You mentioned there is a multiplier for each size bolt to correctly calculate max tensile strength. Is there a chart with that information to quickly calculate tensile strengths?
The Engineering Tool Box site has a detailed explanation of the Tensile Stress Area is (www.engineeringtoolbox.com/bolt-stretching-d_1164.html ) and you can find numerous tables such as this one (www.engineersedge.com/hardware/bolt_root_and_tensile_stress_area_15776.htm )
The theory comes from Materials Engineering or Materials Science, but it is used extensively in any engineering discipline dealing with the safe design of parts under load, such as Mechanical, Aerospace, Civil, Biomedical, etc.
Great to see it demonstrated. Something that could help a lot of people is to learn about pre-tension. In particular, when someone uses their ugga-dugga power tool to put their wheel lug nuts on, and they torque those suckers up to 300+ ft-lbs instead of the intended ~100 ft-lbs and then when going around a corner their wheel falls off and they wonder why the lugs broke.
Assuming you mean pulling a fastener into the plastic (yield) region and then releasing it, not re-pulling the broken one: Once anything is plastically deformed, it has a permanent change of shape. In this example, first look at the horizontal axis on the graph (length). The bolt will spring back the length of the elastic part of the curve, but stay permanently longer by the length of however far it got into the plastic part of the curve. It will now be work hardened (strain hardened) so on the second pull, it will stretch in the elastic part of the curve until approximately the same force that it was pulled to the first time. On a graph of the second pull, that means the height (vertical axis) where the curve changes slope is about the same height as the final height of the curve from the first pull. However, the amount of plastic deformation before it necks (length of the plastic part of the curve where the force is still rising, before the curve drops and the part weakens before breaking) is a limited amount, called elongation to break. So if a sample part has 10mm of elongation at break, and you plastically stretch it 4mm, you can only plastically stretch it 6mm next time before it breaks instead of 10mm.
Different types of fasteners respond differently based on the kind of material they are made from and the heat treatment they undergo. But no matter what, going past the yield point changes the fastener forever. Without intervention, it will never act the same again.
One press channel made comparison between different grade bolts and the results showed higher grade bolts just snapped more violently when certain threshold was reached. I personally would not even know where to buy anything less than grade 8
Your question leads you into the field of statics where you learn to analyze all forces on a system. From this analysis, you would know the force on each fastener and if it was distributed proportional or not.
Knowing how to calculate the strength of this type of fastener reveals how much weaaker it is than the straight tensile strength would imply. This is why deaign is best left to specialists and experts.
I'm curious, where did you get the ''reveals how much weaker it is than the straight tensile strength would imply'' part? What is the tensile strength value implying? If you mean someone seeing 150,000 PSI and thinking it can hold 150,000 lbf then that would just be out of this world dumb. Unless you mean something else?
@@Orgakoyd I've definitely met people who look at the chart, see large numbers like 150,000 and immediately think a bolt can support the weight of an entire semi including loaded trailer. I've also seen people make assumptions like using the area of the head of the bolt, nominal thickness, etc. It turns out things can be more complicated and its worth consulting with someone who knows what they're talking about.
@@Orgakoyd The reveals are standard charts for engineering standards. Tensile strength represents the minimum load you can apply without the fastener breaking. If you apply any load over the Minimum Tensile Strength, there is no guarantee the fastener will not break. Theoretically, you could go up to the minimum tensile strength without the part breaking, but in normal circumstances, you would not want to. As soon as your load passes the yield point, the fastener is permanently damaged (bent - out of the elastic zone) and will never perform the same again. In Engineering, we do not design things to break or only be good for one use. We design things so the load stays down in the safe working range. We add safety factors and do our best to ensure the load never exceeds the yield point. A scene from Apolo 13 comes to mind. Watch it if you have not!. They are trying to design a way to get the stranded astronauts home. The manager asks the engineers if a device can do something. They respond, "It was not designed to do that." He responds with, "I don't care what it is designed to do (with safety factors staying away from the yield point), I want to know what it can do (one time to get the people home even if we have to go close to the yield point."
