A study on the evolution of the contact angle of small punch creep test of ductile materials

Cacciapuoti, B.; Sun, Wei; McCartney, D.G.

doi:10.1016/j.ijpvp.2016.06.002

Cited by 16 publications

(13 citation statements)

References 30 publications

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“…pre L pre = yield L yield (20) Expressing equation (20) in the form of equation (21), it is possible to derive d pre as in equation (22) (22) L pre and L yield are given in equation (23) and in equation (24), respectively, where L 0 is the initial specimen gauge length.…”

Section: Plastic Part Of Pre-strainingmentioning

confidence: 99%

“…During small punch creep tests however, damage starts developing in the secondary stage of the deflection versus time curve, where deformation of the specimen is dominated by dislocation creep. The tertiary region of the deflection versus time curve is characterised by an acceleration of the crack propagation and the deformation of the disk is governed by inter-granular cavitation [23, 24]. A small punch specimen generally experiences the evolution of a necking region, which takes place at an offset from the axis of symmetry of the disk [25–27].…”

Section: Introductionmentioning

confidence: 99%

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Experimental and Numerical Analysis of Initial Plasticity in P91 Steel Small Punch Creep Samples

et al. 2017

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To date, the complex behaviour of small punch creep test (SPCT) specimens has not been completely understood, making the test hard to numerically model and the data difficult to interpret. This paper presents a novel numerical model able to generate results that match the experimental findings. For the first time, pre-strained uniaxial creep test data of a P91 steel at 600 • C have been implemented in a conveniently modified Liu and Murakami creep damage model in order to simulate the effects of the initial localised plasticity on the subsequent creep response of a small punch creep test specimen. Finite element (FE) results, in terms of creep displacement rate and time to failure, obtained by the modified Liu and Murakami model are in good agreement with experimental small punch creep test data. The rupture times obtained by the FE calculations which make use of the non-modified creep damage model are one order of magnitude shorter than those obtained by using the modified constitutive model. Although further investigation is needed, this novel approach has confirmed that the effects of initial localised plasticity, taking place in the early stages of small punch creep test, cannot be neglected. The new results, obtained by using the modified constitutive model, show a significant improvement with respect to those obtained by a 'state of the art' creep damage constitutive model (the Liu and Murakami constitutive model) both in terms of minimum load-line displacement rate and time to rupture. The new modelling method will

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Section: Plastic Part Of Pre-strainingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental and Numerical Analysis of Initial Plasticity in P91 Steel Small Punch Creep Samples

et al. 2017

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“…This happens when large deformations are exhibited by the specimen during the test, that is, from an engineering estimation, when Δ>0.8 mm [5]. However, according to many researchers, during small punch creep test the specimen deformation is caused by bending prior to membrane stretching [30][31][32] and a recent study, confirming this theory, suggests upper limits to Δ, depending on the specimen and the punch dimensions [33], as shown in Table 1. Another empirical relationship, always derived by Chakrabarty's membrane theory, is reported in an annex of the Code of practice [5], and can be used to derive the load to be applied for the SPCT, here given in equation (12), where KSP is a correction factor depending on the tested material.…”

Section: Small Punch Creep Testmentioning

confidence: 93%

“…Difficulties in obtaining good agreement between FE analyses and small punch test output are due to the effects on the specimen time to failure of punch load misalignments, of initial plasticity, and of the approximation of the friction formulation used in the FE analyses for the interactions between the specimens and the testing machine components [33]. An increase of the failure life has been found to be up to 10 times when initial plastic deformation is included in the model [30]; the time to failure can also increase up to 8 times when the friction coefficient between the specimen and the punch varies from 0 to 0.5 [51][52][53].…”

Section: Evaluation Of Current Test Methodsmentioning

confidence: 99%

The role of small specimen creep testing within a life assessment framework for high temperature power plant

Morris

Cacciapuoti

Sun

2017

International Materials Reviews

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The safe operation of components operating at high temperature and pressure faces numerous challenges associated with ageing materials and maintaining commercial viability whilst economies transition to a lower carbon future as part of their climate change commitments. Due to these challenges the plant operator faces increasing pressure to ensure that any capital or operational expenditures are optimised and must ensure that they duly recognise plant age, condition, operating regime and ultimately the planned closure date.This review, for the first time, describes how small specimen creep testing can be applied within a practical and deployable life assessment framework and in conjunction with other assessment techniques. The current state of the art for small specimen creep testing is critically reviewed; this also includes a review of traditional techniques used on site for the metallurgical assessment of material condition, with examples from site investigations and assessment campaigns in both conventional and nuclear plant applications.In order to enhance the current practice for assessing the condition of creep ageing components this review proposes the more proactive use of small specimen testing methods for the in-service condition assessment of power plant materials, notably earlier in the plant lifecycle and within a holistic life assessment framework. This is intended to provide a means of calibrating the time dependent response of the component or system being monitored, thereby providing a key reference in-service strain rate measurement, or material property evaluation, that can subsequently be used with other traditionally deployed assessment methods to define a more targeted and cost-effective forward inspection plan. The review describes how small specimen creep testing methods and other complementary tools can be use in a new and structured approach to life management.The current status of small specimen testing methods, for both conventional and nuclear applications, is described along with a detailed discussion on current practice for in-service creep life assessment, with a case study used to illustrate the main principals. A case study is presented for ageing CMV (0.5%Cr0.5%Mo0.25%V) main steam pipework due to the extensive amount of through life data available, which highlights the particular challenges associated with the interpretation of various types of site outage inspection data, in conjunction with on-load plant operational data. The current approach to the assessment of component condition follows well established inspection based practices defined in various industry good practice guides, with expert elicitation and experience used to judge the condition of the component, system and operational risk on return to service.This review proposes a new approach to the holistic life assessment of high temperature plant, with a particular emphasis on more proactive use of small specimen testing. In addition, the review has 2 highlighted other aspects of the current approach to in-...

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“…Now, the question is how the contact properties influence the test results. Only a few studies have been found in literature, which explicitly focus on this problem [9][10][11][12][13]. The aim of this paper is to fill some of the gaps and to give suggestions about optimal test setups and evaluation strategies.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of the influence of friction in SPT experiments

Abendroth

Zielke

2018

Ubiquity Proceedings

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Virtually all SPT test stands, which are operated in different laboratories, cause contact between different parts of the SPT due to the technical design. These frictional influences can lead to erroneous test results since the force transmitted from the punch to the sample is reduced. This influence can be considerable, particularly in the case of creep tests at high temperatures. The present work analyses various typical experimental setups and the influence of inaccuracies in the setup on the test results. Finally, some requirements and suggestions for an optimized experimental setup are derived.

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A study on the evolution of the contact angle of small punch creep test of ductile materials

Abstract: The work discussed in the present paper reports a novel investigation of the applicability of

Cited by 16 publications

References 30 publications

Experimental and Numerical Analysis of Initial Plasticity in P91 Steel Small Punch Creep Samples

Experimental and Numerical Analysis of Initial Plasticity in P91 Steel Small Punch Creep Samples

The role of small specimen creep testing within a life assessment framework for high temperature power plant

Numerical investigation of the influence of friction in SPT experiments

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