markc Posted September 24, 2002 Share Posted September 24, 2002 Can anyone explain Hooks law - and how I would calculate spring strength using it. Many thanks Mark C Link to comment Share on other sites More sharing options...
Peter Carmichael Posted September 24, 2002 Share Posted September 24, 2002 Formula appears to be: =(12000000*d^4)/(8*C*D^3) where: d is the wire diameter D is the coil diameter C is the count of working coils So 5 coils of 1/4 inch diameter on a 2.25in spring gives: 103 lbs/in Link to comment Share on other sites More sharing options...
R2D2 Posted September 24, 2002 Share Posted September 24, 2002 Hooke’s Law states that the amount an elastic body (Spring) stretches is in direct proportion to the force acting upon it. It is usually expressed in simple terms as F= kx Where F is the force acting on the spring, x is the extension and k is a constant of proportionality which depends on material. This formula is only useful for springs which have a linear behaviour. This law is only true if the elastic limit of the object has not been reached. Calculated Spring Rate ® = Gd^4/8nD^3 pounds per inch where R = Rate, pounds of load per inch of deflection G = modulus of rigidity of material, pounds per square inch d = wire diameter, inches n = number of active coils, which is one less than the total number of coils (for an open spring with ground ends.) D = mean coil diameter, inches There are 4 types of compression spring that need to be considered: 1. Open ends not ground ( n is the same as the total number of coils) 2. Open ends ground (n is one less than the total number of coils) 3. Closed ends not ground (n is two less than the total number of coils) 4. Closed ends ground (n is two less than the total number of coils) G for Chrome Vanadium Spring Steels is 11.5 x 10^6 psi Mean coil diameter = inner diameter of coil + wire diameter Some care is needed to ensure that the operating stress in the coils does not exceed the yield strength of the material that has been used to manufacture the spring. Link to comment Share on other sites More sharing options...
scooby dooby doo Posted September 24, 2002 Share Posted September 24, 2002 Hooke's Law is simply that exptension is proportional to force (within the elastic limit- it also doesn't apply to rubber bands etc) Chris's very applied version of this law seems feasible. I'm slightly surprised at Peter quoting (something that is equally feasible as its the same with a few values filled in) without the rider that it is for a given type of material etc. etc. 😬 To get any values out of the physics it all stems from the calculation for the torsional stiffness of a cylinder. This is the 4th power of its diamater (1st year degree stuff). a spring is then just a coiled version of a torsion spring (done for compactness and stability reasons) HOOPY R706KGU what's a 'hood' 🤔 😬 Link to comment Share on other sites More sharing options...
EFA Posted September 24, 2002 Share Posted September 24, 2002 Nobody has considered the pitch of the coil helix. This issue is more usually addressed by calculating the sectional area of the spring wire perpendicular to the spring load. Taking the wire diameter and converting to setcional area perpendicular to the wire is not good engineering practice and leads to inconsistant results. Fat Arn Visit the K2 RUM website See the Lotus Seven Club 4 Counties Area Website here Link to comment Share on other sites More sharing options...
scooby dooby doo Posted September 24, 2002 Share Posted September 24, 2002 at that level of accuracy surly the shape of the cross section should be properly integrated. springs can be a long way off a circular corss-section, I'm sure I've seen examples where the wire is at least 2 or 3 times wider than it is thick... HOOPY R706KGU what's a 'hood' 🤔 😬 Link to comment Share on other sites More sharing options...
neilsjuke Posted September 29, 2002 Share Posted September 29, 2002 boing time for bed Link to comment Share on other sites More sharing options...
scooby dooby doo Posted September 29, 2002 Share Posted September 29, 2002 said zebedee HOOPY R706KGU come to cam7 - we don't bite ❗ Link to comment Share on other sites More sharing options...
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