About this app

When you run this program for the first time on your Android device, the program creates 21 predefined identical design cases. You need to modify the parameters of these cases for your own design. Then you can save your new design cases for future use or reference.
There are 5 pages in this program. Each page has a page id shown on the top line of the screen. Theses pages contain the following command buttons:
(Main)
Spring Design
Instruction
Spring Materials, Wire Specs
Exit to AndroidOS
(Selection)
Back to Main
Go Designing
(Designing)
Back to Main
Design It!
Save This Design
(Info)
Back to Main
(Material)
Back to Main

UNITS USED:
Force Unit: N
Length Unit: mm
Stress Unit: Mpa

SPRING MATERIALS:
Fourteen common spring materials are included in this program.
1: A228
2: A227a
3: A227b
4: A679HT
5: A229OT1
6: A229OT2
7: A230
8: A231_A232
9: A878
10: A401
11: A313a
12: A313b
13: A313c
14: A313d

SPRING RATE OF AXIALLY LOADED SPRINGS
The mechanics of compression or extension spring can be interpreted from the formulation of forces and stress of just one coil. For a ring coil, two opposite forces of equal magnitude are applied at the each ends. After the force is applied these two ends move a relative distance e. The load is acting parallel to the coil axial. This load is resisted by the spring through a twisting torsion developed in the coil wire. The coil wire total twisting is:

Bar twist angle of one loop = Torque * (One loop length)/(G shear modulus * J torsional inertia)

H = T * L / (G J) = (F * R) * L / (GJ)

Where T = Torque = F * R = Force * Radius = F * D/2
F = Coil Spring Axial Force
L = Length of One Loop = Pi * D
D = Coil Diameter
J = Pi * d ^ 4 /32
d = wire diameter
Pi = 3.14159

Therefore
H = (F * D/2)* (Pi * D )/ (G * Pi * d ^ 4 /32)
= F * D^2 * Pi / ( G * Pi * d^4 / 16)
= 16 * F * D^2/(G * d^4)

One loop’s elongation along axial direction = e = R * H = D * H /2 = 8 * F * D^3/(G * d^4)
Spring Rate for one loop = k = F / e = (G * d^4)/(8 * D^3)
For n loops, total elongation = E = e * n
So the spring rate for the whole spring is F / E = (G * d^4)/(8 * n * D^3)

SPRING END CONDITION
Compression spring can have many end conditions to achieve stability
Closed ends: spring wire end contacts the next loop.
Closed and ground ends: spring wire end ground and contacts the next loop.
Plain ends: spring wire end does not contact next loop
Plain ends ground: spring wire end ground that does not contact next loop

STRESSES AND ALLOWABLE STRESSES
The torsion stress in the compression spring is:

T = (8 F D K )/(Pi * d ^3)
Where K = ( c + 0.2 )/ ( c -1)
C= D/d = spring index