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Motorsport Fabrication Fundamentals: Facts About Forces

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03.36

 00:00 - How we design a component and how the component will be used will affect the loads that are applied to it. 00:06 With this in mind, it's very helpful if we can understand how these forces act and how they'll affect our components so in this module, we'll be covering the 5 fundamental forces. 00:16 The first two types of force we'll deal with are compression and tension. 00:20 If we consider a connecting rod inside an engine for example then during the compression stroke, it's placed in compression as we have two opposing forces trying to squeeze it together. 00:31 The crankshaft is rotating and trying to push the conrod up while the pressure in the cylinder is trying to push it down. 00:38 If we then consider what happens during the exhaust stroke, the piston and conrod are initially moving up and expelling the exhaust gas from the cylinder but when the piston reaches the top of the stroke, the conrod is placed in tension where two opposing forces are trying to stretch the conrod apart. 00:54 The inertia of the piston wants to keep travelling up, however the crankshaft is trying to pull the conrod back down the bore. 01:01 The next force we need to consider is sheer. 01:04 An example of this would be a bolted joint between two steel plates. 01:08 If opposing forces are applied to each steel plate then the bolt is placed in sheer where the forces have the effect of trying to cut through or rip the bolt in two. 01:18 This is an important concept to understand and something we'll be diving into in more detail in an upcoming module where we'll be discussing single and double sheer joints. 01:28 Next we have a bending force which is where a load is applied perhaps into the middle of a beam. 01:34 A simple example of this would be a bookshelf which is well supported at both ends. 01:38 If enough load is applied to the centre of the bookshelf, it will bend. 01:41 When this happens, the top of the shelf is placed in compression where its molecules are being forced together while the underside is placed in tension where the molecules are being pulled apart. 01:52 If sufficient load is placed on the bookshelf then it'll end up failing. 01:55 The last force we need to understand is torsion or in other words a twisting force. 02:00 This is what happens to a fastener every time we use a torque wrench to tighten it. 02:05 We're applying torque to the head of the fastener which has the effect of twisting it. 02:10 The reason that we need to understand these forces is that components tend to be stronger when the forces are applied in certain ways. 02:17 While it's difficult to apply a blanket rule in fabrication, generally it's safe to say that most materials can withstand the most stress and are most reliable in compression and tension so we want to factor this into our designs, attempting to make sure that the loads are applied where possible, purely in tension or compression. 02:35 Particularly avoiding bending and twisting forces whenever we can. 02:39 One of the strongest geometric shapes is a triangle. 02:43 If we consider what happens when the load is applied to one point in the triangle, then it's distributed down each side, applying a compressive force into these two members. 02:52 At the same time the third side of the triangle is placed in tension. 02:56 We see triangular shapes used in many areas of motorsport fabrication. 03:01 One example would be a suspension wishbone which in its simplest form is just a triangle. 03:07 Triangles are also incorporated into tube frame chassis designs and roll cages in order to add strength and rigidity. 03:14 The key takeaway from this module is to understand the different types of forces that'll be applied to the components that we're fabricating. 03:22 In most instances the materials we'll be working with are strongest when they're subjected to pure compressive or tensile forces and we need to keep this in mind when designing a part.

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