Due to their high strength to weight and stiffness to weight ratio, there is a huge shift towards the composite materials from the conventional metals, but composites have poor damage resistance in the transverse direction. Undergoing impact loads, they can fail in wide variety of modes which severely reduces the structural integrity of the component. This paper deals with the homogenization of glass-fibers and epoxy composite with a material introduced as an inelastic inclusion. This nonlinearity is being modelled by kinematic hardening procedure and homogenization is done by one of the mean field homogenization technique known as Mori-Tanaka method. The homogenization process consider two phases, one is the matrix and another is the inelastic inclusion, thus glass-fibers and epoxy are two phases which can be considered as one phase and act as a matrix while homogenizing non-linear composite. Homogenization results have been compared to the matrix at volume fraction zero of the inelastic inclusions and to the inelastic material at volume fraction one. After homogenization, increase of the energy dissipation into the composite due to addition of inelastic material and effects onto the same by changing the properties of the matrix material have been discussed.
In this paper we address the chattering phenomenon which is a common drawback associated with the normal Sliding Mode Control (SMC) law for a basic shape memory alloy (SMA) actuated system. A new method has been proposed to counter this effect by combining the concepts of Fast Terminal SMC and Dynamic controller. A phenomenological model is developed for the SMA which incorporates a piecewise linear hysteresis behavior. This model is used for both open loop as well as closed loop simulations for a linear motion control system. Based on this model, a dynamic terminal sliding mode control law is derived and applied to the system. A normal SMC law with saturation function which is known to reduce chattering is compared with the proposed control law for its effectiveness to curb the issue of chattering versus its ability to faithfully track a desired trajectory. Numerical Simulations indicate that the proposed law is able to reduce the chattering effect sufficiently and at par with the control technique involving saturation function.
Fibers can play a major role in post cracking behavior of concrete members, because of their ability to bridge cracks and
distribute the stress across the crack. Addition of steel fibers in mortar and concrete can improve toughness of the
structural member and impart significant energy dissipation through slow pull out. However, steel fibers undergo plastic
deformation at low strain levels, and cannot regain their shape upon unloading. This is a major disadvantage in strong
cyclic loading conditions, such as those caused by earthquakes, where self-centering ability of the fibers is a desired
characteristic in addition to ductility of the reinforced cement concrete. Fibers made from an alternative material such as
shape memory alloy (SMA) could offer a scope for re-centering, thus improving performance especially after a severe
loading has occurred. In this study, the load-deformation characteristics of SMA fiber reinforced cement mortar beams
under cyclic loading conditions were investigated to assess the re-centering performance. This study involved
experiments on prismatic members, and related analysis for the assessment and prediction of re-centering. The
performances of NiTi fiber reinforced mortars are compared with mortars with same volume fraction of steel fibers.
Since re-entrant corners and beam columns joints are prone to failure during a strong ground motion, a study was
conducted to determine the behavior of these reinforced with NiTi fiber. Comparison is made with the results of steel
fiber reinforced cases. NiTi fibers showed significantly improved re-centering and energy dissipation characteristics
compared to the steel fibers.
In this paper, rate-dependent switching effects of ferroelastic materials are studied by means of a micromechanically
motivated approach. The onset of domain switching is thereby initiated as soon as a related
reduction in energy per unit volume exceeds a critical value. Subsequent nucleation and propagation of
domain walls during switching process are incorporated via a linear kinetics theory. Along with this micromechanical
model, intergranular effects are accounted for by making use of a probabilistic ansatz; to be
specific, a phenomenologically motivated Weibull distribution function is adopted. In view of finite-element-based
simulations, each domain is represented by a single finite element and initial dipole directions are
randomly oriented so that the virgin state of the particular bulk ceramics of interest reflects an un-poled
material. Based on a staggered iteration technique and straightforward volume averaging, representative
stress versus strain hysteresis loops are computed for various loading amplitudes and frequencies. Simulation
results for the rate-independent case are in good agreement with experimentally measure data reported
in the literature and, moreover, are extended to rate-dependent computations.
Active continua with integrated sensor and actuator have proved effective in damping the vibrations of any dynamic system. This work deals with experimentally implementing control algorithms, namely negative velocity and Lyapunov control to actively damp the vibrations of a cantilever beam. A Finite element scheme is used to predict the dynamic response of the beam to transient electrical signals and to compare them with the experimentally obtained results. A distributed PVDF Polyvinylidene fluoride) actuator is used for actuation and an accelerometer is used as a tip velocity sensor.
Copper-based shape memory alloys (SMAs) are prone for grain growth during thermomechanical and betatising treatments. The grain growth of the alloy leads to intergranular cracking on quenching to form martensite in the alloy, which in turn leads to poor mechanical properties including corrosion resistance of the alloy. In the present work, grain refinement of a CuZnAl shape memory alloy was done by adding 0.2 to 0.4 wt% of zirconium, titanium and boron as grain refiners. The effect of these additions on the microstructure and shape memory properties of the alloys were studied. The results show that the Zr and Ti additions reduce the grain size from 1.5 mm to 200 μm and 500 μm, repectively. The Zr-added alloy shows good strain recovery and corrosion resistance compared with the alloy in the other conditions.
In this paper; first a comprehensive understanding of temperature and stress induced phase transformation is presented and a thorough interpretation of martensitic phase transformation is presented. A numerical study of Brinson's model is then presented, in order to explain the capability of the model in reproducing the SMA characteristics under quasi-static thermomechanical loading. A MATLAB code was developed for the Numerical Simulation of Brinson's Constitutive Model. The stress strain curves obtained by the Brinson's model were used to simulate the behavior of SMA wires and Beams under Quasi-static thermo-mechanical loading. Later in the end the applicability of Brinson's model for Hysteresis effects was studied by subjecting the beam model to two cycles of loading and unloading and then the Shape Memory Effect was studied. It was observed that the Brinson's Model needs some modifications for expressing Hysteresis Effects. However for one cycle of loading and unloading, the model well predicted the Super Elasticity and Shape Memory Effects.
This paper deals with the rate and time dependent electrical and mechanical properties of Biaxially stretched Form I PVDF and modeling those properties. Experiments have been done to characterize the rate and time dependent mechanical behavior of PVDF and the rate dependent electrical properties of PVDF. The rate dependent mechanical property of PVDF has been modeled through a Kelvin solid with fractional dashpot and nonlinear spring assuming incompressibility. It is shown in this paper using the model, that the viscoelastic behavior of PVDF is similar to that of a Non-Newtonian fluid. The model predicts the response of PVDF properly within the range or 12% strain. The time dependent behavior of PVDF is modeled through a power law model.