Small Punch Test Research Articles

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.

Mechanical properties assessment of additively manufactured Ti64 alloy using small punch tests

ABSTRACT A study of the mechanical properties of Ti64 alloy through Small Punch Test is presented in this paper. The method and the validity of the correlation coefficients developed for nuclear steels are first verified on wrought alloy and then applied to additive manufactured material. The yield strength values obtained agree with the literature and domains of negative strain rate sensitivity could be highlighted for the microstructure resulting from additive manufacturing. The creep tests carried out showed good agreement between the present results and those reported in the literature on usual creep representations. This allows to validate the models used and to extend the small punch methods to the case of titanium alloys. The results are used for comparing the mechanical behaviour of additive manufactured Ti64 alloy to that of wrought alloys.

Fracture-toughness estimation from small-punch test in hydrogen exhibiting ductile and ductile–brittle fracture modes

In this study, an energy-based fracture toughness estimation method based on a small-punch test in a hydrogen environment, exhibiting either ductile or combined ductile and brittle fracture modes is proposed. For the ductile fracture mode, the energy term due to gas pressure in the small-punch test in hydrogen environment is simply added to the existing energy-based fracture toughness estimation equation. For the combined ductile and fracture mode, modified equations for the plastic energy term are proposed to correct overestimation due to brittle cracking. The estimated fracture toughness values are shown to consistent with the published API X70 and X42 test data.

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.

Quantitative Characterization of Strength Properties of Girth Welded Joints Based on Small Punch Test

Quantitative Characterization of Strength Properties of Girth Welded Joints Based on Small Punch Test

Design of silver containing mesoporous bioactive glass-embedded polycaprolactone substrates with antimicrobial and bone regenerative properties

ObjectivesThe aim of the present study was to design, produce and characterize composite substrates consisting of different formulations of poly(ε-caprolactone) (PCL), as a polymer matrix, and silver-containing mesoporous bioactive glasses (Ag-MBGs) with improved properties for bone tissue engineering. MethodsAg-MBGs were synthesized by an evaporation-induced self-assembly process. Different polymer-to-particles weight ratios were considered (90/10, 80/20, 70/30 wt%). PCL/Ag-MBGs composites substrates were manufactured by melting and molding technique. The effect of Ag-MBGs embedded in the polymer matrix was investigated by morphological (field emission scanning electron microscopy (FE-SEM), SEM and contact angle measurement), structural/functional (small punch and tensile tests), antimicrobial, and in vitro biological analyses. ResultsThe obtained results highlighted that the inclusion of 10% by weight of Ag-MBGs improved the punching performances as well as the tensile Young’s modulus (from 350.3 ± 32.0 MPa for PCL to 473.5 ± 41.0 MPa), without negatively altering the tensile strength of the neat PCL. Indeed, small punch test findings indicated that, over a threshold concentration (10% by weight), the Ag-MBGs acted as "weak points", rather than reinforcement, because the mechanical properties of the composite substrates decreased. The bacterial growth monitoring showed a clear antimicrobial effect against both Gram-negative and Gram-positive, confirmed by reduced cell viability registered after 24 h (2 ×105 CFU/mL for P. aeruginosa and 2.3 ×105 CFU/mL for S. aureus). The results were confirmed in terms of adhesion and adherent growth, reduced at day 3 on PCL samples with 10% of Ag/MBGs. Furthermore, this formulation induced a significant inhibition zone (21 mm for P. aeruginosa, 23 mm for S. aureus). In vitro biological assays confirmed that all formulations of PCL/Ag-MBGs supported periodontal ligament stem cells’ viability and differentiation over time. Particularly, substrates with Ag-MBGs at a concentration of 10% and 20% by weight of Ag-MBGs provided higher values of the percentage of Alamar Blue reduction meanwhile, the highest Ag-MBGs concentration induced a higher expression of alkaline phosphatase activity. SignificanceAg-MBGs proved to be suitable candidates as filler at a specific threshold concentration (10% by weight), considering a compromise among physicochemical, antimicrobial, and pro-regenerative features. These findings provide useful data for the design and development of improved biomaterials with optimized properties, suggesting a potential application in maxillofacial bone and/or periodontal tissue repair.

High-temperature mechanical properties evaluation of 310S stainless steel

ABSTRACT The high-temperature mechanical properties of 310S stainless steel were investigated by uniaxial tensile tests and small punch tests at the temperature from 20℃ to 600℃, and the relationship between the mechanical properties (σYS ,σUTS) and the characteristic loads (Fy, Fm) was established. The results revealed that with increasing temperature, the mechanical properties of 310S decrease, and the characteristic loads obtained by Fy_Mao, Fy_EN and Fy_E3205 are more appropriate for determining the yield strength of materials at high temperatures particularly for Fy_E3205. The fracture pattern observed in the SPT specimens indicated a mixed tough-brittle fracture accompanied by the characteristics of cleavage fracture. Additionally, the ultimate tensile strength of the material and the maximum load Fm increased slightly at 400 ℃ compared to 300 ℃ due to the precipitation of a large number of granular carbides and the increase in the grain size.

Evaluation of defect-related fatigue performance of additive manufacturing GH4169 via small punch test

Suffering from irregularly distributed defects, the fatigue performance of additive manufacturing (AM) GH4169 was scattered and difficult to evaluate. Therefore, the micro-scale small punch fatigue (SPF) test was employed on the deposited and heat-treated GH4169. Convolutional neural networks (CNN) and image processing technology (IPT) were used to extract defect features of SPF samples, respectively. The effects of AM defects on SPF life were analyzed via mathematical models, and the results showed that defect size damaged SPF life the most. Various machine learning (ML) algorithms, including regression based on deep learning (RDL), support vector regression (SVR), and random forest (RF) were employed to anticipate SPF life. Combined with defects features from CNN and IPT, the SVR model showed high prediction accuracy with a coefficient of determination of 0.98, compared with the classic model and other ML models.

Small Punch Test on Jominy Bars for High-Throughput Characterization of Quenched and Tempered Steel

Studying the effect of quench and tempering heat treatments on steel, more specifically screening the effect of the austenitizing, quenching, and tempering conditions on mechanical properties, can be extremely material- and time-consuming when standard tensile testing specimens are employed. Jominy bar end quench testing has been used as a standard method to reduce the resources that are required for this type of screening. Jominy bar testing by itself shows, though, the limitation of yielding only hardness and microstructure as a result. In the last few years, the small punch test (SPT) standard has been developed. This technique can obtain an estimation of tensile mechanical properties with miniaturized specimens, which can be dissected from Jominy bars. The paper proposes a new testing methodology for screening the outcome of heat treatment conditions by combining the Jominy bar testing and SPT. Quench and tempering of API 5L X65Q pipe steel is used as a case study to describe the proposed methodology. The ability of the Jominy with SPT to detect variations in the mechanical properties produced by heat treatments is shown. This methodology can be directly applied as a high-throughput testing approach in the optimization of heat treatments.

Mechanical Properties and Fracture Mechanism of Selective Laser Melting Manufactured Nickel-Based Alloy by Small Punch Test Over a Wide Temperature Range

Mechanical Properties and Fracture Mechanism of Selective Laser Melting Manufactured Nickel-Based Alloy by Small Punch Test Over a Wide Temperature Range

An Improved Correlation for the Estimation of the Yield Strength from Small Punch Testing

This study aims at improving the empirical correlation for estimating the yield strength from small punch tests. The currently used procedure in the European standard EN 10371 to determine the elastic–plastic transition force—based on bi-linear fitting—involves a dependency not only on the onset of plastic flow but also on the work hardening of the material. Consequently, the yield strength correlation factor is not universal but depends on the material properties and on the geometry of the small punch set-up, leading to a significant uncertainty in the yield strength estimation. In this study, an alternative definition of the elastic–plastic transition force is proposed, which depends significantly less on the work hardening of the material and on the small punch geometry. The approach is based on extensive elastic–plastic finite element simulations with generic material properties, including a systematic variation of the yield strength, ultimate tensile strength, and uniform elongation. The new definition of the transition force is based on the deviation of the force-deflection curve from the analytical elastic slope derived by Reissner’s plate theory. A significant reduction of the uncertainty of the yield strength estimation is demonstrated.

Identification of creep parameters from multi‐step relaxation tests on miniaturised specimen

AbstractThe small punch test (SPT) is a miniaturised method for thermo‐mechanical materials testing. The combination of simple specimen geometry and low required specimen volume is ideal for minimally invasive characterisation and monitoring of the current material condition in technological systems, including nuclear plants.The aim of the present study is to identify creep material properties of the chromium steel P91 (X10CrMoVNb9‐1) via small punch testing. It is examined to which extent a single relaxation test is suitable to replace several creep tests at different force levels. The inverse parameter identification method utilises a non‐linear optimisation approach in order to match the results of simulation and experiment. The simulation is performed using finite element analysis (FEA) and the considered material law aims to represent the high‐temperature behaviour of steels. To this end, a modified Liu–Murakami model is specifically used along with linear elasticity and non‐linear isotropic plasticity. We propose a strategy, that can be used to separately identify the Norton‐parameters from multi‐step relaxation tests performed on one specimen. Thereby, the applied strain (displacement, if utilising SPT) is kept constant after initial loading, which enables stress relaxation within the specimen. In case of the SPT, this behaviour yields a decreasing reaction force which approximately approaches a constant value. During the repeated loading phases, specimen failure may occur, due to further plastification of the specimen. Loading and relaxation cycles are repeated until specimen failure.The identified parameters are validated via small punch creep experiments at different force levels. It will be shown that good agreement is observed when comparing the sets of identified parameters.

Exploring the creep and oxidation behaviors of four types of FeCrAl alloys through small punch test at 600 °C: Experiments and simulations

Four types of iron-chromium-aluminum (FeCrAl) alloys, composed of different elements, were used to investigate the creep performance and high-temperature oxidation resistance. The microstructures in the undeformed regions after the small punch creep test (SPCT) remained consistent with the as-received (AR) FeCrAl alloys, while the grain aspect ratio (GAR) decreased and grains elongated in the deformed regions. Amongst the four alloys, Q1 exhibited the worst oxidation resistance, whereas Q4 showed superior oxidation resistance due to the addition of Si. Precipitates were observed in the deformed regions after SPCT but not in undeformed regions, indicating that deformation had a positive effect on element segregation. Creep models including Norton power law, Monkman-Grant relationship, Larson-Miller Parameters, and Fracture-Time law were obtained. Calculation results from these creep models revealed that under low loads Q4 had lower minimum creep rate δm and longer creep fracture time tr compared to other alloys; however, Q3 demonstrated better performance in terms of δm and tr under high loads. This suggests a strong correlation between creep performance and loads. Additionally, finite element method (FEM) was employed to explore the effects of minor variation (±0.005 mm) in specimen thickness on SPT curves and SPCT curves. FEM results indicated that this slight variation alone did not account for discrepancies observed in load-deflection curves; deviations of ±6.1% for δm and ±6.3% for tr were found corresponding to specimens with 0.5 ± 0.005 mm thickness.

Effects of pre-deformation and annealing on the mechanical properties and microstructure of miniaturized FeCrAl-Y-Si alloys

The evolution of mechanical properties and microstructure in FeCrAl alloys with added Y and Si was investigated using miniaturized specimens. The FeCrAl alloys underwent warm rolling, resulting in thicknesses of 1 mm and 2 mm, followed by annealing at temperatures ranging from 600 °C to 1050 °C. Mechanical properties were determined through three distinct methods: conventional uniaxial tensile testing (UTT), micron indentation hardness testing (MIHT), and small punch testing (SPT). Microstructure evolutions were characterized using various techniques, primarily focusing on electron backscatter diffraction (EBSD). Two types of precipitates containing Y, Si, and Al were observed during annealing. Fracture morphologies revealed that as the annealing temperature (AT) exceeded 900 °C, size effect and brittle failures became prominent in SPT specimens. Brittle failures in SPT can be attributed to the segregation of Y, Si, and Al along the grain boundaries, the size effect, and the dispersed distribution of grain sizes. The optimum inter-pass annealing temperature was identified as 700 °C based on grain orientation spread (GOS) maps. SPT and MIHT results were correlated with UTT results when conducted at room temperature (RT, 25 ℃), and a Hall-Petch equation was derived. It was observed that the correlation equations for SPT were significantly influenced by brittle failures, resulting in relatively larger fitting errors. However, these SPT correlation equations proved effective in predicting total elongation compared to MIHT correlation equations and the Hall-Petch equation. The Hall-Petch equation exhibited the lowest average fitting error though limited by deformed grains. MIHT exhibited the strongest correlation with UTT, particularly in terms of yield strength and ultimate tensile strength. The three fitting methods have distinct advantages and shortcomings in characterizing the mechanical properties of Y and Si-added FeCrAl alloys.

Prediction of mechanical properties for typical pressure vessel steels by small punch test combined with machine learning

To understand the fitness of different machine learning methods to small punch test (SPT), three machine learning methods, namely, back propagation (BP) neural network, radial basis function (RBF) neural network and random forest (RF) regression model were used to establish machine learning-based correlation models of SPT load–displacement and uniaxial tensile test true stress–strain curves. Five typical pressure vessel steels were tested to reveal the prediction accuracies of different machine learning methods. Statistical analysis, unveiled the following order of prediction accuracy for pressure vessel steels: BP > RBF > RF. However, the differences in the mean absolute percentage erros between BP and RF decreased from 5.64% to 1.59%, with the training data volume increasing from 50 data sets to 629 data sets. Therefore, if a large training data volume is used, then the three machine learning methods can provide acceptable prediction results. However, if the training data volume is insufficient, then the BP, and RBF neural networks are better choices.

Determination on the fracture toughness of the welded joints of X80 pipeline steels based on small punch test

For the sake of design and integrity assessment of the fracture toughness of high-grade pipelines, it is necessary to carry out accurate fracture toughness assessment of the welded joints. The study of more concise and effective fracture toughness testing methods has important theoretical and engineering value. At present, the fracture control of girth welding joints is mainly based on J integral, CTOD and CTOA. However, it is hard to carry out standard fracture toughness tests at some local narrow areas of the welded joints such as the heat affected zone for the difficulty of sampling. On this basis, this paper aims to propose a method to determine the fracture initiation toughness JIC of the welded joints of high-grade pipeline steels based on the micro-sample test method - small punch test. Firstly, small punch specimen with through-thickness notch was designed. Secondly, the finite element model of the notched specimen was established, and verified by the notched specimen tests of X80 steel. Furthermore, the elastic–plastic material properties of different zones of the welded joint were obtained by the empirical correlation method of small punch test and further used for the determination of J contour integral. The GTN damage parameters were calibrated by the three-point bending tests and further used for the determination of the crack initiation displacement. Finally, the fracture initiation toughness JIC(SPT) of different zones of the welded joint were obtained by the SPT method and verified by the three-point bending test. The results show that the fracture initiation toughness JIC(SPT) of each region of the welded joint obtained by notched SPT specimen were all less than the SENB test results. But there is a good empirical correlation between the two results so that the SPT method can be further modified by establishing an empirical correlation model. The SPT method has good engineering application prospect for the accurately characterization of the different distribution of fracture toughness in different areas of the welded joints.

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.

Computational prediction of chevron cracking during multi-pass cold forward extrusion

The cold forward extrusion is a manufacturing process that is widespread in automated production due to its economic benefits. The cross-section is reduced during this process, which is accompanied by large plastic deformations. It may lead to the chevron cracking, which has to be predicted for flawless production and maintaining economic advantage. Therefore, the multi-pass cold forward extrusion of cylinder made from AISI 1045 was numerically simulated. The central cracks were predicted by the recently proposed uncoupled ductile fracture criteria. These were calibrated using various experiments, including the small punch test with additional fractographic observation. The material model was implemented into Abaqus using the user subroutine so that defects were successfully predicted using an element deletion technique.

Effect of anisotropic mechanism of W-2%wt Y2O3 alloy on DBTT and fracture analysis under small punch testing

The high brittle-to-ductile transition temperature (DBTT) of tungsten is a significant concern that hinders its use as a structural material. This study employs small punch testing over a broad temperature range to investigate the anisotropic mechanism of DBTT in as-hot rolled W-2%wt Y2O3 specimens. RD-TD specimen exhibits the highest EUS(0.75/J), highest ELS(0.08/J) and lowest TSP (∼336 °C) in three oriented materials. Multiple factors were conducted individually, revealing that the similar dislocation density, and fraction of LAGBs are not the primary determinant of the observed variations in DBTT performance. RD-TD specimen with strong {111}<112> γ-fiber texture exhibits the highest Fm that is nearly twice as high as that of RD-ND specimen and almost three times as high as that of TD-ND specimen. The relationship between the grain morphology, such as aspect ratio present on the DBTT as well as fracture mode of the material is apparent. RD-TD specimen boasts superior plastic properties, which displays an annular crack with the dome-like structure at the core and small incisions at the periphery. While, the plasticity of TD-ND and RD-ND specimens are deemed inadequate, as evidenced by the emergence of multiple lengthy and linear cracks in a particular orientation upon initial cracking. The utilization of numerous superimposed loads and the sandwich configuration of Y2O3 particles in tungsten matrix have been discovered to promote the occurrence of delamination in the thickness direction of the RD-TD specimens. The stratified structure, texture, screw dislocations, and grain aspect ratio have been identified as the pivotal factors influencing the anisotropy on DBTT and fracture analysis.

Investigation on regression model for the force of small punch test using machine learning

The analytical solution for the force-deflection curve of the small punch test (SPT) is still a challenge. Machine learning is employed in the present study to establish a model for estimating SPT forces by using the strength of a material. The yield strength and ultimate tensile strength of materials and corresponding SPT force-deflection curves generated by finite element simulations are the training and testing data for machine learning. Pearson correlation analysis was performed first to measure the statistical association between the SPT force at a given deflection and the strength of materials. It was shown that a binary linear regression model was capable of correlating SPT forces to the yield strength and ultimate tensile strength of a material. The model parameters were determined after training, and then this model was tested by testing data. The accuracy of the regression model was verified by hypothetical materials, X70 steel and Incoloy 800H alloy. This study gives a new insight into the relationship between force responses of SPT and material properties, and can promote the development of novel approaches for determining material tensile properties using SPT.