Thermoelastic Properties and Elastocaloric Effect in Rapidly Quenched Ribbons of Ti2NiCu Alloy in the Amorphous and Crystalline State

The thermoelastic properties and the elastocaloric effect (ECE) were studied in rapidly quenched ribbons of the Ti2NiCu alloy samples in amorphous and crystalline states under periodic mechanical tension with a frequency of up to 50 Hz. In the amorphous samples, elastic behavior is observed, described by Hooke’s law, with a high coefficient of thermal expansion α = 1.7 × 10−4 K−1. Polycrystalline ribbons of the Ti2NiCu alloy have the classical shape memory effect (SME), the temperatures of the forward and reverse thermoelastic martensitic transitions being Ms = 345 K, Mf = 325 K, As = 332 K, and Af = 347 K and the coefficient of the dependence of the transition temperature on mechanical stress being β = 0.12 K/MPa. The experimentally measured value of the adiabatic temperature change under the action of mechanical stress (ECE) in the amorphous state of the alloy at room temperature (Tr = 300 K) was ΔT = −2 K, with a relative elongation of ε = 1.5% and a mechanical stress of σ = 243 MPa. For crystalline samples of Ti2NiCu alloy ribbons, the ECE is maximum near the completion temperature of the reverse thermoelastic martensitic transformation Af, and its value was 21 K and 7 K under cyclic mechanical loads of 300 and 100 MPa, respectively. It is shown that the ECE value does not depend on the frequency of external action in the range from 0 to 50 Hz. The specific power of the rapidly quenched ribbon was evaluated as a converter of thermal energy at an external mechanical stress of 100 MPa; its value was 175 W/g at a frequency of 50 Hz. The thermodynamic model based on the Landau theory of phase transitions well explains the properties of both amorphous ribbons (reverse ECE) and alloy ribbons with EPF (direct ECE).

The Thermal Destruction and Coke Formation Intensity Influence on the Delamination and Destruction of Fiber Reinforced Plastics with a Unidirectional Filler under High Temperature Conditions

It is made fiber reinforced plastics (FRP) adhesion properties influence analysis on their destruction at an increase of temperature. Taking into account the thermoelastic properties of fiber reinforced plastics, it is proposed an expression for calculating the load of the composition delamination beginning, and a correlation of the destructive stress in monolayer FRP with the temperature of heating is found. It has been established that the further intensity of delamination and destruction of FRP depends on the temperature of the destruction beginning and coke formation intensity.

THERMAL STIFFNESS – A KEY ACCURACY INDICATOR OF MACHINE TOOLS

Static and dynamic stiffness [N/m] determine the ability of solids to resist constant and variable loads. Both elastic characteristics of a machine tool effect their quality assessment. Thermal stiffness (comprising heat stiffness and temperature stiffness) [W/µm] is a key accuracy indicator of the machine tool's ability to resist temperature influences. The proposed method creates the thermo-physical structure of a machine tool, based on a set of homogeneous heat-active elements and quasi-thermostable links. Quasi-thermostable links retain constant properties when the thermal state of the heat-active elements changes within a given range, building and determining their spatial and temporal relative position. The structural formula is given: < S-thermal link > -<F-function of the thermal behavior of a heat-active element > - <S-thermal link>. When exposed to heat, heat-active elements change their temperature and thermoelastic properties change their temperature and thermoelastic properties with stress, strain, distortion. Thermal behavior F-functions characterize these changes over time. Thermal energy causes a heat exchange in the machine tool and leads to temperature differences, thermoelastic stresses and geometrical deformations. The material used in machine tools enables the thermal conduction, convection and radiation due to its dimensions, volume and surface area, thermal conductivity. Elasticity effects base on thermal linear expansion coefficient, modulus of elasticity, thermal energy storage due to its heat capacity. The analysis of the structural formula defines and describes generalized thermal stiffness indicators of a machine tool as a reaction to thermal effects when the heat sources are constantly active and when the heat source is absent, but only the ambient temperature changes. This paper presents relationships between the thermal stiffness and the thermo-physical property indicators of the machine tool. Examples of thermal stiffness are described for several machine tool types.

MODEL OF DEFORMATION OF FIBROUS MATERIALS OF MULTIDIRECTIONAL REINFORCEMENT WITH NONORIENTED FIBERS

A model of deformation of multidirectional reinforcement fibrous materials with differently oriented fibers is proposed. The solution to the problem is built in two stages. At the first stage, the known properties of fibers and binder are used to determine the effective thermoelastic properties and stress-strain state of the subsystem with fibers oriented in a certain way relative to the main coordinate system. It is based on stochastic differential equations of the physically nonlinear theory of elasticity using the method of conditional moments. At the second stage, using a given distribution function based on the Voigt scheme, a model of deformation of the entire system is constructed from the calculated properties of the subsystems. Strain curves are obtained for simple loading, and the deformation of materials at uniform orientation of fibers is investigated. It was found that a fibrous composite material with differently oriented fibers in a macrovolume is isotropic, and its effective thermoelastic constants substantially depend on the volumetric content of fibers.