Determination of Surface Stresses in X20Cr13 Steel by the Use of a Modified Hardness Measurement Procedure with Vickers Indenter

The paper presents a method for estimating the value of equibiaxial stress in a surface layer of a material by using a modified hardness measurement procedure with a Vickers indenter. A certain characteristic parameter was defined and related to the surface stress. A hybrid approach, based on experimental tests and accompanied by the complementary results obtained by the finite element modelling of X20Cr13 steel in elastic–plastic range, confirmed a linear relationship between the value of the characteristic parameter and the magnitude of equibiaxial stress at the surface. This linear relationship was valid in both elastic and elastic–plastic strain range beyond the yield stress of the material.

Чувствительность дислокационных розеток к форме индентора Берковича на кристаллах LiF и MgO

A peculiar effect, namely, the sensitivity of the shape of dislocation rosettes to the indenter type under indentation of the (001) face of LiF and MgO single crystals has been revealed. It was shown that the dislocation rosettes forming around the Vickers indenter are symmetrical, while the rosettes around the Berkovich one are asymmetric, the edge beams of the dislocation rosettes vary in length, and the screw ones do not show such asymmetry. An orientation effect was found during the penetration of the Berkovich indenter: the shape of the dislocation rosettes and the length of the edge beams change with a change in the orientation of the indenter relative to the crystallographic directions of the sample. It was also shown that the asymmetry of dislocation rosettes is more visible on harder crystals and increases with load growth on the indenter. The factors responsible for the anomaly in the development of dislocation rosettes under indentation in nano and micro scale by the Berkovich indenter of the (001) plane of cubic crystals are established

A Three-Dimensional Elastic-Plastic Contact Analysis of Vickers Indenter on a Deep Drawing Quality Steel Sheet

Three-dimensional finite element-based numerical analysis of Vickers indenter hardness test was conducted to investigate the effect of frictional conditions and material anisotropy on indentation results of deep drawing quality steel sheets. The strain hardening properties and Lankford’s coefficient were determined through the uniaxial tensile tests. The numerical computations were carried out using ABAQUS nonlinear finite element (FE) analysis software. Numerical simulations taken into account anisotropy of material described by Hill (1948) yield a criterion. The stress and strain distributions and loading–unloading characteristics were considered to study the response of the material. It was found that the hardness values seemed to be influenced by the value of the friction coefficient due to the pile-up phenomenon observed. The increasing of the friction coefficient led to a decrease of the pile-up value. Moreover, the width of the pile-ups differed from each other in the two perpendicular directions of measurement. Frictional conditions did not significantly affect the maximum force and the character of load–displacement curves. Frictional regime between the indenter and workpiece caused that the region of maximum residual stresses to be located in the subsurface.

Evaluation of Load Parameters and Hold Time of a Vickers Ultra-Micro Hardness Tester for Measure of Hardness and Modulus of Elasticity of Dental Composites

The aim of this study was to standardize the parameters for testing the hardness and elastic modulus for dental composites. It used the equipment Dynamic Ultra Micro Hardness Tester DUH-211 / DUH-211S (Shimadzu) varying the load and the hold time. two composites were used with various inorganic particles that were embedded and sanded for the assay. one Vickers indenter was used being held nine rows with ten penetrations. For each composite loads were used (20, 50 and 100gf) and times (zero, five and ten seconds). The results showed that the effect of the load and the hold time had influence on the modulus and hardness values of the studied composites. The authors concluded that loads and hold larger team showed greater stability of hardness values and modulus of elasticity for the studied composites and these values for both hybrid composites as for nanoparticulate were dependent on load and time.

Kekerasan mikro resin komposit packable dan bulkfill dengan kedalaman kavitas berbeda

Microhardness of packable and bulkfill composite resin with different cavity depths. Bulkfill composite resin restorations are increasingly popular because the material can be irradiated with a thickness reaching 4 mm, making it easier to apply. The objective of this study was to determine the differences in the microhardness between packable and bulkfill composite resin restorations with a cavity depth of 2 mm and 4 mm. This study was done using 32 Teon molds (5 mm diameter), and grouped randomly into 4 groups in which each consisted of 8 samples. Group 1A, packable composite resin was applied to the mold with a cavity depth of 2 mm. Group 1B, bulkfill composite resin was applied to the mold with a cavity depth of 2 mm. Group 2A, packable composite resin was applied with a depth of 4 mm. Group 2B, bulkfill composite resin was applied with a depth of 4 mm. Each sample was immersed in articial saliva with a pH of 6.8 and stored in an incubator at a temperature of 37°C for 24 hours. The hardness of each sample was tested using Vickers indenter microhardness tester. The data obtained were then analyzed by using two-way ANOVA, followed by Tukey’s test. The results showed that bulkfill composite resin with a cavity depth of 2 mm has the highest average of microhardness (31.09 ± 2.02 VHN), followed by packable composite resin with a depth of 2 mm (17.52 ± 1.25 VHN), bulkfill with a depth of 4 mm (11.97 ± 1.23 VHN) and packable with a depth of 4 mm (3.18 ± 0.85 VHN). The two-way ANOVA analysis showed that there are significant differences between the types of composite resin and cavity depths (p < 0.05), and there is interaction between the types of composite resin and cavity depth (p<0.05). In conclusion, the microhardness of packable composite resin is lower than that of bulkfill at a cavity depth of 2 and 4 mm. ABSTRAKRestorasi resin komposit dengan bulkfill semakin populer karena material tersebut dapat disinar dengan ketebalan sampai 4 mm, sehingga mudah diaplikasikan. Tujuan dari penelitian ini adalah untuk mengetahui perbedaan kekerasan mikro restorasi resin komposit packable dan bulkfill dengan kedalaman kavitas 2 mm dan 4 mm. Penelitian ini dilakukan dengan menggunakan 32 cetakan Teflon (diameter 5 mm), dan dikelompokkan secara random menjadi 4 kelompok yang masing-masing terdiri dari 8 sampel. Kelompok 1A, cetakan diaplikasikan resin komposit packable dengan kedalaman kavitas 2 mm. Kelompok 1B, diaplikasikan komposit bulkfill dengan kedalam 2 mm. Kelompok 2A, diaplikasikan komposit packable dengan kedalaman 4 mm. Kelompok 2B, diaplikasikan komposit bulkfill dengan kedalaman 4 mm. Setiap sampel direndam dalam saliva buatan dengan pH 6,8 dan disimpan dalam inkubator dengan suhu 37 °C selama 24 jam. Setiap sampel diuji kekerasannya menggunakan Vickers indenter microhardness tester. Data yang diperoleh dianalisis dengan ANOVA dua jalur, dilanjutkan uji Tukey’s. Hasil penelitian menunjukkan resin komposit bulkfill dengan kedalaman kavitas 2 mm memiliki rerata kekerasan mikro tertinggi (31,09 ± 2,02 VHN), diikuti oleh resin komposit packable dengan kedalaman 2 mm (17,52 ± 1,25 VHN), bulkfill dengan kedalaman 4 mm (11,97 ± 1,23 VHN) dan packable dengan kedalaman 4 mm (3,18 ± 0,85 VHN). Analisis ANOVA dua jalur menunjukkan bahwa terdapat perbedaan yang signifikan antara jenis resin komposit dan antara kedalaman kavitas (p < 0,05), serta terdapat interaksi antara jenis resin komposit dan kedalaman kavitas (p < 0,05). Kesimpulannya, kekerasan mikro resin komposit packable lebih rendah dibandingkan bulkfill baik pada kedalaman kavitas 2 dan 4 mm.