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Book part
Publication date: 19 December 2016

Radha R. Sharma and Sir Cary Cooper

Abstract

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Executive Burnout
Type: Book
ISBN: 978-1-78635-285-9

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Article
Publication date: 1 March 1959

A.E. Johnson, J. Henderson and V.D. Mathur

The nature of the relation between complex stress creep under conditions of relaxation and complex stress creep under conditions of steady stress was investigated. The…

Abstract

The nature of the relation between complex stress creep under conditions of relaxation and complex stress creep under conditions of steady stress was investigated. The required relation has been examined for an RR59 aluminium alloy at 200 deg. C. and for a magnesium (2 per cent aluminium) alloy at 50 deg. C. For RR59 aluminium alloy at 200 deg. C. and for magnesium (2 per cent aluminium) alloy at 50 deg. C., a reasonably close prediction of the course of relaxation complex stress time curves is given by the mechanical age hardening theory of creep on the basis of steady complex stress creep data. Other mechanical theories tend to predict for a specific relaxed stress a relaxation time in excess of that noted in experiment.

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Aircraft Engineering and Aerospace Technology, vol. 31 no. 3
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 13 January 2021

Dan Wang, Kun Wu, Guanlin Li and Lifeng Wang

The purpose of this paper is to study the mechanical property of three-dimensional (3D) Printed photopolymer (Vero Yellow and Tango Black) with different constant strain…

Abstract

Purpose

The purpose of this paper is to study the mechanical property of three-dimensional (3D) Printed photopolymer (Vero Yellow and Tango Black) with different constant strain rate. According to the experimental results, three constitutive models are used to describe the stress-strain and stress-time relation in the tension and stress relaxation process.

Design/methodology/approach

The Stratasys Objet 260 was used to prepare the four groups of samples with different photopolymers (Vero Yellow and Tango Black). The stress-strain and stress-time relations are obtained by the uniaxial tensile tests and relaxation tests performed at room temperature with different constant strain rates. The generalized Kelvin model (GKM), standard linearized model (SLM) and fractional order model (FOM) are used to describe experimental data by means of the curve-fitting approach.

Findings

Experimental results show that the tension stress increases faster at a higher strain-rate for tensile tests. Relaxation stress is influenced by the preload strain-rate for relaxation tests. For the theoretical fitting, the error comparison between three constitutive models and experimental data are calculated to demonstrate the high accuracy in describing the stress-strain relationship for tension. For stress relaxation, the error comparison confirms higher accuracy of FOM with the largest error within 3%, while the error of GKM and SLM up to 10%.

Originality/value

The paper confirms the viscous-elastic mechanical property of 3D printed photopolymer composites (Vero Yellow and Tango Black) for Stratasys PolyJet. As FOM shows high accuracy both in describing stress-strain and stress-time relation for tension and stress relaxation process, it can be directly used as a constitutive model to predict mechanical properties for engineering application.

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Rapid Prototyping Journal, vol. 27 no. 2
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 1 February 1984

Christopher Orpen

Managerial stress exists and has to be coped with. The author describes a study that demonstrates that cue‐controlled relaxation can be applied to groups of managers to…

Abstract

Managerial stress exists and has to be coped with. The author describes a study that demonstrates that cue‐controlled relaxation can be applied to groups of managers to reduce psychological and physical stress. The study involved 36 middle managers with stress problems who were randomly exposed to treatment and non‐treatment, which consisted of a three‐week programme to teach conditioned relaxation responses to self‐administered cues. Three months after both groups completed measures of psychological strain, physical strain and job satisfaction. Results indicated that the treatment reduced psychological and physical strain and improved job satisfaction, but had a negligible impact on performance and physiological strain.

Details

Journal of Management Development, vol. 3 no. 2
Type: Research Article
ISSN: 0262-1711

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Content available
Book part
Publication date: 19 December 2016

Radha R. Sharma and Sir Cary Cooper

Abstract

Details

Executive Burnout
Type: Book
ISBN: 978-1-78635-285-9

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Article
Publication date: 7 October 2014

V. Kobelev

The purpose of this paper is to derive the exact analytical expressions for torsion and bending creep of rods with the Norton-Bailey, Garofalo and…

Abstract

Purpose

The purpose of this paper is to derive the exact analytical expressions for torsion and bending creep of rods with the Norton-Bailey, Garofalo and Naumenko-Altenbach-Gorash constitutive models. These simple constitutive models, for example, the time- and strain-hardening constitutive equations, were based on adaptations for time-varying stress of equally simple models for the secondary creep stage from constant load/stress uniaxial tests where minimum creep rate is constant. The analytical solution is studied for Norton-Bailey and Garofalo laws in uniaxial states of stress.

Design/methodology/approach

The creep component of strain rate is defined by material-specific creep law. In this paper the authors adopt, following the common procedure Betten, an isotropic stress function. The paper derives the expressions for strain rate for uniaxial and shear stress states for the definite representations of stress function. First, in this paper the authors investigate the creep for the total deformation that remains constant in time.

Findings

The exact analytical expressions giving the torque and bending moment as a function of the time were derived.

Research limitations/implications

The material isotropy and homogeneity preimposed. The secondary creep phase is considered.

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 springs.

Originality/value

The new, closed form solutions with commonly accepted creep models allow a deeper understanding of such a constitutive model's effect on stress and deformation and the implications for high temperature design. The application of the original solutions allows accurate analytic description of creep and relaxation of practically important problems in mechanical engineering. Following the procedure the paper establishes closed form solutions for creep and relaxation in helical, leaf and disk springs.

Details

Multidiscipline Modeling in Materials and Structures, vol. 10 no. 3
Type: Research Article
ISSN: 1573-6105

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Article
Publication date: 1 April 1959

A.E. Johnson, J. Henderson and V.D. Mathur

As stated in general terms in a previous paragraph, in the ease of this material the following complex stress relaxation tests were made: two pure torsion tests from…

Abstract

As stated in general terms in a previous paragraph, in the ease of this material the following complex stress relaxation tests were made: two pure torsion tests from initial stresses of 4 tons/sq. in. and 3 tons/sq. in.; two tests having a stress ratio T/S=0·4 and having initial stress values of T=1·6, S=4 and T=1·2, S=3 tons/sq. in. in the two cases; two tests having a stress ratio T/S=0·8 and having initial stress values T=3·2, S=4 and T=2·62, S=3·28 tons/sq. in. respectively; and finally one test having a stress ratio T/S=1·5 and having an initial stress value T=4·5 and S=3 tons/sq. in. (i.e. a total of seven tests).

Details

Aircraft Engineering and Aerospace Technology, vol. 31 no. 4
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 4 December 2017

Stefan Holmström, Frits De Haan, Ulrich Führer, Rami Pohja and Jaromir Janousek

There are a number of different approaches for calculating creep-fatigue (CF) damage for design, such as the French nuclear code RCC-MRx, the American ASME III NH and the…

Abstract

Purpose

There are a number of different approaches for calculating creep-fatigue (CF) damage for design, such as the French nuclear code RCC-MRx, the American ASME III NH and the British R5 assessment code. To acquire estimates for the CF damage, that are not overly conservative, both the cyclic material softening/hardening and the potential changes in relaxation behavior have to be considered. The data presented here and models are an initial glimpse of the ongoing European FP7 project MATISSE effort to model the softening and relaxation behavior of Grade 91 steel under CF loading. The resulting models are used for calculating the relaxed stress at arbitrary location in the material cyclic softening curve. The initial test results show that softening of the material is not always detrimental. The initial model development and the pre-assessment of the MATISSE data show that the relaxed stress can be robustly predicted with hold time, strain range and the cyclic life fraction as the main input parameters. The paper aims to discuss these issues.

Design/methodology/approach

Engineering models have been developed for predicting cyclic softening and relaxation for Gr. 91 steel at 550 and 600°C.

Findings

A simple engineering model can adequately predict the low cycle fatigue (LCF) and CF softening rates of Gr. 91 steel. Also a simple relaxation model was successfully defined for predicting relaxed stress of both virgin and cyclically softened material.

Research limitations/implications

The data are not yet complete and the models will be updated when the complete set of data in the MATISSE project is available.

Practical implications

The models described can be used for predicting P91 material softening in an arbitrary location (n/Nf0) of the LCF and CF cyclic life. Also the relaxed stress in the softened material can be estimated.

Originality/value

The models are simple in nature but are able to estimate both material softening and relaxation in arbitrary location of the softening curve. This is the first time the Wilshire methodology has been applied on cyclic relaxation data.

Details

International Journal of Structural Integrity, vol. 8 no. 6
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 20 October 2014

Czesław Kundera and Jerzy Bochnia

– This paper aims to investigate the suitability of additive manufacturing to produce O-ring seals.

Abstract

Purpose

This paper aims to investigate the suitability of additive manufacturing to produce O-ring seals.

Design/methodology/approach

The O-rings were made by the PolyJet-Matrix technology using four different digital materials and then tested for relaxation properties under static and dynamic (sliding) conditions. The approximation of the relaxation curves involved modelling with a Prony series.

Findings

The PolyJet-Matrix technology offers new opportunities to model elastomeric elements, with examples being the O-rings produced and tested for their relaxation properties. Describing the behaviour of the particular materials fabricated with this technology by using relaxation functions will extend the knowledge base on digital materials.

Research limitations/implications

The four types of photopolymers used in the experiment differed in viscoelastic properties. The analysis of the stress relaxation of the O-ring models was performed at four different step displacements of the loading element.

Practical implications

The test results may be useful for the design of O-ring seals made of new elastomeric materials. The relaxation properties of the O-rings made of such materials can be applied to analyse the dynamics of seals, for instance, face seals.

Originality/value

The originality of the work lies in the use of digital materials to design and produce elastomeric elements with different relaxation properties, which was confirmed by the test results. This paper presents results of a relaxation analysis for a ring model and the material that the ring is made of. It also discusses how 3D printing and digital materials can be applied in practice.

Details

Rapid Prototyping Journal, vol. 20 no. 6
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 1 February 2003

Isao Ajiki and Ron Postle

The viscoelastic properties of the sewing thread before and after loading in the sewing process were investigated. Sewing threads are subjected to dynamic tension and…

Abstract

The viscoelastic properties of the sewing thread before and after loading in the sewing process were investigated. Sewing threads are subjected to dynamic tension and friction in the sewing process. In order to compare polyester, cotton and silk sewing threads, the fineness of the threads were selected to be almost equal. There are some differences between the stress extension curves of the parent thread and the sewn thread except for the polyester sewing thread. The phenomenon of inverse relaxation occurs for high levels of retraction. The stress‐inverse relaxation index for the polyester sewing thread is larger than for other threads and the inverse relaxation for silk thread is small. From the creep curves, the sewn threads show higher secondary creep and lower instantaneous recovery than the parent threads.

Details

International Journal of Clothing Science and Technology, vol. 15 no. 1
Type: Research Article
ISSN: 0955-6222

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