Small Punch Research Articles

Exploiting small punch test for mechanical characterization of cold sprayed deposits

Conventional testing procedures often encounter challenges to characterize the mechanical properties of deposits of limited thickness such as coatings. To overcome this limitation, the literature has explored various miniature-testing methods, and, among these, the small punch test has emerged as a promising solution offering the main advantage of requiring a minimal volume of material. This study focuses on cold sprayed deposits in as-sprayed and thermally treated conditions and presents the results of an experimental campaign of mechanical characterization of 316L steel and copper deposits. In parallel, small punch tests are simulated numerically with inverse analysis to estimate comprehensively the stress-strain curves. Results suggest an extremely brittle behavior of the as-sprayed specimens and a good agreement between the experimental and numerical estimations of the mechanical properties of the ductile thermally treated specimens. Ultimately, the findings highlighted the sensibility of the small punch test to the microstructure and its gradients of cold sprayed deposits.

The efficacy of hyaluronic acid fragments with amino acid in combating facial skin aging: an ultrasound and histological study

BackgroundVarious techniques have been employed in aesthetic medicine to combat skin aging, in particular that of the facial region. Hyaluronic acid is utilized to enhance moisture levels and extracellular matrix molecules. This study aims to histologically assess the effects of low molecular weight hyaluronic acid fragments combined with amino acids (HAAM) on facial skin rejuvenation through intradermal microinjections.MethodsA total of twenty women, with an average age of 45 and ranging from 35 to 64 years old, participated in the study, including 8 in menopause and 12 in the childbearing age group. Mesotherapy was used to administer HAAM to the patients. Prior to and three months after the treatment, each patient underwent small circular punch biopsies. Ultrasound examinations were conducted using B-mode, capturing 2D images in longitudinal or transverse orientations with frequencies ranging from 5 to 13 Mega-hertz (MY LAB X8, ESAOTE, Genova, Italy). A total of 60 ultrasound examinations were taken, with 30 collected before treatment and 30 after treatment.ResultsThe histological analysis demonstrates an increase in fibroblast activity resulting in the production of Type III reticular collagen, as well as an increased number of blood vessels and epidermal thickness. However, the analysis of ultrasound data before and after treatment showed no statistical difference in skin thickness in malar area, chin and mandibular angle.ConclusionsHistological assessments indicate that subcutaneous infiltration of HAAM has a substantial impact on the dermis of facial skin.

Small punch evaluation of mechanical properties for 310S stainless steel considering pre-strain effect

Strain strengthening technology is widely used in practical engineering to increase the allowable stress of materials in pressure vessel manufacturing. Small punch analysis was performed using less material in this study to analyse the influence of pre-strain on the mechanical properties of 310S stainless steel. The results indicated that the material yield strength and ultimate tensile strength increased with pre-strain deformation. Similarly, the small punch characteristic parameters increased owing to the influence of the pre-strain, proving that the small punch test could estimate the evolution of mechanical properties along with pre-strain deformation. Small punch characteristic parameters at different deformation stages were analysed. In addition to the maximum load, small punch parameters at the inflection point were used in the ultimate tensile strength estimation. The small punch deformation features and stress distribution were discussed based on numerical simulations. Finally, an ultimate tensile strength estimation method based on membrane stretching model was proposed. Additionally, the strain hardening parameters considering the effect of pre-strain deformation were discussed.

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.

Application of small punch test to estimate mechanical behaviour of SUS304 austenitic stainless steel

The small punch test with an application of a relatively small specimen has recently become a reliable material mechanics testing method. In this study, the small punch test is set up based on the conventional mechanical testing machine for SUS304 stainless steel to evaluate the mechanical properties of SUS304 steel at different displacement rates of the punch in quasi-static loading condition in the case of with and without heat treatment. Although heat treatment has an insignificant effect on the microstructure and hardness of the material, the mechanical properties of the material in the small punch test are greatly reduced after heat treatment. Both cases with and without heat treatment have a similar tendency for the rate - sensitivity of the applied force - displacement curve. A higher value of force is applied to obtain the same value of displacement at a low displacement rate in the stable plastic deformation zone. Meanwhile, the maximum value of applied force is higher at a higher displacement rate in the stage that initiation of crack might appear. In the examined range of displacement rate, a positive rate - sensitivity of displacement at the maximum force. Therefore, a correlation between equivalent fracture strain and fracture toughness of the material can be achieved.

Fracture analysis of hydrogen-embrittled API X52 pipes at low temperature

This paper quantifies the effect of temperature (ranging from room temperature (RT) to -90 °C) on fracture toughness for hydrogen-embrittled API X52 by combining small punch (SP) test data and finite element (FE) damage analysis. For the FE damage analysis, a multi-axial fracture strain damage model was used, and the parameters were determined by analyzing the tensile and SEN(T) test data in air at RT. The hydrogen-enhanced ductile fracture was considered using the hydrogen-embrittlement constant, which was determined by analyzing the SP test results in hydrogen. Due to the effect of the interaction between strength and hydrogen-induced ductility loss on fracture toughness, the predicted fracture toughness in terms of temperature does not show a monotonic decrease up to -90 °C; rather, it decreases up to -30 °C, then increases slightly before decreasing again. Fracture mechanics analysis of a hydrogen-embrittled pipe with an axial surface crack using the determined fracture toughness values showed that the maximum pressure decreased slightly (less than 9 %) with decreasing temperature up to -90 °C, suggesting that the effect of temperature on the maximum pressure would not be so significant for API X52.

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.

Failure analysis of an AISI 310 stainless steel beam reinforcement fracture during service in a rolling beam furnace

This work investigated the premature failure of a beam reinforcement made of austenitic stainless steel AISI 310 used in the entrance of a rolling beam furnace working continuously at cycles from 650 to 850 °C. Fracture surface and microstructural investigations allowed to identify the fracture mechanism as fatigue failure. The fracture was probably initiated at the oxidized grain boundaries at an early stage of service life, when no microstructure degradation was present, while most of the fatigue crack propagation occurred after the precipitation of secondary phases. The microstructure investigation revealed severe microstructure degradation with the presence of intermetallic sigma (σ) phase (area fraction = 19 %) and M23C6 carbides (area fraction = 1 %), which were formed during the high-temperature exposure. Cracking of σ phases and decohesion at σ /austenite matrix interfaces were observed near the fracture and in the small punch test samples. Such discontinuities provide an easy path for crack propagation.

An improved analysis of small punch deformation for evaluating tensile properties

Small punch (SP) method is a promising technique for evaluating tensile properties using small volumes of test material, yet its applicability is bound by large errors in estimation of tensile yield strength (YS) using the yield force (FY) determined by the existing two tangent, offset or bilinear function fitting methods. In this study, a yield force (FY) based on the occurrence of yielding across the specimen thickness is identified through finite element analysis and a methodology is formulated for determination of FY from experimental data, supported with acoustic emission (AE) technique. The YS-FY correlation for various structural steels, Inconel and Aluminium exhibit excellent linearity and standard errors within ±7 %. Based on the onset of plastic instability in SP deformation at an inflection point (Fs, us) of force-deflection curve, the specimen deflection us is shown to correlate with tensile uniform strain better than parameter um (deflection at peak load). The tensile properties of neutron irradiated SS 316 evaluated from SP tests using the methodologies and SP-tensile correlations formulated in this work, are found to be within 6–8 % of the uniaxial tensile test results.

Evaluation of effect of spheroidization heat treatment on mechanical properties via small punch test

Due to the long time high temperature thermal action, pearlite heat-resistant steel 15CrMo is prone to pearlite spheroidization, which reduces its strength and makes it difficult to meet the actual service requirements. Therefore, quantifying the effect of pearlite spheroidization is an important factor in evaluating the high temperature performance of 15CrMo steel. In this study, the mechanical properties of 15CrMo steel were tested by uniaxial tension (UT), small punch tensile (SPT) test; the microstructure of 15CrMo steel after spheroidization heat treatment (SHT) was obtained by image processing technique to obtain the geometric characteristic parameters of pearlite spheroidization phase (PSP); the influence of spheroidization characteristics and properties were analyzed by mathematical and statistical analysis, and the results showed that the PSP size had the greatest influence on the properties; based on this, the linear relationship models between the spheroidization parameters and the mechanical properties of UT and SPT results were established with high accuracy of prediction.

Use of the small punch test for mechanical characterization of co– based laser cladding joint

This work evaluates the capacity of the small punch test (SPT) to determine the mechanical properties of wear-resistant cobalt-based fabricated by laser cladding. The joint is made up of three zones: the cladding material, the interface, and the base material, each of which must be characterized individually. SPT specimens extracted from each zone were tested and the mechanical properties were obtained by using various correlations. The validity of these correlations was evaluated by comparing the properties obtained for the base and cladding metals with those obtained by standard tests. With this verification, the properties of the interface, which is a mixture of the base metal and the cladding, were extracted. The mechanical properties of the joint change with the hardness, which depends on the microstructure and the thermal distribution of the different zones. The results demonstrate the suitability of the SPT for characterizing layers of laser cladding, providing values similar to those obtained with tensile or fracture tests. The increase in strength and decrease in toughness in the interface and the cladding metal were in agreement with the microstructure in each zone.

Effect of inhomogeneous microstructure on the stress corrosion cracking behavior of 316LN stainless steel weld joint under high-temperature and high-pressure water small punch test

The stress corrosion cracking (SCC) behavior of 316LN stainless steels (SS) weld joint in high-temperature and high-pressure (HTHP) water were investigated by the newly developed HTHP water small punch test. The results indicated that SCC behavior of weld joint were strongly influenced by the inhomogeneous microstructure. Intergranular fracture dominated the SCC process of heat affected zone (HAZ) and partial hardening was believed to be the main reason for the increased sensitivity of HAZ to SCC. All samples exhibited cleavage fracture characteristics, indicating that film-induced cleavage dominated the SCC process of SS and its welded joints in HTHP water.

Investigating effects of element composition on the microstructure and mechanical properties of three types FeCrAl alloys through small punch test

This study investigated the effects of element composition on the microstructure and mechanical properties of three FeCrAl alloys (denoted as Q1, Q2, Q3). The addition of reactive elements (REs) 2 wt% Mo resulted in a 60 % refinement of grain size and an increase in kernel angle misorientation (KAM). Alloy texture was notably influenced by elemental composition, and γ texture (111)[01¯1] exhibited higher energy than (111)[12¯1]. The {110} 〈111〉 slip system exhibited greater resistance to deformation and lower susceptibility to activation than {123} 〈111〉. The yield load (Py-CEN), maximum load (Fm), and fracture energy (Esp) of the alloys at 298 K, 573 K, 723 K, 873 K, and 1023 K were evaluated through small punch test (SPT). The Fm of the three alloys were two-staged with notable temperature dependence. In this context, Q1 exhibited the lowest absolute slope of 2.97 (Q2: 3.44, Q3: 3.46) in the second stage. Furthermore, the Esp value of Q3 was the lowest at room temperature (RT, 298 K) and the highest at high temperatures (873 K and 1023 K) among the three alloys. The obtained results of SPT at different temperatures suggested a strong temperature dependence in the mechanical properties.

Evaluating the tensile properties of high-strength stainless steels using small punch testing.

Accurately measuring the mechanical properties of high-strength stainless steels is of great significance for ensuring structural safety, predicting long-term performance and optimizing design. However, the standardized tensile test specimens used to obtain strength properties must be fabricated from bulk materials from an in-service structure or component, result in the loss of structural integrity or a reduction in remaining service life. Small punch tests require only miniscule material samples and are widely used to estimate in-service component material characteristics. This study performed small punch tests on three high-strength stainless steels-X17CrNi15-2, 15-5PH, and PH13-8Mo-to obtain the correlations between the small punch tests and the uniaxial tensile test results for each material. The estimated yield stresses obtained from the small punch tests were distributed within a factor of 1.5 on both sides of the unity line when compared with those obtained from the uniaxial tensile tests; the ultimate strength values estimated from the small punch tests correlated quite well with those obtained from the uniaxial tensile tests. An iterative finite element analysis was subsequently established to simulate the small punch tests and thereby obtain the coefficients for a Ludwik power law correlation representing the true stress-strain properties. The finite element predicted force-deflection curves agreed well with the small punch test results, which were also compared with the predictions obtained from empirical equations proposed in previous studies. Finally, the fracture mechanisms of the small punch test specimens were characterized through scanning electron microscopy, indicating that the dimple fracture mechanism dominated the failure mode. The results of this study are expected to inform the application of small punch test to evaluate in-service high-strength stainless steel materials.

Correlation between in-Situ small punch and conventional test result in evaluating hydrogen embrittlement susceptibility of API X70 base and weld under hydrogen gas mixture

The presence of microstructural heterogeneity within welded joints, combined with environmental factors, can have detrimental effects on the service life of engineering structural components. This study explores the effect of hydrogen/methane (H2/CH4) gas mixture under various volume fractions of hydrogen on the deformation and fracture behavior of a welded API X70 pipeline material employing the small punch test method. The welded metal showed more vulnerable to hydrogen-assisted fracture in comparison to the base metal, as evinced by a notable reduction in the volume fraction of hydrogen required for the transition from ductile to brittle behavior. The hydrogen embrittlement indexes obtained through the small punch test method are more severe than those obtained through conventional test methods. The direct utilization of small punch test results for the assessment of hydrogen compatibility in structural materials may yield overly conservative estimations. Quantitative parameters derived from the small punch test of both materials, along with fracture morphologies, were analyzed to establish a correlation between the hydrogen embrittlement indexes obtained through the small punch test and those obtained through conventional test methods. The small punch test method appears capable of detecting hydrogen embrittlement sensitivity resulting from adverse microstructural features existing in the metal matrix.

Evaluation of creep properties considering the friction effect of the small punch test

In contrast to the Uniaxial Creep Test (UCT), where each stress produces a corresponding strain, the Small Punch Creep Test (SPCT) generates displacement in response to applied loads. Therefore, for the direct application of SPCT in creep damage assessment, it becomes imperative to convert the displacement and load data into the strain and stress parameters observed in the UCT. Unlike the UCT, which applies the load directly to the specimen, the SPCT indirectly imposes the load on the specimen through a punch ball. This divergence in loading methods introduces friction between the specimen and the punch ball during the SPCT. This study delves into the analysis of the friction coefficient between the specimen and punch ball using the Finite Element Method (FEM). Additionally, we explore the relationship between the specimen's minimum thickness and the friction coefficient. In conclusion, we propose a correlation between the creep properties of the two test methods, with the objective of accurately capturing the influence of friction between the specimen and punch ball in the SPCT.

On the simulation of the small punch creep test—applied to 316L(N) austentic steels

ABSTRACT This paper describes a numerical analysis to predict the deformation and time to rupture of the small punch creep test for 316 L(N) austenitic steel. The constitutive model incorporates elasto-plastic nonlinear kinematic hardening and creep with primary, secondary and tertiary creep calibrated to the RCC-MRx code data. The computations are assessed by comparing with experimental data for a 500 µm thick sample clamped with a diameter of 5 mm loaded with a force 300,400 and 500N at 700°C. The model predicts the experimental observations quite well with respect to minimum deflection rate and time to rupture and its location using a local critical strain criterion. A very important feature is that the deformation and total effective strain distribution at rupture are almost identical for all loads as function of the time divided by the time to rupture.

Small punch test for investigating circumferential creep in cladding tubes

Several methods have been developed to determine the axial creep properties of nuclear fuel cladding tubes. However, the anisotropic creep properties of nuclear fuel cladding tubes requires that their circumferential creep behaviour be evaluated as well. Nonetheless, this task remains extremely challenging owing to need to employ unaltered cylindrical cladding tube specimens directly and the general low accuracy of the methods developed for this purpose. The present work addresses these issues by developing a modified small punch creep test (SPCT). Equations are proposed to calculate the creep stress and strain of the modified SPCT. The accuracy of the equations is analysed using the finite element method. Finally, the methodology is applied to investigate the circumferential creep behaviour of an FeCrAl nuclear fuel cladding tube experimentally. These results clearly demonstrate that the modified SPCT is suitable for investigating the creep behaviour of irregularly shaped material specimens with anisotropic creep properties. Moreover, the semi-cylindrical specimens employed in the modified SPCT also enable the effective fracture strain of the specimen to be easily determined.

An Interpretation between Small Punch Creep and Uniaxial Tensile Creep Test: Computational and Empirical Approach

The relationship between Small Punch (SP) creep testing and uniaxial tensile creep testing is crucial for translating findings from the innovative SP methodology to more conventional testing paradigms. This study involves both computational and empirical approaches to correlate the two testing methods effectively. The computational approach primarily utilizes finite element analysis (FEA) to model and simulate the stress states and deformation behaviors in SP creep tests. The empirical approach involves developing empirical relationships based on experimental data from both SP and uniaxial tensile creep tests. By integrating computational and empirical approaches, researchers can achieve a robust and reliable interpretation of SP creep test data in terms of conventional tensile creep test results.

Study of mechanical properties of RPV base and weld material using SPT technique

Small Punch Test (SPT) is one of the miniature test techniques used for evaluating tensile properties when limited dimension of material is available for standard mechanical test or handling of large specimen is difficult, especially while dealing with irradiated materials. In order to use SPT for determination of mechanical properties, it is crucial to establish correlation coefficients by comparing results obtained by SPT with that from standard tensile tests. Present work involves developing correlation coefficients and evaluation of tensile properties of reactor pressure vessel (RPV) steel using SPT technique. Specimen dimensions used for SPT was 10x10x0.5 mm3. These specimens were prepared from Charpy V-Notch specimens, which were earlier subjected to standard impact testing. Correlation coefficient for RPV material was established by comparison of SPT data with the tensile properties obtained using standard tensile test. Subsequently, SPT data was acquired on RPV thermal material and tensile properties were obtained using the correlation coefficient for validation. This paper describes the SPT set-up used during the current studies and methodology used for establishing the correlation coefficient on RPV base material.