Papers by Keyword: Thermal Instability

Abstract: This study focus on the effects of both water content and cement stabilization on the fire behavior of earth bricks. To observe the effect of cement stabilization, two materials are formulated: raw earth with only soil and water, and stabilized bricks with soil, water and cement (3.5% by mass of soil). Since the material’s mechanical strength can strongly influence its fire behavior, the raw bricks were compacted at 50 MPa to reach a compressive strength similar to the one of stabilized bricks. Four different water contents were tested; dry state obtained with oven drying and three others achieved through equalization at 50%, 75% and 100% of relative humidities. Bricks are then subjected to an ISO 834-1 standard fire. Results show that water content has caused a thermal instability behavior on the raw earth bricks after equalization at 50% and 75% relative humidities. Thermally stable bricks displayed a noticeable diffusion of cracks on their heated face. Furthermore, cement stabilization helps to prevent from thermal instabilities.

Abstract: In this study, shape memory alloy (SMA) wires were embedded within a matrix to become a composite beam. Active shape control property of the SMA that controls the deflection of the composite beam was studied using finite element method (FEM). The values of recovery stresses of the SMA were determined using the Brinson’s model. A non-linear finite element formulation that is based on the von Karman strain and the Timoshenko’s beam theory was developed for this purpose. The Newton-Raphson method was then used to solve the formulation to obtain the transverse deflection of the beam. It was found that the effect of moment recovery on the beam deflection is significant where it is possible that the deflection of the beam due to external loading can be greatly suppressed.

Abstract: In recent years carbon nanotube (CNT) has been combined with polymers to take advantage of the extremely high strength and stiffness of the CNT. This paper reports a study on the thermal instability of carbon nanotube reinforced composites (CNTRC) plate subjected to uniform temperature rise. Finite element method (FEM) formulation was developed based on the first order shear deformation theory. The extended rule of mixture was used to determine the effective properties of the CNTRC plate. The CNTRC plate was functionally graded in its thickness direction. The results of the thermal instability were validated using past results and several parametric studies were then conducted using the developed formulation. The parametric studies showed that the critical temperature of the CNTRC was increased with the increase of the CNT volume fraction and the FG-4 configuration gave the highest critical temperature.

Abstract: The Cu-12.8wt%Fe alloys are prepared in a vacuum induction furnace and then drawn to Cu-Fe composite wires with the drawing ratio of 8.2. The thermal stability of Fe filaments in the deformed Cu-12.8wt% Fe composite wires under different annealed temperature is investigated. The results show that the instability of the Fe filaments in the Cu-Fe composites is controlled by the longitudinal boundary splitting, then the splitting Fe filaments subsequently evolve into the cylinders. The thermal instability of the cylindrical Fe filaments is controlled by the two instability modes of Rayleigh perturbation and two dimensional Ostwald coarsening. The model calculations of two modes indicate that the perturbation breakup of cylindrical Fe filaments firstly occurs at the ones with smaller diameter. The breakup time of cylindrical Fe filaments decreases with the increasing of the annealing temperature. The coarsening diameters of cylindrical Fe filaments increase in linear proportion with the holding time. The smaller is the diameter of cylindrical Fe filaments, the larger is the coarsening rate.

Abstract: In automotive applications, a particular area of concern is the relation between thermoelastically induced hot spots and noise and vibration in brake system. The finite element methods have been extensively used for thermal analysis applied to brake components. The two-dimensional model has been extended to an annular three-dimensional disc model in order to consider more realistic braking condition. In a conventional braking analysis, the interface pressure is assumed either constant or inversely proportional to radius. However, under the dynamic braking conditions, the frictional heat generated during braking causes thermoelastic distortion that modifies the contact pressure distribution. This paper describes the thermo-elastic instability arising from friction heat generation in braking and proposes the finite element methods to predict the variation of temperature and thermal deformation under single braking and repeated braking mode.

Abstract: As the automobile industry develops, the demand for automobiles that provide more comfortable ride and safety is also increasing. In the conventional braking analysis, frictional heat generation is only related to wheel speed, friction material, and the interface pressure. However, under the dynamic braking conditions, the frictional heat causes the thermo-elastic distortion that leads to more concentrated distribution of contact pressure and hence more and more non-uniform temperature. This paper describes the thermo-elastic instability arising from friction heat generation in braking and proposes the finite element methods to predict the variation of temperature and thermal deformation.