Influence Of Temperature History Research Articles

Influence of Temperature History and Flow Mixing on the Vapor-Phase Speciation of Uranium Oxide Nanoparticles

Influence of Temperature History and Flow Mixing on the Vapor-Phase Speciation of Uranium Oxide Nanoparticles

Influence of temperature history on calcium leaching resistance of hydraulic concrete

In order to find out how temperature history affect leaching resistance, the leaching depths and compressive strength loss rate of pastes under three different temperature histories have been studied, the result shows that, with the progress of leaching, the compressive strength of samples continue to decrease, but the rate of decrease gradually slows down, and the leaching resistance of temperature match curing cured sample is better than that of standard curing cured, while the leaching resistance of circadian cycle curing cured sample is worse than that of standard curing cured.

Transformation from Measured Strains to Viscoelastic Stresses considering Temperature History for Concrete Dams

Strain and stress monitoring is an important approach for evaluating the stress state of concrete dams. Since the hydration rate of cement increases with increasing temperature, the parameters of the thermal and mechanical properties of concrete are related to its temperature and temperature history. However, the influence of temperature history has not been taken into account in theories of transformation from measured strains to stresses used for analysis of concrete dams. Hence, significant errors can occur in stress evaluations of concrete dams. In this paper, based on the equivalent age theory and deformation method, we investigate a transformation equation from measured strains to viscoelastic stresses that considers the temperature history and describe the calculation steps in detail. The new algorithm is implemented by a comparative analysis of the viscoelastic stresses transformed from measured strains with and without considering the temperature history for a typical concrete dam located in northwestern China. The analysis results show that the trends of the transformed stresses with and without considering the temperature history are essentially the same, while the maximum normal stress difference is 0.49 MPa in the early stage.

Research on Method of Separating Autogenous Shrinkage from Thermal Deformation of Concrete at Early Ages

In order to separate early-gae autogenous shrinkage from thermal deformation, it is the key to measure accurately thermal expansion coefficient of concrete at early ages. By analysing deeply the research status of early-age thermal expansion coefficient of concrete, the influences of temperature history on early-age autogenous shrinkage and the selection of thermal expansion coefficient are discussed. Moreover, based on the existing methods of separating early-gae autogenous shrinkage from thermal deformation, the more reasonable two-phase separating method considering concrete ages is provided.

Thermal Stress Analysis of Mass Concrete that Considers Influence of Temperature History

Thermal Stress Analysis of Mass Concrete that Considers Influence of Temperature History

SELECTING A TEMPERATURE TIME HISTORY FOR PREDICTING FATIGUE LIFE OF MICROELECTRONICS SOLDER JOINTS

Temperature cycling tests are standard industry practice for determining the thermomechanical fatigue life of solder joints. Industry-standard temperature profiles usually start from room temperature, then go to a high temperature, then to a cold temperature, and then back to room temperature. In addition, most of the time, the temperature profile contains dwell times at the highest and lowest temperatures. The dwell time at a high temperature corresponds to the on-state storage of the device, and the cold-temperature dwell time simulates the off-state storage of the device. In this study, the actual temperature history of a Ball Grid Array (BGA) package in a laptop computer was measured in situ. Experimental reliability studies were conducted using the in situ measured temperature history as well as industry-standard temperature history. This article presents the influence of temperature history on solder joint fatigue life. In order to measure deformations in the solder joint under cycling loading, a new Moire interferometry grating replication technique was developed to be able to measure strain field during fatigue testing.

An orthotropic theory of viscoplasticity based on overstress for thermomechanical deformations

An infinitesimal, orthotropic theory of viscoplasticity based on overstress for thermo-mechanical loading (TVBO) is presented. The total strain rate is the sum of elastic, inelastic and thermal strain rates. An orthotropic constitutive law is postulated for each strain rate using the characteristics of orthotropic matrices and previous isotropie formulations of the viscoplasticity theory as a guide. All material functions and constants can be functions of current temperature and no influence of temperature history is modeled. Yield surfaces and loading/unloading conditions are not used in the theory in which the inelastic strain rate is solely a function of the overstress. the difference between stress and the equilibrium stress, a state variable of the theory. A comparatively simple theory is obtained which is capable of modeling important phenomena like creep, relaxation, rate sensitivity, hysteresis, tension/compression asymmetry and nearly elastic regions. It is also possible to model quasielastic behavior in one direction while the others behave viscoplastically. The theory is shown to reduce to a previously proposed formulation for inelastic incompressibility and isotropy.

Influence of temperature history on strain‐induced austenite transformation in 304 stainless steel

Experimental investigations were undertaken to find temperature history effects on strain‐induced austenite transformation in metastable 304 stainless steel. Interrupted static tension tests were performed at temperatures 0 and — 15°C. During the first stage of deformation specimens were deformed at temperature T1. During the second stage temperature T2 was applied. Cases T1 > T2 and T1 < T2 were examined. Final amounts of α’ martensite XM were measured magnetically.A method for their summation of martensite amounts was sought for and a conclusion was obtained showing that the final amount of martensite can be calculated by the relationship XM= f(ε)|T2 where ε = εT1, + εT2 ±Δε. The corrective strain Δε depends on εT1. Its connection with true stress – true plastic strain curve at temperature T1 is discussed in this investigation.

Material Behavior Under Thermal Loading

Material behavior under thermo-mechanical and isothermal loading cases is studied. The influence of constraint on thermo-mechanical deformation behavior is identified using a two-bar structure. Some of the possible microstructural mechanisms that may be operative under thermo-mechanical loading conditions are discussed. Isothermal tests are reported in the temperature range 20 to 600°C. Additional isothermal tests with step increases and decreases in temperature are performed to study the influence of temperature history on material behavior. During these tests, transient material behavior indicated temperature-strain history effects. Constitutive equations that capture essential features of material behavior under isothermal and thermo-mechanical loading cases are examined. Preliminary predictions of cyclic stress-strain loops are compared to experimental response. Further work is needed to incorporate temperature-strain history effects into constitutive equations.

Natural and artificial heterogeneous nucleation in polymer crystallization

AbstractAn outline is given of heterogeneous nucleation as the main starting point for crystallization of unoriented polymer melts and solutions. The influence of temperature history on nucleation is discussed. As little is known about naturally occurring nucleants, the nature of several types of artificial nucleating agents is described. Potential mechanisms of heterogeneous nucleation are discussed against the background of various theoretical models. Experimental methods of measurement of nucleation density or of nucleation frequency may give some indication as to which mechanism is operative. The main conclusion is that heterogeneous nucleation is governed by “active sites” in the surface of the nucleants.

Influence of Temperature History on the Response of Psychrophiles to Different Incubation Temperatures

Influence of Temperature History on the Response of Psychrophiles to Different Incubation Temperatures