R. Senthur Pandi

Bio: R. Senthur Pandi is an academic researcher from Thiagarajar College of Engineering. The author has contributed to research in topics: Shape-memory alloy & Absorption (acoustics). The author has an hindex of 3, co-authored 12 publications receiving 27 citations.

Structural, Thermal and Magnetic Characterization of Ni-Mn-Ga Ferromagnetic Shape Memory Alloys

Abstract: Ni-Mn-Ga Ferromagnetic Shape Memory Alloys (FSMA) are highly interested in industrial actuators and energy harvesters because of its uniqueness in microstructure and multiple phases of these materials at different temperatures. The type of crystal structure, lattice parameters and magnetic properties depend on the alloy composition. The transformation and crystallographic properties are usually mapped to average number of valence electrons per atom. The present work deals with the fundamental characterization of single crystal and polycrystalline nature of these alloys. Though, the polycrystal shows low magnetic field induced stain (MFIS), the easy preparation techniques and cost effective aspects compared with the single crystals makes an impressive interest in dealing with that. The structural, thermal and magnetic parameters are observed and compared for these single and polycrystals.

Thermal and Magnetic studies of Ni-Mn-Ga/PU Polymer Composites

Abstract: The present work deals with the preparation and fundamental characterization of Ni–Mn–Ga/PU polymer composites. The magnetic behavior and surface morphology of these composites have been studied by the vibration sample magnetometer and scanning electron microscope respectively. Thermal characterization has been carried out by differential scanning calorimetry.

Amplitude Stress in Ni-Mn-Ga Polymer Composites Bonded with PZT Sensors and Actuators

Abstract: A new experimental set up to measure acoustic attenuation in ferromagnetic shape memory alloy and composites was designed and built. Acoustic attenuation in polyurethane (PU) polymer composites with Ni-Mn-Ga particulate fillers have been reported which exhibits greater vibration absorption than polymer/magnetostrictive composites due to the rearrangement of twin variants in Ni-Mn-Ga particles. Amplitude stress wave has been analysed for three different test samples. Above the low frequency, the acoustic attenuation is gradually decreased from PU to Ni-Mn-Ga/PU. The Ni-Mn-Ga/PU polymer composite is shown to be ideal for applications that require absorption of mechanical energy.

Temperature dependent damping studies of Ni-Mn-Ga polymer composites

Abstract: Mechanical properties of ferromagnetic shape memory alloy (FSMA) polyurethane (PU) polymer composites are studied using dynamic mechanical analysis (DMA) at different temperatures. The sample used in the study is Ni-Mn-Ga/PU polymer composite. DMA studies reveal that the mechanical modulus decreases, when the temperature increases. The peak in internal friction (tanδ) appears twice due to martensite transformation of the reinforced particles and glass transition of the polymer matrix. The strain is due to the motion of twin boundaries rather than the phase transformations. Twin boundary motion is found to be the root cause for the martensite-austenite transformation and vice versa, and leads to enhanced damping mechanism. Speculations on twin boundaries of this sample to show concrete evidence on change in internal friction (tanδ) are still underway. This paper proposes that Ni-Mn-Ga/PU polymer composites can be used as efficient dampers.

Transformation Behavior of Ni-Mn-Ga Ferromagnetic Shape Memory Alloy

Abstract: Ni-Mn-Ga Ferromagnetic Shape Memory Alloy (FSMA) has been prepared by melt casting technique. The alloy was annealed at different temperatures. The samples are characterized in prepared condition and after three different annealing treatments. Microstructure of the alloy has been investigated using SEM at room temperature. Microstructure study reveals that the magnetic domains run diagonally across the surface. Differential Scanning Calorimetry (DSC) result shows the ferromagnetic transition temperature of the alloy is 105°C. In-situ study of structure during heating has revealed that the martensite to austenite transformation takes place in the temperature range of 28°C to 36°C. The present study focuses the effect of annealing on phase transformation and magnetic transformation temperature of Ni-Mn-Ga alloy. It has been observed that the thickness of the martensite plate increases as the alloy is annealed at 950°C for 30 hrs.

Self-repair of structural and functional composites with intrinsically self-healing polymer matrices: A review

Abstract: Self-healing is a smart and promising way to make materials more reliable and longer lasting. In the case of structural or functional composites based on a polymer matrix, very often mechanical damage in the polymer matrix or debonding at the matrix–filler interface is responsible for the decrease in intended properties. This review describes the healing behavior in structural and functional polymer composites with a so-called intrinsically self-healing polymer as the continuous matrix. A clear similarity in the healing of structural and functional properties is demonstrated which can ultimately lead to the design of polymer composites that autonomously restore multiple properties using the same self-healing mechanism.

Thermal conductivity, coefficient of linear thermal expansion and mechanical properties of LDPE/Ni composites

Abstract: Thermophysical and mechanical properties of low density polyethylene (LDPE) filled with nickel powder (10 μm) is reported. The composites are characterized by XRD, SEM, DSC and TGA. XRD analysis indicates that Ni affects the crystallinity of LDPE, whereas, scanning electron micrographs reveals formation of Ni clusters/conducting chains especially for high filler concentration. The DSC and TGA data show a marginal decrease in peak melting point and a moderate enhancement in thermal stability, respectively with increasing volume % of Ni in LDPE. Thermal conductivity of the composite increases by ~240 % with addition of 25 volume % of nickel and we confirm that the measured data is in excellent agreement with a percolation based model. Coefficient of thermal expansion (CTE) of LDPE decreases by ~38 % for composite with 25 volume % of Ni. The measured CTE agrees well with the estimates of a recent model which takes into account the interphase volume and interaction between filler particles and polymer. An overall improvement in mechanical properties is also observed for LDPE/Ni composites and the results are explained in the light of existing models.

Effect of mechanical milling induced strain and particle size reduction on some physical properties of polycrystalline yttrium iron garnet

Abstract: The effect of mechanical milling induced strain and particle size reduction on structural, micro-structural and magnetic properties of un-milled and milled polycrystalline samples of yttrium iron garnet, Y3Fe5O12 (YIG), for different duration, 3, 6, 9 and 12 h, have been studied using X-ray powder diffractometry, scanning electron microscopy, infrared spectroscopy, Mossbauer spectroscopy, high field magnetization and low field (0.5 Oe) ac susceptibility measurements. YIG on milling is found to decompose into Y3Fe5O12 and yttrium ortho-ferrite, YFeO3, phases, as reflected from various characterizations. The infrared and Mossbauer spectroscopic studies give an indication for the loss of oxygen on milling. The shift in Neel temperature with particle size reduction has been described by finite size scaling. The observed changes in M–H loop are mainly due to strain induced increase in surface anisotropy on milling. The two transitions have been observed in the thermal variation of ac susceptibility curves, corresponding to ferrimagnetic YIG-phase and another due to weak ferromagnetic YFeO3-phase.