Depth-sensing Indentation Research Articles

Depth-sensing indentation-based studies of surface mechanical behavior and fatigue damage evolution of an austenitic stainless steel subjected to cyclic straining

In this paper the depth-sensing indentation (DSI) testing was used to study the elasto-plastic behavior and damage evolution in the surface layers of 304 stainless steel subjected to low-cycle fatigue loadings. For this purpose, the load–penetration depth (P−h) curves on the surface layers of cyclically deformed specimens corresponding to various stages of fatigue process were measured, from which the indentation characteristic parameters (HV, S, hr and Wp) were extracted to evaluate the surface elasto-plastic behavior of the stainless steel during cyclic deformation. Based on the indentation characteristic parameters, the basic mechanical properties (E, σy and n) were estimated using Dao et al.’s analysis algorithm to establish the constitutive descriptions of the fatigued surface layers. In terms of the continuum damage mechanics, a new damage indicator parameter, the indentation plastic work (Wp), was proposed to characterize the fatigue crack-initiation damage for the stainless steel, and its evolution character during fatigue cycling was analyzed. In this study the deformation microstructures formed in near-surface regions of fatigued specimens were also examined using OM and TEM techniques to provide the micro-mechanisms for the surface mechanical behavior and fatigue damage evolution. It is finally suggested that the DSI testing could provide a potential nondestructive evaluation method for the early detection of fatigue damage of engineering components and structures in alternating service conditions.

Measuring the mechanical properties of polymer–carbon nanotube composites by artificial intelligence

Polymer-Carbon nanotube composites (PCNCs) are a new class of composite materials, which is receiving significant attention both in academia and industry. In this paper, the application of Artificial Intelligence (AI) to the measurement of the elastic modulus of PCNCs was investigated. This is the first time that an AI-based modeling algorithm is used as an alternative tool for nano-indentation methods such as depth-sensing indentation (DSI). To build the model, 138 pair input-target data were gathered from the literature, randomly divided into 88 and 50 data sets and then were respectively trained and tested by the proposed AI model. In the set of the models, matrix type, nanofiller type, processing method, nanofiller content and method of analysis were introduced to the AI model as input layers, while the elastic modulus (either quasi-static E or dynamic [Formula: see text]) is used as output parameter. Although the modeling process is done with a nanometer sensitivity, the training and testing set results of the explicit formulations obtained by the AI model showed that artificial intelligent methods have strong potential and can be applied for the measurement of the elastic modulus of PCNCs as a non-destructive testing.

Effect of High Doses Beta Irradiation on the Micromechanical Properties of Surface Layer of Glass-Filled Polypropylene

The presented article deals with the research of micro-mechanical properties in the surface layer of modified Polypropylene filled by 25% of glass fibers. These micro-mechanical properties were measured by the Depth Sensing Indentation - DSI method on samples which were non-irradiated and irradiated by different doses of the β - radiation. Radiation doses used were 0, 66 and 99 kGy for filled Polypropylene with the 6% cross-linking agent (triallyl isocyanurate). The change of micromechanical properties is greatly manifested mainly in the surface layer of the modified polypropylene where a significant growth of microhardness values can be observed.

Surface Layer Micro-Hardness of Modified LDPE by Radiation Cross-Linking after Temperature Load

The presented article deals with the research of surface layer ́s micro-mechanical properties of modified LDPE by radiation cross-linking after temperature load. These micro-mechanical properties were measured by the DSI (Depth Sensing Indentation) method on samples which were non-irradiated and irradiated by different doses of the β – radiation and then were temperature loaded. The purpose of the article is to consider to what extent the irradiation process influences the resulting micro-mechanical properties measured by the DSI method. The LDPE tested showed significant changes of indentation hardness and modulus after temperature load.

Pile-Up Correction of Mechanical Characteristics of Individual Phases in Various Steel by Depth Sensing Indentation

The Oliver–Pharr method has extensively been adopted for measuring hardness and elastic modulus by indentation techniques. However, the method assumes that the contact periphery sinks in, which limits the applicability to the materials pile-up [1]. This study proposes an improved methodology to calculate the real mechanical characteristics of individual phases in various steels with significant pile-up. Pile-up correction of mechanical characteristics is based on ratio of pile-up height and contact depth. Pile-up height was measured by atomic force microscopy (AFM). The effect of grain boundaries on the shape and size of the pile-up lobes was also discussed.

Characterization of Sputter-Deposited NiTi Thin Film by Nanoindentation

NiTi shape memory alloy thin film sputter-deposited on a large scale silicon wafer was characterized by means of instrumented (depth-sensing) indentation technique. Thickness of deposited thin film was measured by calotest device. Microstructure of thin film was observed using differential interference (Nomarski) contrast. It was shown that the local mechanical properties are different in areas containing different phases (austenite and martensite) according to different deposition conditions (kinetic energy of deposited atoms when impacting the substrate surface).

Influence of Microstructure on Tribological Properties and Nanohardness of Silicon Carbide Ceramics

The influence of microstructural variations on the tribological properties and nanohardness of liquid phase sintered silicon carbide (LPS SiC) has been observed. In order to modify the microstructures samples were further heat treated at 1650°C and 1850°C for 5 hours to promote grain growth. The depth-sensing indentation tests of SiC materials were performed at several peak loads in the range 10-400 mN. The pin-on-flat dry sliding friction and wear experiments have been made on SiC ceramics in contact with Al2O3 ceramic ball at 10-50 N loads in an ambient environment. The nanohardness of samples with plate-like microstructure was about 34 GPa i.e. 3 GPa higher than nanohardness of SiC with fine globular microstructure. The SiC materials with coarser plate-like microstructure had similar COF (0.4-0.55) and better wear resistance (one order of magnitude at normal forces 10-20N) than SiC materials with fine globular microstructure.

Micro-abrasive wear resistance of CoB/Co2B coatings formed in CoCrMo alloy

New data for micro-abrasion wear resistance of CoB/Co2B coating was obtained through a ball cratering test. The coating was formed on the surface of a CoCrMo alloy using the powder-pack boriding method. The boriding process was carried out at 1223 K over 5 h of treatment resulting in the formation of CoB/Co2B coating with a total thickness of 28 μm approximately. Both hardness and Young's modulus profile through the cobalt borides were evaluated by Berkovich depth-sensing indentation using a load of 25 mN. The wear coefficients of CoB and Co2B formed on CoCrMo alloy were evaluated by a Plint TE-66 micro-abrasion tester using SiC particles dissolved in deionized water as abrasive slurry. The results demonstrated that the cobalt borides have wear coefficients higher than CoCrMo and improve their micro-abrasion wear resistance. Furthermore, a wear-mode map was developed to identify the two and three body abrasion mechanisms and the transition between them modifying the concentration of SiC in the slurry and the magnitude of applied load.

Mono- and multiple TiN(/Ti) coating adhesion mechanism on a Ti–13Nb–13Zr alloy

Mono- and multiple TiN(/Ti) coatings deposited on Ti–13Nb–13Zr alloy substrates by the filtered arc deposition system were examined using scratch testing and depth-sensing indentation in terms of the relationship between the coating adhesion, deformation mechanism, and microstructure, and mechanical properties at the film/substrate interface. The results show that multilayer TiN/Ti coatings offer a greater resistance to cracking and delamination than monolithic TiN coatings under the same conditions on the Ti–13Nb–13Zr alloys substrates. And increasing the number of layers for TiN multilayer coating improves the coatings adhesion. In contrast, for the coatings on the Ti–13Nb–13Zr alloys substrates that were heat-treated to a higher hardness, the limited deformation in the substrates improved remarkably the coating adhesion indiscriminately. The substrate mechanical properties play the major roles in controlling the coating adhesion, and increasing thickness and layers of the TiN multilayer have a limited improvement to the adhesion of coating.

Improvement of PA6 Mechanical Properties by Radiation Cross-Linking

Influence of mechanical properties of the hard surface layer of modified polyamide 6 is studied. Mechanical properties are acquired by nanohardness test with using the DSI method (Depth Sensing Indentation). Hard surface layers are created by radiation cross-linking technology. This technology allows polymer materials modification followed by the change of their end-use properties. The surface layer of polymer material is modified by ionizing β - radiation. When the polymer material is exposed to the β radiation, it is possible to observe changes of the surface layer at applied load. Radiation cross-linking usually improves strength, reduces creep, contributes to chemical resistance improvement, and in many cases improves tribological properties.

Irradiation of Polyamide Measured by Micro-Indentation Test

Cross-linking is a process in which polymer chains are associated through chemical bonds. This research paper deals with the possible utilization of irradiated polyamide. Influence of the intensity of irradiation on micro-indentation hardness was investigated. Material properties created by β – radiation are measured by micro-indentation test using the DSI method (Depth Sensing Indentation). Hardness increased with increasing dose of irradiation at everything samples; however results of micro-indentation test shows increasing in micro-mechanical properties of surface layer. The highest values of micro-mechanical properties were reached radiation dose of 99 kGy, when the micro-mechanical values increased by about 18%.

Scratch- and wear-resistant photoluminescent silicone epoxy coatings on floor tiles

Photoluminescent silicone epoxy resins were prepared by physical dispersion of SrAl2O4:Eu2+, Dy3+ pigments. The resin was deposited on ceramic tiles for flooring by automatic drawdown and left to harden at ambient conditions. Morphology of the coated tiles was measured by contact gage profilometry and field emission gun scanning electron microscopy. Mechanical response was investigated by pencil and cross-hatch scratch tests; depth-sensing indentation measurements were performed using Vickers and flat punch indenters. Tribological response of the coated tiles was measured by progressive and constant load scratch tests and dry sliding linearly reciprocating ball-on-flat tests, respectively. Intensity of photoluminescent radiations and the corresponding decay time were estimated by digital imaging. The photoluminescent coatings feature high hardness, scratch and wear endurance as well as good clarity. Being the resin designed for spontaneous drying and suitable for easy-to-automate and versatile deposition processes, it is the ideal candidate for the decoration of a large variety of substrates as well as for the repowering and/or retrofitting of previous installations.

Influence of deposition conditions on electrical and mechanical properties of Sm2O3-doped CeO2 thin films prepared by EB-PVD (+IBAD) methods. Relationship between investigated film and substrate at indentation

The study of polycrystalline CeO2 + xSm2O3 (x = 0, 10.9–15.9 mol %) thin films deposited by Electron Beam Physical Vapour Deposition (EB-PVD) and Ionic Beam Assisted Deposition (IBAD) techniques on the Si substrate was devoted to the influence of deposition conditions used, namely composition x, deposition temperature Tdep and Ar+ ion bombardment as well as the structure and (micro)structure on the (micro)hardness H using the differential hardness, Hdif, as a parameter. The investigations were made using, as in our recent papers, the depth sensing indentation (DSI) technique. The study was focused on the depth dependence of the film/substrate system response on the indentation response from the surface of films up to the film/substrate interface. This study has shown that the critical indentation depth, where the influence of substrate is negligible, can be observed for some CeO2 films doped with Sm2O3 as well as for undoped CeO2 films, both deposited at Tdep = 200°C without IBAD as well as using IBAD. Besides it, a wavy character of differential curve due to the inhomogeneities of films was observed with good reproducibility at some films. It was proven, that the method of differential hardness measurement is applicable for the determination of critical indentation depth as well as for the study of microstructure response of thin films from the film surface up to the film/substrate interface. Results of this study are described and discussed.

Diffusion Boride Coatings in CoCrMo Alloy and Some Indentation Properties

Some mechanical properties for cobalt boride (CoB and Co2B) coatings were obtained using the Vickers depth-sensing indentation technique. The coatings were developed on the surface of a CoCrMo alloy using the powder-pack boriding process at temperatures between 1223 and 1273 K using different exposure times for each temperature. Vickers indentations were conducted at constant distances from the surface using loads ranging from 15 to 450 mN. For the entire set of experimental conditions, the behavior of the indentation properties was examined as a function of the indentation loads. Universal expressions were used to determine the apparent or real hardness, the indentation Young’s modulus, and fracture toughness of the CoB and Co2B coatings. The results indicated that the CoB and Co2B coatings exhibited an apparent hardness of 20 and 17 GPa, respectively, in which the fracture toughness of the cobalt boride coatings only varied slightly in the set of experimental conditions proposed in this work.

Influence of Irradiation Doses on Mechanical Properties of Glass Fiber Filled PBT

The submitted paper compares mechanical properties of the hard surface layer of modified PBT filled by 35% of glass fibers. Hard surface layer was made by radiation cross-linking technology which allows polymer materials modification followed by the change of their end-use properties. The surface layer of polymer material is modified by β – radiation. When the polymer material is exposed to the β – radiation, it is possible to observe changes of the surface layer at applied load. The mechanical properties were measured by nanohardness test with using the DSI method (Depth Sensing Indentation).

Micro-Hardness of PA6 Influenced by Beta Irradiation

In this paper, the effect of the electron beam irradiation on the indentation hardness, indentation modulus and indentation creep have been studied by means of the Depth sensing indentation (DSI). Cross-linking is a process in which polymer chains are associated through chemical bonds. Radiation doses of 33, 66 and 99 kGy were used for unfilled polyamide 6 with the 7% crosslinking agent (triallyl isocyanurate). Beta irradiation of the examined thermoplastic caused the growth of values of material parameters as micro-hardness, indentation modulus or indentation creep etc. From this point of view, there may be new application in areas with mechanical properties higher than their original properties. This study compared the mechanical properties of irradiated and non-irradiated PA6.

Influence of Irradiation Doses on Mechanical Properties of PA6

The presented article deals with influence of mechanical properties of the hard surface layer of modified polyamide 6. The mechanical properties were acquired by nanohardness test with using the DSI method (Depth Sensing Indentation). Hard surface layer was created by radiation cross-linking technology. This technology allows polymer materials modification followed by the change of their end-use properties. The surface layer of polymer material is modified by β - radiation. When the polymer material is exposed to the β radiation, it is possible to observe changes of the surface layer at applied load.

Temperature-dependent microindentation data of an epoxy composition in the glassy region

The short-term instrumented microindentation technique was applied for assessing the influence of temperature in the glassy region on the time-dependent mechanical properties of an average epoxy resin mix near to its native state. Linear viscoelasticity theory with the assumption of time-independent Poisson ratio value forms the basis for processing the experimental results. The sharp standard Berkovich indenter was used to measure the local mechanical properties at temperatures 20, 24, 28, and 35 °C. The short-term viscoelastic compliance histories were defined by the Kohlrausch–Williams–Watts double exponential function. The findings suggest that depth-sensing indentation data of thermorheologically simple materials influenced by different temperatures in the glassy region can also be used, through the time-temperature superposition, to extract viscoelastic response functions accurately. This statement is supported by the comparison of the viscoelastic compliance master curve of the tested material with data derived from standard macro creep measurements under pressure on the material in a conformable state.

Analysis of Mechanical Properties of Individual Phases in Steels by Depth Sensing Indentation

The macroscopic mechanical properties of steel are highly dependent upon microstructure, morphology, and distribution of each phase present. Nanomechanical testing (Depth sensing indentation) provides a straightforward solution for quantitatively characterizing each of these phases because it is very powerful technique for characterization of materials in small volumes. Measuring the intrinsic properties of each phase separately in multiphase materials gives information that is valuable for the development of new materials and for modelling [1]. In this work, depth sensing indentation has been used to reveal mechanical properties of different phases in steel sheets.

Analysis of PA 6 nanocomposites — indentation and creep behavior as a function of temperature and load level using different indentation techniques

The short-term performance (Martens hardness and indentation modulus) and the time-dependent creep behavior of polyamide 6 (PA 6) and two PA 6 nanocomposites containing 3.5 wt % montmorillonite (MMT) or 5 wt % halloysite nanotubes (HNT) were analyzed by different depth-sensing indentation techniques in the nano-, microand macro-range of loading as a function of applied load (0.08— 100 N) and temperature (-80—60 °C). Additionally, WAXD and DSC measurements were made to establish the morphology-property relationships of the investigated materials while taking into account the skin-core structure of the injection-moulded samples.