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Article
Publication date: 1 March 1987

N.J. Marais and J.B. Martin

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…

Abstract

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.

Details

Engineering Computations, vol. 4 no. 3
Type: Research Article
ISSN: 0264-4401

Article
Publication date: 10 October 2016

Vladimir Kobelev

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…

Abstract

Purpose

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).

Design/methodology/approach

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.

Findings

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.

Research limitations/implications

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

Practical implications

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.

Originality/value

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.

Details

Multidiscipline Modeling in Materials and Structures, vol. 12 no. 3
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 1 February 1990

J.S. Hwang and R.M. Vargas

Solder joint long‐term reliability is an ultimate requirement for electronics packaging. Solder joint failure, however, can involve complex mechanisms. One of many basic…

Abstract

Solder joint long‐term reliability is an ultimate requirement for electronics packaging. Solder joint failure, however, can involve complex mechanisms. One of many basic failure processes in metals/alloys is the creep phenomenon. Creep is defined as a time‐dependent deformation when a material is subjected to a stress for a prolonged period of time. This time‐dependent deformation can theoretically occur at any temperature above absolute zero. However, creep‐dominant failure normally occurs under high temperature in relation to the melting point of the material. Common solders are low temperature alloys with melting point or liquidus/solidus temperature in the range of 120–320°C. Therefore a detectable creep process under low level of mechanical load is expected even at ambient temperature. This paper presents the preliminary data on the comparative creep rate of twenty‐two common solder alloys and attempts to correlate the creep rate to the tensile strength, modulus, melting point and microstructure of alloys. The alloys under study include Sn/Pb, Sn/Pb/Ag, Sn/Ag, Sn/Sb, Sn/Pb/Bi, Sn/Pb/Sb, Sn/Bi, Sn/In, and Pb/In systems. This paper also discusses the proposed mechanisms for solder creep phenomena. It is hoped that the data in this work will provide additional fundamental mechanical properties of various solder alloys, which are much needed to facilitate the design of reliable solder joint structure.

Details

Soldering & Surface Mount Technology, vol. 2 no. 2
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 April 2003

F. Guo, J. Lee and K.N. Subramanian

In an attempt to improve service life of lead‐free Sn‐based electronic solder joints, compatible reinforcements were introduced by in‐situ and mechanical mixing methods…

Abstract

In an attempt to improve service life of lead‐free Sn‐based electronic solder joints, compatible reinforcements were introduced by in‐situ and mechanical mixing methods. The reinforcements affect the steady‐state creep rate and the strain for the onset of tertiary creep of the solder joints. However, neither of these parameters, when considered alone, can be used for evaluating the reliability of solder joints. The Larson‐Miller parameter, and a new parameter proposed in the paper, can incorporate test parameters to arrive at a reliability prediction methodology. The role of these reinforcements in homogenising creep strain within the joint is analysed. The observed creep behaviour of these composite solders is discussed on the basis of interfacial bonding strength between the reinforcement and the solder matrix.

Details

Soldering & Surface Mount Technology, vol. 15 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 1 February 2009

V.K. Gupta, S.B. Singh and S. Ray

A mathematical model has been developed to predict steady state creep response of a rotating disc made of SiC (particle/whisker) reinforced 6061Al matrix composite. The…

Abstract

A mathematical model has been developed to predict steady state creep response of a rotating disc made of SiC (particle/whisker) reinforced 6061Al matrix composite. The model is used to investigate the effect of SiC morphology on the creep behavior of composite disc. The steady state creep behavior has been described by Sherby’s creep law. The creep stresses and creep rates are significantly affected by the morphology of SiC. The steady state creep rates in whisker reinforced disc are observed to be significantly lower than those observed in particle reinforced disc.

Details

Multidiscipline Modeling in Materials and Structures, vol. 5 no. 2
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 21 September 2010

Feng Tai, Fu Guo, Jianping Liu, Zhidong Xia, Yaowu Shi, Yongping Lei and Xiaoyan Li

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…

Abstract

Purpose

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.

Design/methodology/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.

Findings

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.

Originality/value

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.

Details

Soldering & Surface Mount Technology, vol. 22 no. 4
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 12 September 2016

Neno Toric, Rui Rui Sun and Ian W. Burgess

This paper aims to propose a methodology to remove inherent implicit creep from the Eurocode 3 material model for steel and to present a creep-free analysis on simply…

Abstract

Purpose

This paper aims to propose a methodology to remove inherent implicit creep from the Eurocode 3 material model for steel and to present a creep-free analysis on simply supported steel members.

Design/methodology/approach

Most of the available material models of steel are based on transient coupon tests, which inherently include creep strain associated with particular heating rates and load ratios.

Findings

The creep-free analysis aims to reveal the influence of implicit creep by investigating the behaviour of simply supported steel beams and columns exposed to various heating regimes. The paper further evaluates the implicit consideration of creep in the Eurocode 3 steel material model.

Originality/value

A modified Eurocode 3 carbon steel material model for creep-free analysis is proposed for general structural fire engineering analysis.

Details

Journal of Structural Fire Engineering, vol. 7 no. 3
Type: Research Article
ISSN: 2040-2317

Keywords

Article
Publication date: 1 February 1992

MATTHEW R. KUHN and JAMES K. MITCHELL

The discrete element method (DEM) was used to stimulate creep processes in granular materials. The authors present the main features of the numerical model, which include…

Abstract

The discrete element method (DEM) was used to stimulate creep processes in granular materials. The authors present the main features of the numerical model, which include a new viscous mechanism for particle sliding, a new feedback technique for maintaining constant stress during creep, and a scaling technique that allowed monitoring the long‐term creep behaviour of a granular assembly. The creep behaviour of the numerical model exhibited the essential characteristics of soil creep—a creep rate that decreased rapidly with time, an increase in the creep rate with the applied deviator stress, and the beginning of creep rupture. The model's numerical performance is discussed, and representative results are presented.

Details

Engineering Computations, vol. 9 no. 2
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 12 April 2022

Ruifan Meng

Creep behavior of concrete at high temperature has become a major concern in building structures, such as factories, bridges, tunnels, airports and nuclear buildings…

Abstract

Purpose

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.

Design/methodology/approach

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.

Findings

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.

Originality/value

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

Details

Engineering Computations, vol. 39 no. 7
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 28 June 2021

Mian M. Ajmal, Mehmood Khan, Angappa Gunasekaran and Petri T. Helo

Project scope creep is a nightmare and nearly intolerable task. Most project managers struggle to curtail the expanse and degree of scope creep. This study examines…

1959

Abstract

Purpose

Project scope creep is a nightmare and nearly intolerable task. Most project managers struggle to curtail the expanse and degree of scope creep. This study examines different likely project scope creep factors associated with the construction industry projects.

Design/methodology/approach

After many brainstorming sessions with construction stakeholders, several project scope creep factors were identified. Then, a detailed survey was executed in big construction projects of the United Arab Emirates (UAE). The data were analyzed using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA).

Findings

The results derived and validated five conspicuous factors leading to project scope creep. Respectively, the highest and the lowest impact on project scope appears to be imposed by tasks/specifications and complexity/uncertainty.

Practical implications

It offers crucial support to the project stakeholders in scrutinizing different factors that stand as hurdles to project success and allows them to seek remedies to resolve them.

Originality/value

It is among the first study in the region that identifies and validates the factors that hinder construction project success.

Details

Engineering, Construction and Architectural Management, vol. 29 no. 7
Type: Research Article
ISSN: 0969-9988

Keywords

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