Cavitation Peening: A Review

The most popular surface modification technology used to enhance the mechanical properties of metallic materials is shot peening. Shot peening improves fatigue life and strength by introducing local plastic deformation pits. However, the pits increase surface roughness, which is a disadvantage for fatigue properties. Recently, cavitation peening, in which cavitation bubble collapse impacts are used, has been developed as an advanced surface modification technology. The advantage of cavitation peening is the lesser increase in surface roughness compared with shot peening, as no solid collisions occur in cavitation peening. In conventional cavitation peening, cavitation is generated by injecting a high-speed water jet into water. However, cavitation peening is different from water jet peening, in which water column impacts are used. In the present review, to avoid confusing cavitation peening and water jet peening, fundamentals and mechanisms of cavitation peening are described in comparison to water jet peening, and the effects and applications of cavitation peening are reviewed compared with the other peening methods.

Influence of whitening dentifrices and mechanical brushing on color change and surface roughness of bulk fill resins

The use of whitening dentifrices during oral hygiene may cause surface modifications such as color change (ΔE) and increase surface roughness (Ra) of composite resin. Aim: This study aimed to evaluate the effect of whitening dentifrices and mechanical brushing on color change and surface roughness of Bulk Fill (Filtek Bulk Fill - F) and (Aura Bulk Fill - A) composite resins. Materials and methods: Sixty cylindrical specimens were fabricated of each composite resin. After initial color evaluations (Konica Minolta CM-700d), with D65 standard illuminant, and the surface roughness (Surfcorder SE 1700, Kosalab), the specimens were assigned (n=10) according to the whitening dentifrice used: True White (T), Colgate Total 12 Professional Whitening (D), Luminous White Advanced (L). Specimens were submitted to mechanical brushing (10,000 cycles); new color and surface roughness evaluations were taken. Data were analyzed by ANOVA, Duncan test and Dunnet test were used to identify differences between groups (α=5%). Results: The results showed that the tooth brushing time promoted a significant increase in ΔE of the FT group. The FD group exhibited intermediate values of ΔE and was similar to all groups tested. There was a significant increase in the surface roughness of the AD and AT groups after the mechanical tooth brushing. Conclusion: The results showed no significant changes were observed in surface roughness for F groups after toothbrushing. It be concluded that the color change and surface roughness of the composite resins after toothbrushing are dependent on the interaction between the composition of the composite resin and the characteristics of the dentifrice.

Mercerization Effect on Morphology and Tensile Properties of Roselle Fibre

Natural fibres are preferred compared to synthetic fibres because of several advantages such as biodegradable, lightweight, low cost and good mechanical properties. Roselle is one of the plants found to be suitable to be used to produce natural fibres. Although natural fiber reinforced composites are becoming widely used, several weaknesses such as lack of good interfacial adhesion, low melting point and poor resistance to moisture absorption are harmful to its further acceptance. Chemical treatment is a method that can improve the interfacial bonding, stop water absorption, clean the fibre and increase surface roughness. In this study, roselle fibres were immersed in Sodium hydroxide (NaOH) with 3 different concentration (3, 6, and 9%). The results before and after treatment were compared. Scanning electron microscope was used to examine the surface morphology. Tensile properties of roselle fibre were performed to study the tensile properties. Results shows that the higher concentration of NaOH will increase the surface roughness and have higher ability to clean the fibre. For tensile properties, 6% of NaOH give the highest tensile strength. It can be concluded that, 6% of NaOH is the most suitable concentration to clean roselle fibre and while maintaining good tensile properties.

EFFECT OF AIR JET COOLING ON SURFACE ROUGHNESS AND TOOL WEAR

The main goal of this work is to investigate the use of air jet cooling on machining process. Surface roughnessand tool are chosen as parameter to analyze of air jet cooling effects; and turning process with AISI 1010 materialused in the experimental study. Surface roughness was measured for several air jet pressures and in two air jetpositions. Every five minutes of machining time, tool wear was measured until reach 30 minutes. Initial resultsshow that the use of air jet cooling with proper selection of position and pressure; possible to reduce tool wear andto increase surface roughness.

Studies of the Fiber-Matrix Interphase for Controlled Energy Absorption and Strength

Hybrid polysiloxane-based sizings with embedded silica and silica/latex nanoparticles were studied to improve Interfacial Shear Strength (IFSS) and energy absorption using the micro-droplet test method. The sizing mixture comprised of mixed polysiloxane with silica nanoparticles has been screened by varying one parameter at a time. The best mechanical performance was observed in the following concentration range: 1.0–2.0 wt% tetraethoxysilane (TES)/3-glycidoxypropyltrimethoxy silane (GPS) mixture, and 1.0–3.0 wt% Ludox® silica nanoparticles; 1.0–1.5 TES/GPS ratio, and 20 nm silica nanoparticles size. Increase of nanoparticles size leads to a decline in both strength and energy absorption, whereas chemical modification of nanoparticles surface has no significant effect compared to the baseline. The study also shows that the combination of hard (silica) and soft (latex) nanoparticles works best to maximize the strength and energy absorption. Hard particles increase surface roughness that increases interfacial strength and energy absorption during debonding whereas rubber particles contribute to improved energy absorption. Possible rational for such sizing composition/material property relationship will be discussed.

Reduced Microstructure Adhesion Provided by Gas-Expanded Liquid Deposited Gold Nanoparticles

In order to alleviate or eliminate the occurrence of stiction during the actuation of microstructures, the real contact area available for contact must be reduced. Au nanoparticles were intentionally deposited using gas-expanded liquids onto polysilicon cantilever beam arrays to increase surface roughness. The nanoparticle-coated beams were subjected to an actuation voltage of 120 V. Following actuation, the adhesion of beams was quantified by estimating the apparent work of adhesion. Au nanoparticles deposited onto these microstructures were shown to drastically reduce the effects of in-use stiction. Capillary adhesion due to condensation of ambient moisture was effectively eliminated.