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fog37
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- Spring and its shear, torsion, tensile stresses...
Hello Forum,
After watching a video on how some insects can achieve amazing accelerations (hundreds of gs) by using their bodies like springs (instead of just using muscle generated forces to propel themselves), I started thinking about springs again and wanted to check some concepts and intuition with you.
Let's consider a simple linear spring of larger diameter ##D## and smaller wire diameter ##d##. By pulling the string's end, we apply a longitudinal tensile force ##F# which elongates the string (see figure below).
As a simplistic reminder, stress=force, strain=deformation, torsion stress is about changing the cross-sections mutual's angles, shear stress is about shifting the cross-sections of a beam/wire/member parallel to each other.
The figure below shows the spring being pulled and completely untwisted (which means that it means that it originally was in a twisted state). And to untwist something, a torsional stress must be applied!
View attachment 336565
This also means that the longitudinal force ##F## elongates the spring by causing the wire to (un)twist, i.e. there is a torsional stress that does that. The torsional stress, implicitly, causes a shear stress which is is internal to the wire and not directly visible (we can have shear without torsion). In very raw terms, the force ##F## gets "translated" into twist and shear stresses.
Is my understanding correct?
How is a spring made? A spring is created by first turning the wire into a coiled shape and freezing it into that shape (prestressing process) so that is permanently stays in that shape (same ideas a prestressed concrete). What is the benefit of a spring? Obviously, springs compress/stretch linearly storing and releasing potential energy...We would not be able to do that with a simple straight piece of wire not into the shape of spring. The clever shaping of a wire and freezing it into that stressed condition (like when we cure an epoxy by analogy) allows us to use the fact that is can be reversed in shape (compressed/decompressed) to store energy.
Thank YOU!
After watching a video on how some insects can achieve amazing accelerations (hundreds of gs) by using their bodies like springs (instead of just using muscle generated forces to propel themselves), I started thinking about springs again and wanted to check some concepts and intuition with you.
Let's consider a simple linear spring of larger diameter ##D## and smaller wire diameter ##d##. By pulling the string's end, we apply a longitudinal tensile force ##F# which elongates the string (see figure below).
As a simplistic reminder, stress=force, strain=deformation, torsion stress is about changing the cross-sections mutual's angles, shear stress is about shifting the cross-sections of a beam/wire/member parallel to each other.
The figure below shows the spring being pulled and completely untwisted (which means that it means that it originally was in a twisted state). And to untwist something, a torsional stress must be applied!
View attachment 336565
This also means that the longitudinal force ##F## elongates the spring by causing the wire to (un)twist, i.e. there is a torsional stress that does that. The torsional stress, implicitly, causes a shear stress which is is internal to the wire and not directly visible (we can have shear without torsion). In very raw terms, the force ##F## gets "translated" into twist and shear stresses.
Is my understanding correct?
How is a spring made? A spring is created by first turning the wire into a coiled shape and freezing it into that shape (prestressing process) so that is permanently stays in that shape (same ideas a prestressed concrete). What is the benefit of a spring? Obviously, springs compress/stretch linearly storing and releasing potential energy...We would not be able to do that with a simple straight piece of wire not into the shape of spring. The clever shaping of a wire and freezing it into that stressed condition (like when we cure an epoxy by analogy) allows us to use the fact that is can be reversed in shape (compressed/decompressed) to store energy.
Thank YOU!