The present research introduces a new method namely mandrel indentation test (MIT) to evaluate surface hardness of rocks and building stones and comparing its results with the Vickers hardness test ...results. For performing the test, first, its apparatus was designed and built from hard and rigid steel in a turning workshop. Then, it was used on 50 common carbonate building stones including 30 limestones and 20 travertines in the laboratory. Also, surface hardness of the stones was evaluated by the Vickers hardness test. The values of mandrel indentation hardness (MIH) for the building stones were obtained between 31.75 and 113.85 kgf/mm2, and the values of Vickers hardness (HV) were obtained between 286.11 and 1361.98 kgf/mm2. The developed correlation analysis results together with the obtained Pearson, Spearman, and Kendall correlation coefficients indicated that the values of the surface hardness resulted from this approach is strongly correlated to the values of the Vickers test by a direct linear relation. The stablished simple regression analysis has confirmed the results of the correlation analysis by a determination coefficient of 0.841. Five well‐known statistical indexes were used to assess accuracy performance degree of the developed regression model. As an important finding of the research, the introduced approach has high potential and accuracy for evaluating surface hardness of the studied building stones. Finally, a classification system was proposed to classify different building stones based on their surface hardness. Based on the classification, the studied building stones are classified as very soft to moderately hard with low hardness ratio.
•This study introduces a new test method and its apparatus namely mandrel indentation test.•The test evaluates surface hardness of rocks and building stones in the laboratory.•The obtained results from the mandrel indentation test were compared with the Vickers hardness test results.•The values of the mandrel indentation hardness and Vickers hardness are strongly correlated to each other.•A classification was proposed to classify building stones based on surface hardness values.
The use of continuous fiber as reinforcement is well known to improve the mechanical performance of thermoplastic printed laminated composites. However, it is difficult to optimize the rigidity and ...energy absorption of continuous fiber reinforced composite components, since the inherent conflict between strength and ductility. For this purpose, this study focused on the design and characterization of continuous fibers reinforced polyamide (PA)-based composites, prepared via 3D printing, with synergistic enhancement of the strength and ductility. Continuous carbon and Kevlar fibers were used as reinforcements for production of printed non-hybrid and hybrid composites. The quasi-static indentation (QSI) test and structural evolutions analysis of composites were conducted to evaluate the mechanical properties and reveal the deformation and failure mechanisms. A Volume Average Stiffness (VAS) model and a hybrid effect model were introduced to predict the effective stiffness and to analyze the hybrid effect on the energy absorption capabilities of the printed hybrid composites, respectively. The results showed that the addition of the continuous carbon and Kevlar fibers with a certain designed improved toughness of the composite, which led to an enhancement of the energy absorption properties. The deformation and failure mechanisms of hybrid continuous fiber reinforced composites highly depended on the designed position of fibers. For the printed hybrid composites, the highest indentation force could be achieved when continuous Kevlar fiber layers were placed at the rear side. While the highest energy absorption capability of the printed composites was captured when continuous carbon fiber layers were positioned at the rear side.
In the present study, a semi-empirical modeling of the mechanical response in pile-up mode is obtained by deriving the load-depth relationship during the indentation loading cycle. The advantage ...compared to the relations previously used is that this new expression is a function of the predictable criterion of the mode of deformation, (hf/hm), which makes it possible to distinguish the sink-in mode from the pile-up mode. A comparison between the proposed expression and the results of the instrumented indentation tests shows excellent agreement.
The deformation and failure behavior of any coating governs the performance of the resulting coating system. In the present work, we numerically and experimentally examine the fundamental deformation ...mechanisms of CrAlN coating on Si substrate, particularly its cracking behavior under indentation processes. For this purpose, CrAlN coatings deposited on monocrystalline Si substrates by pulsed DC magnetron sputtering were subject to indentation procedures with different depths. Subsequent characterization of top surface and cross-sectional morphologies demonstrates a strong dependence of coating profile and microstructures on the initial surface condition of the substrate. Specifically, uniform CrAlN coatings with a thickness of 1.1 μm and densified columnar microstructures were prepared on a polished Si substrate. Berkovich nanoindentation test with an indentation depth of 530 nm derives the mechanical properties of the prepared CrAlN coating. The corresponding finite element simulation reveals the propensity of cracking initiation accompanied by the stress concentration at three edge corners of the dent. Subsequent microindentation test with an indentation depth of 1.09 μm demonstrates the coexistence of plastic deformation and brittle fracture of CrAlN coating. In particular, surface radial cracks within CrAlN coating are experimentally and theoretically observed, and the cracking processes are analyzed in detail by finite element simulations.
•A finite element framework coupled with cohesive zone model is established to describe the crack initiation and propagation in CrAlN coatings magnetron-deposited on Si substrate.•The simulated load-displacement curves for nanoindentation of CrAlN coatings are in good agreement with the experimentally measured ones.•The stress distribution of CrAlN coatings reveals that stress concentration, mainly at the contact points is responsible for the propensity of crack initiation.•The plastic deformation and brittle fracture of CrAlN coating coexist in the microindentation process, and the initiation and propagation process of four well-developed radial cracks generated on the indented surface can be well revealed by FE simulations.
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•A size-independent instrumented spherical indentation test (ISIT) to predict fracture toughness of wheel steels.•Correlate fracture toughness and Charpy impact energy (CVN) of wheel ...steels by ISIT.•An alternative representative stress–strain method to predict tensile properties by ISIT.•Rapid evaluation of trade-offs between yield strength and CVN of wheel steels under various cooling rates.
In this paper, an improved size-independent instrumented spherical indentation test (ISIT) method was proposed to determine tensile strength and fracture toughness on wheel rims of two different types of wheel steels. Additionally, Charpy impact specimens were taken from three specific positions on the wheel rims and subjected to standard Charpy impact testing. The resulting Charpy impact energy (CVN) were matched with the fracture toughness measured by ISIT (KIc,IT) at the same positions. There was a clear linear correlation between CVN and the square of KIc,IT, which was consistent with the established relationship between both properties as determined by conventional Charpy impact and compact tension tests. Therefore, we expanded the ISIT method to study the impact of cooling rates on the variation of yield strength and Charpy impact energy across the wheel rim. To accomplish this, we designated additional testing points on the wheel rim using the ISIT method. The investigation found trade-offs between strength and impact toughness of wheel steels under different cooling rates. The above findings demonstrated the effectiveness of using the ISIT method, which facilitated high-resolution fracture toughness measurement, to establish accurate correlation between CVN and fracture toughness of wheel steels. Moreover, this ISIT method can be employed to regulate heat treatment of material properties to meet specific application requirements.
In the present study, a semi-empirical modeling of the mechanical response in pile-up mode is obtained by deriving the load-depth relationship during the indentation loading cycle. The advantage ...compared to the relations previously used is that this new expression is a function of the predictable criterion of the mode of deformation, (hf/hm), which makes it possible to distinguish the sink-in mode from the pile-up mode. A comparison between the proposed expression and the results of the instrumented indentation tests shows excellent agreement.
In the present study, a semi-empirical modeling of the mechanical response in pile-up mode is obtained by deriving the load-depth relationship during the indentation loading cycle. The advantage ...compared to the relations previously used is that this new expression is a function of the predictable criterion of the mode of deformation, (hf/hm), which makes it possible to distinguish the sink-in mode from the pile-up mode. A comparison between the proposed expression and the results of the instrumented indentation tests shows excellent agreement.
•Revealing orientation relationship, stability and adhesion strength of TiB/dual-phase Ti alloy interfaces.•The α-Ti nucleus is more energy favored to nucleate within β-Ti than at TiB/β-Ti ...interface.•Strong interfacial bonding of in-situ TiB contributed to enhancing load-bearing capacity of Ti6Al4V alloy.
To better understand the strengthening mechanism of in-situ formed TiB reinforcements in dual-phase Ti6Al4V alloy, the interface characters and properties of α-Ti/β-Ti/TiB system were thoroughly investigated with the combined use of high-resolution transmission electron microscopy (HRTEM), ab-initio calculations, and indentation tests. The ab-initio calculations suggest that the highly coherent (100)TiB/(1¯21)β-Ti phase boundary (PB) has fairly low interface energy of 0.082 J/m2 with an exceptionally high adhesion strength of 6.04 J/m2, owing to the formation of strong interfacial Ti–B ionic bonds. The semi-coherent (201¯)TiB/(0001)α-Ti interface shows a relatively higher interface energy of 1.442 J/m2 but still with a fairly high adhesion strength of 4.95 J/m2. With the obtained interfacial energetics, thermodynamics analyses were further carried out to explore the nucleation mechanism of α-Ti in TiB reinforced Ti6Al4V composite. Superior to the heterogeneous nucleation at TiB/β-Ti interface, the homogeneous nucleation of α-Ti within the β-Ti phase can be more energy-preferred, due to its lower nucleation energy barrier and critical radius. Further indentation tests under various loads of different modes confirmed a remarkably enhanced load-bearing capacity of dual-phase Ti6Al4V alloys, under the critical significance of the strong interfacial bonding achieved by reinforcements of in-situ formed TiB.
TÜBİTAK UME Hardness Laboratory has been working on instrumentation in the field of hardness metrology since 2005 and three generations of hardness standardizing machines were developed since then to ...be used as reference (calibration/standardizing) machines in Türkiye. In former designs conventional hardness methods such as Rockwell, Brinell and Vickers scales were the main scope of the projects. In the final Project that was supported and funded by TÜBİTAK UME to develop three hardness standard machines to be used as national standards for the conventional hardness scales mentioned, the Instrumented Indentation Test (IIT) was also aimed at and some parameters like Martens hardness, creep, indentation hardness, (elastic and plastic) indentation work, etc. were also implemented onto the machines developed. It was a good occasion that the measurands in Rockwell hardness and IIT were the same, force and indentation depth besides time and this made it easier to realize the IIT on the same machine with a more suitable design to achieve the highest accuracy in terms of the measurands mentioned. In this paper the new design of the Rockwell-Brinell-Vickers hardness standard machine developed also for Martens hardness in macro range (3 kgf – 150 kgf) and preliminary Martens hardness measurements are explained.
