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Stress, Strain, and Young’s Modulus
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The Young’s Modulus is an important criterion for picking materials. Review the graph below that shows the characteristics of different materials. Note that polymers span the largest range (in terms of order of magnitude), due to how many options engineers have to rearrange their monomer composition.
Hoop Stress
Sometimes when we are designing tanks, engines, cooling channels, and other round geometry in a pressurized system, we need to know that it will be able to withstand the pressure. See this figure below for how to calculate Hoop stress based on pressure, wall thickness, radius, and mean diameter.
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In the equation used to calculate preload, there is a variable, K, known as the K-Factor or the “Nut Factor”. When torquing a bolt, most of the torque just becomes friction between the head of the bolt and the surface, or the nut and the surface. Only ~10% is translated into actual tensile clamping force. The K-Factor represents this friction between surfaces.
Tensile Stress Stress
When forces pull apart a bolt, this is called tensile stress (same equation as stress initially mentioned at the start of the LSET). Because of Newton’s Third Law, every action has an equal and opposite reaction, preload from a bolt that clamps down on a surface will also pull the bolt apart creating tensile stress. This is why a bolt cannot be tightened too much, as the bolt can fail if tensile stress becomes greater than its ultimate strength. |
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Bolt Spacing
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