Mean Hardness Values Research Articles

Discriminating power of selected physical properties of seeds of various rapeseed (Brassica napus L.) cultivars

In this study, the seeds of open-pollinated winter rapeseed cultivars, hybrid winter rapeseed cultivars, open-pollinated spring rapeseed cultivars and hybrid spring rapeseed cultivars were investigated. The physical, optical, mechanical, geometric and image texture properties of rapeseeds were compared. Statistical models were developed based on the analyzed parameters to discriminate between seed groups. Most parameters effectively discriminated between cultivars of winter and spring rapeseed, including true density, porosity, L*, a*, b*, and spectral values at 400 nm, 470 nm, 500–530 nm, 560–620 nm, 640–650 nm and 690 nm. Four homogeneous groups were identified based on linear dimensions: F (surface area), S (width) and shape factors W6 (circularity ratio), Rb (Blair-Bliss coefficient) and W13 (roundness). No statistically significant differences in the mean values of hardness or area under the force-displacement graph were observed between seed groups. The model developed based on image texture variables from channel Y (luminance) was characterized by the highest discrimination accuracy of 82–87%. The experimental groups were classified with 89–92% accuracy in the model combining the best variables from each group of physical parameters. Total classification accuracy in neural networks reached 75% for a validation set comprising geometric properties and 91–92% for a validation set containing physical characteristics.

Interaction among Nutritive, Textural, and Sensory Properties of Rabbit Sausages

The nutritive, textural, and sensory properties of commercial fresh rabbit sausages and their interactions were evaluated. The mean contents of moisture, protein, fat, ash, and carbohydrate were 43.89 ± 1.66%, 9.82 ± 2.71%, 22.37 ± 1.7%, 2.99 ± 0.10%, and 20.94 ± 3.05%, respectively. Conversely, the mean values of hardness, adhesiveness, springiness, cohesiveness, gumminess, and chewiness were 103.36 ± 3.48 N, −4.54 ± 1.58 N s, 3.38 ± 0.67 mm, 0.15 ± 0.03, 16.07 ± 3.20 N, and 55.73 ± 20.44 N mm, respectively. The moisture and protein contents showed significant negative correlation while three remaining nutritive properties showed significant positive correlation with textural properties (P<0.05 for all parameters). The score for nonparametric ranking of sensory properties like appearance/colour, flavour, juiciness, and tenderness ranged from 28.28 to 38.78, 29.41 to 35.91, 30.06 to 37.38, 26.75 to 40.69, and 29.03 to 36.75, respectively. In conclusion, rabbit sausages formulated with low quantities of moisture and protein result in hard sausages with low acceptability by sensory panellist. To improve the sausages, it is recommended that processors develop an optimal formulation.

Evaluation of Isolated Impact of Trans Fatty Acids on Short Dough Product

AbstractIn this study, the effects of trans fatty acids (TFAs) on rheological properties of dough (elastic moduli (G’), loss moduli (G”), complex modulus (G*)) and textural properties of dough and cookie (hardness) were studied. Two different groups of fat samples having different TFA composition but similar solid fat content (SFC) were prepared. Samples of the first group (group 1) had TFA between 0.0 and 56.23 %, while the samples of the second group (group 2) contained trans isomers ranging from 0.0 to 44.40 %. Texture measurements of different doughs and cookies prepared with different fat samples were performed. Texture measurements indicated that hardness values of doughs increased from 3950 ± 420 to 5498 ± 506 g in group 1 and 4700 ± 501 to 6787 ± 369 g in group 2 with increased amounts of TFAs. A particularly high, almost three‐fold increase in complex modulus values was observed in the dough samples containing the highest TFA levels compared with samples containing 0.0 % TFA. Although not significantly different, mean hardness and relative sound intensity values of cookies displayed an initial decreasing trend and then both parameters had maximum values when the TFA content was at maximum in both groups.

Evaluating the Effects of Medical City Wastewater on Water Quality of Tigris River

Physiochemical characteristics of Tigris river water were examined monthly to assess the possible impacts of wastewater discharged from Baghdad Medical City hospital for the period from October 2012 to September 2013. Four sites were selected during this study; the first was located about 500 meters before the Medical City Complex to act as control. The second was the discharge point of Medical City discharge. The third was almost 500 meters away south the second site, and the forth was located about 1500 meters away from the third site. Water samples were collected monthly from these four sites, at depth of approximately 10-20 cm of water surface and subjected for determination several physiochemical variables such as temperature, pH, Electrical Conductivity (EC), turbidity, DO, COD, BOD, total hardness, chlorides and nitrate. The obtained results showed that air and water temperature mean values varied from 13.0 ± 2.86 to 31.0 ± 5.28 C ° and from 12.0 ±3.12 to 29.0 ±4.33 C° respectively. Also, mean turbidity values were found to range from 10.0±5.64 to 138.0±14.58 NTU while EC mean value was situated between 621.0±44.67 µS/cm and 1549.0±162.83µS/cm. However, this study has found that the mean values of EC, turbidity, chemical oxygen demand, chlorides, total hardness, and nitrate in site 2 (discharge point) were significantly (P≥0.001) higher than those of other sites during the study period. In general, it was found that Tigris river water tends to be alkaline with pH mean values ranging from 7.0 ± 0.42 to 8.8± 0.68 while DO mean values varied from 2.5±0.62 to 9.6±0.94 mg/l. The BOD mean values were found to range from1.7±0.26to5.0 ±1.86 mg/l, while COD mean values varying from56.6±8.98 to688.6±112.42 mg/l. In addition, the current results have shown that total hardness mean values were very high and ranged between 235.0±24.56and 530.0±78.68 mg/l while chlorides mean values ranging from45.0±10.44 to 143.6±21.26 mg/l, but nitrate mean values were found with the range of 2.5±0.86and 28.8±4.98 mg/l. These results, however, have been found to be mostly exceeding those of the permissible limits for Iraqi and WHO standards for protecting surface water.

Characterization of the interface between cast-to Co-Cr implant cylinders and cast Co-Cr alloys

Statement of problemThe affordable Co-Cr cast alloy should provide an ideal interface with prefabricated cast-to cylinders from the same alloy family. The alloy microstructures should be maintained up to the interface, and porosities and reaction regions should be absent, and sufficient bond strength between alloys should be provided. PurposeThe purpose of this in vitro study was to evaluate the metallurgical interfacial compatibility between Co-Cr dental casting alloys and a prefabricated Co-Cr dental implant cast-to-cylinder. Material and methodsA Co-Cr alloy was cast to Co-Cr implant cylinders. Specimens were cross-sectioned longitudinally and divided into as-cast and heat-treated groups. The microstructures of specimens were evaluated by optical and scanning electron microscopy. The elemental composition of as-received prefabricated implant cylinders and diffusion characteristics of cast interfacial regions were determined by energy dispersive x-ray spectroscopy. Vickers hardness values were defined across the interface on cast specimens and for the as-received implant cylinders. ANOVA and Tukey honest significant differences tests were used for the statistical evaluation of hardness values. ResultsNo significant reaction regions or porosity were present in the interface. Microstructural aspect and interdiffusion indicated a metal-metal bond between the Co-Cr implant cylinder and cast alloy. Mean hardness values demonstrated a significant rise across the interface (373.5 ±12.8; 363.8 ±12.6, respectively) from the wrought cylinder (338.6 ±10.5; 329 ±9.7, respectively) to the cast alloy (399.8 ±7.4; 392.3 ±10.3, respectively) for the as-cast and heat-treated conditions, respectively. ConclusionsCo-Cr casting alloy cast on to prefabricated Co-Cr implant cylinders provided interfaces which appear to fulfill the requirements of the established criteria.

Comparative evaluation of hardness of four provisional restorative materials: An in vitro study

Purpose: The present in vitro study was conducted to evaluate and compare the hardness of four commercially available provisional restorative materials. Materials and Methods: The groups in the study were Protemp 4 group, Integrity group, Systemp C and B group, and Structure 2SC group ten specimens of dimensions 64 mm × 3.5 mm × 12.3 mm × 65 mm × 13.5 mm of each material was made. Moreover, a total of forty specimens were used in the study and were tested for micro hardness and the values obtained were evaluated. One-way analysis of variance was applied to the data, and post hoc test was carried out for intercomparison between groups. Results: The findings showed that mean hardness value of Protemp 4 which had the highest value of 65.990 Vickers hardness number (VHN) followed by integrity 60.300 VHN followed by 57.210 VHN in Structure 2SC and least of 56.520 VHN in System C and B group and it was found to be statistically significant. The post hoc test revealed there was evident between Voco (Structure 2SC) and Systemp C and B materials; there was no statistical difference in mean hardness of the material in comparison with Protemp 4 and Integrity. Conclusion: Protemp 4 showed the highest hardness followed by integrity, Structure 2SC and Systemp C and B.

Effect of Food Simulating Agents on the Hardness and Bond Strength of a Silicone Soft Liner to a Denture Base Acrylic Resin.

Statement of the Problem:Bonding failure between acrylic resin and soft liner material and also gradual loss of soft liner resiliency over time are two impending challenges frequently recognized with a denture base embraced with a resilient liner. Since patients drink various beverages, it is crucial to assess the influences of these beverages on physical characteristics of soft liners.Purpose:This in vitro study envisioned to assess the influence of food simulating agents (FSA) on the hardness of a silicone soft liner by employing a Shore A durometer test and also evaluate its bond strength to a denture base resin by using tensile bond strength test.Materials and Methods:To test the hardness of samples, 50 rectangular samples (40 mm × 10 mm × 3 mm) were prepared from a heat-polymerized polymethyl methacrylate (Meliodent). Mollosil, a commercially available silicone resilient liner, was provided and applied on the specimens following the manufacturer’s directions. In order to test tensile bond strength, 100 cylindrical specimens (30 mm × 10 mm) were fabricated. The liners were added between specimens with the thicknesses of 3 mm. The specimens were divided into 5 groups (n=10) and immersed in distilled water, heptane, citric acid, and 50% ethanol. For each test, we used 10 specimens as a baseline measurement; control group. All specimens were kept in dispersed containers at 37ºC for 12 days and all solutions were changed every day. The hardness was verified using a Shore A durometer and the tensile bond strength was examined by an Instron testing machine at a cross-head speed of 5 mm/min. The records were analyzed employing one-way ANOVA, Tukey’s HSD, and LSD tests.Results:The mean tensile bond strength ± standard deviation (SD) for Mollosil was as follows for each group: 3.1 ± 0.4 (water), 1.8 ± 0.4 (citric acid), 3.0 ± 0.4 (heptane), 1.2 ± 0.3 (50% ethanol), and 3.8 ± 0.4 (control). The hardness values for each group were: 28.7 ± 2.11 (water), 33.2 ± 2.82 (citric acid), 39.2 ± 4.8 (heptane), 32.3 ± 3.56 (50% ethanol) and 22.2 ± 2.08 (control). Mean values for hardness indicated that all of the food simulating agents significantly increased hardness of the Mollosil soft liner compared to the control group (p<0.05). The results of tensile bond strength depicted that water and FSA decreased the bond strength of the soft liner -denture base resin compared to the control group and it was statistically significant (p<0.05).Conclusion:The food simulating agents could influence the mechanical properties of silicone soft liners; hence, clinicians should inform their patients concerning their possible adverse effects and complications.

Quality optimization in briquettes made from rice milling by-products

In order to produce briquettes that meet the needs of consumers, different combinations of raw materials and methods were used to produce rice-husk briquettes using a locally fabricated multi-piston press. Particle size, husk–bran ratio, drying method, and water temperature for briquetting were the main influencers of the hardness of rice-husk briquettes at constant pressure. The briquetting process increased the density of rice husk from 120 to 600kg/m3. The average time for making nine briquettes (loading, compressing, ejection, and transfer to drying tray) was 3.6min (150 briquettes/h) using the locally fabricated piston press. Briquettes produced using fine particles (<0.3mm), hot (97°C) water, husk–bran ratios of 0:1, 1:2, 1:1, 1:0, 2:1, and dried in the sun for 21days had mean hardness values of 132, 89, 76, 62, and 31N. Four types of fuel briquettes were produced: husk–bran–palm press fiber (HBF), husk–bran–palm press sludge (HBS), husk–bran only (HBO), and husk–biochar–clay (HBC). The four types of briquettes recorded shorter start-up time (<5min) than charcoal (10min). The average flame temperatures of HBF, HBS, and HBO during the first 20min were higher (898°C) than the average temperature of charcoal (546°C). The characteristics of HBF and HBO briquettes provide the best option for consumers, especially those in the rice parboiling industry, as these briquettes recorded the following values for hardness (170 and 101N, respectively), start-up time (2 and 3min), burning rate (126 and 145g/min), specific fuel consumption (121 and 136g/l), and flame temperature (684°C and 728°C). It was concluded that briquettes could be produced from rice-milling by-products with acceptable quality using this affordable technology.

Parameter Design for Hardness of Metal Filled Epoxy Matrix

Epoxy is blended with metal fillers to enhance its performance and application for tooling. Material used contains aluminium particles (Rencast CW47), blended with brass separately. Brass is added into the matrix based on 10%, 20% and 30% of the epoxy mix weight ratio. Using Taguchi method, controls factor such as pre-curing temperature (A), filler percentage (B), degassing time (C), curing time (D) and post curing temperature (E) are selected parameters in order to determine optimum conditions. Noise strategy is adopted for material cooling via ambient (N1) and oven temperatures (N2), which gave different hardness values of the epoxy composite. Optimum parameters were decided based on the prediction of S/N ratio, where A = Room temperature, B = 20%, C = 60 minutes, D = 14 hours and E = 1800C. The most significant control factor is de-gassing time for both fillers, and percentage of filler to weight ratio of epoxy mixture is optimum at 20%. It was found that brass gave higher mean hardness values, (Hv = 24.1) compared to copper (Hv = 22.7) and aluminium filled epoxy (Hv = 22.3) based on the prediction run, and suitable as additional filler to improve the surface toughness of epoxy matrix as inserts. Confirmation run was conducted according to the optimum parameters and validated the gain values for brass at 7.98. Fillers enhance the mechanical properties of epoxy matrix by increasing hardness of mould cavity and core. This work helped to design the best control factors to produce optimum hardness conditions for filled epoxy matrix.

Hydrothermal Degradation Behavior of Y‐TZP Ceramics Sintered by Nonconventional Microwave Technology

Different factors such as the characteristics of starting powders, their processing, the sintering technique and the final sintering temperature were assessed with the goal to improve the low‐temperature degradation (LTD) resistance of 3Y‐TZP materials without compromising on the mechanical properties. The degradation of hydrothermally treated specimens was studied by AFM, nanoindentation technique, micro‐Raman spectroscopy, and electron microscopy. 3Y‐TZP previously prepared in laboratory by colloidal processing, and sintered by microwave method at low temperature (1200°C) led to excellent mechanical and LTD resistance, as compared to dental restorations based on Y‐TZP commercial material. In the former, the presence of m‐phase was almost nonexistent even after 200 h of exposure to LTD conditions and the initial mechanical properties were maintained, giving 16 and 250 GPa mean values for hardness and Young's modulus, respectively. The influence of the fast‐technology by microwave heating is presented with a nonconventional sintering method to fabricate 3Y‐TZP ceramics for dental application with very high resistance against LTD and optimized mechanical properties.

Study Regarding the Influence of Polymerization Mode of Light Unit on Surface Microhardness of Composite Resins

The aim of the study was to compare the surface microhardness of composite resins polymerized in different mode of light unit. Three commercial composite resins: Charisma (Heraeus Kulzer Co.), Filtek Z 250 (3M ESPE Co.) and G-aenial Anterior (GC Company Co.), were used in this study. Fifteen samples of each material were obtained by placing the composite resin in plastic rings having 2 mm high and 6 mm inner diameter. All composite samples were cured using blue light-emitted diode G 0010 (SKI, China). Five samples were cured using ramp mode of the light unit, five samples were cured using single light: high intensity (constant) mode and five samples were cured using pulse mode. The samples were finished and polished and then stored in distilled water, at room temperature for 48 hours. The samples were subjected to microhardness evaluation using microhardness tester (Micro-Vickers Hardness System CV-400DMTM, CV Instruments Namicon). A 50 g load was applied through a Vickers indenter. For each sample three indentations were made in different areas of the sample and the value of Vickers hardness was calculated as a mean result of the three recordings. Statistical Mann-Whitney U test and Kruskal-Wallis test were used to compare the values of surface hardness. Polymerization of all three composite resins using pulse mode leaded to significantly lowest mean hardness values and single light high intensity mode to the highest values. Filtek Z250 composite resin showed the highest microhardness mean values in all three polymerization mode and Charisma the lowest values. Surface microhardness of composite resins is influenced by different modes of light unit. Single light high intensity mode of polymerization leaded to the highest values of microhardness, followed in descending order by ramp and pulse mode. The best results regarding the surface microhardness was recorded for Filtek Z250composite resin, followed in descending order by G-aenial Anterior and Charisma.

Comparison Study on Casein Phosphopeptide-Amorphous Calcium Phosphate Paste and Fluoride Gel on Remineralization of Demineralized Enamel Lesions

Objective: Tooth surface undergoes continuous remineralization and demineralization. The aim of this study was to compare the effect of Caseinphosphopeptide-amorphous calcium phosphate (CPPACP) paste and Fluoride gel on the microhardness of demineralized enamel lesions. Methods: Frothy eight specimens of premolar teeth were chosen and randomly divided to 4 groups of 12. After the initial measurement of micro-hardness the specimens were immersed in demineralizing solution for 4 day and then the measurements were recorded again. Two groups (GL and G3) were treated with CPP-ACP and Fluoride gel respectively according to manufacturer’s instruction. Two other groups (G2 and G4) were treated with CPP-ACP and fluoride gel every week for three months. After the treatments all specimens were taken into PH-cycling and the microhardness for each one were measured again. For data analysis, the Repeated Measures ANOVA test and the LSD tests were performed. In each group the percentage of micro-hardness recovery was measured. Results: Repeated Measures ANOVA and LED Test showed that the mean value of hardness was significantly decreased after demineralization in all groups (p=0.01). There was no significant difference in mean hardness value in groups (GL, G3) after treatment (p=0.1, p=0.12) In groups (G2, G4) the mean hardness value were significantly increased (p<0.0001, p=0.1). It is noticeable that the CPP-ACP was significantly more efficient than the fluoride gel. Conclusion: CPP-APC paste and fluoride gel both increase the micro-hardness of enamel when administrated for long time and repeated application.

Surface analysis of alumina ceramic exposed to shock waves produced by plasma expander

Material surface treatment by plasma expander is relatively recent. Plasma expander is based on the inverse pinch effect. The shock waves produced by plasma expander may also promote modifications in ceramic materials exposed to the expander. These modifications are mainly made by ablation phenomenon. This work was intended to verify the shock wave effects on the ionic ceramic samples with high dielectric constant. The alumina ceramic samples were formed by both uniaxial and isostatic pressing methods and sintered at 1650 °C. They were also produced with addition 0.15 wt% of MgO in order to obtain a high densification. The ceramic samples were divided in groups and exposed to 700, 1000 and 1440 pulses during 20 min. These pulses were generated by nitrogen plasma expander at 13.0 Pa and 6 kV. After plasma exposure, there was an increase in roughness parameter values of Al2O3 ceramic surface. The treatment by plasma expander did not modify the hydrophilic characteristic of the alumina ceramic samples. The results of hardness test presented no significant changes on hardness mean values.

Evaluation of color and textural properties of chicken meat momos

Purpose – The aim of the present study was to evaluate the textural, color, sensory and microbiological properties of meat momos. Design/methodology/approach – Three different levels of boiled chopped chicken meat, namely, T1 (45 per cent chicken meat), T2 (50 per cent chicken meat) and T3 (55 per cent chicken meat) were taken as filling material for preparation of meat momos. Findings – There was no significant difference in lightness (L*), redness (a*) and yellowness (b*) values. The mean hardness, adhesiveness, springiness, cohesiveness, gumminess and chewiness values also differed non significantly. Salmonella and Coliform were not detected in freshly prepared chicken momos. No significant difference was observed for total plate count and the sensory attributes except meat flavor intensity. The overall sensory scores were found to be significantly (p &lt; 0.05) higher for T2 treatment than other two treatments. Research limitations/implications – The trials are needed to carry out further study to evaluate storage stability of developed momos. Originality/value – Meat momos available in the market are not standardized and do not have a defined nutrient content. The standardization and quality evaluation of chicken meat moms can provide the platform for their commercialization at industrial level.

Characterization of a wollastonite glass-ceramic material prepared using sugar cane bagasse ash (SCBA) as one of the raw materials

Glass-ceramic material prepared with sugar cane bagasse ash as one of the raw materials was characterized to determine some important properties for its application as a coating material. X-ray diffraction patterns showed that wollastonite-2M (CaSiO3) was the major glass-ceramic phase. The Rietveld method was used to quantify the crystalline (60wt.%) and vitreous (40wt.%) phases in the glass-ceramic. The microstructure (determined by scanning electron microscopy) of this material had a marble appearance, showing a microporous network of elongated crystals with some areas with dendritic, feather-like ordering. Microhardness data gave a mean hardness value of 564.4HV (Vickers-hardness), and light microscopy disclosed a greenish brown colored material with a vitreous luster.

Evaluation of an induction‐assisted friction stir welding technique for super duplex stainless steels

The microstructure changes and the mechanical properties of a friction stir welded (FSW) super duplex stainless steel (GX2CrNiMoN26‐7‐4) were analyzed. A PCBN tool was used to weld 5‐mm‐thick plates at a constant rotational speed of 300 rpm, at 100 and 200 mm/min, under two different conditions: conventional FSW and Induction‐Assisted FSW (IA‐FSW). Preheating technique allows welding with a reduction in forge forces close to 31% at the same welding speed, or doubling speed (200 mm/min) at the same axial force, obtaining sound welds. No sigma phase was detected in the welds, and the clear grain size reduction led to an increase in mean hardness value and the tensile strength of the stir zone. Ferrite percentage was found to be between 50 and 70% through the welds. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Effects of curing mode and moisture on nanoindentation mechanical properties and bonding of a self-adhesive resin cement to pulp chamber floor

ObjectiveThis study aimed to investigate the effect of dentin surface moisture and curing mode on microtensile bond strength (MTBS) and nanoindentation characteristics of a self-adhesive resin cement. MethodsForty-four extracted human molars were distributed into four groups according to dentin surface moisture (dry or wet) and curing mode of the resin cement (light or chemical). Clearfil SA Cement (Kuraray Noritake Dental, Japan) was used for cementation of composite cores to the pulp chamber dentin. The specimens were sectioned into beams for MTBS test at the pulpal floor. Nanoindentation hardness and creep of the cement layer were measured under 100mN load with 30s hold segment. Data were statistically analyzed using two-way ANOVA and Weibull distribution of MTBS (α=0.05). ResultsMoisture, curing mode or their interaction did not significantly affect mean MTBS values that ranged 17.6–22.6MPa (p>0.05); however, the lowest characteristic strength was found in moist chemically cured group. Hardness ranged 437–512MPa, and was not affected by the experimental factors (p>0.05). Nanoindentation creep ranged 9.3–10.9% with the chemically cured groups showing the highest values, indicating lower cross-linking and deformation resistance of their polymer network. SignificanceAdditional moisture on dentin surface did not contribute to adhesion of the anhydrous self-adhesive resin cement to dentin. Light-curing, despite attenuation through the composite core, was beneficial and improved nanoindentation creep resistance of the cement. The difference was not, however, reflected in the mean bond strength or hardness values.

Mechanical properties of dental tissues in dolphins (Cetacea: Delphinoidea and Inioidea)

(1) Mammalian teeth play a major role in food acquisition and processing. While most mammals are heterodont and masticate their food, dolphins are homodont with simplified tooth morphology and negligible mastication. Understanding mechanical properties of dental tissues in dolphins is fundamental to elucidate the functional morphology and biomechanics of their feeding apparatus. This paper aims to study the hardness and elastic modulus of enamel and dentine in dolphins. (2) Teeth of 10 extant species (Inioidea and Delphinoidea) were longitudinally sectioned, polished and mounted in a UMIS nanoindenter. Indentations were performed from dentine to outer enamel. Hardness and elastic modulus were calculated using the Oliver–Pharr method. (3) Mean values of hardness and elastic modulus were similar on buccal and lingual surfaces. While dentine hardness was statistically similar among species, enamel hardness varied from 3.86GPa (±0.4) in Steno bredanensis (rough-toothed dolphin) to 2.36GPa (±0.38) in Pontoporia blainvillei (franciscana). For most species, there was a gradational increase in hardness values from inner to outer enamel. Enamel and dentine elastic modulus values clearly differed among species. In enamel, it ranged from 69.32GPa (±4.08) in the rough-toothed dolphin to 13.51GPa (±2.80) in Stenella coeruleoalba (striped dolphin). For most species, elastic modulus values were highest at inner and outer enamel. (4) Differences in mechanical properties between species, and within the enamel of each species, suggest functional implications and influence of ultrastructural arrangement and chemical composition.

The effect of remelting various combinations of new and used cobalt-chromium alloy on the mechanical properties and microstructure of the alloy

Remelting previously cast base metal alloy can adversely affect the mechanical properties of the alloy and necessitates addition of new alloy. To study the effect of remelting different combinations of new and used cobalt-chromium (Co-Cr) alloy on its mechanical properties and microstructure. Using induction casting, 24 tensile test specimens were prepared for eight different combinations of new and used Co-Cr alloy. The test specimens were assessed for yield strength and percentage elongation. Microhardness was evaluated using Vickers's hardness tester. The tensile testing was carried out on a 50 kN servo-hydraulic universal testing machine. Microstructure analysis was done using an optical photomicroscope on the fractured samples after acid etching. The mean values (±standard deviation) and coefficient of variation were calculated. Student's 't' test was used for statistical analysis. Statistical significance was assumed at P=.05. The mean yield strength of eight different combination groups were as follows: group A: 849 MPa, group B ₁ : 834 MPa, group B ₂ : 915 MPa, group B ₃ : 897 MPa, group C ₁ : 874 MPa, group C ₂ : 859 MPa, group D ₁ : 845 MPa, and group D ₂ : 834 MPa. The mean percentage elongation for the different groups were as follows: group A: 7%, group B ₁ : 7%, group B ₂ : 8%, group B ₃ : 7%, group C ₁ : 8%, group C ₂ : 7%, group D ₁ : 7%, and group D 2 : 8%. The mean hardness values were as follows: group A: 373 VHN, group B ₁ : 373 VHN, group B ₂ : 346 VHN, group B ₃ : 346 VHN, group C ₁ : 364 VHN, group C ₂ : 343 VHN, group D ₁ : 376 VHN, and group D ₂ : 373 VHN. Repeated remelting of base metal alloy for dental casting without addition of new alloy can affect the mechanical properties of the alloy. Microstructure analysis shows deterioration upon remelting. However, the addition of 25% and 50% (by weight) of new alloy to the remelted alloy can bring about improvement both in mechanical properties and in microstructure.

Hardness cartography to increase the nanoindentation resolution in heterogeneous materials: Application to a Ni-based single-crystal superalloy

Statistics on nanoindentation experiments performed on a fourth-generation Ni-based single-crystal superalloy reveal a bimodal hardness distribution, with two mean hardness values only 2.5% away from each other. Using a hardness cartography technique combined with the statistical analysis proved that the hardness values are not randomly distributed but correspond exactly to the dendrites and the interdendritic regions. In this context, hardness cartography is shown to push back the resolution limit of the nanoindentation test.