Small punch creep (SPC) testing represents an effective way to rapidly assess the creep performance of novel materials and potentially monitor degradation of in-service components. Recent progress in standardisation has also led to improvements in data analysis. However, estimation of equivalent uniaxial stresses is still somewhat challenging and has hindered wider usage of the small punch technique. In this study, the creep properties of two candidate materials for structural applications in future fusion reactors were assessed via SPC. These included the baseline structural material, Eurofer97, and a more recently developed 14Cr Oxide Dispersion Strengthened (ODS) steel (14YWT). Having been assessed at 550 °C, the 14YWT demonstrated superior creep life and significantly lower rates of deformation, but also exhibited reduced ductility. The Modified Chakrabarty (MCH) approach was employed to estimate equivalent uniaxial creep stresses. This methodology appeared to work well with the Eurofer97 but struggled when applied to 14YWT, making accurate estimation of the 14YWT performance difficult. Since the MCH approach was developed for ductile materials, its predictive capabilities may have been limited by the low ductility of 14YWT.

The use of small specimen test techniques (SSTT) to determine the mechanical properties of irradiated materials has been studied over the past decades both in fission and fusion programs, but also to characterise and optimise new materials by nuclear and non-nuclear communities. Currently a number of activities are running that focus on the standardisation of SSTT to determine fracture toughness properties for fusion reactor materials (IAEA [1], EUROfusion [2], F4E [3]), and to support the long-term operation of light-water reactors (CRIEPI [4]). The determination of the T0 reference temperature (ASTM E1921 [5]) has been successfully achieved by testing small compact tension (C(T)) specimens (W = 8mm, B = 4mm) of non-irradiated and irradiated pressure vessel materials. However, some concerns exist regarding the use of the Master Curve (MC) on ferritic-martensitic steels, not only with SSTT but also with standard specimens. The main concern is the slope of the MC [6, 7], that seems to be steeper than the standard one. In this paper, the fracture toughness of Eurofer97 has been obtained by testing small C(T) specimens with the geometry selected in IFMIF-DONES (W = 9.2mm, B = 4.6mm) in the transition region. T0 has been determined and compared to the one obtained from 0.5T-C(T) specimens (both normalised to 1T). The scatter of the results has also been assessed to validate the scatter description of the MC.

Under the auspices of International Atomic Energy Agency (IAEA), a coordinated research project (CRP) entitled “Towards the Standardization of Small Specimen Test Techniques for Fusion Applications” has started since 2017. The overall objective of the project is to provide a set of guidelines for small specimen test techniques (SSTT) based on commonly agreed best practices on main test techniques including tensile, creep, low cycle fatigue, fracture toughness, and fatigue crack growth rate. This will act as the first step of a full standardization of the SSTT. Fusion structural materials, i.e., reduced activation ferritic/martensitic (RAFM) steels, are used for testing. In addition, the project will create a comprehensive mechanical property database of RAFM steels tested by SSTT. For the fracture toughness task of the CRP, three testing methods including Master Curve, local approach for ductile crack growth and cleavage fracture, and ductile approach at room temperature will be evaluated. This report focuses on developing guidelines for the round-robin Master Curve testing based on the ASTM standard E1921-19b “Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range” and commonly agreed best practice from researchers at Oak Ridge National Laboratory (ORNL), Centre for Energy, Environment and Technology (CIEMAT), and UK Atomic Energy Authority (UKAEA).

Small punch creep tests of unnotched and notched 8 mm discs of new austenitic steel Sanicro 25 were performed at 700 degrees C. Side notches through the disc thickness proposed by Lacalle of different lengths ranging from 3.0 to 4.5 mm were applied for this study. It was found that the notch length influences the time to rupture and the minimum displacement rate, however no apparent signs of crack initiation were observed on the recorded time displacement and time-displacement rate curves at 400 N force. The shortest time to rupture and fastest displacement rate were obtained for notch length of 3.5 mm, while the longest time to rupture and slowest displacement rate were obtained for notch length of 4.25 mm. The fracture of Sanicro 25 discs had signs of a "star" shape, with multiple cracks, which indicates lower ductility. A larger circular cap which is obvious for materials with high ductility was not present in all the small punch tests performed.

Most of the maintenance operations in offshore platforms are performed by using service vessels approaching to boat landing systems, which are secondary structures attached to the main structure of the wind turbine. These systems guarantee certain structural integrity conditions thay may be jeopardised by the aggressive marine environment, which may cause corrosion processes if the structural material is not conveniently protected. The main strategy to avoid corrosion in this type of structures is to provide protective coatings, which in this particular case must have an adequate behaviour not only against the proper marine environment, but also against the abrasion and the impact loads generated by the violent contacts between the service vessel and the boat landing system. This work develops a comprehensive analysis to define a protective coating that provides simultaneously an adequate corrosion protection and a sufficient resistance against abrasion and impact loads. Based on industrial practice and a literature review, a number of tentative proposals were established, combining different metallization strategies, epoxy intermediate layers and external paints. The proposals were successively subjected to corrosion, abrasion and impact tests, discarding, after each set of tests, those providing unsatisfactory results. The final solution consists of 3 consecutive layers: thermal sprayed aluminium, a two-component polyamine cured pure epoxy, and a two-component chemically curing aliphatic acrylic polyurethane topcoat.

( )This paper presents an experimental and numerical study of the effect of specimen thickness on the effective notch toughness K-mat(rho) for cleavage fracture measured using Single Edge Notch Bend (SENB) specimens containing a U-notch instead of a fatigue pre-crack. These specimens are typically used to measure a material's effective notch toughness K-mat(rho) and to assess failure of a structure containing a non-sharp defect using the Notch Failure Assessment Diagram (NFAD). Both the experimental data and the Finite Element (FE) failure predictions show a significant influence of specimen thickness onK(mat)(rho), over and above the microstructural weakest link effect arising from differences in the volume of the plastic zone. K-mat(rho) is a function of not only the in-plane effect of the notch radius, but also an out-of-plane constraint loss which itself is enhanced by the presence of the notch radius. Significant out-of-plane constraint loss occurred for notched specimens with a ratio of thickness B to width W of 0.5, a geometry that if pre-cracked would have met the minimum thickness requirement mandated by ASTM E182 Doubling the thickness to B/W = 1.0 was sufficient to eliminate the out-of-plane constraint loss. The use of experimentally measured K-mat(rho) values in an NFAD assessment of a structure may therefore be non-conservative if B/W<1.0.

The extension of the operation period of nuclear plants requires an accurate characterisation of the vessel materials, in order to monitor their embrittlement due to neutron irradiation. This need poses a challenge, since the availability of specimens inside the vessels to characterise their evolution is rather scarce. Therefore, innovative techniques have to be applied, in order to reduce the number of tests and the volume of the specimens. In this paper, the Master Curve approach has been employed, combined with the use of small punch notched specimens. The Master Curve methodology allows to evaluate the embrittlement of the material using a single parameter: the reference temperature, T0. This parameter has been estimated for several steels by means of modified small punch specimens, which are characterised by their reduced dimensions: only 10 × 10 × 0.5 mm. The obtained results have been compared with those obtained by means of conventional testing and a methodology to estimate T0 by means of small punch tests together with the Master Curve has been proposed.

The Master Curve approach allows the full characterisation of the ductile to brittle transition region (DBTR) of ferritic steels to be performed with a reduced number of tests. In this paper, the approach has been combined with the application of the small punch (SP) test. Modified SP specimens have been successfully employed to estimate the fracture toughness values of a pressure vessel steel and three structural steels. In addition, a methodology has been proposed, including a validity criterion for the performed tests. The estimated reference temperatures have been compared to the values obtained by means of full-scale conventional techniques. A unique simple relationship between both methodologies has been established for all the analysed materials. Therefore, this paper confirms the suitability of the small punch testing technique for the characterisation of the DBTR of several ferritic steels. It is a promising, simple and cost-effective test, which can be performed with simple equipment.

A new standard is currently being developed under the auspices of ECISS/TC 101 WG1 for the small punch testing technique for the estimation of both tensile and creep properties. Annex G of the new standard is covering the assessment and evaluation of small punch creep (SPC) data. The main challenge for estimating uniaxial creep properties from SPC data is the force to equivalent stress conversion between SPC and uniaxial creep tests. In this work a range of SPC assessment methodologies, benchmarked for the standard, are compared for verifying the best practice used in the standard. The estimated equivalent stresses for SPC are compared to uniaxial creep stresses at equal rupture times, using three alternative models. In-depth analyses are performed on SPC and uniaxial creep data for P92, F92 and 316 L steel tested within an inter-laboratory round robin. The formulation for SPC equivalent creep strain rate in the standard is also assessed.

The Master Curve approach has been widely applied to characterize the ductile to brittle transition region of ferritic steels. In order to further optimise the available material to be tested, great efforts have been recently performed to combine it with miniature testing techniques. One of the most promising is the small punch testing technique, currently under standardisation process in Europe. In this paper, small punch modified specimens with a lateral notch for the estimation of fracture toughness have been employed to obtain the reference temperature, T0, of a pressure vessel steel. The influence of the applied notch length has been analysed and a valid range has been proposed. In addition, the validity criterion of the tests for the estimation of T0 has been further verified, confirming its suitability. Finally, results have been compared with those obtained with conventional fracture mechanics specimens and previous works. As a result, a methodology to estimate the reference temperature by means of small punch tests with notch lengths of approximately 4.4 mm has been proposed, turning it into a promising candidate for the characterisation of the transition regime.

The behaviour of the materials in ductile-brittle transition region must be known when performing structural integrity assessments of nuclear reactor vessels working under the effects of neutron irradiation. The characterisation of this region has been usually carried out by means of Charpy impact tests. Just during last few years new approaches based on direct fracture mechanics tests have begun to be used. In most of these cases, the Master Curve methodology, which allows the transition region to be characterised using only one parameter (T0 reference temperature), has been employed. In this paper the transition region of two materials –one vessel steel and one common structural steel-has been characterised by means of Small Punch Tests. First of all, this zone has been characterised using conventional specimens and the results were compared with those of Charpy impact tests. Finally a new approach based on the use of notched Small Punch samples together with Master Curve methodology has been proposed.

The Small Punch Creep test has proven to be a suitable technique for assessing the properties of in-service components. It is a reliable, efficient and cost-effective test for predicting the behaviour of the material. The aim of this paper is to analyse the influence of different factors on the Small Punch Creep (SPC) tests. The influence of the specimen clamping has been studied, experimentally and by means of finite element models on different materials. In the analysed conditions, it has been proven that the influence of the upper die on the tests results is generally relatively insignificant, even in the absence of upper die.Furthermore, the use of different materials at the punch has also been analysed. In order to achieve this goal, SPC tests have been carried out on two light alloys (AZ31 and AlSi9Cu3) at 473 and 523 K. Three different balls have been employed: ceramic, tungsten-carbide and steel balls. It has been proven that for the creep ductile alloy (AZ31), there is no apparent effect on the specimen response. On the other hand, for the creep brittle alloy (AlSi9Cu3), a different trend of the material response is shown, dependent on the ball used. As a result, there seems to be a significant influence of the friction between the punch and the specimen on the tests results, related to the material behaviour.

A parametric study of small punch tests on miniaturized discs under constant deflection rate and constant force has been performed to study the influence of various upper die conditions on the test results. A comparison between the experimental results and the simulations by means of the finite element method is presented, under different clamping conditions. Heat resistant steel P22 has been selected for this investigation. The elasto-plastic behaviour of the disc was described by multilinear isotropic hardening. Norton power-law and exponential creep constitutive relationships have been applied in the ANSYS FE model of the SPT arrangement under creep conditions. The investigation confirms relatively small influence of the upper die conditions for both types of small punch tests for the steel under investigation. (C) 2016 Elsevier Ltd. All rights reserved.

Thermal cutting processes introduce changes in the heat affected zone (HAZ), which can lead to a significant reduction of the service life of components. In order to assess their influence, different cutting processes have been analysed on a structural steel. The characterization of the reduced volumes of HAZ posed a major challenge, since conventional techniques require greater pieces of material. Alternative miniature techniques had to be applied, such as Small Punch tests and microhardness measurements, from which the material tensile properties and fracture toughness values have been obtained. Results show that oxyfuel HAZ exhibit minor alterations of the material, while plasma cutting seems to improve the material tensile properties and fracture toughness. Besides, the suitability and accuracy of the Small Punch technique for similar applications can be derived from this work, turning it into a promising candidate to perform integrity assessments of actual components.

The low-density values of light alloys have made them ideal candidates for reducing the weight of structural components. Given their relatively low melting points, it is vital to characterise the behaviour of these materials at high temperature working conditions. In this paper, the Small Punch Creep (SPC) testing technique is applied to evaluate the creep properties of AlSi9Cu3 and AZ31 alloys, which respectively exhibit brittle and ductile fractures. By comparing the SPC results with the uniaxial ones, a relationship between miniature and conventional tests has been established. Three different approaches have been employed, by comparing tests which share (i) the same time to rupture, (ii) the Larson-Miller and (iii) the Orr-Sherby-Dorn parameter. Regardless of the behaviour of the material, the applied methods lead to the same relationships, proving their accuracy. Furthermore, the SPC tests have been used to obtain creep master curves and the usual creep engineering parameters, which are in good agreement with those obtained by means of conventional methods, confirming the suitability of the SPC technique for this purpose.

The Small Punch Creep (SPC) test, first introduced by Parker in 1993, has been in continuous development ever since. Currently, it has a widespread utilization in the nuclear and aerospace industry, being mainly applied to steel characterisation. Thanks to its potential, especially for the reduced size of the samples and shorter testing times than the conventional tests, its application in light alloys has been proposed. The use of light alloys in several sectors is growing continuously, since they contribute to reduce the weight of components. In this work, the behaviour of the magnesium alloy AZ31 has been analysed at temperatures between 398 K and 523 K. A relationship between conventional and SPC tests has been established, by comparing time to rupture, as well as the Larson-Miller (LM) and Orr-Sherby-Dorn (OSD) parameters. On the other hand, the LM and OSD parameters have been obtained from the results of the SPC tests (turned into their equivalent uniaxial values) and they have been compared to the ones derived from the conventional tests, confirming the potential of this testing technique and its accuracy for the extrapolation of times to rupture in creep conditions. (C) 2016 Elsevier Ltd. All rights reserved.

This paper presents the analysis of the notch effect on granite and limestone fracture specimens. The research is based on the results obtained in an experimental programme composed of 84 fracture specimens, combining the two materials and 7 different notch radii varying from 0.15 mm up to 10 mm. The notch effect is analysed through the evolution of the apparent fracture toughness and the application of the Theory of the Critical Distances.The results reveal a significant notch effect in the limestone, whereas the notch effect in the granite is negligible for the range of notch radii analysed. Both observations are justified by the corresponding critical distance of the material. (C) 2014 Elsevier B.V. All rights reserved.