Mechanical properties of β-HMX

Twinning, slip and catastrophic flow in niobium

This paper reports the effect of laser power density on the evolving properties of laser metal deposited titanium alloy. A total of sixteen experiments were performed, and the microstructure, microhardness and surface roughness of the samples were studied using the optical microscope (OP), microhardness indenter and stylus surface analyzer, respectively. The microstructure changed from finer martensitic alpha grain to coarser Widmastätten alpha grain structure as the laser power density was increased. The results show that the higher the laser power density employed, the smoother the obtained surface. The microhardness initially increased as the laser power density was increased and then decreased as the power density was further increased. The result obtained in this study is important for the selection of proper laser power density for the desired microstructure, microhardness and surface finish of part made from Ti6Al4V.

Degradation of a nano-cutting tool: An MD simulation

Cavitation erosion of several oxy-fuel sprayed coatings tested in deionized water and artificial seawater

The aim was to perform comparative analysis of bioactive, contemporary bulk-fill resin-based composites (RBCs) and conventional glass-ionomer materials for flexural strength (FS), diametral tensile strength (DTS), and Vickers hardness number (VHN) in the presence of thermocycling. Five restorative materials [Tetric N-Ceram Bulk Fill; smart dentin replacement (SDR) Flowable Material; Bioactive restorative material (ACTIVA Bulk Fill); Ketac Universal Aplicap; and GC Fuji II] were evaluated for DTS, FS, and VHN. Half the samples in each material group were ther-mocycled. The DTS was performed under compressive load at a cross-head speed of 1.0 mm/min. The FS was assessed by three-point bending test at a cross-head speed of 0.5 mm/min. The VHN was determined using a Vickers diamond indenter at 50 gf load for 15 seconds. Differences in FS, DTS, and VHN were analyzed using analysis of variance (ANOVA) and Tukey post hoc tests at a = 0.05 level of significance. N-Ceram, ACTIVA, and SDR demonstrated the highest and comparable (p > 0.05) FS. The SDR had the highest DTS value (141.28 ± 0.94), followed by N-Ceram (136.61 ± 1.56) and ACTIVA (129.05 ± 1.78). Ketac had the highest VHN value before and after thermocycling. ACTIVA showed mechanical properties (FS and DTS) comparable with bulk-fill resin composite materials. ACTIVA showed potential for durability, as VHN was comparable post-thermocycling. Bioactive materials showed acceptable DTS and FS values. However, hardness was compromised compared with included materials. ACTIVA Bulk Fill shows potential for dentin replacement but it needs to be covered with a surface-resistant restorative material. Further studies to improve surface characteristics of ACTIVA Bulk Fill are recommended.

Aim:The aim of this study was to evaluate the remineralizing potential of three different remineralizing agents (GC tooth Mousse, Clinpro tooth crθme and SHY-NM) on demineralized tooth surfaces using micro CT and microhardness.Materials and Methods:Forty five freshly extracted mandibular premolars were collected and enamel specimens were prepared. The samples were assigned to three groups with fifteen specimens in each group. The specimens were then demineralized using McInne's demineralizing solution in two cycles. After that, remineralization was carried out in two cycles for 30 days using Casein phosphopeptide - Amorphous calcium phosphate (CPP - ACP), 0.21% sodium fluoride - Tricalcium phosphate (f-TCP) and Calcium Sodium Phosphosilicate (CSP) containing tooth pastes for groups I, II, III respectively. The specimens were evaluated for Linear attenuation co-efficient using micro CT (Scanco™) and Vicker's Micro Hardness (Schimadzu™) testing at different time periods. The results were tabulated and statistically analysed.Results:It was observed that all the three remineralizing agents used in the study significantly increased the Linear Attenuation Co-efficient and Vicker's hardness number values of the enamel specimens following 15 days and 30 days application.Conclusion:CPP – ACP showed the better remineralizing potential than the other two agents and there was no statistical significant difference between f-TCP and CSP groups.

Vicker's Hardness of glass

Microstructures and mechanical behavior of Inconel 718 fabricated by selective laser melting

In this research, nanoindentation responses of Fe-10%Cr bi-crystal structures containing [Formula: see text][Formula: see text] and [Formula: see text][Formula: see text] tilt grain boundaries (GBs) have been investigated using atomistic simulation technique. Deformation analyses identify the nucleation of [Formula: see text], [Formula: see text] and [Formula: see text] types of dislocations within the material. The [Formula: see text] slip planes are found to be more active than the [Formula: see text] and [Formula: see text] slip planes. Load-displacement response and corresponding changes in contact area have been recorded and used to measure material hardness and reduced modulus. The lengths of the nucleated dislocations are measured and used to estimate dislocation density within the plastic zone beneath the indenter. Dislocation motion has been found to be much easier in model with [Formula: see text]3 boundary and the early interaction of the dislocation with the boundary affects the shape of the load-displacement curve, contact area on the indented surface, and the volume of the plastic zone. The hardness of the material has been found to be affected primarily by the interaction of the dislocation with the boundary, rather than by the dislocation density within the plastic zone. Both the boundaries exhibit maximum resistance to slip transmission even at the maximum indentation depth.

We investigated the effect of different dietary substances on deciduous and permanent enamel. Enamel specimens were prepared from human teeth (n = 108 deciduousmolars and n = 108 permanentpremolars). We measured the chemical parameters (pH, titratable acidity, viscosity, calcium, phosphate, fluoride concentration and degree of saturation) of nine dietary substances. The teeth were immersed in the respective substance (2 × 2min; 30°C; shaking), and we measured the baseline surface hardness (SH) in Vickers hardness numbers (VHN), and the changes in SH after 2min (ΔSH2-0) and the 4min (ΔSH4-0) immersion. We analysed the differences between deciduous and permanent teeth using the Wilcoxon test and correlated ΔSH to the different chemical parameters. Deciduous teeth were significantly softer (549.53 ± 59.41 VHN) than permanent teeth (590.15 ± 55.31 VHN; p < 0.001) at baseline, but they were not more vulnerable to erosive demineralization. Only orange juice, which presented milder erosive potential, caused significantly more demineralisation in deciduous teeth at ΔSH4-0. Practically all chemical parameters significantly correlated with ΔSH (p < 0.05). Substances with lower pH, higher titratable acidity, lower Ca, higher Pi and lower F concentrations, higher viscosity and more undersaturated solutions presented more erosive demineralisation. Different parameters in dietary substances affect erosive demineralisation in deciduous and permanent teeth, but we generally observed no differences in susceptibility to erosion between both types of teeth; only orange juice (less severe acid conditions) caused perceptible differences. We observe that permanent teeth are harder than deciduous teeth, but most substances cause no perceptible difference in erosive demineralisation in both types of teeth.

The current in vitro study evaluated the Vickers hardness number (VHN) and hardness ratio of four bulk-fill composites (VisCalor bulk; Admira Fusion x-tra; x-tra fil; and GrandioSO x-tra-Voco, Cuxhaven, Germany) to assess the risk of bacterial colonization in comparison with standard composite materials. Thirty samples were prepared for each group. The VHN of both the external (top) and internal surface (bottom) was determined with a micro-hardness tester (200 g load for 15 s), and the hardness ratio was also calculated for each sample. Subsequently, storage in an acidic soft drink (Coca-Cola, Coca-Cola Company, Milano, Italy) was performed; for each group, 10 samples were stored for 1 day, while another 10 were stored for 7 days and the remaining 10 were kept in water as controls. A significant reduction in VHN was shown for all the groups when comparing the external versus internal side (P < 0.05), although the hardness ratio was greater than 0.80, resulting in an adequate polymerization. Regarding the acid storage, all the groups showed a significant decrease of VHN when compared with the controls, both after 1 day (P < 0.05) and after 7 days (P < 0.001). All the products showed adequate depth of cure without further risk of bacterial colonization. However, acid exposure negatively affected micro-hardness values, which might promote subsequent colonization.

OBJECTIVE: To compare the result of "casein phosphopeptide amorphous calcium phosphate" with "sodium fluoride" (900 ppm) in remineralization of enamel after orthodontic debonding. METHODOLOY: This study was performed on premolars. Teeth were distributed into 3 groups A, B and C. The baseline microhardness of samples was measured. To create artificial demineralization, all samples were dipped in demineralizing solution. Surface microhardness (SMH) was re-measured for demineralization. Then, CPP-ACP was applied on teeth of gp B and NaF (900 ppm) was applied on teeth of gp C for remineralization. All teeth were cycled between deionized water and surface treatment for 12 weeks. The SMH of gp B and gp C was re-measured for remineralization. Paired t-test and Independent t-test were practiced to match MH before and after demineralization while keeping P value &lt; 0.05. One way ANOVA was practiced to match mean difference in baseline MH and after demineralization. RESULTS: The baseline SMH of enamel decrease after demineralization. After application of test materials, mean SMH increased by 230.2 VHN and 207.5 VHN respectively. The %age of SMHR reveal the recovery rate of 41.2% in CPP-ACP and 19.1% in NaF group. CONCLUSION: For treating post orthodontic demineralized lesions, a remineralizing cream having casein phosphopeptide stabilized amorphous calcium phosphate is useful with some mineral and aesthetic improvements. KEYWORDS: Casein Phosphopeptide Amorphous Calcium Phosphate (CPP-ACP), Sodium Fluoride (NaF), Surface Microhardness (SMH), Vickers Hardness Number (VHN), Rmineralization.

In this work, the synthesis, characterization and mechanical properties of sintered In situ Ni-based quaternary superalloy (Ni–9Fe–22Cr–10Co) were studied. All the Ni–9Fe–22Cr–10Co quaternary alloy specimens were consolidated via spark plasma sintering technique at temperature range and sintering pressure of 850–1100 °C and 50 MPa, respectively. The densification of sintered alloys was obtained through Archimedes technique while the micro-indentation hardness of the alloys was conducted using Vickers microhardness tester. The specimens were characterized using the optical microscope and scanning electron microscope equipped with energy-dispersive spectroscopy while the phase identification was carried using X-ray diffractometer. The microstructural characterization results revealed that the relative density, surface morphology as well as the micro-indentation hardness properties depend on the sintering temperature. In addition, it was observed that high sintering temperature aided grain refinement and bulk compaction of the material leading to high relative density. XRD analysis shows the formation of Ni–Fe and Co–Fe as the major phases. Generally, the densification and grain size of the alloys increased with increasing sintering temperature with optimum results obtained at a temperature of 1100 °C and sintered density of 98% while the maximum Vickers hardness value of 439.17 HV1 was recorded.

An assessment has been made of the primary dislocation slip systems in the explosives pentaerythritol tetranitrate (PETN) and cyclotrimethylene trinitramine (RDX) using a combination of dislocation etching and microhardness indentation techniques. Hardness measurements were made on all major habit faces as a function of temperature and load. These showed that, within the attainable temperature range (PETN 293 to 353 K, RDX 293 to 373 K) no change in hardness occurred which could be associated with the development of deformation mechanisms additional to those operating at room temperature. The hardness values of both materials were consistent with values obtained in some previous measurements (PETN 17 kg mm−2, RDX 39 kg mm−2). Solvent etching with acetone (5 sec at 274 K) proved to be an excellent method for revealing the emergent ends of growth and mechanically induced dislocations in PETN. Etching of microhardness indentations confirmed that observable slip traces comprised dislocations. These migrated up to 160μm (20g load) from the indentation point on both {110} and {101} faces. The alignments defined a {110} primary slip plane. Parallel experiments with RDX yielded evidence of highly localized slip around the indentation mark (90μm, 50g load). Two alignments of etch pits were noticeable. The better defined of these lay at the intersection of the (010) plane with the habit faces. The second could not be defined absolutely but most probably corresponds to the intersection of either the (011) or (012) plane with the surfaces. Consideration of the Burgers vectors of dislocations which are likely to glide in these planes lead us to speculate that the primary slip systems are, PETN {110} [001], and RDX (010) [001]. Such an assignment would be consistent with the relative hardness of the two materials.

This study explores the fabrication of bone scaffolds using a composite ink of poly-ε-caprolactone (PCL), polyhydroxybutyrate (PHB) and synthesized fluorapatite (FHAp) via response surface methodology optimization to achieve optimal Vickers hardness number (VHN). Characterization with X-ray diffraction confirms FHAp presence and increased crystallinity post-sintering, while Fourier-transform infrared spectroscopy reveals fundamental material interactions. Results show PCL’s softening effect at higher concentrations, PHB’s contribution to decreasing hardness and FHAp’s significant role in reinforcing the composite. Contour plots demonstrate peak hardness at lower PCL and PHB concentrations (&lt;11% wt/v) with 18% wt/v FHAp. The optimum hardness values were found at PCL, PHB and FHAp of 9.754% wt/v, 9.473% wt/v and 24.608% wt/v, respectively, yielding 185.34 VHN. These findings offer insights into optimizing composite concentrations for tailored mechanical properties crucial in bone scaffold design, advancing regenerative medicine and tissue engineering.