Design Equation for Minimum Required Thickness of a Cylindrical Shell Subject to Internal Pressure Based on Von Mises Criterion

Design equation (4.3.1) for the minimum required thickness of a cylindrical shell subjected to internal pressure in Part 4 “design by rule (DBR)” of the ASME Boiler and Pressure Vessel Code, Section VIII, Division 2 [1] is based on the Tresca Yield Criterion, while design by analysis (DBA) in Part 5 of the Division 2 Code is based on the von Mises Yield Criterion. According to ASME PTB-1 “ASME Section VIII – Division 2 Criteria and Commentary”, the difference in results is about 15% due to use of the two different criteria. Although the von Mises Yield Criterion will result in a shell wall thickness less than that from Tresca Yield Criterion, Part 4 (DBR) of ASME Division 2 adopts the latter for a more convenient design equation. To use the von Mises Criterion in lieu of Tresca to reduce shell wall thickness, one has to follow DBA rules in Part 5 of Division 2, which typically requires detailed numeric analysis performed by experienced stress analysts. This paper proposes a simple design equation for the minimum required thickness of a cylindrical shell subjected to internal pressure based on the von Mises Yield Criterion. The equation is suitable for both thin and thick cylindrical shells. Calculation results from the equation are validated by results from limit load analyses in accordance with Part 5 of ASME Division 2 Code.

Parametric Analysis of a Spiraled Shell: Learning from Nature’s Adaptable Structures

In our current building design philosophy, structural design is based on static predictions of the loads a building will need to withstand and the services it will need to provide. However, one study found that 60% of all buildings are demolished due to obsolescence. To combat our obsolescence-demolition culture, we turn to Nature for lessons about adaptable structural design. In this paper, we investigate the structural adaptability of the T. terebra spiraled turret shell through finite element modeling and parametric studies. The shell is able to change its structure over time to meet changing performance demands—a feat of adaptability that could transform our current infrastructure design. Modeling the shell’s growth process is an early and simple attempt at characterizing adaptability. As the mollusk deposits material overtime, its shell wall thickness changes, and its number of whorls increases. We designed parametric studies around these two modes of growth and investigated their effect on structural integrity and living convenience for the mollusk. By drawing parallels between the shell structure and human structures, we demonstrate connections between engineering challenges and Nature’s solutions. We encourage readers to consider biomimicry as a source of inspiration for their own quantitative studies for a more sustainable world.

A Bayesian Approach for Estimating the Thinning Corrosion Rate of Steel Heat Exchanger in Hydrodesulfurization Plants

Fuel consumption has been increasing in recent years, especially that of diesel and jet fuel. For this reason, the necessity to build new plants to reduce their sulfur content has arisen. Sometimes, just revamping existing plants is feasible, but determining which pieces of equipment are in the appropriate condition to be reused is also necessary. In order to select the equipment, it is essential to have information about the wall thickness of vessels. Sometimes, the information is limited; consequently, the application of advanced statistical techniques is needed. The Bayesian Data Analysis (BDA) used in this study has the goal of determining a more accurate, unobserved thinning rate distribution for existing heat exchangers, taking into consideration all the information available about the thinning rate of the heat exchangers that cool down the effluent of the hydrotreating reactors in Mexican oil refineries. The information obtained from BDA was compared with existing shell wall thickness obtaining favorable results.

Nanograined surface shell wall controlled ZnO–ZnS core–shell nanofibers and their shell wall thickness dependent visible photocatalytic properties

The core–shell form of ZnO–ZnS based heterostructural nanofibers (NF) has received increased attention for use as a photocatalyst owing to its potential for outstanding performance under visible irradiation.

Microencapsulation of diglycidyl 1,2-cyclohexanedicarboxylate by in situ polymerization: preparation and characterization

Microcapsules containing a glycidyl ester-type epoxy resin were successfully synthesized by in situ polymerization, with poly(melamine-urea-formaldehyde) as the shell material and diglycidyl 1,2-cyclohexanedicarboxylate (DGCHD) as the core substance. Scanning electron microscopy was performed to investigate the surface morphology and shell wall thickness of the microcapsule. The fabrication, diameters and thermal decomposition behavior of the resultant microcapsules were studied by means of Fourier transform infrared spectroscopy, laser particle size analysis, and thermogravimetric analysis (TGA), respectively. Results indicated that the highest loading of DGCHD in the as-prepared microcapsules was about 89.1 wt.% and that the mean diameter of the capsules was in the range of 50–130 μm, which can be adjusted by changing the feeding mass ratio of the core/shell material and emulsifying rate, respectively. TGA results showed that the microencapsulated DGCHD degraded in two distinguishable stages.

Modeling of Dimensional Accuracy in Three Dimensional Printing for Light Alloy Casting

The purpose of this paper is to develop mathematical model to investigate the influence of shell casting parameters. Three input parameters such as shell wall thickness (SWT), Pouring temperature (PT) and weight density (WD) were selected to give output in the form of average outer diameter (AOD) as dimensional accuracy. After identification of component, technological prototypes were produced. In this work three dimensional printing (3DP) has been used as rapid shell casting to make shell mould by using Zcast 501 powder with different shell wall thickness for six different light alloy materials. Measurements on a coordinate-measuring machine helped in calculating the dimensional tolerances of the castings produced. For obtaining tight casting tolerances the dimensional accuracy of component is the most important element. The thickness, curing time and orientation of the shell molds, play an important role in providing a high quality of the cast part in time. The dimensional accuracy was found to be more in the case of maximum layer thickness and horizontal position of the component. The investigation has led to conclusions as the Quadratic models were developed for the response. The F - value is 23.93, which implies that the model as well as lack of fit is significant. The value of Prob > F is less then the standard value 0.05, which indicates model terms are significant. With the help of Post curing, shell Mold temperature was not found to affect the dimensional accuracy of the castings, significantly. It was observed that high pouring temperatures also produced castings with better dimensional accuracy. This study will provide main effect of the inputs on average outer diameter as dimensional accuracy in three dimensional printing of light alloys castings. Statistically in this case B, C, A2, B2, C2, AB, BC is the model terms which contributes significantly to the model developed for dimensional accuracy.

Comparison of Hybrid Rapid Mouldings for Zinc Alloy Castings

In this work comparison of hybrid rapid moulds (prepared with three dimensional printing shells supported with dry, green and molasses sand) have been made for techno-economic analysis, for zinc (Zn) alloy shell casting. The comparison has been made on the basis of mechanical properties and dimensional accuracy. Time-temperature curves have been drawn to understand solidification of molten Zn alloy in hybrid moulds of different thicknesses. The results of study suggest that it is feasible to reduce shell wall thickness of hybrid mould cavity from recommended 12mm to 1mm. All castings prepared are consistent with the permissible range of IT grades and are acceptable as per ISO standard UNI EN 20286-1 (1995). Further green sand based hybrid prototypes at 3mm shell wall thickness, shows better dimensional accuracy and mechanical properties.