VL Sateesh

Bio: VL Sateesh is an academic researcher from National Aerospace Laboratories. The author has contributed to research in topics: Composite number & Bending of plates. The author has an hindex of 4, co-authored 5 publications receiving 28 citations.

Low Cycle Fatigue Evaluation of NiTi SESMA Thin Wires

Abstract: This paper presents experimental studies on low cycle fatigue (LCF) life of super-elastic shape memory alloy (SESMA) wires. The effect of frequency of the loading and amplitude of the strain on the fatigue life has been studied individually. Various loading frequencies have been considered to study the effect of frequency, by keeping the amplitude constant. From the experimental data, it was found that the LCF life of the SESMA reduces with increase in the frequency. The effect of amplitude on the LCF life of SESMA has also been studied, and it was found that the SESMA cycled at lower net strain has more fatigue life than the one cycled at higher net strain. Further, the plastic strain accumulation is also more in the samples tested at the higher net strain loadings. The modulus of austenite is found to be by and large independent of the frequency and amplitude of the loading. Further, martensitic unloading modulus is same for all the minimum strain amplitudes.

Development and wind tunnel evaluation of a shape memory alloy based trim tab actuator for a civil aircraft

Abstract: This paper presents the development and wind tunnel evaluation of a shape memory alloy (SMA) based smart trim tab for a typical two seater civil aircraft. The SMA actuator was housed in the port side of the elevator for the purpose of actuating the trim tab. Wind tunnel tests were conducted on a full scale horizontal tail model with elevator and trim tab at free stream speeds of 25, 35 and 45 m s−1, and also for a number of deflections of the elevator (30° up, 0° neutral and 25° down) and trim tab (11° and 21° up and 15° and 31° down). To measure the hinge moment experienced by the trim tab under various test conditions, two miniaturized balances were designed and fabricated. A gain scheduled proportional integral (GSPI) controller was developed to control the SMA actuated smart trim tab. It was confirmed during the tests that the trim tab could be controlled at the desired position against the aerodynamic loads acting on it for the various test conditions.

A study of the polarization–electric-field nonlinear effect on the response of smart composite plates

Abstract: Polarization–electric-field (P–E) interaction results in rendering the stress tensor non-symmetric and in a nonlinear force term in the equilibrium equation. In this paper, an attempt is made to study these (P–E) nonlinear effects on the static response of laminated composite plates with piezo actuators. Further, this paper also focuses on finding the most effective piezo lay-up and ply orientation which gives the maximum deflections. Four different piezo lay-up configurations and three ply orientations are considered. It has been observed from the study that width-wise strips show more transverse bending and twisting. However, full length piezo layers show maximum longitudinal bending. The results of nonlinear analysis show a more considerable softening trend in deformations than that of the linear analysis in the case of longitudinal bending and twisting. In the case of transverse bending this nonlinear effect shows a hardening trend. Further, it has been observed that the influence of P–E nonlinearity depends on the stiffness of the core material, the geometric arrangement of piezo patches, the boundary conditions and the actuation voltage.

A posteriori processing for estimation of low cycle fatigue failure in SESMA wires

Abstract: Super elastic shape memory alloys (SESMA) are promising materials for damping applications due to their inherent hysteresis associated solid–solid reversible phase transformations. These transformations induce a large recoverable strain in the material. In most of the applications, SMA is used in the form of thin wires subjected to low cycle fatigue. This paper presents the experimental investigations on low cycle fatigue behavior of the SESMA thin wires subjected to various loading conditions. An attempt is also made to estimate the low cycle fatigue life of SESMA. The dissipated energy during the transformation is used as the key parameter to estimate the life cycles. From the results it can be seen that the estimation of the life cycles are well in agreement with the experimental fatigue life of the SESMA samples.

Effects of Lüders-like bands on NiTi fatigue behaviors

Abstract: Although the formation of Luders bands in NiTi polycrystalline structures (strips/tubes) has been well reported and is believed to have considerable influence on the material's fatigue behaviors, there is no direct experimental evidence showing the relation between the band formation and the material's fatigue failure. For each NiTi polycrystalline strip in this study, a strain-controlled isothermal test was firstly conducted to check the pseudoelastic properties and then a stress-controlled fatigue test was performed with synchronized optical observation on the evolution (cyclic nucleation/annihilation) of Luders bands in the strip. It is found that the fatigue failure crack always occurs within the band or at the band front, because the band formation is an indicator of the weak zones of the samples and the cyclic band nucleation/annihilation accelerates microstructure degradation in those zones. Under the same loading scheme of the fatigue tests, the samples with bands have much shorter fatigue life than the samples without bands. The experiments provide the bases for future theoretical study on the interaction between the martensitic phase transformation and the plasticity/defects and give some hints for developing a proper fatigue criterion for the softening material in engineering applications.

The development of neural stimulators: a review of preclinical safety and efficacy studies.

Abstract: Objective Given the rapid expansion of the field of neural stimulation and the rigorous regulatory approval requirements required before these devices can be applied clinically, it is important that there is clarity around conducting preclinical safety and efficacy studies required for the development of this technology. Approach The present review examines basic design principles associated with the development of a safe neural stimulator and describes the suite of preclinical safety studies that need to be considered when taking a device to clinical trial. Main results Neural stimulators are active implantable devices that provide therapeutic intervention, sensory feedback or improved motor control via electrical stimulation of neural or neuro-muscular tissue in response to trauma or disease. Because of their complexity, regulatory bodies classify these devices in the highest risk category (Class III), and they are therefore required to go through a rigorous regulatory approval process before progressing to market. The successful development of these devices is achieved through close collaboration across disciplines including engineers, scientists and a surgical/clinical team, and the adherence to clear design principles. Preclinical studies form one of several key components in the development pathway from concept to product release of neural stimulators. Importantly, these studies provide iterative feedback in order to optimise the final design of the device. Key components of any preclinical evaluation include: in vitro studies that are focussed on device reliability and include accelerated testing under highly controlled environments; in vivo studies using animal models of the disease or injury in order to assess efficacy and, given an appropriate animal model, the safety of the technology under both passive and electrically active conditions; and human cadaver and ex vivo studies designed to ensure the device's form factor conforms to human anatomy, to optimise the surgical approach and to develop any specialist surgical tooling required. Significance The pipeline from concept to commercialisation of these devices is long and expensive; careful attention to both device design and its preclinical evaluation will have significant impact on the duration and cost associated with taking a device through to commercialisation. Carefully controlled in vitro and in vivo studies together with ex vivo and human cadaver trials are key components of a thorough preclinical evaluation of any new neural stimulator.

Lüders-like band front motion and fatigue life of pseudoelastic polycrystalline NiTi shape memory alloy

Abstract: We conducted tensile fatigue tests on polycrystalline NiTi strips with in-situ optical observation on the evolution of the localized deformation (Luders-like band) in order to trace the deformation history of the fatigue-failure material point in the strips under various loadings. It is found that the band front motion triggering localized cyclic phase transformation leads to a short fatigue life while the “elastic” deformation (without the band front motion) results in a much longer life whose failure crack nucleates away from the immobile band front. The results provide hints to derive a material fatigue criterion from the structure fatigue tests.

Fatigue and fracture of wires and cables for biomedical applications

Abstract: Fine wires and cables play a critical role in the design of medical devices and subsequent treatment of a large array of medical diagnoses. Devices such as guide wires, catheters, pacemakers, stents, staples, functional electrical stimulation systems, eyeglass frames and orthodontic braces can be comprised of wires with diameters ranging from 10s to 100s of micrometres. Reliability is paramount as part of either internal or external treatment modalities. While the incidence of verified fractures in many of these devices is quite low, the criticality of these components requires a strong understanding of the factors controlling the fracture and fatigue behaviour.1,2 Additionally, optimisation of the performance and reliability of these devices necessitates characterisation of the fatigue and fracture properties of its constituent wires. A review of cable architecture and stress states experienced during testing is followed by an overview of the effects of changes in material composition, microstructure, pr...