Study on hardness and wear resistance of shot peened AA7075-T6 aluminum alloy

AA7075-T6 aluminum alloy samples were shot peened at various shot peening pressures in the range of 10-70 psi to study their mechanical and tribological properties under dry and mineral oil lubrication conditions. The surface roughness of the shot peened AA7075-T6 samples apparently increased with increased shot peening pressure. The best bearing surface was obtained when the shot peening process was carried out at the highest shot peening pressure of 70 psi. It was found that the increased shot peening pressure increased the hardness and decreased the wear of the shot peened samples. The shot peened samples tested under the mineral oil lubrication condition also had lower wear for higher shot peening pressures due to the combined effects of their higher surface wear resistance and better bearing surfaces. The results clearly showed that using the mineral oil lubricant during sliding apparently decreased the wear of the shot peened samples as a result of the lubricating effect of the lubricant. It could be deduced that the tribological properties of the shot peened AA7075-T6 samples under the dry and lubrication conditions were affected by the shot peening pressur

An investigation of the properties of conventional and severe shot peened low alloy steel

The effects of the conventional shot peening and severe shot peening process on the mechanical and tribological properties of shot peened AISI 4340 high strength steel were systematically investigated. Comparing with the conventional shot peened sample, the ultrafine grain surface layer with a depth of about 20 μm generated by the severe shot peening process can enhance the hardness and wear resistance of the treated material. However, deeper dimples generated by the high media velocity in the severe shot peening process resulted in a higher surface roughness, which is considered as a side effect of this method reducing the fatigue life of the material. Applying a smaller shot size with an appropriate intensity can be used to peen the severe shot peened samples to not only reduce the surface roughness and friction coefficient but also improve the wear resistance for these samples

Mechanical and Tribological Properties of Graphene Modified Epoxy Composites

The effects of graphene content on the mechanical and tribological properties of epoxy composites were systematically investigated. The stiffness, hardness and elastic modulus of the composites increased with increased graphene content due to the higher hardness and elastic modulus of graphene sheets than those of epoxy matrix. The friction and wear of the composites measured using steel ball-on-disc microtribological test decreased with increased graphene content due to the solid lubricating effect of graphene sheets. It could be concluded that the mechanical and tribological properties of the epoxy composites could be significantly influenced by the incorporation of graphene sheets

Cytotoxic Prenyl and Geranyl Coumarins from the Stem Bark of Casimiroa edulis

Phytochemical investigation of the methanolic extract of the stem bark of Casimiroa edulis afforded four coumarins. Various spectroscopic experiments were used to characterize the isolated coumarins. The structures were identified as auraptene (K-1), suberosin (K-2), 5-geranyloxypsoralen (bergamottin) (K-3), and 8-geranyloxypsoralen (K-4), based on the chemical and spectral analysis. Among these compounds, suberosin (K-2) and 5-geranyloxypsoralen (bergamottin) (K-3) were isolated for the first time from this genus, and auraptene (K-1) was isolated from this plant for the first time. Cytotoxicity of pure compound K-4 and sub-fraction MD-3 was evaluated against HeLa and T47D cell lines and moderate activity was found with an IC50 value in the range 17.4 to 72.33 μg/mL

Sesquiterpene from Myanmar Medicinal Plant (<em>Curcuma comosa</em>)

Curcuma comosa (Zingiberaceae) is widely grown in tropical and subtropical areas of Asia, like Thailand, Indonesia, Malaysia, and Myanmar. In Myanmar, the rhizome of Curcuma comosa is called Sa-nwin-ga, and local people had used it as a traditional medicine for stomach ache, diabetes mellitus, and hypertension. This species produces secondary metabolites of phenolic and nonphenolic groups. Phenolic groups like diarylheptanoids and flavonoids. While nonphenolics are terpenoids, especially sesqui- and monoterpenes. In this chapter, the group of sesquiterpene compounds from Curcuma comosa starts from the isolation technique, followed by the elucidation of the molecular structure, and their activity tests have been discussed

Coumarins from Myanmar edible fruit tree (Casimiroa edults)

Abstract: This research expresses the phytochemical study from the Myanmar edible fruit tree, Casimiroa edulis (Rutaceae). The result revealed that the isolation and identification of two furanocoumarins (bergapten 1 and isopimpinellin 2) from the stem bark of this plant. Their molecular structures were elucidated and identified by using NMR spectroscopy in combination with IR, UV and HRMS spectra data, respectively. Furthermore, these two compounds were investigated for their anti-diabetic activity. According to the result, bergapten 1 and isopimpinellin 2 are not essentially good for anti-diabetic activity. This is the first report of two furanocoumarins from the Myanmar edible fruit tree

Structure and electrochemical behavior of nitrogen doped diamond-like carbon thin films with or without platinum and ruthenium doping

Human activities have released toxic metals such as Zn, Pb, Cd, Cu and Hg, etc. into the environment. Nowadays, the presence of toxic metals in the aquatic ecosystem implicates directly to biota and indirectly to human beings. Therefore, fast detection and determination of toxic metals in aqueous solutions are a tough challenge for analysts. Diamond-like carbon (DLC) is a type of carbon, which consists of both sp2 (graphite like) and sp3 (diamond like) bonds, and an environmentally friendly material. In addition, DLC films can be produced at room temperature and achieve similar properties to those of diamond films, so they have been explored as electrode materials for heavy metal tracing. However, high electrical resistivity of DLC films has confined their electrochemical applications. DLC films used as electrodes for electrochemical applications must be conductive. Nitrogen is an effective donor in DLC films because of its five valance electrons. Therefore, nitrogen is used as a dopant for making conductive nitrogen doped diamond-like carbon (N-DLC) films. However, an incorporation of nitrogen in DLC films lowers the corrosion resistance of DLC films by degrading sp3-bonded cross-linking structure through increased sp2 bonds though it can increase the electrical conductivity of the films. Poor corrosion resistance of N-DLC films can affect the electrochemical performance of the films such as sensitivity, long-time response stability, durability and repeatability.DOCTOR OF PHILOSOPHY (MAE

EVALUATION OF ANTIOXIDANT, ANTIDIABETIC, AND CYTOTOXIC ACTIVITIES OF THE SECONDARY METABOLITE COMPOUNDS FROM THE THREE PLANTS SPECIES COLLECTED IN TAUNGGYI REGION (MYANMAR)

The present study describes the isolation and structure elucidation of secondary metabolite compounds from Myanmar medicinal plants. Thirteen known compounds were identified from the stem bark of Casimiroa edulis, four were discovered for the first time from this genus. At the same time, three known sesquiterpenes, and a phenylpropanoid were isolated from the rhizomes of Curcuma comosa and Asparagus racemosus. Their structures were identified by comparison of experimental and published spectroscopic data. Some isolated compounds were evaluated for their antioxidant activity using the DPPH assay. All of them were showed no significant activity. Compounds KNWT-1 to KNWT-7, KNWT-14, 15, and 16 were evaluated for their cytotoxicity against HeLa and T47D cell lines. KNWT-2, 7, 15, 16 showed moderate cytotoxic activity with IC50 value in the ranging from 10.93-77.18 g/mL. Although all isolated compounds were known, this was the first phytochemical study from Taunggyi medicinal plants

Thermal, mechanical and tribological properties of polycarbonate/acrylonitrile-butadiene-styrene blends

Polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) were blended by varying ABS content. The thermal, mechanical and tribological properties of the PC/ABS blends were systematically characterized. Increasing ABS content in the PC/ABS blends decreased thermal stability of the blends, as a result of the lower thermal stability of the ABS than that of the PC. Although the tensile strength of the PC/ABS blends apparently decreased with increased ABS content, the PC/ABS blend with 10 wt% of ABS had the highest tensile strength, because of improved processability of the blend. The friction and wear of the ABS measured against a steel ball of 6 mm in diameter were higher than those of the PC. As a result, a higher ABS content in the PC/ABS blends resulted in higher friction and wear of the blends. The scratch results showed that scratching with a 5 mm steel ball generated a scratch with a shorter length and lower depth on the PC than on the ABS, which indicated better scratch resistance of the PC. Therefore, the PC/ABS blend with 50 wt% of PC had better scratch resistance than the ABS, due to the influence of the PC embedded in the blend

Tribological behavior of polyurethane immersed in acidic solution

Polyurethane (PU) samples were immersed in a 1 M HCl solution for different durations from 0 to 90 days to investigate the influence of immersion time on the tribological performance of the samples. The effects of thermal, mechanical, and surface properties of the PU on its tribological performance were also investigated with respect to immersion time. It was found that the friction coefficient of the PU measured against a steel ball significantly decreased with increased immersion time due to the lubricating and cooling effects of absorbed water in the PU during the immersion. The decreased friction of the PU led to the improved wear resistance of the polymer, though the mechanical strength of the PU was reduced by the prolonged immersion due to the increased plasticization of the polymer. The experimental results clearly indicated that the immersion of the PU in the acidic solution for a certain period significantly influenced the tribological performance of the polymer