerk (time derivative of acceleration), to assess the user’s stability while they walk with crutches. The adopted methodology has been tested on a total of 10 participants. Five are temporary users of assistive devices with one being a long-term user and the other four novice users, and five are disabled participants who use those assistive devices permanently. Preliminary results show differences between novice users, long-term users, and physically disabled users. The approach is promising and could improve the assessment of crutch user stability, allowing for the correction of gait for individuals while using an inexpensive non-contact setup and preventing unnecessary falls.

ACS Style

Achilles Vairis; Suzana Brown; Maurice Bess; Kyu Bae; Jonathan Boyack. Assessing Stability of Crutch Users by Non-Contact Methods. International Journal of Environmental Research and Public Health 2021, 18, 3001 .

AMA Style

Achilles Vairis, Suzana Brown, Maurice Bess, Kyu Bae, Jonathan Boyack. Assessing Stability of Crutch Users by Non-Contact Methods. International Journal of Environmental Research and Public Health. 2021; 18 (6):3001.

Chicago/Turabian Style

Achilles Vairis; Suzana Brown; Maurice Bess; Kyu Bae; Jonathan Boyack. 2021. "Assessing Stability of Crutch Users by Non-Contact Methods." International Journal of Environmental Research and Public Health 18, no. 6: 3001.

Conference paper
Published: 06 February 2021 in Transactions on Petri Nets and Other Models of Concurrency XV
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The goal of this project is to remotely analyze the gait of people walking with crutches. To that objective, the use of video analysis based on the open-source software OpenPose is compared with the data collected from a sensor mounted on a human subject. The results show that the average value of acceleration between the video analysis and the sensor differs by 0.05%. All steps are clearly identified and synchronized. As a consequence, it is possible to validate non-contact acceleration data from video analysis with an inexpensive setup described in this paper. The results show a promise that this non-contact method can be used to assess the gait of disabled people with assistive devices in remote locations.

ACS Style

Achilles Vairis; Johnathan Boyak; Suzana Brown; Maurice Bess; Kyu Hyun Bae; Markos Petousis. Gait Analysis Using Video for Disabled People in Marginalized Communities. Transactions on Petri Nets and Other Models of Concurrency XV 2021, 145 -153.

AMA Style

Achilles Vairis, Johnathan Boyak, Suzana Brown, Maurice Bess, Kyu Hyun Bae, Markos Petousis. Gait Analysis Using Video for Disabled People in Marginalized Communities. Transactions on Petri Nets and Other Models of Concurrency XV. 2021; ():145-153.

Chicago/Turabian Style

Achilles Vairis; Johnathan Boyak; Suzana Brown; Maurice Bess; Kyu Hyun Bae; Markos Petousis. 2021. "Gait Analysis Using Video for Disabled People in Marginalized Communities." Transactions on Petri Nets and Other Models of Concurrency XV , no. : 145-153.

Journal article
Published: 29 December 2020 in Metals
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The aim of this work was to weld thin sheets (2 mm) of Al 7075 in a butt joint configuration using friction stir welding and to identify the appropriate tool geometry and optimum process parameters. Two tools were produced with heat treatable low alloy steel WNr 1.6582/DIN 34CrNiMo6 with a different pin diameter (3 mm and 4 mm). Welding was performed at a range of rotation speeds 1000–2500 rpm and various welding speeds 80–800 mm/min. The tensile strength was measured to evaluate mechanical properties. Results showed that despite the difficulties in friction stir welding thin plates, sound joints can be produced in a repeatable manner, without visible wear on the welding tool. The mechanical strength of the welds showed a decrease (33.75%) over that of the parent material. The mechanical strength was less affected by rotation speed than welding speed and there was a significant decrease in tensile strength compared to the parent material.

ACS Style

Andreas Dimopoulos; Achilles Vairis; Nectarios Vidakis; Markos Petousis. On the Friction Stir Welding of Al 7075 Thin Sheets. Metals 2020, 11, 57 .

AMA Style

Andreas Dimopoulos, Achilles Vairis, Nectarios Vidakis, Markos Petousis. On the Friction Stir Welding of Al 7075 Thin Sheets. Metals. 2020; 11 (1):57.

Chicago/Turabian Style

Andreas Dimopoulos; Achilles Vairis; Nectarios Vidakis; Markos Petousis. 2020. "On the Friction Stir Welding of Al 7075 Thin Sheets." Metals 11, no. 1: 57.

Research articles
Published: 25 September 2020 in Science and Technology of Welding and Joining
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Linear friction welding was used to join Ti–3Al–8V–6Cr–4Mo–4Zr alloy under different pressures, and the microstructure, texture evolution and mechanical properties of the joint were investigated. Results show that the incomplete continuous dynamic recrystallisation (CDRX) occurs during welding, which refines the grains and produces a large number of subgrains in the thermo-mechanically affected zone (TMAZ) and weld centre zone (WCZ). At a higher friction pressure, the width of the WCZ becomes narrower, with the decrease of grain size and the increase of recrystallisation degree. In addition, the texture in the WCZ has changed from {112} to {110}, while the texture in the TMAZ remains at {110}. The tensile properties of the two joints are similar to the base metal (BM), and the microhardness in WCZ and TMAZ are also close to that in BM due to the incomplete CDRX and the decrease of alpha phase.

ACS Style

Xinyu Wang; Wenya Li; Qing Ye; Xiawei Yang; Tiejun Ma; Achilles Vairis. Linear friction welding of a beta titanium alloy: experimental investigations on microstructure evolution and mechanical properties. Science and Technology of Welding and Joining 2020, 25, 1 -12.

AMA Style

Xinyu Wang, Wenya Li, Qing Ye, Xiawei Yang, Tiejun Ma, Achilles Vairis. Linear friction welding of a beta titanium alloy: experimental investigations on microstructure evolution and mechanical properties. Science and Technology of Welding and Joining. 2020; 25 (8):1-12.

Chicago/Turabian Style

Xinyu Wang; Wenya Li; Qing Ye; Xiawei Yang; Tiejun Ma; Achilles Vairis. 2020. "Linear friction welding of a beta titanium alloy: experimental investigations on microstructure evolution and mechanical properties." Science and Technology of Welding and Joining 25, no. 8: 1-12.

Journal article
Published: 19 June 2020 in Polymers
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Polyimides rank among the most heat-resistant polymers and find application in a variety of fields, including transportation, electronics, and membrane technology. The aim of this work is to study the structural, thermal, mechanical, and gas permeation properties of polyimide based nanocomposite membranes in flat sheet configuration. For this purpose, numerous advanced techniques such as atomic force microscopy (AFM), SEM, TEM, TGA, FT-IR, tensile strength, elongation test, and gas permeability measurements were carried out. In particular, BTDA–TDI/MDI (Ρ84) co-polyimide was used as the matrix of the studied membranes, whereas multi-wall carbon nanotubes were employed as filler material at concentrations of up to 5 wt.% All studied films were prepared by the dry-cast process resulting in non-porous films of about 30–50 μm of thickness. An optimum filler concentration of 2 wt.% was estimated. At this concentration, both thermal and mechanical properties of the prepared membranes were improved, and the highest gas permeability values were also obtained. Finally, gas permeability experiments were carried out at 25, 50, and 100 °C with seven different pure gases. The results revealed that the uniform carbon nanotubes dispersion lead to enhanced gas permeation properties.

ACS Style

Andreas A. Sapalidis; Panagiotis I. Karantzis; Achilles Vairis; Stephanos F. Nitodas; Stéphan Barbe; Evangelos P. Favvas. A Study of the Reinforcement Effect of MWCNTs onto Polyimide Flat Sheet Membranes. Polymers 2020, 12, 1381 .

AMA Style

Andreas A. Sapalidis, Panagiotis I. Karantzis, Achilles Vairis, Stephanos F. Nitodas, Stéphan Barbe, Evangelos P. Favvas. A Study of the Reinforcement Effect of MWCNTs onto Polyimide Flat Sheet Membranes. Polymers. 2020; 12 (6):1381.

Chicago/Turabian Style

Andreas A. Sapalidis; Panagiotis I. Karantzis; Achilles Vairis; Stephanos F. Nitodas; Stéphan Barbe; Evangelos P. Favvas. 2020. "A Study of the Reinforcement Effect of MWCNTs onto Polyimide Flat Sheet Membranes." Polymers 12, no. 6: 1381.

Journal article
Published: 27 April 2020 in Sustainability
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Sustainability in additive manufacturing refers mainly to the recycling rate of polymers and composites used in fused filament fabrication (FFF), which nowadays are rapidly increasing in volume and value. Recycling of such materials is mostly a thermomechanical process that modifies their overall mechanical behavior. The present research work focuses on the acrylonitrile-butadiene-styrene (ABS) polymer, which is the second most popular material used in FFF-3D printing. In order to investigate the effect of the recycling courses on the mechanical response of the ABS polymer, an experimental simulation of the recycling process that isolates the thermomechanical treatment from other parameters (i.e., contamination, ageing, etc.) has been performed. To quantify the effect of repeated recycling processes on the mechanic response of the ABS polymer, a wide variety of mechanical tests were conducted on FFF-printed specimens. Regarding this, standard tensile, compression, flexion, impact and micro-hardness tests were performed per recycle repetition. The findings prove that the mechanical response of the recycled ABS polymer is generally improved over the recycling repetitions for a certain number of repetitions. An optimum overall mechanical behavior is found between the third and the fifth repetition, indicating a significant positive impact of the ABS polymer recycling, besides the environmental one.

ACS Style

Nectarios Vidakis; Markos Petousis; Athena Maniadi; Emmanuel Koudoumas; Achilles Vairis; John Kechagias. Sustainable Additive Manufacturing: Mechanical Response of Acrylonitrile-Butadiene-Styrene over Multiple Recycling Processes. Sustainability 2020, 12, 3568 .

AMA Style

Nectarios Vidakis, Markos Petousis, Athena Maniadi, Emmanuel Koudoumas, Achilles Vairis, John Kechagias. Sustainable Additive Manufacturing: Mechanical Response of Acrylonitrile-Butadiene-Styrene over Multiple Recycling Processes. Sustainability. 2020; 12 (9):3568.

Chicago/Turabian Style

Nectarios Vidakis; Markos Petousis; Athena Maniadi; Emmanuel Koudoumas; Achilles Vairis; John Kechagias. 2020. "Sustainable Additive Manufacturing: Mechanical Response of Acrylonitrile-Butadiene-Styrene over Multiple Recycling Processes." Sustainability 12, no. 9: 3568.

Journal article
Published: 08 April 2020 in Journal of Manufacturing Processes
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In this study, the Ti-4Al-0.005B (TA5, Chinese brand) titanium alloy was used in a specially designed T-joint joined by friction stir welding, where two plates served as the skins and one plate served as the stringer with two separate welds. The base material (BM) has a typical rolling microstructure, consisting of α grains deformed along the rolling direction. The grains in the heat-affected zone (HAZ) are coarser than those in the BM, while the grains in the thermo-mechanically affected zone are deformed along the shear direction. When the temperature is higher than the β transus in the welding process, there are lamellar α phase structures in the stir zone (SZ). When the temperature is lower than the β transus in the welding process, there are fine equiaxed grains in the SZ due to sufficient dynamic recrystallization, while the grains in the first weld are slightly larger than those in the second weld due to their longer exposure to the thermal cycle of the second weld. The microhardness of the first weld decreases following the second weld, and the area of lowest microhardness occurs in the HAZ on the advancing side near the first weld. The microhardness of SZ at the position of 0.5 mm from the upper surface is slightly higher in the thickness direction. In the tensile tests, the initial position of the fracture occurs in the area where the skin and the stringer are joined by FSW. With the increase of tool rotation speed from 450 rpm to 850 rpm, the tensile strength increases first and then decreases along the direction of skin and stringer. In addition, a coupled Eulerian-Lagrangian (CEL) numerical model is developed to investigate the temperature distribution and material flow during FSW, showing stronger correlation with the experiments.

ACS Style

Yu Su; Wenya Li; Xichang Liu; Fuyang Gao; Yan Yu; Achilles Vairis. Strengthening mechanism of friction stir welded alpha titanium alloy specially designed T-joints. Journal of Manufacturing Processes 2020, 55, 1 -12.

AMA Style

Yu Su, Wenya Li, Xichang Liu, Fuyang Gao, Yan Yu, Achilles Vairis. Strengthening mechanism of friction stir welded alpha titanium alloy specially designed T-joints. Journal of Manufacturing Processes. 2020; 55 ():1-12.

Chicago/Turabian Style

Yu Su; Wenya Li; Xichang Liu; Fuyang Gao; Yan Yu; Achilles Vairis. 2020. "Strengthening mechanism of friction stir welded alpha titanium alloy specially designed T-joints." Journal of Manufacturing Processes 55, no. : 1-12.

Articles
Published: 25 September 2019 in Materials and Manufacturing Processes
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In this study, AA5083 aluminum alloy T-joints were properly welded, where both of the corners were successfully joined with stationary shoulder friction stir welding. According to the microstructure, the joint can be divided into base material, heat affected zone, thermo-mechanically affected zone, weld nugget zone and weld nugget overlap zone. The microhardness near the first weld is lower than that near the second weld as a result of the additional heating during the second weld process. In tensile test, the highest tensile strength of the skin and the stringer has reached 50.8% and 56.9% of the base material, respectively. All fractures have occurred near the heat affected zone of the first weld pass, while the fracture mode is ductile. Numerical modeling shows that the maximum strain is located in the area close to the welding tool, and the strain gradient near the advancing side is significantly higher than that near the retreating side. In addition, the degree of material flow is even along the thickness direction of the plate during stationary shoulder friction stir welding, and the material distribution is asymmetric on both sides of the weld due to different material flows in the advancing side and retreating side.

ACS Style

Yu Su; Wenya Li; Vivek Patel; Achilles Vairis; Feifan Wang. Formability of an AA5083 aluminum alloy T-joint using SSFSW on both corners. Materials and Manufacturing Processes 2019, 34, 1737 -1744.

AMA Style

Yu Su, Wenya Li, Vivek Patel, Achilles Vairis, Feifan Wang. Formability of an AA5083 aluminum alloy T-joint using SSFSW on both corners. Materials and Manufacturing Processes. 2019; 34 (15):1737-1744.

Chicago/Turabian Style

Yu Su; Wenya Li; Vivek Patel; Achilles Vairis; Feifan Wang. 2019. "Formability of an AA5083 aluminum alloy T-joint using SSFSW on both corners." Materials and Manufacturing Processes 34, no. 15: 1737-1744.

Article
Published: 20 September 2019 in Metals and Materials International
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The microstructure and mechanical properties of bobbin tool friction stir welded joints for 2219-T87 aluminum alloy using different welding speeds were investigated based on the experimental results together with a thermo-mechanical model developed. The stir zone created in the joint shows a dumbbell shape. As welding speed increases, both the width and grain size of stir zone decrease. The symmetrical hardness distribution forms across the joint thickness, while the asymmetric hardness is measured along the width of the stir zone. The hardness of the stir zone on the retreating side is lower than that on the advancing side. The hardness profile presents a W-shape, with the minimum values measured increasing with welding speed. The tensile residual stresses increase gradually towards the center of the joint from the outer surface, presenting a symmetrical feature as well. As welding speed increases, both the tensile strength and elongation show a maximum value 70% of joint efficiency. Tensile fracture occurs in the stir zone and shows a symmetrical surface with three different layer fracture modes identified. In layers I and III, the fracture surface presents 45° direction, while fracture propagates along the S-line in layer II.

ACS Style

Quan Wen; Wenya Li; Vivek Patel; Yanjun Gao; Achilles Vairis. Investigation on the Effects of Welding Speed on Bobbin Tool Friction Stir Welding of 2219 Aluminum Alloy. Metals and Materials International 2019, 26, 1830 -1840.

AMA Style

Quan Wen, Wenya Li, Vivek Patel, Yanjun Gao, Achilles Vairis. Investigation on the Effects of Welding Speed on Bobbin Tool Friction Stir Welding of 2219 Aluminum Alloy. Metals and Materials International. 2019; 26 (12):1830-1840.

Chicago/Turabian Style

Quan Wen; Wenya Li; Vivek Patel; Yanjun Gao; Achilles Vairis. 2019. "Investigation on the Effects of Welding Speed on Bobbin Tool Friction Stir Welding of 2219 Aluminum Alloy." Metals and Materials International 26, no. 12: 1830-1840.

Journal article
Published: 31 August 2019 in Journal of Manufacturing Processes
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An extensive investigation on the effect of linear friction welding parameters on the microstructure, texture distribution and mechanical properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy joints was performed. Results indicate that a critical shear velocity is necessary to be reached to obtain a sound joint. The width of the thermomechanically-affected zone (TMAZ) was reduced with friction pressure or/and shear velocity, while the width of the weld center zone (WCZ) remained constant. In WCZ, a microstructure of recrystallized β grains with acicular α laths was formed, and the grain size became smaller with friction pressure. Electron back scattered diffraction was carried out to analyze the texture development with welding parameters. With the increase in friction pressure, the intensity of {112} β texture increased; in the case of α texture, the intensity of T texture increased while decreased for the rest. By examining mechanical properties, strong relationships between maximum hardness and β grain size, as well as between joint elongation and PAZ width, were identified.

ACS Style

Xinyu Wang; Wenya Li; Tiejun Ma; Xiawei Yang; Achilles Vairis. Effect of welding parameters on the microstructure and mechanical properties of linear friction welded Ti-6.5Al-3.5Mo-1.5Zr-0.3Si joints. Journal of Manufacturing Processes 2019, 46, 100 -108.

AMA Style

Xinyu Wang, Wenya Li, Tiejun Ma, Xiawei Yang, Achilles Vairis. Effect of welding parameters on the microstructure and mechanical properties of linear friction welded Ti-6.5Al-3.5Mo-1.5Zr-0.3Si joints. Journal of Manufacturing Processes. 2019; 46 ():100-108.

Chicago/Turabian Style

Xinyu Wang; Wenya Li; Tiejun Ma; Xiawei Yang; Achilles Vairis. 2019. "Effect of welding parameters on the microstructure and mechanical properties of linear friction welded Ti-6.5Al-3.5Mo-1.5Zr-0.3Si joints." Journal of Manufacturing Processes 46, no. : 100-108.

Review
Published: 08 July 2019 in Critical Reviews in Solid State and Materials Sciences
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Increasing demand of lightweight structures with exceptional properties elicits materials processing and manufacturing technologies to tailor blanks in order to achieve or enhance those prerequisite properties. Friction stir processing (FSP) is a solid-state material processing technique, which was derived from friction stir welding (FSW). Initially, FSP was invented to refine the microstructure in way that superplasticity in a material can be achieved. Afterward, FSP has gained much more attraction as a solid-state grain refinement technique to improve the mechanical, tribological, and corrosion properties in a wide range of low strength non-ferrous and high strength steels. FSP is well capable to produce material with microstructure in range of few micron to nanoscale, depending on the processing conditions. Researchers have investigated FSP at different process parameters such as tool rotation and travel speeds, number of passes, and additional cooling in order to evaluate the impact on the resulting properties for different alloys. Recently, FSP has begun to modify the microstructure and properties in hard alloys and superalloys with some modifications in FSP tooling system. Furthermore, FSP has shown great potential to repair or modify the weld or coating structure by microstructure refinement. Therefore, the present review will discuss the state-of-the-art of FSP under the main categories of microstructure evolution, and effect of process parameters. This review also provides a comprehensive summary of research progress on FSP in different materials i.e. aluminum, magnesium, copper, and steels with the contents much emphasized on the microstructure refinement in terms of average grain size and resulting properties like hardness, tensile, wear, and corrosion. Finally, FSP as a new post-processing approach in weld or coating structure has been discussed.

ACS Style

Vivek Patel; Wenya Li; Achilles Vairis; Vishvesh Badheka. Recent Development in Friction Stir Processing as a Solid-State Grain Refinement Technique: Microstructural Evolution and Property Enhancement. Critical Reviews in Solid State and Materials Sciences 2019, 44, 378 -426.

AMA Style

Vivek Patel, Wenya Li, Achilles Vairis, Vishvesh Badheka. Recent Development in Friction Stir Processing as a Solid-State Grain Refinement Technique: Microstructural Evolution and Property Enhancement. Critical Reviews in Solid State and Materials Sciences. 2019; 44 (5):378-426.

Chicago/Turabian Style

Vivek Patel; Wenya Li; Achilles Vairis; Vishvesh Badheka. 2019. "Recent Development in Friction Stir Processing as a Solid-State Grain Refinement Technique: Microstructural Evolution and Property Enhancement." Critical Reviews in Solid State and Materials Sciences 44, no. 5: 378-426.

Full paper
Published: 18 March 2019 in Advanced Engineering Materials
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In this study, the dissimilar S31042 and S34700 austenitic stainless steels joints are welded with linear friction welding (LFW). The history of shear stress at the interface and axial shortening during LFW, the microstructure evolution and mechanical properties of the joint are studied. Results show that axial shortening develops during the equilibrium and deceleration phases. The shear stress reaches a maximum during deceleration as a metallurgical bond forms in sections of the interface. The weld center zone is a narrow layer with a thickness of about 380 µm, where there are fine equiaxed grains with a strong {112} texture. Elongated grains are present in the thermo‐mechanically affected zone due to the shear stress. The average tensile strength and elongation of the joints are measured to be 577 MPa and 33.3%, respectively. All tensile test samples fail at the base material of S34700, as the tensile strength of the joint is equal to or better than that of the base S34700.

ACS Style

Yu Su; Wenya Li; Xinyu Wang; Tiejun Ma; Yanmo Li; Yongchang Liu; Achilles Vairis. On the Process Variables and Weld Quality of a Linear Friction Welded Dissimilar Joint between S31042 and S34700 Austenitic Steels. Advanced Engineering Materials 2019, 21, 1 .

AMA Style

Yu Su, Wenya Li, Xinyu Wang, Tiejun Ma, Yanmo Li, Yongchang Liu, Achilles Vairis. On the Process Variables and Weld Quality of a Linear Friction Welded Dissimilar Joint between S31042 and S34700 Austenitic Steels. Advanced Engineering Materials. 2019; 21 (7):1.

Chicago/Turabian Style

Yu Su; Wenya Li; Xinyu Wang; Tiejun Ma; Yanmo Li; Yongchang Liu; Achilles Vairis. 2019. "On the Process Variables and Weld Quality of a Linear Friction Welded Dissimilar Joint between S31042 and S34700 Austenitic Steels." Advanced Engineering Materials 21, no. 7: 1.

Review
Published: 26 February 2019 in Metals
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Friction stir welding (FSW) has enjoyed great success in joining aluminum alloys. As lightweight structures are designed in higher numbers, it is only natural that FSW is being explored to join dissimilar aluminum alloys. The use of different aluminum alloy combinations in applications offers the combined benefit of cost and performance in the same component. This review focuses on the application of FSW in dissimilar aluminum alloy combinations in order to disseminate research this topic. The review details published works on FSWed dissimilar aluminum alloys. The detailed summary of literature lists welding parameters for the different aluminum alloy combinations. Furthermore, auxiliary welding parameters such as positioning of the alloy, tool rotation speed, welding speed and tool geometry are discussed. Microstructural features together with joint mechanical properties, like hardness and tensile strength measurements, are presented. At the end, new directions for the joining of dissimilar aluminum alloy combinations should guide further research to extend as well as to improve the process, which is expected to raise further interest on the topic.

ACS Style

Vivek Patel; Wenya Li; Guoqing Wang; Feifan Wang; Achilles Vairis; Pengliang Niu. Friction Stir Welding of Dissimilar Aluminum Alloy Combinations: State-of-the-Art. Metals 2019, 9, 270 .

AMA Style

Vivek Patel, Wenya Li, Guoqing Wang, Feifan Wang, Achilles Vairis, Pengliang Niu. Friction Stir Welding of Dissimilar Aluminum Alloy Combinations: State-of-the-Art. Metals. 2019; 9 (3):270.

Chicago/Turabian Style

Vivek Patel; Wenya Li; Guoqing Wang; Feifan Wang; Achilles Vairis; Pengliang Niu. 2019. "Friction Stir Welding of Dissimilar Aluminum Alloy Combinations: State-of-the-Art." Metals 9, no. 3: 270.

Journal article
Published: 05 December 2018 in Materials Science and Engineering: A
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The microstructural evolution across the friction-stir-welded dissimilar AA5083-H112 to AA2024-T351 aluminum alloy joints was characterized via electron backscatter diffraction (EBSD), aiming to identify the effect of inhomogeneous microstructures on the tensile properties and cyclic deformation behavior along with the influence of loading history. Results show that the top region of the stir zone (SZ) mainly consisted of AA2024 which was initially positioned on the retreating side during welding. On the AA5083 side, the lowest density of the geometrically-necessary dislocations (GNDs) assessed from the local misorientations of 0°~2° appeared in the SZ, while it occurred in the heat-affected zone (HAZ) of the AA2024 side. The fractions of recrystallized grains in the AA5083 SZ and AA2024 SZ were ~73% and ~34%, respectively. Strain localization and the resultant failure occurred in the lowest hardness zone of the AA5083 side. The extent of cyclic hardening increased as the stress amplitude increased. Both plastic strain amplitude and plastic strain energy density decreased with increasing number of cycles at higher total strain amplitudes. In the stepwise cyclic deformation tests in the form of ascending-descending loading, the prior cyclic deformation process tended to generate more stabilized structure and performance.

ACS Style

P.L. Niu; W.Y. Li; Achilles Vairis; D.L. Chen. Cyclic deformation behavior of friction-stir-welded dissimilar AA5083-to-AA2024 joints: Effect of microstructure and loading history. Materials Science and Engineering: A 2018, 744, 145 -153.

AMA Style

P.L. Niu, W.Y. Li, Achilles Vairis, D.L. Chen. Cyclic deformation behavior of friction-stir-welded dissimilar AA5083-to-AA2024 joints: Effect of microstructure and loading history. Materials Science and Engineering: A. 2018; 744 ():145-153.

Chicago/Turabian Style

P.L. Niu; W.Y. Li; Achilles Vairis; D.L. Chen. 2018. "Cyclic deformation behavior of friction-stir-welded dissimilar AA5083-to-AA2024 joints: Effect of microstructure and loading history." Materials Science and Engineering: A 744, no. : 145-153.

Journal article
Published: 14 November 2018 in Materials Science and Engineering: A
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The microstructure, microtexture evolution and mechanical properties of a linear friction welded two-phase Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy joint were investigated. Results show clear microstructural differences at the joint center and edge. A martensitic and acicular α microstructure was found in the weld center zone (WCZ) at the joint center and a Widmanstatten microstructure can be identified in the WCZ at the joint edge. Further away from the WCZ, the microstructural differences smoothed out. The cross-weld crystallographic texture was assessed using electron back scattered diffraction. There are different α texture components in WCZ and thermomechanically-affected zone, but the β textures are similar in these two areas. The microstructural differences at the joint center and edge are the cause of the differences in microhardness distribution and tensile properties along the welding direction. Following post weld heat treatment, the inhomogeneity in both microstructure and mechanical properties were reduced.

ACS Style

Xinyu Wang; Wenya Li; Tiejun Ma; Xiawei Yang; Achilles Vairis. Microstructural evolution and mechanical properties of a linear friction welded two-phase Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy joint. Materials Science and Engineering: A 2018, 743, 12 -23.

AMA Style

Xinyu Wang, Wenya Li, Tiejun Ma, Xiawei Yang, Achilles Vairis. Microstructural evolution and mechanical properties of a linear friction welded two-phase Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy joint. Materials Science and Engineering: A. 2018; 743 ():12-23.

Chicago/Turabian Style

Xinyu Wang; Wenya Li; Tiejun Ma; Xiawei Yang; Achilles Vairis. 2018. "Microstructural evolution and mechanical properties of a linear friction welded two-phase Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy joint." Materials Science and Engineering: A 743, no. : 12-23.

Journal article
Published: 30 October 2018 in Journal of Manufacturing Processes
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In this study, a near-alpha titanium alloy (Ti-6Al-2Zr-1Mo-1V) was welded with linear friction welding (LFW). The microstructural evolution and mechanical properties of the joint were evaluated. Results show that grains are remarkably refined in the weld center zone due to dynamic recrystallization because of the effect of thermo-mechanical coupling, while the fractions of deformation grains, sub-structure grains and recrystallized grains are significantly different from those of the base metal (BM). The room temperature tensile strength of the welded joint is not lower than that of the BM, because all the failure occurs in the BM. It is more interesting to find that the joint impact toughness is increased by 19.1% compared to the BM.

ACS Style

Yu Su; Wenya Li; Xinyu Wang; Tiejun Ma; Xiawei Yang; Achilles Vairis. On microstructure and property differences in a linear friction welded near-alpha titanium alloy joint. Journal of Manufacturing Processes 2018, 36, 255 -263.

AMA Style

Yu Su, Wenya Li, Xinyu Wang, Tiejun Ma, Xiawei Yang, Achilles Vairis. On microstructure and property differences in a linear friction welded near-alpha titanium alloy joint. Journal of Manufacturing Processes. 2018; 36 ():255-263.

Chicago/Turabian Style

Yu Su; Wenya Li; Xinyu Wang; Tiejun Ma; Xiawei Yang; Achilles Vairis. 2018. "On microstructure and property differences in a linear friction welded near-alpha titanium alloy joint." Journal of Manufacturing Processes 36, no. : 255-263.

Journal article
Published: 30 October 2018 in Journal of Materials Science & Technology
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Double-side probeless friction stir spot welding (DP-FSSW) of AA2198 alloy was conducted to investigate the microstructure and mechanical properties. Compared with common single-side probeless friction stir spot welding (P-FSSW), the plastic strain during DP-FSSW is nearly symmetrical with respect to the bondline to suppress the extension of hook defect, which is detrimental to the joint mechanical strength. With DP-FSSW, a fully metallurgically bonded region has formed due to severe plastic deformation at high temperatures. Tensile/shear tests show that the joint strength could exceed 8 kN, which is comparable to P-FSSW and refill FSSW, and all fractures happen in a shear failure mode as cracks extend along the interface of two sheets. The microhardness profile exhibits a uniform distribution along the thickness direction, in which the hook defect shows the lowest value.

ACS Style

Q. Chu; W.Y. Li; H.L. Hou; X.W. Yang; Achilles Vairis; C. Wang; W.B. Wang. On the double-side probeless friction stir spot welding of AA2198 Al-Li alloy. Journal of Materials Science & Technology 2018, 35, 784 -789.

AMA Style

Q. Chu, W.Y. Li, H.L. Hou, X.W. Yang, Achilles Vairis, C. Wang, W.B. Wang. On the double-side probeless friction stir spot welding of AA2198 Al-Li alloy. Journal of Materials Science & Technology. 2018; 35 (5):784-789.

Chicago/Turabian Style

Q. Chu; W.Y. Li; H.L. Hou; X.W. Yang; Achilles Vairis; C. Wang; W.B. Wang. 2018. "On the double-side probeless friction stir spot welding of AA2198 Al-Li alloy." Journal of Materials Science & Technology 35, no. 5: 784-789.

Journal article
Published: 16 October 2018 in Journal of Manufacturing Processes
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AA2198 joints were produced using the probeless friction stir spot welding (P-FSSW). Numerical modeling of the process based on the Coupled Eulerian-Lagrangian technique was developed to investigate the material flow. The modeling and experimental observations provide a consistent interpretation of the circumferential material flow which has some inward radial flow at the top surface. As the welding process advances, the flow is directed downwards, producing a spiral contracting pattern. The simulation results show that the hook defect is formed as the material in the bottom sheet is squeezed upwards in a symmetrical fashion with respect to the centerline, matching well with the experimental results.

ACS Style

Q. Chu; X.W. Yang; W.Y. Li; A. Vairis; W.B. Wang. Numerical analysis of material flow in the probeless friction stir spot welding based on Coupled Eulerian-Lagrangian approach. Journal of Manufacturing Processes 2018, 36, 181 -187.

AMA Style

Q. Chu, X.W. Yang, W.Y. Li, A. Vairis, W.B. Wang. Numerical analysis of material flow in the probeless friction stir spot welding based on Coupled Eulerian-Lagrangian approach. Journal of Manufacturing Processes. 2018; 36 ():181-187.

Chicago/Turabian Style

Q. Chu; X.W. Yang; W.Y. Li; A. Vairis; W.B. Wang. 2018. "Numerical analysis of material flow in the probeless friction stir spot welding based on Coupled Eulerian-Lagrangian approach." Journal of Manufacturing Processes 36, no. : 181-187.

Journal article
Published: 01 October 2018 in Journal of Materials Science & Technology
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In this work, a third generation Al-Li alloy has been successfully spot welded with probeless friction stir spot welding (P-FSSW), which is a variant of conventional friction stir welding. The Box-Behnken experimental design in response surface methodology (RSM) was applied to optimize the P-FSSW parameters to attain maximum tensile/shear strength of the spot joints. Results show that an optimal failure load of 7.83 kN was obtained under a dwell time of 7.2 s, rotation speed of 950 rpm and plunge rate of 30 mm/min. Sufficient dwell time is essential for heat conduction, material flow and expansion of the stir zone to form a sound joint. Two fracture modes were observed, which were significantly affected by hook defect. In addition to mechanical testing, electron backscattering diffraction (EBSD) and differential scanning calorimetry (DSC) were used for microstructure evolution and property analysis. The precipitation of GP zone and Al3Li as well as the ultrafine grains were responsible for the high microhardness in the stir zone.

ACS Style

Q. Chu; W.Y. Li; X.W. Yang; Junjun Shen; Achilles Vairis; W.Y. Feng; W.B. Wang. Microstructure and mechanical optimization of probeless friction stir spot welded joint of an Al-Li alloy. Journal of Materials Science & Technology 2018, 34, 1739 -1746.

AMA Style

Q. Chu, W.Y. Li, X.W. Yang, Junjun Shen, Achilles Vairis, W.Y. Feng, W.B. Wang. Microstructure and mechanical optimization of probeless friction stir spot welded joint of an Al-Li alloy. Journal of Materials Science & Technology. 2018; 34 (10):1739-1746.

Chicago/Turabian Style

Q. Chu; W.Y. Li; X.W. Yang; Junjun Shen; Achilles Vairis; W.Y. Feng; W.B. Wang. 2018. "Microstructure and mechanical optimization of probeless friction stir spot welded joint of an Al-Li alloy." Journal of Materials Science & Technology 34, no. 10: 1739-1746.

Conference paper
Published: 01 October 2018 in TENCON 2018 - 2018 IEEE Region 10 Conference
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The purpose of this research is to propose an improvement of a low-end device, such as crutches that can be used in more challenging environments. The alternative design centers on crutch shoes for non-cohesive and unpaved footpaths. Another goal is to keep the cost of the crutch shoe comparable to conventional crutch shoes. For that purpose, the proposed design was made so that it could be retrofitted to the existing device easily. In the proposed design, the von Mises stresses which develop at the contact surface between the crutch and the terrain are comparable to those encountered by the human foot and considerably lower than the conventional design case, allowing the crutch to extend the range of surfaces that it can be used on. The final cost of the proposed crutch shoe will not be excessive compared to the conventional one, while offering considerable advantages with its versatility.

ACS Style

Achilles Vairis; Soo Hee Kim; Suzana Brown; Ali M. Masoumifar. A Proposed Design of a Versatile Mobility Aid for Challenging Environments. TENCON 2018 - 2018 IEEE Region 10 Conference 2018, 0712 -0716.

AMA Style

Achilles Vairis, Soo Hee Kim, Suzana Brown, Ali M. Masoumifar. A Proposed Design of a Versatile Mobility Aid for Challenging Environments. TENCON 2018 - 2018 IEEE Region 10 Conference. 2018; ():0712-0716.

Chicago/Turabian Style

Achilles Vairis; Soo Hee Kim; Suzana Brown; Ali M. Masoumifar. 2018. "A Proposed Design of a Versatile Mobility Aid for Challenging Environments." TENCON 2018 - 2018 IEEE Region 10 Conference , no. : 0712-0716.