Indentation Test Method Research Articles

Micro-scale evolution of mechanical properties of glass-ceramic sealant for solid oxide fuel/electrolysis cells

The structural integrity of the sealant is critical for the reliability of solid oxide cells (SOCs) stacks. In this study, elastic modulus (E), hardness (H) and fracture toughness (KIC) of a rapid crystallizing glass of BaO–CaO–SiO2 system termed “sealant G” are reported as determined using an indentation test method at room temperature. A wide range of indentation loads (1 mN–10 N) was used to investigate the load-dependency of these mechanical properties. Values of 95 ± 12 GPa, 5.8 ± 0.2 GPa and 1.15 ± 0.07 MPa m0.5 were derived for E, H and KIC using the most suitable indentation loads. An application relevant annealing treatment of 500 h at 800 °C does not lead to a significant change of the mechanical properties. Potential self-healing behavior of the sealant has also been studied by electron microscopy, based on heat treatment of samples with indentation-induced cracks for 70 h at 850 °C. Although the sealant G is considered to be fully crystallized, evidence indicates that its cracks can be healed even in the absence of a dead load.

Finite Element Modeling of Articular Cartilage to Characterize Biomechanical Properties: The Effect of Cartilage Surface Curvature

Degeneration and loss of articular cartilage in the synovial joint have been recognized as the main source of osteoarthritis which leads to pain, swelling and limit the joint mobility. Extensive experimental and computational studies have been performed to study the mechanical behavior and characterize the biomechanical properties of articular cartilage. However, a lack of attention was made on the curvature of the cartilage surface by assuming it was a flat surface. This assumption was inappropriate since the synovial joints possessed curved geometrical shape and may contribute to inaccuracies in characterizing the articular cartilage biomechanical properties. This study aims to examine the effects of the curvature of the cartilage surface in finite element modeling which incorporated with the experiment method to characterize biomechanical properties of articular cartilage. In this study, the biomechanical behavior of contact pressure and pore pressure were investigated at different radius of cartilage surface using the finite element method. The cartilage biomechanical properties of elastic modulus and permeability of the bovine humeral head were then characterized using a combination of indentation test and finite element method. It was found that the cartilage curvature produced a 6% difference in contact pressure and a 39% difference in pore pressure distribution compared to the flat surface cartilage in finite element analysis. Furthermore, significant observation in the characterized biomechanical properties was obtained where the differences of the cartilage curvature reached 33% for elastic modulus and 56% for permeability. Based on the results, the surface curvature of articular cartilage could play an important role in the computational modeling and characterization of its biomechanical properties.

Semi-analytical model for flat indentation of metal materials and its applications

The increasing use of small material components in a wide range of industrial fields necessitates the development of an accurate and robust indentation testing method. To this end, this paper proposes an Energy-density-equivalence for a Flat Indentation (E-FI) model based on the energy density equivalent principle. The proposed model describes the relationships among the material parameters of Hollomon’s power law (H-law), flat indenter diameter, energy, and indentation displacement. An E-FI Method (E-FIM) that determines the H-law parameters of materials through the indentation test is also developed. The energy-displacement curves forward-predicted by the E-FI model (based on known H-law parameters of materials) and the H-law parameters of materials given by the E-FIM (based on known energy-displacement curves) are consistent with the results of Finite Element Analysis (FEA) and the H-law parameters of materials used as the input for FEA, respectively. Using E-FIM, the goodness of fit for both stress–strain curves with H-law, predicted based on the displacement with 2% signal interference, and that for stress–strain curves without interference is more than 0.98. The stress–strain relations predicted by E-FIM were consistent with the results obtained via uniaxial tensile tests of ten ductile materials.

Evaluation of Fracture Behavior of Oxide Scale Formed on Carbon Steel Using Indentation Test and Acoustic Emission Method

Evaluation of Fracture Behavior of Oxide Scale Formed on Carbon Steel Using Indentation Test and Acoustic Emission Method

Characterization method of the layer thickness of surface residual stress based on instrumented indentation testing

Based on dimensional analysis and finite element analysis (FEA), a test method was developed to determine the layer thickness of the surface residual stress using instrumented indentation testing. The relative loading curvatures of the stressed and stress-free P-h curves were obtained from the FEA results. The platform region of the curve of the relative loading curvature versus the indentation depth was used to estimate the residual stress, and the residual stress layer thickness was obtained by considering the turning point of the curve. According to the error analysis results, the proposed method is valid for estimating the residual stress layer thickness by carefully considering the material properties. The proposed method was reduced to the instrumented indentation testing method to determine the uniform residual stress when the indentation depth was far smaller than the layer thickness.

Welding Temperature Distribution and Residual Stresses in Thick Welded Plates of SA738Gr.B Through Experimental Measurements and Finite Element Analysis.

A numerical and experimental study of welding temperature distribution and residual stresses in thick welded plates of SA738Gr.B was conducted. Within the framework of numerical investigations, the temperature field of SA738 thick plate welding was simulated and analysed by using 2-D modelling technology. The temperature field was checked by using the thermal cycle curve with the aim of increasing the computational accuracy and efficiency, and the temperature field was verified by using the thermal cycle curve and heat affected zone. The welding stress field was analysed based on the temperature field, and the indentation test method was used to verify the stress field, and the error was controlled to within 12.5%. With the help of a welding model established for SA738Gr.B thick-plate welding the sequence was simulated. Seen from welding sequence 1 to welding sequence 3, transverse stress S11 changed significantly, decreasing by 14% and 17% respectively, adjusting the welding sequence can reduce welding residual stresses.

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.

RSM Performance Characteristics Improving Due to the Application of the Nanostructured Carbon-containing Coating “Superlattice”

This article presents the results of the experimental researches on nanostructured carbon-containing PVD coatings based on titanium and chromium (Cr/C; CrN/CNx, Ti/C; TiN/CNx) deposited on a disk Ø 20 × 5 mm made of steel ShKh15 (MX15). Coatings were obtained on the UNICOAT 600SL installation (Russia). In the course of the research, such parameters as coatings adhesion to the substrate, their hardness and elastic modulus, as well as friction coefficients were determined by using the indentation, scratch testing and tribological testing methods, respectively, on the CSM equipment (Switzerland). The low values of the friction coefficient (Cr/C − 0,02, Ti/C − 0,07; CrN/CNx - 0,15; TiN/CNx − 0,13) suggest that they are promising to be used in the friction pairs of the drive actuating mechanism, and the high hardness values (from 3,000 to 3,700 units on the HV scale) are promising in highly loaded drives under extreme operating conditions.

Determining of the machine compliance using instrumented indentation test and finite element method

.At present time the importance of indentation measurements once again increases. As modern and perspective measurement method it allows to measure various mechanical properties while only needing micro volumes of materials. While standard hardness measurement methods examine only the plastic response of sampled material, Depth Sensing Indentation (DSI) testing is founded on real-time recording of applied force and resulting travel of indenter. This allows to evaluate both plastic and elastic response of examined material during the indentation process which in turn allows for calculation of various static material properties in very small volumes of samples. The big advantage of this approach is saving of time (especially on sample preparation), however the data analysis – and thus results – could be influenced by certain factors. Those worth noting are surface quality of the sample, wear of the indenter head, its shape and material, and also the compliance of testing machine’s frame. If we consider the frame of testing machine having non-zero compliance, inevitably there will occur not only displacement of indenter but also displacement of frame itself, especially noticeable while using high loads. This negatively influences the results of such measurement. This work’s aim is to calculate the compliance of test machine’s frame using Finite Element Method model and 1 mm in diameter steel ball indenter. The result of this work is addition of virtual spring to the FEM model and fine tuning of its stiffness. This should allow us to minimize the influence of frame’s compliance on the results of future measurements.

Fracture toughness estimation for high-strength rail steels using indentation test

In this paper, tensile properties and mode I critical stress intensity factor (KIc) are measured on the railhead of six types of high-strength rail steels using standard testing methods. An instrumented ball indentation testing method is then developed to estimate fracture toughness for the six rail steels based on continuum damage mechanics. Critical damage parameter, determined by combining repeated loading-unloading tensile tests and a ductile damage model, is used to characterize a critical contact depth under indentation that is used to calculate the specific indentation energy, and thus the fracture toughness for indentation (KInd). Comparison between KInd and KIc for the six high-strength rail steels suggests that the current indentation testing method can successfully rank the six high-strength rail steels for their fracture toughness.

Fatigue response evaluation of stainless steel SS 304 L(N) and SS 316 L(N) through cyclic ball indentation studies

This paper presents the results of an experimental investigation of fatigue response of stainless steel SS 304 L(N) and SS 316 L(N) using cyclic ball indentation test method. A Tungsten Carbide (WC) spherical ball of 1.57 mm diameter is used for applying compression-compression fatigue cycling on the test specimen having a nominal thickness of 5 mm; the displacement response is monitored as a function of every cycle of loading. The study focused on cases where the stainless steel specimens were welded by two different welding processes – Activated flux TIG welding and conventional multi-pass TIG welding. Fatigue response was monitored at locations of weld zone, heat affected zone (HAZ) and base metal to identify the effect of microstructure variation on fatigue response. It is observed that there is a steady increase in depth of penetration of the spherical indenter due to fatigue cycling; however, after a number of cycles, there is a sudden increase in depth of penetration which indicates the failure of the material beneath the indenter. The specimens after cyclic ball indentation were examined using a scanning electron microscope and one could observe the presence of secondary cracking in the penetrated region of the specimen.

Investigation on tribological behaviour of boron doped diamond coated cemented tungsten carbide for cutting tool applications

In this paper, tribological performance of boron doped diamond (BDD) films and boron doped graded layer diamond thin films (BDD/transition layer/NCD) were studied in detail. The widely used cemented tungsten carbide (WC-6wt%Co) was selected as a substrate material for diamond coating. Diamond films were deposited on WC-Co by Hot-filament CVD reactor (HFCVD) setup. Tribology experiment was conducted using a reciprocating tribometer with a normal load of 30N and a sliding velocity of 10mm/s for a constant stroke length of 3mm. Silicon nitride (Si3N4) ball was used as a counterpart to study the friction and wear behaviour of diamond films. The surface morphology, topography & roughness of the diamond films were analysed using scanning electron microscope and atomic force microscope respectively. The hardness of the thin diamond films was measured by using Berkovich nano indentation test method. In MCD coating (sp3 C-C) the wear rate increases with increase in hardness. On the contrary for NCD (sp2 graphite), wear rate decreases with decrease in hardness because of the corresponding phases. The test results found that BDD and boron doped graded layer shows a stable lowest friction coefficient values of 0.004 and 0.003 compared with conventional microcrystalline diamond films (0.007). On the other hand, the wear diameter of the silicon nitride ball for BDD and boron doped graded layer are found to be 620μm and 785μm, relatively lower in comparison with microcrystalline diamond films (897μm). The wear track width was measured by scanning electron microscope and shows that BDD and boron doped graded layer indicates lower wear track width 564μm and 596μm compared with microcrystalline diamond films (712μm). Raman mapping was conducted on the wear track of the diamond films to know about the phase pure diamond (sp3) and partly graphite phases (sp2) which in turn contributes for the distinct residual stresses in thin films. The obtained lower friction coefficient for BDD on WC-Co cutting tool can be suitable for machining of aluminium based metal matrix composites effectively.

Study of Fatigue Properties of Materials through Cyclic Automated Ball Indentation and Cyclic Small Punch Test Methods

One of the important inputs while estimating the remaining life of critical components is the fatigue property of materials. Fatigue data, in the form of stress vs. cycles to failure (or) strain vs. cycles to failure (or) fatigue crack growth rate data is used to predict the residual life. Material’s fatigue property degrades with time and usage; hence, it is appropriate to use the current properties for remaining life assessment. Often the quantity of material available for generating fatigue data is limited, especially, if the material is scooped out of existing component of a power plant. Further, fatigue response being probabilistic in nature, requires multiple specimens to be tested at any given stress/strain levels. This has prompted us to develop test procedures to determine the fatigue data of materials from a limited volume of material. This paper presents the results of cyclic ball indentation test method as well as cyclic small punch test method that is used to generate the fatigue data at different stress levels. There are several fine details relating to these test techniques – viz., establishing a equivalent damage criteria for failure life with standard LCF/HCF test specimens. The influence of one of the variables, viz., friction at the specimen-tool interface of a small punch test is investigated through numerical simulation and the results are presented here.

Interface bonding of NiCrAlY coating on laser modified H13 tool steel surface

Bonding strength of thermal spray coatings depends on the interfacial adhesion between bond coat and substrate material. In this paper, NiCrAlY (Ni-164/211 Ni22 %Cr10 %Al1.0 %Y) coatings were developed on laser modified H13 tool steel surface using atmospheric plasma spray (APS). Different laser peak power, Pp, and duty cycle, DC, were investigated in order to improve the mechanical properties of H13 tool steel surface. The APS spraying parameters setting for coatings were set constant. The coating microstructure near the interface was analyzed using IM7000 inverted optical microscope. Interface bonding of NiCrAlY was investigated by interfacial indentation test (IIT) method using MMT-X7 Matsuzawa Hardness Tester Machine with Vickers indenter. Diffusion of atoms along NiCrAlY coating, laser modified and substrate layers was investigated by energy-dispersive X-ray spectroscopy (EDXS) using Hitachi Tabletop Microscope TM3030 Plus. Based on IIT method results, average interfacial toughness, Kavg, for reference sample was 2.15 MPa m1/2 compared to sample L1 range of Kavg from 6.02 to 6.96 MPa m1/2 and sample L2 range of Kavg from 2.47 to 3.46 MPa m1/2. Hence, according to Kavg, sample L1 has the highest interface bonding and is being laser modified at lower laser peak power, Pp, and higher duty cycle, DC, prior to coating. The EDXS analysis indicated the presence of Fe in the NiCrAlY coating layer and increased Ni and Cr composition in the laser modified layer. Atomic diffusion occurred in both coating and laser modified layers involved in Fe, Ni and Cr elements. These findings introduce enhancement of coating system by substrate surface modification to allow atomic diffusion.

Mechanical Behaviour of Skin: A Review

Objective: The mechanical behaviour or the Young’s Modulus of the skin is measured as a ratio of the stress applied to the skin in vitro or in vivo over the skin deformation. The Young’s Modulus of skin is an important factor to estimate the characteristics of skin, to determine the course of a disease or to follow a cosmetic application. Methods: The mechanical behaviour of the skin is measured by changing the shape of skin by employing tensile, indentation, and suction and torsion tests. Results: Out of all the skin’s mechanical testing methods, suction tests are a common choice for skin testing, as they are easy to apply in vivo and consider both in-plane and normal loading conditions. Skin is found to be highly anisotropic and viscoelastic, with a range of Young’s Modulus between 5 kPa and 140 MPa. Conclusion: This paper reviews in vivo and in vitro reported values for Young’s Modulus of human skin for tensile, indentation, suction and torsion mechanical testing methods.

Estimation of Tensile Properties of Pressure Vessel Steel Through Automated Ball Indentation and Small Punch Test

Extraction of mechanical properties of in-service materials through small specimen test techniques has become attractive in the recent years. Of the available small specimen test techniques, automated ball indentation (ABI) and small punch test (SPT) methods have proved to be more promising. These test methods are basically non-destructive in nature and are proficient enough to extract the flow properties of the materials using small volume specimen. In this work, tensile properties of a pressure vessel steel (P12) have been estimated through ABI and SPT. The objective is to compare the capability of these test methods in determining the tensile properties. The influence of lubrication (between the indenter and the specimen) on the ABI response is also investigated. The ABI response is found to be similar and the effect on the tensile properties was under 2 %. The tensile properties estimated from ABI and SPT are found to be in good agreement with conventional tensile test results. Nevertheless, in case of SPT, the error in the estimation of yield strength and ultimate tensile strength using empirical correlations is significantly high. However, the use of analytical formulations to convert the SPT load–displacement response to stress–strain curve are found to be reliable, since the error in the estimated properties is considerably less. The ABI process is numerically simulated to study the stress–strain field beneath the indenter. The maximum strain occurs at the edge of the contact indicating the material displacement along the radial direction. The plastic zone beneath the indenter resemble hemispherical shape which is in agreement with the expanding cavity model. The nature of stress changes from compressive (right below the indentation axis) to tensile at the edge of contact. This indicates that radial cracks may initiate on the specimen and propagate outwards. The pile-up is significantly higher in the case of frictionless contact between the indenter and the specimen but found to converge for a value of around 0.2.

In Situ Mechanical Testing Techniques for Real-Time Materials Deformation Characterization

In situ mechanical property testing has the ability to enhance quantitative characterization of materials by revealing the occurring deformation behavior in real time. This article will summarize select recent testing performed inside a scanning electron microscope on various materials including metals, ceramics, composites, coatings, and 3-Dimensional graphene foam. Tensile and indentation testing methods are outlined with case studies and preliminary data. The benefits of performing a novel double-torsion testing technique in situ are also proposed.

Determination of fracture toughness of brittle materials by indentation

Fracture toughness is one of the crucial mechanical properties of brittle materials such as glasses and ceramics which demonstrate catastrophic failure modes. Conventional standardized testing methods adopted for fracture toughness determination require large specimens to satisfy the plane strain condition. As for small specimens, indentation is a popular, sometimes exclusive testing mode to determine fracture toughness for it can be performed on a small flat area of the specimen surface. This review focuses on the development of indentation fracture theories and the representative testing methods. Cracking pattern dependent on indenter geometry and material property plays an important role in modeling, and is the main reason for the diversity of indentation fracture theories and testing methods. Along with the simplicity of specimen requirement is the complexity of modeling and analysis which accounts for the semi-empirical features of indentation fracture tests. Some unresolved issues shaping the gap between indentation fracture tests and standardization are also discussed.

427 遮熱コーティングの界面靭性評価法の標準化

The adhesion is one of the important and basic properties in thermal spray coatings. The standard tensile test method "ISO 14916" is usually used to evaluate the adhesive strength of coatings. On the other hand, the indentation test method has some advantage to evaluate the interfacial fracture toughness as the adhesive strength from the following reasons; the specimen preparation and the specimen preparation are easy in comparison with the typical testing method. Collaborative research has been conducted by the committee on Standard development in Japan Thermal Spray Society to establish the standard test method which evaluates interfacial fracture toughness of thermal spray coatings by using a conventional Vickers indenter. This paper reports on differences among collaborators in round robin tests performed in this committee and discusses about the validity of the test method and test conditions through the results of round robin test and finite element analysis. Based on the results of the collaborative investigations, the constraints of test conditions were found to evaluate the interfacial fracture toughness by the indentation tests. Comparison among collaborators reveals that the interfacial fracture toughness can be obtained with small scattering from the indentation test under the constraints.

The Measurement of Mechanical Properties of Pipe Steels in Service through Continuous Ball Indentation Test

With the development of petroleum, chemical and energy industries and urban gas network, the amount of pipelines in China has grown rapidly in recent years, meanwhile it leads more accidents. The main reason is that some pipelines have gradually served into their late period or even extend period of the pipeline design or expect life. However, we usually cannot use conventional destructive test methods to measure the performance of pipelines in service, so that we cannot make an accurate assessment of the remaining life of the pipelines. This brings serious challenge to the safety management of pipeline transportation in China. In order to investigate a new method to non-destructively test the mechanical properties of pipe steels, the yield strength and tensile strength of pipe steels including low carbon pipe steels 20, the low carbon micro-alloyed pipe steel L415, L360, and stainless pipe steels used in China were measured through the methods of continuous ball indentation test and conventional tensile test in this paper. The measured results by the destructive and non-destructive test methods were compared and analyzed in detail in this paper. It is concluded that the continuous ball indentation test method can be used to measure the yield strength and tensile strength of pipe steels feasibly and accurately.