Small Punch Test Method Research Articles

Determination of the fracture toughness of carburized Pyrowear 53 steel for planetary gears by the small punch test method

The aim of the current study was to determine the fracture toughness of different zones in carburized Pyrowear 53 steel using the small punch test (SPT) method. Firstly, Pyrowear 53 steel was quenched and tempered using different processing parameters to obtain core materials with varied microstructures and fracture toughness. The results obtained for the core material in standard fracture toughness tests were then compared with the SPT results, which allowed the determination of a formula correlating the fracture energy integral, JSPT, from the SPT with JQ integrals obtained from standardized compact tension specimens. In the next stage, Pyrowear 53 steel was carburized at 925 °C and divided into the following zones: (1) a carburized layer (up to 0.5 mm from the surface), (2) a transition layer (from 0.5 to 1.5 mm), and (3) a core zone (more than 1.5 mm). Each zone was characterized in terms of its microstructure and tensile properties using miniaturized test specimens. Finally, the fracture toughness values of the core zone (JSPT = 78–102 kJ/m2), the transition layer (JSPT = 71–80 kJ/m2), and the carburized layer (JSPT = 8.1–9.1 kJ/m2) were determined based on the obtained SPT results. It was shown that the use of such a relatively simple SPT method with the proposed energy-based approach seems to be a promising way of determining the fracture toughness of thin layers or local changes in the fracture behavior of surface-treated materials.

SPT approach for assessing mechanical properties of materials

The Round Robin Test of the Small Punch Test (SPT) method represents a critical step in establishing its reliability and applicability for assessing the mechanical properties of materials used in power plants. The mechanical properties of materials, such as strength and deformation characteristics, are of paramount importance in ensuring the structural integrity and safety of power generation facilities. The SPT method, a widely adopted in-situ testing technique, holds promise as a cost-effective means of evaluating these properties. However, its precision and consistency in different geological and operational contexts remain subjects of investigation. This study presents the results and findings from a comprehensive Round Robin Test aimed at rigorously assessing the SPT method's performance and suitability for characterizing materials within power plants. Multiple testing campaigns were conducted across diverse sites and material conditions, encompassing varying geological formations, moisture content, and temperature ranges. The objective was to evaluate the SPT method's repeatability, reproducibility, and accuracy in different operational environments.

The small punch test: An overview of previous research

The knowledge of material properties is a key factor in designing structures which withstand the challenges of their lifetime. Small Punch (SP) test is a material testing method which has the advantage of lean material usage. In this study, an overview is presented on the SP testing method. The aim of this paper is to help researchers by collecting articles about different research fields of SP testing. With the experiences from previous research a promising theme is proposed for future analysis in connection with SP testing.

Effect of Hydrogen Pressure and Punch Velocity on the Hydrogen Embrittlement Susceptibility of Pipeline Steels Using Small Punch Tests under Gaseous Hydrogen Environments at Room Temperature

The in situ small punch (SP) test method is a simple screening technology developed to assess the hydrogen embrittlement (HE) characteristics of structural steels. This method can easily adjust the influencing parameters such as test temperature, gas pressure, and punch velocity depending on the hydrogen service environment. With increased hydrogen consumption, using pipelines for mass hydrogen transportation is being considered. This study evaluated the HE susceptibility of API-X52 and API-X70 steels, considering the hydrogen usage environment. The study investigated the effects of hydrogen pressure and punch velocity on the HE behaviors of each pipe steel at room temperature using the SP energy and relative reduction in thickness (RRT) to determine their effect on HE susceptibility quantitatively. The study found that hydrogen pressure produced a different HE effect; the lower the hydrogen pressure, the more HE was relieved. Particularly, when the punch velocity was high, such as 1 mm/min, the HE effect was significantly relaxed. However, when the punch velocity was below 0.01 mm/min, HE occurred even at low hydrogen pressure conditions, meaning hydrogen diffusion within the specimen during the SP testing reached a critical hydrogen concentration to create a brittle fracture. Both pipeline steels showed similar HE behaviors under a wide range of H2 pressures and punch velocities, showing an inverse S-curve for quantitative factors of SP energy and RRT against the H2 pressure at 1.0 mm/min punch velocity. The study classified the observed HE behaviors into four types based on quantitative and qualitative aspects. These findings confirm that the in situ SP test is a useful screening technique, and the factor RRT can be effectively applied to the HE screening of pipeline steels in low and high-pressure hydrogen environments.

Creep constitutive law prediction via short-term evaluation using a small size testing method

To efficiently assess the mechanical reliability and long-term durability of solid oxide fuel cells (SOFCs) and solid oxide electrolyser cells (SOECs), a suitable creep test method and prediction of the material response is necessary. This study investigates the effectiveness of the small punch (SP) testing method for Ni–YSZ composites and in rapidly determining the constitutive creep law for SOFC materials. The creep properties of Ni–YSZ composites are evaluated under a 1% H2 environment at temperatures of 800–900 °C and stresses of 36–58 MPa. The finite element method is used to simulate the SP tests and generate numerical creep curves. These curves are fitted to the experimental curves to obtain the parameter set in the creep constitutive law of the strain hardening model. The numerical and experimental creep curves are well-fitted with only a 0.44% difference and convergent parameter sets equal to C1=1.0× 10−12, C2=1.03, C3 = -1.70, C4=96.78 in the strain hardening law, indicating the usefulness of the SP method and creep constitutive law for characterising and predicting the creep properties of SOFC constituent materials. This study highlights the importance of accurate characterisation of creep properties for predicting the long-term performance and reliability of SOFCs.

A modified small punch testing scheme to investigate the circumferential mechanical behavior of nuclear fuel cladding tubes

The manufacturing process of nuclear fuel cladding tubes endows them with anisotropic material properties. In this study, a small punch testing (SPT) method was established to investigate the circumferential tensile behavior of nuclear fuel cladding tubes. The specimen of the proposed SPT method was bended and stretched in a single stress state under a punching force. The proposed SPT method was then used to analyze the circumferential tensile behavior of a FeCrAl fuel cladding tube. Finite element simulation results indicated that the SPT method established herein determined ultimate tensile stress with higher accuracy than standard SPT because the plastic strain in the proposed method under maximum force is considerably smaller than that in standard SPT. Moreover, the proposed method can more accurately determine yield stress compared with standard SPT, as reflected by the elastic stage in the load–displacement curve that was a straight line. The test results indicated that the proposed SPT can be used to accurately determine the circumferential yield stress and ultimate tensile stress of nuclear fuel cladding tubes.

Study of Mechanical Properties of Membrane-Electrode Assemblies for Proton Exchange Membrane Fuel Cells By the Small-Punch Technique

Mechanical properties of membrane-electrode assemblies (MEAs) are most relevant for the durability of proton-exchange membrane fuel cells (PEMFCs) [1]. During operation, the MEA must endure eventual changes in the static pressure of anodes and cathodes caused by changes in power demand, gases flow rate, and/or water generation, accompanied by hygrothermal cycles, that cause mechanical stresses in the membrane, leading to cracks and possible fatal failure [2]. In parallel, the mechanical properties of MEAs change irreversibly during power production as a consequence of membrane and electrodes corrosion [3]. Therefore, it is of interest to characterize the mechanical properties of MEAs before assembly, and after operation.The small-punch is a new technique for testing mechanical properties of solids. It consists of measuring the deformation of a disc of the testing material with a ‘small puncher’, while recording the load (force) exerted by the puncher and the deflection produced on the specimen (Fig. 1a) [4]. The plot load vs deflection allows estimating mechanical strength, fracture toughness, impact, and tensile properties. Most interesting is that the disk specimen can be as small as a few millimeters, which makes the small-punch technique very appropriate when the amount of sample is limited, and for localized studies of mechanical properties.In this communication, results of the small-punch technique are shown for the study of MEAs operated in single PEMFCs (Fig. 1b). The analysis is carried out of the local mechanical properties on new and degraded MEAs. First results show that local mechanical properties of the aged MEA correlate well with gas feeding conditions and reflect laterally inhomogeneous degradation (Fig. 1b).Acknowledgement: The work is partially financed by the ELHYPORT project (PID2019−110896RB-I00), Spanish Ministry of Science and Innovation.[1] X. Huang, R, Solasi, Y. Zou, M. Feshler, K. Reifsnider, D. Condit, S. Burtlatsky, T. Madden, J. Polymer Science: Part B: Polymer Physics, Vol. 44, 2346–2357 (2006).[2] Z. Lu, M. Lugo, M.H. Santare, A.M. Karlsson, F.C. Busby, P. Walsh, J. Power Sources 214 (2012) 130-136.[3] M. Pestrak, Y. Li, S.W. Case, D.A. Dillard, M.W. Ellis, Y-H. Lai, C. S. Gittleman, J. Fuel Cell Sci. Technol. (2010), 7(4): 041009.[4] EN 10371:2021 Metallic materials - Small punch test method. CEN, Brussels (2021) Figure 1

Mechanical Properties Study of Miniature Steel Specimens Based on the Small Punch Test and Simulation Methods.

The small punch test (SPT) can be very convenient to obtain mechanical properties due to its unique advantages from small-volume samples, and has gained wide popularity and appreciation among researchers. In this paper, the SPT test and finite element (FE) simulations were performed for three alloys, and the yield stresses (σYS) and ultimate tensile strengths (σUTS) from the uniaxial tensile test (UTT) were correlated with the yield force (Fy) and maximum force (Fm) of the small punch test (SPT) before and after compliance calibration. Finally, the effect of specimen size on the SPT curves was discussed. The results showed that the deviation between SPT test and FE simulation was due to the loading system stiffness, which was confirmed by the loading system compliance calibration test. The SPT curves before and after calibration have less influence on the empirical correlation results for σUTS, while the correlation results for σYS depend on the method used to determine Fy in the SPT curve. Finally, the simulation results indicated that the effect of specimen size on the force–displacement curve in the SPT is slight. This work also provides a reference for subsequent researchers to conduct empirical correlation studies using different specimen sizes.

Small punch testing of Al-TiB2 composites fabricated by spark plasma sintering: A computational and experimental study

The Small Punch Test (SPT) method is especially useful for quantifying the mechanical properties of metallic materials in cases where the material available for testing is limited or for in service monitoring. However, the applicability of this method to metal matrix composites has not yet been fully established. In the present study, Al-TiB2 composite billets with TiB2 particle volume fractions of 5%,10% and 15% were manufactured using Spark Plasma Sintering (SPS). Thin specimens with 0.5 mm thickness were cut from the billets, and SPT experiments were conducted until failure. Well-accepted analytical techniques were utilized to determine the Al-TiB2 composite effective yield stress for all TiB2 particle volume fractions. It was shown, that standard analytical methods for characterizing the effective yield stress were adequate only for TiB2 volume fractions of up to 5%. The experimental mechanical response up to and including failure was reproduced for all Al-TiB2 compositions by finite element analysis incorporating a continuum damage mechanics approach. The computational analysis revealed that for high TiB2 volume content, the region of the SPT loading curve which is commonly associated with specimen yielding, may represent a mixture of yielded and damaged areas. Since the damage distribution in the specimen influences the specimen flexural modulus, standard analytical relations cannot be used to determine the composite yield stress and computational methods must be used. This finding may explain the inconsistent results reported in the literature with regard to the accuracy of the SPT method in determining the effective yield stress for metal matrix composites.

Derivation of material properties using small punch and shear punch test methods

The Small Punch (SP) and Shear Punch (ShP) tests are well established mechanical test approaches that have found application in several industrial sectors for material ranking and mechanical property estimation, particularly where more conventional approaches are inhibited. Despite the advantages that the two test methodologies have to offer, the main drawback is the complex understanding of the mechanical data generated from the experiments and how it can be correlated to more recognised properties. Typically, the most desired properties relate to the uniaxial properties of yield stress, ultimate tensile strength and ductility, but to date, there is no single robust and overarching approach for correlating such properties for a wide array of metallic materials that exhibit varying levels of ductility. This paper will for the first time directly compare properties obtained from a series of uniaxial tensile, SP and ShP tests across several metallic materials, and look to establish and correlate equivalent properties across the different test types. The materials investigated range from commercially pure entities to more advanced alloy systems. The generated results, empirical relationships and numerical simulations will inform which materials can be correlated across the different test regimes, and identify why the relationship in certain materials breaks down.

Influence of Specimen Surface Roughness on Hydrogen Embrittlement Induced in Austenitic Steels during In-Situ Small Punch Testing in High-Pressure Hydrogen Environments

An in-situ small punch (SP) test method has recently been developed as a simple screening technique for evaluating the properties of metallic materials used in high-pressure hydrogen environments. With this method, the test conditions including temperature and gas pressure can easily be adjusted to those used in practice. In this study, specimens of STS316L steel and 18 wt% Mn steel were prepared at two different surface roughness, fabricated using wire-cutting and mechanical polishing. Their effects on hydrogen embrittlement (HE) were evaluated using in-situ SP testing at both room temperature and a lower temperature where HE was shown to occur under 10 MPa hydrogen. Both steels were evaluated using two variables obtained from in-situ SP testing, the SP energy, and the relative reduction of thickness (RRT), to quantitatively determine the effect of specimen surface roughness on HE susceptibility. Their fracture characteristics due to HE under 10 MPa hydrogen showed little difference with surface finish. Surface roughness had a negligible influence on these quantitative factors describing HE, indicating that it is not a dominant factor to be considered in in-situ SP testing when it is used to screen for HE compatibility in steels used in high-pressure hydrogen environments.

Development of impact small punch test for investigating energy absorption

Energy absorption of steel with Transformation-induced Plasticity (TRIP) under bending deformation needs to be carefully examined at very high strain rates for its new applications in the automotive industries. Energy absorption members made of the steel can suppress severe damages by traffic accidents. However, it is difficult to apply three-point bending test based on the split Hopkinson pressure bar (SHPB) method because a use of a thick pre-cracked specimen is required for such materials with high toughness. In contrast, if the impact small punch test, which dominant deformation mode of a relatively-small specimen is bending, is established, its experimental arrangement might become simpler and the SHPB technique is applicable. In this study, a novel and reliable impact small punch testing method based on SHPB technique with high accuracy is developed for an investigation on impact energy absorption of the steel with TRIP. Besides, its design, feasibility and validity are confirmed by finite element simulation for austenitic stainless steel SUS304, a representative of steel with TRIP. The obtained experimental as well as computational results show that the developed testing apparatus for impact small punch test based on SHPB technique is reliable and reasonable for the investigation on impact energy absorption of the high toughness material including steel with TRIP.

Quantitative evaluation of hydrogen embrittlement susceptibility in various steels for energy use using an in-situ small punch test

Recently, as hydrogen has been increasingly applied in the field of new energy, it has become necessary to evaluate the mechanical characteristics of hydrogen embrittlement (HE) when materials are used to reduce costs as well as ensure safety in hydrogen facilities. However, to obtain a large amount of data in a short period of time and ensure reliability when selecting materials used in hydrogen energy applications, a simple test method for screening the HE susceptibility of materials under high-pressure hydrogen environments should be established and applied. In this study, the HE behaviors of three structural steels to be used in the hydrogen energy field were examined at room temperature and low temperatures under high-pressure hydrogen environments using the newly established in-situ small punch test method. The effects of test temperature and punch velocity on the HE susceptibility of each steel were quantitatively evaluated using the characterizing factor, known as the relative reduction of thickness.

Derivation of Material Properties Using Small Punch and Shear Punch Test Methods

Derivation of Material Properties Using Small Punch and Shear Punch Test Methods

Evaluation of Transition Temperature in Reactor Pressure Vessel Steels 6using the Fracture Energy Transition Curve from a Small Punch Test

The small punch (SP) test is one of the small specimen test techniques, and standardization of the SP test method for evaluating the mechanical properties of metallic materials is in progress. In this study, the impact transition temperature of reactor pressure vessel steels (RPV) in nuclear power plants was estimated using the draft standard SP test method. The SP fracture energy (ESP) and normalized SP fracture energy (ENSP) of the RPV steels were evaluated at various temperatures, and their transition curves were derived and compared to the transition curve in the Charpy V notch (CVN) test. The SP transition region appeared at a much lower temperature range than that of the CVN owing to the size and notch effect. Ductile brittle transition temperature (DBTT) in the SP transition curve showed a linear relationship with DBTT and T41J in the CVN transition curve. The ductile to brittle transition behaviors of SP specimens were analyzed using fractographs and compared with the transition curves in ESP and ENSP. ENSP started to decrease at the temperature at which the SP ductile to brittle transition behavior occurred, and this means that the ENSP transition curves were in good agreement with transition behavior in the SP test. However, the ESP transition curves did not match transition behavior. Using DBTT in the ENSP transition curve is appropriate to estimate the CVNDBTT and T41J.

Microstructural and mechanical anisotropy of selective laser melted IN718 superalloy at room and high temperatures using small punch test

The nature of melting and solidification phenomena during selective laser melting (SLM) process leads to a strong crystallographic texture in the as-built SLM components which causes mechanical anisotropy. This anisotropy is usually reduced by either optimization of the laser scanning strategy during the SLM process or high-temperature heat treatment. Microstructure and mechanical anisotropy of SLMed Inconel 718 (IN718) superalloy were investigated in this study by means of XRD, SEM, EBSD and small punch testing (SPT) method at room and high temperatures. The SPT data were validated against uniaxial tensile testing and corresponding equations were proposed to determine yield and ultimate tensile strengths of the fabricated parts. Significant differences in mechanical behavior of the side and top views were mainly achieved due to the contribution of (100) columnar grains texture. It was found that the IN718 SLM parts possess 54% greater maximum force in the side view compared to the top one at room temperature. However, the side view maximum force lowered about 37% at 650 °C, while no significant decrease was observed for the top view sample. Fractography of small punched specimens showed ductile fracture surface for the side view compared to transgranular brittle surface for the top view at room temperature. Both views exhibited more brittle fracture at elevated temperature with different fracture surface morphologies, intergranular in the side view and cleavage along with Laves phases in the top view. The present work clearly demonstrates that SPT can successfully predict mechanical anisotropy in the as-built SLM IN718 superalloy.

Вплив значення коефіцієнта тертя на діаграму продавлювання дискового мікрозразка з урахуванням процесу руйнування

Determining changes in mechanical characteristics, such as yield strength and tensile strength, of structural materials during their service life under the influence of operating loads and the working environment is a very important task of ensuring reliable and safe operation of working equipment. The use of uniaxial tensile tests for this purpose is not always possible because of the limited availability of material for the manufacture of specimens and the inevitable disruption of structural integrity. Therefore, indirect control methods are being developed, one of which is the small punch test method. The essence of this method consists in punching of a fixed specimen by a spherical indenter with recording the load-displacement curve. Mechanical characteristics are determined by the parameters of this diagram using correlation dependencies. In improving the methods for determining the mechanical characteristics of small punch test, there is a need to use numerical modeling, one of the parameters of which is the friction coefficient in contact pairs. The purpose of this work was to investigate the influence of the friction coefficient on the punching diagram in the numerical simulation of the disk microspecimen deformation process, taking into account the fracture process. The Gurson–Tvergaard–Needleman (GTN) model was used to account for the fracture process. According to the study results, it was found that when the coefficient of friction changes from 0 to 0,36, the punching diagrams at the stages of elastic and elastic-plastic deformation of the specimen do not differ significantly. When the maximum load value is reached, there is a discrepancy in the punching diagrams. It was found that an increase in the friction coefficient leads to a decrease in the maximum load and the punching depth upon failure. The difference between the maximum load values is 27 %, the penetration depth is 14 %. It was determined that the closest to the experimental load-displacement curve was the curve determined by numerical simulation with a friction coefficient equal to 0, 18.

Establishment of an in-situ small punch test method for characterizing hydrogen embrittlement behaviors under hydrogen gas environments and new influencing factor

The hydrogen embrittlement (HE) behaviors of structural materials used to handle hydrogen must be tested at their use environments. In this study, an in-situ small punch (SP) test method was established to characterize HE behaviors of SA372 and STS304 steels under hydrogen gas environments at high pressures and low temperatures. In addition, a new influencing factor, relative reduction of thickness (RRT) was proposed to quantify the HE sensitivity of structural steels. Under 10 MPa H2 gas environment, load-displacement curves obtained and fractographic morphologies of the recovered specimens were analyzed to investigate the HE behaviors based on punch velocity and test temperature. When the HE sensitivity was evaluated by RRT, STS304 steel appeared to be vulnerable to HE as compared to SA372 steel across the tested temperature range. As a result, it was found that in-situ SP test and RRT can be used to quantify the HE sensitivity for structural materials screening regardless of test environments.

Understanding the fatigue response of small volume specimens through novel fatigue test methods – Experimental results and numerical simulation

This paper presents the current understanding relating to fatigue response of materials that are small in volume and tested through cyclic automated ball indentation and cyclic small punch test methods. The paper covers both the experimentation and numerical simulation aspects. Recently, researchers have proposed the hydraulic bulge test as another test method for fatigue life evaluation. All these test methods provide an indication of failure due to fatigue loading. For any given material, each one of the test methods causes its own state of stress (bi-axial or tri-axial), which is different from the uni-axial state of stress for a standard specimen, which makes the correlation of strain-life data between test methods to be difficult. In view of this, a numerical simulation of cyclic ball indentation, cyclic small punch test, and hydraulic bulge test has been carried out. The results of numerical simulation suggest that the mean stress for cyclic ABI and cyclic SPT tests are different, but the failure life data can be corrected using Goodman or similar mean stress correction methods.

Evaluation of Creep Properties in Anode Materials for Solid Oxide Fuel Cells by Using Small Punch Testing Method

To assess the mechanical reliability and durability of solid oxide fuel cells (SOFCs), a suitable creep test method needs to be developed. The objective of this study is to examine the potential of small punch (SP) method as a simple creep testing method for SOFCs. In this study, the creep properties of Ni-YSZ composites were evaluated at temperatures of 800-900˚C, and at stresses of 47.3 to 89.8 MPa under 1% hydrogen environment. The obtained creep curves by the SP method showed three stages: initial transition creep, secondary creep, and tertiary stages. The central displacement versus time data obtained by the SP method was found to be characterized by a power law relationship. Even though quantitative comparisons need to be made with conventional methods, the above result suggests the usefulness of the SP methods for characterizing the creep properties in constituent materials of SOFCs.