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Lightweight alloys are of major concern, due to their applicability, in transport and industry applications. The purpose of this paper is to perform a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique, through investigation of creep behavior. Additionally, possible explanations on the time dependent behavior and the influence of the hold period at maximum load and the loading rate on the elastic modulus and hardness results are also analyzed and discussed.

In this work, a comprehensive analysis of time dependent properties of aluminum alloy by nanoindentation technique was performed, by varying the loading rate, the maximum applied load and the loading time. The stress exponent values are derived from the displacement‐holding time curves. The present experimental setup includes three different approaches: variation of loading rate, maximum applied load and loading time. The creep deformation mechanisms of the alloy, which are dependent on experiment setup, are discussed and the characteristic “elbow” behavior in the unloading part of the curves is also reported.

The authors found that the stress exponent values obtained are dependent on the applied peak loads and indentation loading rates. Nanoindentation creep testing of aluminum AA6082‐T6 revealed significant creep displacements, where the strain rate reached a steady state after a certain time and the stress decreased with time as the displacement increased during the creep process. The slopes of strain rate versus stress curves (exponent of power‐law creep) for different maximum loads and various holding times, were investigated.

The stress exponent of the constant‐load indentation creep, in all three types of experiments, was found to reduce at low load region. In case of different holding load and time, the stress exponent increased almost linearly and increased very rapidly as the indent size increased, exhibiting an intense size effect.

The study of nanoindentation as a reliable method to extract creep properties as well as for fundamental understanding of deformation mechanisms at small length scales is an open interesting field. The observed creep behavior is attributed to time-dependent plastic deformation based on loading rates. There is a lot of work in the field of nanoindentation in order to understand the dynamic effects on nanomechanical properties. The paper aims to discuss these issues.

The deformation mechanism is investigated under two experimental approaches (high and low loading rates, respectively) during nanoindentation. The effect of loading rate in the nanomechanical properties, during nanoindentation creep of zinc layer on hot dip galvanized (HDG) steel, is discussed through nanoindentation.

Analysis of this research effort is emphasized on nanoindentation stress exponent, a critical parameter for the life time and reliability of nano/micro-materials and systems. The corrosion resistance was studied by electrochemical impedance spectroscopy (EIS) and localized EIS.

The study of nanoindentation as a reliable method to extract creep properties as well as for fundamental understanding of deformation mechanisms at small length scales is an open interesting field. The observed creep behavior is attributed to time-dependent plastic deformation based on loading rates. The deformation mechanism is investigated under two experimental approaches (high and low loading rates, respectively) during nanoindentation. The effect of loading rate in the nanomechanical properties, during nanoindentation creep of zinc layer on HDGsteel, is discussed through nanoindentation. Analysis of this research effort is emphasized on nanoindentation stress exponent, a critical parameter for the life time and reliability of nano/micro- materials and systems. The corrosion resistance was studied by EIS and localized EIS.

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 work described in this paper is part of a programme concerned with the plastic, creep, and relaxation properties of metals under complex stress systems at elevated temperatures.which is being carried out in the Engineering Division of the N.P.L. It comprises data on the criterion of departure from elastic behaviour, of a low carbon steel over the temperature range 20–550 deg. C, and of an aluminium alloy over the temperature range 20–200 deg. C, and the creep properties under complex stress systems of the low carbon steel at 350 deg. C, and of the aluminium alloy at 150 and 200 deg. C.

An exact analysis is presented for the creep deformation of solder interconnects subjected to the actions of bending moment, twisting moment and axial force. Dimensionless interaction curves and charts which relate the variables, interconnect geometry, solder material properties, axial force, bending moment, twisting moment, bending stress, shearing stress, curvature rate and twist rate are also provided for engineering practice convenience. The constitutive relationship of the 96.5Sn3.5Ag solder interconnects is described by the Garofalo‐Arrhenius steady‐state creep equation.

In this addendum, the purpose of this paper is to introduce the new creep law for the description of the different stages of creep. The introduced creep law generalizes the creep law used in Kobelev (2014).

The new generalized creep law demonstrates the relationship between creep rate and stress as well as accounts the time dependence in different creep regimes. In the stage of primary creep there is explicit time dependence of creep rate. In the stage of secondary creep the creep rate exhibits – analogously to the original creep law – no explicit dependence on time.

The closed form expressions giving the torque and bending moment as a function of the time are provided. The method is applicable for definite other stress functions in the creep law.

The arbitrary creep law allows the separation of time and spatial variables; exponential and power-law time dependence.

The results of creep simulation are applied to practically important problem of engineering, namely for simulation of creep and relaxation of helical and disk spring, driveshafts, torque elements of machine dynamics.

The new creep model with fractional derivative of time dependence is introduced. The closed form solutions for new creep model allow simple formulas for creep effect on stress and deformation and the implications for high temperature design.

With the continued miniaturisation of electronics equipment, a more detailed examination of the mechanical behaviour of solders is required to ensure reliability in performance. The paper reviews various aspects of the interpretation of the creep response of lead‐containing and lead‐free alloys. It demonstrates the necessity of acquiring stress‐rupture data over as long a period as possible to avoid non‐conservative extrapolation. For example, at 75°C, the transition in slope of the applied stress vs time to rupture plot occurs after about 1,000 h for Sn‐37Pb, although for the lead‐free alloys examined no such transition is observed within this timescale. Sometimes, deformation may be a more appropriate failure criterion than rupture, and it is shown that for Sn‐37Pb this may result in substantially shorter failure times than utilising a rupture criterion. The quality of life estimation methods then depends upon the extent of this stage when the creep rate is a minimum. The Y factor (t_m : t_r) where t_m is the time spent in steady state or within 10 per cent of the minimum creep rate, for all the solders examined at 75°C generally falls into the 20‐30 per cent range. Estimations of creep life may substantially under predict because of this.

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.

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.

A solution algorithm for the transient analysis of bodies undergoing creep under constant or time varying loads is presented. The constitutive equation adopted is of the form: έc=γσm. The finite element formulation is carried out in terms of displacements and creep strains as internal variables. The time discretization is achieved with a trapezoidal time integration scheme. The creep strains are condensed out to give an equation for displacement increments involving a modified stiffness matrix and force vector. A Newton—Raphson iterative scheme is used for the non‐linear creep strain rate‐stress relation, and creep strains are updated at the end of the time step. The algorithm has been implemented in NOSTRUM for two‐dimensional structural and plane continuum problems, with a von Mises type potential function governing the multiaxial creep constitutive relationship. Numerical results are presented.