Surface to Through-Wall Crack Transition Model for Circumferential Cracks in Pipes

In the present paper, finite element analyses were performed to update and also extend the applicable ranges of the existing KI and COD solutions for non-idealized through-wall cracks. Then, a surface to through-wall crack transition model was proposed based on these solutions. The proposed model provides a criterion which determines when the final surface crack should transition to a through-wall crack. It also provides a criterion to determine the two crack lengths (at the inner and outer diameter surfaces) of the initial non-idealized through-wall crack. Furthermore, crack growth of non-idealized through-wall cracks can be simulated by using the proposed method. Finally, the proposed model was verified by demonstrating that it can well predict the surface to through-wall transition behavior when compared to the natural crack growth simulations.

Development of Magnetic-Field Assisted Finishing (MAF) Process for Chromium-Alloyed Low Carbon Steel Sheet Metal

Magnetic-Field Assisted Finishing (MAF) is a polishing process that utilizes a slurry mixture made of ferrous and abrasive particles in a liquid medium, known as a brush. The brush attached to a magnetic tool directly interacts with the surface of a workpiece and removes any imperfections and defects in the surface giving a smooth and nice surface finish. In this study, two distinct MAF setups were applied to the surface of chromium alloyed low carbon steel sheets to achieve the surface finish. The preliminary studies were conducted on one setup to understand the polishing behavior of the sheets and the other setup was designed to polish larger areas of the sheets to mimic the practical sheet producing environment. The effect of processing conditions such as types and sizes of abrasives, brush composition, and finishing time to attain the final surface roughness of the sheets was studied. The brush with the weight composition of 4:1:1.5 (iron: 3 μm black ceramic: silicone) was found to be the optimal condition for polishing the sheet metal samples. The optimal conditions obtained were applied to the larger scaled experimental setup. The final surface roughness of 38 nm and 220 nm were achieved in these experimental setups, respectively.

Analysis of Causes of Baby Stroller Construction Damage

The paper deals with the complaint between the manufacturer and the customer. The object of the dispute is a damaged stroller construction made by welding Al-Mg-Si aluminum alloy profiles with the final surface layer produced by anodic oxidation. The aim of the analysis is to identify clearly the causes of breaking the aluminum structure using fractographic and metallographic techniques.

Influence of Polishing Systems on Surface Roughness of Composite Resins: Polishability of Composite Resins

SUMMARY Objectives: The objective of this in vitro study was to compare, with a threshold value of 200 nm, the surface roughness obtained when using 12 different polishing systems on four different composite resins (microfill, nanofill, and two nanohybrids). Methods and Materials: A total of 384 convex specimens were made using Durafill VS, Filtek Supreme Ultra, Grandio SO, and Venus Pearl. After sandblasting and finishing with a medium-grit finishing disc, initial surface roughness was measured using a surface roughness tester. Specimens were polished using 12 different polishing systems: Astropol, HiLuster Plus, D♦Fine, Diacomp, ET Illustra, Sof-Lex Wheels, Sof-Lex XT discs, Super-Snap, Enhance/Pogo, Optrapol, OneGloss and ComposiPro Brush (n=8). The final surface roughness was measured, and data were analyzed using two-way analysis of variance. Pairwise comparisons were made using protected Fisher least significant difference. Results: There were statistical differences in the final surface roughness between polishing systems and between composite resins (p<0.05). The highest surface roughness was observed for all composite resins polished with OneGloss and ComposiPro Brush. Enhance/Pogo and Sof-Lex Wheels produced a mean surface roughness greater than the 200-nm threshold on Filtek Supreme Ultra, Grandio SO, and Venus Pearl. Data showed that there was an interaction between the composite resins and the polishing systems. Conclusions: A single polishing system does not perform equally with all composite resins. Except for Optrapol, multi-step polishing systems performed generally better than one-step systems. Excluding Enhance/Pogo, diamond-impregnated polishers led to lower surface roughness. Durafill VS, a microfill composite resin, may be polished more predictably with different polishers.

Analysis of the Assembly Joint at Deformation of Matched Objects

Maintenance is a system-specific activity that the purpose of which is to maintain or to increase time, performance and quality of machines and equipment use. The demand for technological equipment is still rising, resulting in often complicated and lengthy repairs. It is necessary to analyze the tools used in the construction of assembly joints and to describe the deficiencies that may occur during assembly. When contacting a material tool using a particular technology and assembly, it is necessary to analyze the impact on the final surface quality of the material.

Fabrication of SiC Off-axis Aspheric Mirror by Using Robot Polishing

Two silicon carbide (SiC) lightweight off-axis aspheric mirrors were fabricated by using robot polishing technology. One is a primary mirror with dimension 380mm×328mm, the other is a tertiary mirror with dimension 294mm×238mm. The robot polishing technology is the combination of CCOS technology and a 6-axises industrial robot. The setup of robot polishing system is discussed, and the mirror aspheric grinding, surface polishing and figuring process are reported in this paper. The final surface shape error of primary mirror is 11.4nm RMS, and the tertiary is 12.1nm RMS. The capability of off-axis aspheric mirror fabricating on robot polishing system is verified.