Is nonlinear stiffness allowed for SPRING1 elements?

#1

I’m trying to set up a model using SPRING1 elements with a nonlinear spring constant.

As a test, to make sure I’m formatting things correctly, the following input file works using a linear constant and gives the expected result.

*NODE,NSET=NALL
1,0.,0.,0.
*ELEMENT,TYPE=SPRING1,ELSET=EALL
1,1
*SPRING,ELSET=EALL
1
1.E6
*BOUNDARY
1,2,3
*STEP
*STATIC
*CLOAD
1,1,10.
*NODE PRINT,NSET=NALL
U,RF
*END STEP

However when I change the spring to be nonlinear, such as the following, and using any arbitrary set of spring constants:

*NODE,NSET=NALL
1,0.,0.,0.
*ELEMENT,TYPE=SPRING1,ELSET=EALL
1,1
*SPRING,NONLINEAR,ELSET=EALL
1
-1.E6,-1.
0.,0.
1.E6,1.
*BOUNDARY
1,2,3
*STEP
*STATIC
*CLOAD
1,1,10.
*NODE PRINT,NSET=NALL
U,RF
*END STEP

ccx exits with the error:

*ERROR reading *SPRING: a degree
of freedom was specified
(no decimal point in entry),
however, there are neither
SPRING1 nor SPRING2 elements
in the input deck
*ERROR reading *SPRING. Card image:
1
*ERROR in calinput: no material was assigned
to element 1

Am I doing something wrong? Are nonlinear SPRING1 elements supported? If it matters I’m using version 2.17.

#2

Hello ,
have you looked in the manual ? or tested / looked into the attached examples ?
maybe you find there a solution:

image

#3

This was bothering me again. I believe there’s a bug, maybe in the input deck parsing. I found that if I create a simple model when there’s a SPRING2 element in addition to a nonlinear SPRING1, ccx computes successfully and gives the expected result with forces shared correctly between the two springs.

*NODE,NSET=NALL
1,0.,0.,0.
2,-5.,0.,0.

*ELEMENT,TYPE=SPRING1,ELSET=E1
1,1
*SPRING,ELSET=E1,NONLINEAR
1
-1.,-1.
0.,0.
1.,.01
30.,1.

*ELEMENT,TYPE=SPRING2,ELSET=E2
2,1,2
*SPRING,ELSET=E2
1,1
10.

*BOUNDARY
1,2,3
2,1,3
*STEP,NLGEOM
*STATIC
*CLOAD
1,1,10.
*NODE PRINT,NSET=NALL,FREQUENCY=99999
U,RF
*END STEP

Yet if I remove the SPRING2 element leaving the SPRING1 definition unchanged, which seems like it still should solve, ccx still exits with the error in the original post.

*NODE,NSET=NALL
1,0.,0.,0.
2,-5.,0.,0.

*ELEMENT,TYPE=SPRING1,ELSET=E1
1,1
*SPRING,ELSET=E1,NONLINEAR
1
-1.,-1.
0.,0.
1.,.01
30.,1.

*BOUNDARY
1,2,3
2,1,3
*STEP,NLGEOM
*STATIC
*CLOAD
1,1,10.
*NODE PRINT,NSET=NALL,FREQUENCY=99999
U,RF
*END STEP