Concrete Filled Steel Tubes (CFST) as machine elements
Concrete filled steel tubes as machine elements was my final year project during my Bachelor's of Technology in Mechanical Engineering course at Sardar Patel College of Engineering. This project was supervised by Dr. Nilesh Raykar and my team mates were Karanveer Dubey and Akshit Sanghavi.
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Abstract:
Roller tubes/shafts are an indispensable part of modern industrial world. They are used in roller conveyors, steel mills, printing presses and variety of consumer products and industries. Most of these rollers are made of steel.
While designing of these rollers, apart from the static load that will act on the tube/roller, a large area has to be dedicated in order to prevent the tube from buckling. The aim of the project is to determine how effective a shaft can be if this area (which is dedicated to prevent buckling) is replaced by a solid and inexpensive filler like concrete.
The project focuses on how buckling governs the strength of a tube and how this additional stress can be redirected towards an inexpensive material.
Buckling takes place only in compression and concrete is well known for its compressive strength. Unlike steel, concrete is much cheaper and it will make a big difference in applications with large number of such elements like in rolling conveyor.
Image for representation purpose only
Cross sections of the specimen tubes
Specimens:
The specifications of the stainless-steel specimen are as follows:
Length: 330mm
Outer diameter: 18mm
Thickness: 0.2mm
D/t ratio: 90
Concrete: 2 parts cement: 1 part water (cured for 20 days under water)
The tubes were procured from local hardware stores. For concrete filled tubes, the specimens were capped on one end by using 3D printed caps. The concrete was then poured into the specimen and was allowed to set for 2-3 days. Once the concrete was set, the cap was removed and the specimen were submerged under water to cure for 20-30 days.
Experiment:
Experiments were planned on the inhouse UTM machine of Mechanical Engineering department of Sardar Patel College of Engineering. Following are the details of machine.
Maximum load = 25kN
Maximum displacement = 60mm
The machine also has software that connects to a computer. The type of loading and the maximum load can be set with the software, making the testing safe
Three-point bend tests were performed on hollow and concrete filled specimens. The tubes were made of aluminum and stainless steel. Notable increase was observed in the strength of aluminum tubes whereas the increase in load bearing capacity of steel tubes was fivefold.
Summery of experiments:
The concrete filled tubes follow a general stress strain curve with a elastic and plastic region. This shows their behavior is governed by the nature of material and not by the shape of deformation of cross section.
The thin tubes also had a local deformation due to concentered force of the plunger and this resulted in crushing of the cross section leading to eventual collapse of the specimen. This local deformation was also much lower in concrete filled tubes.
