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Creep behavior of concrete at high temperature has become a major concern in building structures, such as factories, bridges, tunnels, airports and nuclear buildings. Therefore, a simple and accurate prediction model for the high-temperature creep behavior of concrete is crucial in engineering applications.

In this paper, the variable-order fractional operator is introduced to capture the high-temperature creep behavior of concrete. By assuming that the variable-order function is a linear function with time, the proposed model benefits from the advantages of both formal simplicity and the physical significance for macroscopic intermediate materials. The effectiveness of the model is demonstrated by data fitting with existing experimental results of high-temperature creep of two representative concretes.

The results show that the proposed model fits well with the experimental data, and the value of order is increasing with the increase of the applied stress levels, which meets the fact that higher stress can accelerate the rate of creep. Furthermore, the relationship between the model parameters and loading conditions is deeply analyzed. It is found that the material coefficients are constant at a constant temperature, while the order function parameters are determined by the applied stress levels. Finally, the variable-order fractional model can be further written into a general equation of time and applied stress.

This paper provides a simple and practical variable-order fractional model for predicting the creep behavior of concrete at high temperature.

The purpose of this paper is to investigate the creep properties of Sn‐0.7Cu composite solder joints reinforced with optimal nano‐sized Ag particles in order to improve the creep performance of lead‐free solder joints by a composite approach.

The composite approach has been considered as an effective method to improve the creep performance of solder joints. Nano‐sized Ag reinforcing particles were incorporated into Sn‐0.7Cu solder by mechanically mixing. A systematic creep study was carried out on nano‐composite solder joints reinforced with optimal nano‐sized Ag particles and compared with Sn‐0.7Cu solder joints at different temperatures and stress levels. A steady‐state creep constitutive equation for nano‐composite solder joints containing the best volume reinforcement was established in this study. Microstructural features of solder joints were analyzed to help determine their deformation mechanisms during creep.

The creep activation energies and stress exponents of Ag particle‐enhanced Sn‐0.7Cu lead‐free based composite solder joints were higher than those of matrix solder joints under the same stress and temperature. Thus, the creep properties of nano‐composite solder joints are better than those of Sn‐0.7Cu solder joints.

The findings indicated that nano‐sized Ag reinforcing particles could effectively improve the creep properties of solder joints. A new steady‐state creep constitutive equation of nano‐composite solder joints was established. Deformation mechanisms of Sn‐0.7Cu solder and nano‐composite solder joints during creep were determined.

In order to evaluate the rheological properties of asphalt more comprehensively and effectively, and to explore and discuss the practicability of relevant models in the evaluation of the rheological properties of asphalt.

Based on the rheological and viscoelastic theories, temperature scanning, frequency scanning and multiple stress creep recovery (MSCR) tests of different modified asphalt were carried out by dynamic shear rheometer (DSR) to obtain relevant viscoelastic parameters and evaluate the high temperature properties of different modified asphalt. Based on the time-temperature equivalence principle, the main curve was constructed to study the viscoelastic properties of asphalt in a wider frequency domain. The main curve was fitted with the CAM model, and the rheological properties of different modified asphalt were evaluated through the analysis of model parameters. The creep stiffness and creep velocity of different modified asphalt were obtained through the rheological test of bending beam (BBR), and the low-temperature performance of different modified asphalt was analyzed by using Burgers model to fit the creep compliance.

The results show that the high temperature rheological properties of several modified asphalt studied in the test are ranked from best to worst as follows: PE modified asphalt > SBS modified asphalt > SBR modified asphalt. Short-term aging can improve the high temperature performance of asphalt, and different types of modifiers can promote or inhibit this improvement effect. Based on BBR test and Burgers model fitting analysis, SBR modified asphalt has the best low temperature performance, followed by SBS modified asphalt, while PE modified asphalt has poor low temperature performance, so it is not suitable to be used as road material in low temperature area.

Combined with effective evaluation methods, the rheological properties of asphalt at different temperatures and angles were systematically evaluated, and the evolution of rheological properties of asphalt characterized by model parameters was further analyzed by advanced model simulation.

This study aims to investigate the thermal creep behavior of steel frame assemblies with shear tab connections subjected to transient-state fire temperatures. Different key parameters are investigated to study their effect on the global response of the steel frames in fire.

Finite element (FE) models of connection assemblies are first analyzed using Abaqus under transient-state temperature conditions and validated against experimental work available in the literature. Upon acquiring the validated conditions, parametric studies are carried out to study the effect of key geometric and heating parameters on the overall response of the frame assembly to fire temperatures. Thermal creep material is also incorporated in the analyses through a user-defined subroutine, and a comparison between including and excluding creep material is illustrated to show the effect of thermal creep on the structural behavior.

The results reported herein indicate that having a rigid column increases the thermal-induced axial forces, thus increasing the development of thermal creep strains. Slow heating rates can cause axial stress relaxation in the restrained beam and increase the mid-span deflection and consequently the development of beam catenary action. The results also show that reaching higher initial cooling temperatures and having longer cooling phase durations result in more tensile forces at the end of the cooling phase.

Previous studies were limited to isolated steel connections under steady-state conditions. This study investigates the creep behavior of shear tab connection assemblies under transient-state conditions of fire when creep effects are explicitly considered. This can provide a rational and realistic assessment of the steel behavior in fire events.

This paper aims to investigate the creep properties of the bulks of low-Ag Cu/Sn-Ag-Cu-Bi-Ni/Cu micro solder joints from 298 to 358 K. The creep constitutive modelling was developed. Meanwhile, the creep mechanism of the bulks of Cu/Sn-Ag-Cu-Bi-Ni/Cu micro solder joints was discussed.

The creep properties of the bulks of low-Ag Cu/Sn-Ag-Cu-Bi-Ni/Cu micro solder joints from 298 to 358 K were investigated using the nanoindentation method.

The results of the experiments showed that the indentation depth and area increased with increasing temperatures. At the test temperature of 298-358 K, the creep strain rate of the bulks of the micro solder joints increases with the rising of the tested temperature. The values of creep stress exponent and activation energy calculated for the bulks of Cu/Sn-Ag-Cu-Bi-Ni/Cu micro solder joints were reasonably close to the published data. At the tested temperatures, dislocation climb took place and the dislocation climb motion was controlled by the dislocation pipe mechanism, and the second-phase particles enhancement mechanism played a very important role.

This study provides the creep properties of low-Ag Cu/Sn-Ag-Cu-Bi-Ni/Cu solder joints at different temperatures. The creep constitutive modelling has been developed for low-Ag Cu/Sn-Ag-Cu-Bi-Ni/Cu solder joints.

DURING the last few years a programme of creep tests under general stress systems at high temperatures has been carried out at the N.P.L., using four metallic alloys which were chosen as being representative of basic groups of materials used in practice in machinery operating at high temperatures. This work, it was hoped, would fulfil, at least partly, the great need for experimental data in this field, as opposed to the comparative abundance of theoretical work available, and also enable a critical examination of the merits of this theoretical work to be made. The materials chosen in order of examination were a cast 0–17 per cent carbon steel, an aluminium alloy (R.R. 59), a magnesium alloy (containing 2 per cent aluminium), and a nickel‐chromium alloy (Nimonic 75). Each material was tested at temperatures lying within the normal working range of the material in question. Thus the 0–17 per cent carbon steel was tested at 350, 450 and 550 dcg. C. (662, 842 and 1,022 deg. F.), the aluminium alloy at 150 and 200 deg. C. (302 and 392 dcg. F.), the magnesium alloy at 20 and 50 deg. C. (68 and 122 dcg. F.), and the nickel‐chromium alloy at 550 and 650 dcg. C. (1,022 and 1,202 deg. F.).

The purpose of this study is to describe the mechanism of single-crystal high-temperature creep deformation, predict the creep life more accurately and study the creep constitutive and lifetime models with microstructure evolution.

The mechanical properties of nickel-based single-crystal superalloy are closely related to the γ' phase. Creep tests under four different temperature and stress conditions were carried out. The relationship between creep temperature, stress and life is fitted by numerical method, and the creep activation energy is obtained. The creep fracture surface, morphology and evolution of strengthening phase (γ') and matrix phase (γ) during different creep periods were observed by scanning electron microscope. With the increase of creep temperature, the rafting time is advanced. The detailed morphology and evolution of dislocations were observed by transmission electron microscope (TEM).

With the increase of creep temperature, the rafting time is advanced. The detailed morphology and evolution of dislocations were observed by TEM. Dislocations are mainly concentrated in the γ channel phase, especially at high temperature and low stress.

A creep constitutive model based on the evolution of γ' phase size and γ channel width was proposed. Compared with the experimental results, the predicted creep life is within 1.4 times error dispersion band.

The purpose of this paper is to study the temperature cycling reliability of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu micro solder joints compared with Sn-5Sb/Cu and SAC305/Cu micro solder joints, which has important engineering and theoretical significance for the research of micro solder joint reliability. This paper also aims to provide guidance for the selection of solder for third-generation semiconductor power device packaging.

The shear strength, plasticity, bulk solder hardness and creep performance of three kinds of micro solder joints before and after temperature cycling were studied by nanoindentation and micro shear experiments. Scanning electron microscopy and energy dispersive spectrometry were used to analyze the fracture mode, fracture position and compound composition of the solder joints.

The bulk solder hardnesses and shear strengths of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu solder joints were higher than those of Sn-5Sb/Cu and SAC305/Cu solder joints before and after temperature cycling. The indentation depth, creep displacement and creep rate of bulk solders of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu solder joints were the smallest compared with those of Sn-5Sb/Cu and SAC305/Cu solder joints after the same number of cycles. In addition, the fracture mode and fracture position of the micro solder joints changed before and after temperature cycling.

A new type of solder was developed with excellent temperature cycling performance.

The purpose of this paper is to investigate the effect of imposing linear and quadratic composition gradients on the steady state creep behavior of a rotating functionally graded Al‐SiC_P disc operating under a radial thermal gradient.

Mathematical model to describe steady state creep behavior in rotating discs made of isotropic aluminum composite containing linear and quadratic distributions of Silicon Carbide (SiC_P) in the radial direction has been formulated. The discs are assumed to operate under a radial thermal gradient originating due to braking action as estimated by FEM analysis. The steady state creep behavior of the discs under stresses developing due to rotation has been determined following Sherby's law. Based on the developed model, the distributions of stresses and strain rates have been obtained and compared for various functionally graded material (FGM) discs containing the same average amount (20 vol per cent) of dispersoid. The creep response of a composite disc with uniform SiC_P content of 20 vol per cent and operating under a radial thermal gradient has also been computed for comparison with the results obtained for FGM discs.

The study reveals that the distribution of stresses and strain rates in a rotating composite disc operating under a radial thermal gradient are significantly affected by different particle distributions with in the disc. The creep stresses and steady state creep rates in a rotating FGM disc can be significantly reduced by employing more SiC_P particles in the middle compared to the inner and the outer radii.

The study provides an understanding of the required tailoring of composition in order to control creep stresses and creep rates in a rotating FGM disc operating under a radial thermal gradient.

IN 1946, a short conference on creep in metals was held at the initiative of the National Physical Laboratory. The aircraft gas turbine was then relatively new. It had been developed during the war as a small fighter engine with outstanding power/weight ratio and short life. Since then it has been applied successfully to commercial aircraft and to ship propulsion and its use in power generation is being actively explored. These applications require in general larger engines, longer lives (up to 100,000 hours in many cases), and high thermal efficiency.