Swati Ghosh Acharyya

Shape memory alloy smart knee spacer to enhance knee functionality: Model design and finite element analysis

In this paper we introduce Shape Memory Alloy (SMA) for designing the tibial part of Total Knee Arthroplasty (TKA) by exploiting the shape-memory and pseudo-elasticity property of the SMA (e.g. NiTi). This would eliminate the drawbacks of the state-of-the art PMMA based knee-spacer including fracture, sustainability, dislocation, tilting, translation and subluxation for tackling the Osteoarthritis especially for the aged people of 45-plus or the athletes. In this paper a Computer Aided Design (CAD) model using SolidWorks for the knee-spacer is presented based on the proposed SMA adopting the state-of-the art industry-standard geometry that is used in the PMMA based spacer design. Subsequently Ansys based Finite Element Analysis is carried out to measure and compare the performance between the proposed SMA based model with the state-of-the art PMMA ones. 81% more bending is noticed in the PMMA based spacer compared to the proposed SMA that would eventually cause fracture and tilting or translation of spacer. Permanent shape deformation of approximately 58.75% in PMMA based spacer is observed compared to recoverable 11% deformation in SMA when same load is applied on both separately.In this paper we introduce Shape Memory Alloy (SMA) for designing the tibial part of Total Knee Arthroplasty (TKA) by exploiting the shape-memory and pseudo-elasticity property of the SMA (e.g. NiTi). This would eliminate the drawbacks of the state-of-the art PMMA based knee-spacer including fracture, sustainability, dislocation, tilting, translation and subluxation for tackling the Osteoarthritis especially for the aged people of 45-plus or the athletes. In this paper a Computer Aided Design (CAD) model using SolidWorks for the knee-spacer is presented based on the proposed SMA adopting the state-of-the art industry-standard geometry that is used in the PMMA based spacer design. Subsequently Ansys based Finite Element Analysis is carried out to measure and compare the performance between the proposed SMA based model with the state-of-the art PMMA ones. 81% more bending is noticed in the PMMA based spacer compared to the proposed SMA that would eventually cause fracture and tilting or translation of spacer. Permanent shape deformation of approximately 58.75% in PMMA based spacer is observed compared to recoverable 11% deformation in SMA when same load is applied on both separately.

Self-healing phenomena of graphene: potential and applications

Abstract The present study investigates the self healing behavior of both pristine and defected single layer graphene using a molecular dynamic simulation. Single layer graphene containing various defects such as preexisting vacancies and differently oriented pre-existing cracks were subjected to uniaxial tensile loading till fracture occurred. Once the load was relaxed, the graphene was found to undergo self healing. It was observed that this self healing behaviour of cracks holds irrespective of the nature of pre-existing defects in the graphene sheet. Cracks of any length were found to heal provided the critical crack opening distance lies within 0.3-0.5 nm for a pristine sheet and also for a sheet with pre-existing defects. Detailed bond length analysis of the graphene sheet was done to understand the mechanism of self healing of graphene. The paper also discusses the immense potential of the self healing phenomena of graphene in the field of graphene based sub-nano sensors for crack sensing.

Tunable intrinsic magnetic phase transition in pristine single-layer graphene nanoribbons

In this paper, we report on the interesting phenomenon of magnetic phase transitions (MPTs) observed under the combined influence of an electric field (E) and temperature (T) leading to a thermo-electromagnetic effect on the pristine single-layer zigzag graphene nanoribbon (szGNR). Density functional theory-based first principles calculations have been deployed for this study on the intrinsic magnetic properties of graphene. Interestingly, by tuning electric field (E) and temperature (T), three distinct magnetic phase behaviors, para-, ferro- and antiferromagnetic are exhibited in pristine szGNR. We have investigated the unrivaled positional parameters of these MPTs. MPT occurring in the system also follows a positional trend and the change in these positional parameters with regard to the size of the szGNR along with the varied E and T is studied. We propose a bow-tie schematic to induce the intrinsic magnetism in graphene and present the envisaged model of the processor application with the reported intrinsic MPT in szGNR. This fundamental insight into the intrinsic MPTs in graphene is an essential step towards developing graphene-based spin-transfer torque magnetoresistive random access memory, quantum computing devices, magnonics and spintronic memory application.

Shape-memory-alloy-based smart knee spacer for total knee arthroplasty: 3D CAD modelling and a computational study

This study introduced a shape memory alloy (SMA)-based smart knee spacer for total knee arthroplasty (TKA). Subsequently, a 3D CAD model of a smart tibial component of TKA was designed in Solidworks software, and verified using a finite element analysis in ANSYS Workbench. The two major properties of the SMA (NiTi), the pseudoelasticity (PE) and shape memory effect (SME), were exploited, modelled, and analysed for a TKA application. The effectiveness of the proposed model was verified in ANSYS Workbench through the finite element analysis (FEA) of the maximum deformation and equivalent (von Mises) stress distribution. The proposed model was also compared with a polymethylmethacrylate (PMMA)-based spacer for the upper portion of the tibial component for three subjects with body mass index (BMI) of 23.88, 31.09, and 38.39. The proposed SMA -based smart knee spacer contained 96.66978% less deformation with a standard deviation of 0.01738 than that of the corresponding PMMA based counterpart for the same load and flexion angle. Based on the maximum deformation analysis, the PMMA-based spacer had 30 times more permanent deformation than that of the proposed SMA-based spacer for the same load and flexion angle. The SME property of the lower portion of the tibial component for fixation of the spacer at its position was verified by an FEA in ANSYS. Wherein, a strain life-based fatigue analysis was performed and tested for the PE and SME built spacers through the FEA. Therefore, the SMA-based smart knee spacer eliminated the drawbacks of the PMMA-based spacer, including spacer fracture, loosening, dislocation, tilting or translation, and knee subluxation.

Distinguishing Effect of Buffing Operation on Surface Residual Stress Distribution and Susceptibility of 304L SS and 321 SS Welds to Chloride Induced SCC

Stress corrosion cracking (SCC) of austenitic stainless steels (ASS) and its weldments in presence of chloride ions is a key concern in its successful application. AISI 304L SS in surface milled, turned, ground conditions have high tensile residual stresses on the surface which lead to early cracking in an aggressive environment. Spot welds of AISI 321 SS have shown multiple failures due to chloride induced SCC as a result of high magnitude of tensile residual stresses and improper post weld heat treatment. The present study proposes a simple surface engineering method to prevent the initiation of stress corrosion cracking in austenitic stainless steel and its welds in presence of chloride ions. 304L SS in milled, turned and ground conditions and 321 SS in spot welded condition was subjected to surface buffing operation. Surface roughness was calculated using a surface profilometer and residual stresses were determined. Residual stress distribution, and phase transformation were calculated using X-ray diffraction measurements. The detailed microstructural characterization was performed using field emission scanning electron microscopy (FESEM). 304L plates and 321 SS welds in buffed and un-buffed conditions were tested for SCC susceptibility by exposing these to boiling MgCl2 as per ASTM G36. Results showed that 304L SS and 321 SS were resistant to SCC in buffed conditions as no cracking occured even after prolnged exposure to boiling MgCl2. Buffing being a very simple, economic and portable operation can be easily applied on large components of AISI 304L SS after the conventional surface finishing operations and AISI 321 SS weld also can be extended to components in service in an aggressive environment. Introduction Austenitic stainless steels have good corrosion resistance and mechanical properties. However, these become highly susceptible to SCC when subjected to different surface finishing and welding operations [1-3]. Laser peening and shot peening are generally used for enhancing SCC resistance, but these processes induce plastic strain in the material and are not economic. Hence a simple and economic route is essential in preventing SCC. We have shown in our previous report that simple surface buffing can be used to enhance the SCC resistance of austenitic stainless steels [4]. The present study substantiates the effectiveness of buffing in preventing the initiation of Cl induced SCC of austenitic stainless steel in presence of chloride ions. 304L SS in milled, turned and ground conditions and 321 SS in spot welded condition when subjected to surface buffing operation. Residual Stresses 2018 – ECRS-10 Materials Research Forum LLC Materials Research Proceedings 6 (2018) 139-144 doi: http://dx.doi.org/10.21741/9781945291890-22 140 Experimental Materials and methods In the present study two steels namely, AISI 304L SS (C 0.03, Cr 18, Ni 8, Mn 1.6, P 0.04, Si 0.4,S 0.03, balance Fe) wt %, and AISI 321 SS welds (C 0.024, Cr 17.41, Ni 9.14, Mn 1.64, Ti 0.23, Mo 0.37, P 0.04, Si 0.4, S 0.03) wt% were used. AISI 304L SS samples were cut into a dimension of 100 mm X 25 mm X 5 mm plates and they were solution annealed in order to remove the internal stresses present in the material. AISI 304 L SS was subjected to three different surface working conditions namely a) milling b) turning and c) grinding operations at a feed rate of 0.1mm/rev to remove 0.5 mm from the surface [7]. Subsequently, the samples were buffed at 3600 rpm using and 50μm was removed from the surface. In another study, AISI 321 SS tubes having 72 mm diameter, 3 mm thickness and length of 3.6 m having spot welds on the surface were subjected to buffing and 50μm was removed. Both the samples were tested for SCC susceptibility in buffed and unbuffed condition. During buffing compressive forces are applied on the sample substrate as shown in the schematic given below (Figure 1). The buffing wheel is rotated at a set speed and is rastered on the surface of the workpiece imparting compressive stresses to the entire surface of the workpiece. No Ti2N particles were present in the near surface region of buffed samples in each case. Fig 1: a) Schematic of the buffing operation b) cross sectional micrograph of 321 SS in buffed condition and c) cross sectional micrograph of 321 SS in un-buffed condition. Surface roughness measurements Surface roughness measurements were done on all samples using a surface profilometer (contact mode) with a scan length of 1μm at a scan speed of 0.01 mm/sec with a minimum resolution step of 1 nm. 321 SS ring samples were measured using an optical surface profilometer (non contact mode) with a scan length of 1mm at a scan speed of 47μm/sec with a resolution of 0.2 nm. The average roughness (Ra) was determined in each case. XRD phase analysis XRD studies were conducted on all the samples to confirm the phases present in the material using BRUKER G8 powder XRD, Cu-Kα source, λ= 1.54 Å, Bragg angle, 2θ from (30-100o), step size 0.01 and step/scan 0.5 at an accelerating voltage of 40kV and 30 A. Residual stress measurements Residual stresses measurements were conducted on Xstress G2R (High-resolution XRD) to find the surface residual stresses present in the material. By using CrKα source, applied voltage 27 kV, a current of 70 mA, λ= 2.28, Bragg angle 147.6o was kept constant for all the samples, (hkl 311) peak was considered for diffraction with a step size of 0.1o [5]. Collimeter diameter 4 mm and exposure time of 20 s was used. The multiexposure side inclination and fixed (χ) chi method was adopted, at 0o and 90o for each measurement. 2D stress state was assumed sinχ technique was applied for residual stress analysis. Residual Stresses 2018 – ECRS-10 Materials Research Forum LLC Materials Research Proceedings 6 (2018) 139-144 doi: http://dx.doi.org/10.21741/9781945291890-22 141 Determination of SCC resistance The SCC susceptibility of AISI 304L SS and AISI 321 SS in buffed and un-buffed condition was determined using ASTM G 36 [6] in surface worked and welded conditions respectively. SCC test was conducted for 3 h and 9 h in AISI 304L SS samples and 5 h and 10 h in AISI 321 SS samples. As per ASTM G 36, 600 g of magnesium chloride hexahydrate (MgCl2.6H2O) was melted and test temperature was maintained at 155± 1o C throughout the test. Care has been taken to prevent vapor losses Results and Discussion Surface roughness measurements: Surface roughness values (Ra) for different surface working conditions have been tabulated in Table1. In both 304L SS and 321 SS surface roughness in buffed conditions was much less as compared to un-buffed conditions. Higher the surface roughness, greater the tendency to form localized pockets of high chloride concentration and early initiation of SCC. Table 1: Average surface roughness values of 304L SS and 321 SS in un-buffed and buffed conditions Material Material conditions Surface roughness (Ra) in μm 304L SS Milled 2.1 ± 0.15 Turned 4.3 ± 0.30 Ground 0.6 ± 0.04 Milled + Buffed 0.13 ± 0.06 Turned + Buffed 0.11± 0.04 Ground + Buffed 0.08 ± 0.02 321 SS Spot welded 1.74±0.24 Spot welded +Buffed 0.94±0.12 XRD studies Figure 2 shows the XRD spectra of 304L SS under different surface working conditions. Solution annealed sample showed austenitic (γ) phase and other surface worked samples showed strain-induced martensite (αʹ) phase due to the metastable nature of austenitic stainless steel. Fig. 2: Shows the XRD spectra of 304L SS in different surface working conditions. Figure 3 shows the XRD spectra of the spot welded region of 321 SS in both buffed and unbuffed condition. Characteristic austenitic peaks were observed in both the cases together with the presence of stress induced martensite. The number of peaks for stress induced martensite was Residual Stresses 2018 – ECRS-10 Materials Research Forum LLC Materials Research Proceedings 6 (2018) 139-144 doi: http://dx.doi.org/10.21741/9781945291890-22 142 much higher for buffed condition. The Ti2N present in the surface layers of 321SS gets removed on buffing. Optical microstructures support the observation. Fig. 3: Shows the XRD spectra of 321 SS in spot welded and spot welded followed by a buffed condition Residual stress measurements Table 2 gives the residual stresses of 304L SS and 321 SS under different conditions. The measurements were taken in longitudinal and transverse direction. The result shows that for 304L SS in milled, turned and ground conditions have high magnitude of tensile residual stresses. A similar result has been reported in earlier studies performed by some of the authors [7-8]. However, compressive residual stresses were found to be present on the surfaces in buffed condition. Similarly, the HAZ and the fusion zone of spot welds of 321 SS were found to have tensile residual stresses in un-buffed condition and compressive residual stresses in buffed condition. Table 2: residual stress values of 304L SS and 321 SS in different conditions 304L SS conditions 0o (MPa) 90o (MPa) Milled 740±86 639±71 Turned 397±82 69±85 Ground 192±40 15±39 Milled + Buffed -386±21 -378±16 Turned + Buffed -523±17 -504±26 Ground + Buffed -481±22 -409±16 321 SS conditions 0o (MPa) 90o (MPa) Base material -239±23 -306±57 Spot + buffed -351±17 -433±24 Determination of susceptibility to stress corrosion cracking (SCC) Figure 4 and Figure 5 shows the FESEM surface micrographs of 304L SS in a) milled b) turned c) ground before and after buffing after exposure to 3 h and 9 h of SCC test respectively. The results showed that the samples in milled ground and turned condition were highly susceptible to SCC, whereas the samples in buffed condition after 3 h and 9 h of exposure. Pit initiation was observed in some cases after 9 h of exposure due to the preferential dissolution of martensite on the surface. Residual Stresses 2018 – ECRS-10 Materials Research Forum LLC Materials Research Proceedings 6 (2018) 139-144 doi: http://dx.doi.org/10.21741/9781945291890-22

Area-elficient interlayer signal propagation in 3D IC by introducing electron spin

Through Silicon Via (TSV) is the major technology in order to transmit data among various devices in 3D IC. Therefore higher concentration of TSV is required for higher packing density in 3D IC. In order to obtain high density of TSV, the dimensions of TSV needs to be reduced. This may be achieved by increasing the surface area per layer which will benefit in packing of more components for any operation including logic implementation. In this paper we introduce electron spin rather than charge for the first time for interlayer signal transmission in 3D IC resulting in area efficiency. Ansys electromagnetic simulator (Maxwell 2D and 3D) and OOMMF simulation supported by theoretical analysis specifies an average of 90% area reduction per layer of 3D IC as compared to state-of-the art TSV.

One-step synthesis of bulk quantities of graphene from graphite by femtosecond laser ablation under ambient conditions

Abstract Bulk synthesis of few-layer graphene (FLG) for industrial applications still remains a challenge for researchers. Here, we report a very simple technique for bulk synthesis of FLG by femtosecond laser ablation of graphite powder suspended in ethanol without the requirement of a controlled environment. Graphite powder, with an average particle size <20 μm, was suspended uniformly in ethanol and ablated at room temperature using fs pulses (wavelength ~800 nm and an input beam diameter ~8 mm) followed by ultrasonication to obtain FLG with a lateral size of ~1 μm. Raman spectroscopy and high-resolution transmission electron microscopy data confirmed the nature and morphology of the FLG. The quality and number of layers in the FLG could be controlled by tuning the laser parameters.

Novel Ti-Nb alloys with improved wear resistance for biomedical implant application

The present study involved fabrication of titanium niobium based alloys having elastic modulus close to that of human bone and subsequently determining the wear resistance of these alloys for biomedical application. In the present study three beta stabilized titanium niobium alloys having composition Ti-24Nb-4Zr-8Sn, Ti-35Nb-4Sn and Ti-29Nb-13Ta-7Zr were made by vacuum arc melting. The alloys were then aged at 1000 C for 6 hours in an argon atmosphere. Detailed microstructural characterization and phase identification was carried out using scanning electron microscopy and x-ray diffraction respectively. The hardness of the samples were measured by micro hardness measurements. The wear resistance and the friction coefficient of the samples were measured by testing in Ringers solution (simulated body fluid). The results showed improved wear resistance of the fabricated alloys.

Thermo-magnetic shape control of nano-ferromagnetic particle doped shape memory alloy for orthopedic devices and rehabilitation techniques

Recent advancement in smart materials facilitated the use of Shape Memory Alloy(SMA) in treatment of different orthopedic problems and rehabilitation technique to treat paralyzed patients. But Shape Memory alloy lacks the controllability while regaining the shape from martensite to austenite during thermal loading. Therefore, in this paper we introduced a mechatronic device which provides the control over the shape change of new hybrid material having property of SMA and shape memory property of anticipated material is verified by finite element analysis in COMSOL Multiphysics. In the proposed methodology the shape is controlled by generating a controlled thermo-magnetic loading, and hybrid material formed by doping a nano-ferromagnetic particle in porous NiTi SMA. For the proof of the concept an experiment is carried out by using a bimetallic strip, microcontroller, sensor and proper feedback circuitry system and it is observed that for the supply of 4V and bent angle for flex sensor between 0 to 40 degree, current through the solenoid is 3.63A producing Magnetic field of 1.42mT and for flex sensor b ent angle 4 0 to 7 5 degree the current through the solenoid is 1.2A producing Magnetic field of 0.47mT for same supply and if the flex sensor bent angle increases more than 75 degree then the voltage supply cutoffs which indicate the absence of Magnetic field.