Material plastic properties characterization using a generic algorithm and finite element method modelling of the plane-strain small punch test

In this paper, a novel plane strain small punch test (SPT) method is proposed for material plastic properties characterization. The plane strain SPT is different from the standard SPT in the two ways: (a) a long thin rectangular specimen (with dimensions of about 20mm×8mm×0.5mm) is used, and (b) the resulting test tool components - such as punch head and upper and lower die - are also different. The punch head is a prism with a half-circular shape and the upper and lower die consists of left and right long blocks, with a chamfer at each of the inner top corners of the lower die. The tool components have been designed and assembled and the plane strain small punch tests have been performed to obtain the punch force and the corresponding central displacements of the specimen. This information is then used to characterize the material's plastic parameters

Simulation of the small punch creep test with consideration of variation of material properties

A new finite element model of the small punch creep test is described. The material constitutive relationship for creep considered is a simple Norton power law: in this study the exponent in the power law is varied for each element to simulate the random behaviour of creep. The influence of this random variation, and the effect of the friction factor between the punch and specimen, on the deformation and stress field has been investigated

A solution for estimating the tensile yield strength from small specimens

The small punch test is an innovative test that utilises small disc-shaped specimens to assess the mechanical behaviour of materials. The main advantage is the relatively small specimen size. In this article, a modified analytical solution for the small punch maximum bend strength is proposed that is based on classical plate theory. A clear linear relationship is observed between the tensile yield strength σYS and the small punch maximum bend strength σy for both alloys and metal matrix composites. Copyright by ASTM Int'l (all rights reserved)

On the interpretation of results from small punch creep tests

The small punch creep testing method is highly complex and involves interactions between a number of non-linear processes. The deformed shapes that are produced from such tests are related to the punch and specimen dimensions and to the elastic, plastic, and creep behaviour of the test material, under contact and large deformation conditions, at elevated temperature. Owing to its complex nature, it is difficult to interpret the small punch test creep data in relation to the corresponding uniaxial creep behaviour of the material. One of the aims of this paper is to identify the important characteristics of the creep deformation resulting from ‘localized’ deformations and from the ‘overall’ deformation of the specimen. Following this, the results of approximate analytical and detailed finite element analyses of small punch tests are investigated. It is shown that the regions of the uniaxial creep test curves dominated by primary, secondary, and tertiary creep are not those that are immediately apparent from the displacement versus time records produced during a small punch test. On the basis of the interpretation of the finite element results presented, a method based on a reference stress approach is proposed for interpreting the results of small punch test experimental data. Future work planned for the interpretation of small punch tests data is briefly addressed

Experimental and numerical analysis of initial plasticity in P91 steel small punch creep samples

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 potentially lead to improved capability for SPCT data interpretatio

Use of small specimen creep data in component life management: a review

Small specimen creep testing techniques are novel mechanical test techniques that have been developed over the past 25 years. They mainly include the sub-size uniaxial test, the small punch creep test, the impression creep test, the small ring creep test and the two-bar creep test. This paper outlines the current methods in practice for data interpretation as well as the state-of-the-art procedures for conducting the tests. Case studies for the use of impression creep testing and material strength ranking of creep resistant steels are reviewed along with the requirement for the standardisation of the impression creep test method. A database of small specimen creep testing is required to prove the validity of the tests

Small Punch Test - assessment of the possibilities of the methodology and its limitations

Predmetom bakalárskej práce je zhrnutie a zhodnotenie súčasného stavu znalostí o relatívne novej metóde skúšania materiálov, tzv. penetračnej skúške (Small Punch Test). Sú naznačené prednosti aj obmedzenia metódy a uvedené problémy, s ktorými sa penetračné skúšky potýkajú pri zavádzaní do aplikačnej praxe. Okrem rozboru základných princípov penetračných skúšok je v práci kladený dôraz na popis rozdelenia skúšok na základe používaných konfigurácií skúšobných strojov a ostatných parametrov skúšok. V práci sú taktiež uvedené postupy používané k stanoveniu základných materiálových charakteristík z penetračných skúšok vrátane ich korelácie s výsledkami štandardných materiálových skúšok.The Bachelor’s thesis is aimed to sum up and consider actual state of knowledge about a relatively new method used for testing materials called Small Punch Test. There are pros and cons of the method with troubles at the application process stated in the thesis. We can read something about the basic idea of small punch testing. A big effort was spent to sort many types of tests according to used configurations of testing machines and another testing parameters. There are stated techniques used for determination some basic material properties from small punch testing also with methods of correlation to results obtained from standard material tests in the thesis.

On the effects of friction modelling on small punch creep test responses: a numerical investigation

This paper shows the results of finite element (FE) analyses of Small Punch Creep Testing (SPCT) of a P91 steel at 600°C using two different approaches to model the friction between the specimen and the punch. The numerical results obtained by using the “classical” Coulomb friction model (i.e. constant friction coefficient) have been compared with those obtained by a more modern formulation, which takes into account the effects of local loading conditions, i.e. the contact pressure, between the contacting bodies (the small disc specimen and the punch) on the coefficient of friction. The aim of the work is to investigate the effects of the friction formulation used for the calculations on the numerical results representing the output of the test, i.e. the variation of the punch displacement versus time and the time to rupture. The calculations, carried out for various load levels, showed that the friction coefficient is not constant at all positions on the contacting surface between the punch and the specimen during the deformation process. The maximum value for the coefficient of friction is reached at the contact edge, which is a very important region in the specimen, because this is the position at which most of the creep deformation occurs. As expected, the displacement versus time curve (that is usually the only output obtained from experimental SPCTs) is affected by friction formulation which is used, as this directly influences the stress and strain fields in the specimen

Modelling the small punch tensile behaviour of an aerospace alloy

The small punch (SP) test is a widely accepted methodology for obtaining mechanical property information from limited material quantities. Much research has presented the creep, tensile and fracture responses of numerous materials gathered from small-scale testing approaches. This is of particular interest for alloy down selection of next-generation materials and in situ mechanical assessments. However, to truly understand the evolution of deformation of the miniature disc specimen, an accurate and detailed understanding of the progressive damage is necessary. This paper will utilise the SP test to assess the tensile properties of several Ti–6Al–4V materials across different temperature regimes. Fractographic investigations will establish the contrasting damage mechanisms and finite element modelling through DEFORM software is employed to characterise specimen deformation

Determination of high temperature material properties of 15-15Ti steel by small specimen techniques

This report presents the final results from the round robin test program on thin-walled cladding tubes in the EERA-JPNM pilot project TASTE. The test methods and assessment procedures used for the assessment of 15-15Ti steel are presented in a previous TASTE report 1. In this report the test results from different test types are assessed, compared and evaluated. The collation of results, mainly on tensile properties shows good agreement between tests methods. An open question remains if there is some anisotropy between the axial and the hoop direction of the tubes. Results from ring tension indicate lower strength values than the test performed in the axial direction. However, the ring tension calculated estimates do not take bending and friction into account. Tensile strength estimates from miniature Small punch tests samples (3 mm in diameter and 0.25 mm thick) indicate no anisotropy whereas tests on the full wall thickness (0.45 mm) with larger puncher balls indicate a reduction towards the INR measured tensile strength (Ring Tension) in the hoop direction. The ring compression test estimates based on calibration at room temperature by ENEA showed surprisingly good performance in estimating the tensile strength at higher temperatures despite the complex stress distribution for this type of test. The few tests performed for determining creep properties, i.e. small punch creep tests, were not successful in describing the expected creep properties. The SPC specimen (as was the case for some SP "tensile test") showed premature cracking at a very early stage of the test for the cold worked material. As a whole it seems that the different types of tests complement each other and together gives an overall picture of the strength and ductility of the tube material. The classical tests such as the ring compression test and the ring tension test gave good estimates on the hoop strength whereas the small punch tests seemingly give an estimate for the weaker direction.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes