/PROP/TYPE32 (SPR_PRE)

Format

Definitions

Example (Pretension)

#RADIOSS STARTER
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#-  1. LOCAL_UNIT_SYSTEM:
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/UNIT/2
unit for prop
#              MUNIT               LUNIT               TUNIT
                  kg                   m                   s
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/PROP/SPR_PRE/11/2
PRETENSIONNER
#                  M                               sensor_ID     Ilock
                 .05                                       1         0
#              Stif0                  F1                  D1                  E1               Stif1
              100000                   0                 .25                   0                   0
#funct_ID1 funct_ID2                                Ascale_2            Ascale_1            Fscale_F
         1         0                                       0                   0                   0 
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/SENSOR/TIME/1
pretentionner
#         Tdelay
                 0.1
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/FUNCT/1
Loading force function vs displacement after sensor activation
#                  X                   Y
                  -1                   0                                                            
                 -.1                  95                                                            
                   0                 100                                                            
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#ENDDATA

Comments

1. Pretension elements are /SPRING elements with two nodes. These elements can be used to model seat belt pretensioners or apply pretension to a bolt.
2. The pretension element can be visualized as a piston with slide length $D_1$ that moves to create the pretension force.
3. The pretension element force starts after sensor activation and can be defined using a linear or nonlinear force:
   • The linear model is defined by entering any two of these parameters; force at activation ( $F_1$ ), piston slide length ( $D_1$ ), initial internal energy ( $E_1$ ), and loading stiffness ( $Sti{f}_1$ )

     The other two parameters are calculated using:

     $E_1=-\frac{1}{2}{D}_1{F}_1$ and $Sti{f}_1=-\frac{F_1}{D_1}$

     
     
     Figure 1.

   • The nonlinear model is defined by entering curves as a function of displacement, fct_ID₁ or as a function of time, fct_ID₂. If either function is used, the previous input for $F_1$ , $E_1$ and $Sti{f}_1$ are ignored. If both functions fct_ID₁ and fct_ID₂ are defined, the function fct_ID₂ acts as a scaling function of fct_ID₁. The pretension force is then defined as:(1)
     $$F_1=Fscale\_\text{F}\cdot f\left(\frac{x-x_0}{Ascale\_1}\right)\cdot g\left(\frac{t-t_0}{Ascale\_2}\right)$$
     Where,

     $t_0$

     Time at sensor activation.

     $x_0$

     Length at sensor activation with $f\left(x\right)\cdot g\left(t\right)\ge 0$

     $g\left(t\right)=1$ , if fct_ID₂ = 0

     $f\left(x\right)=1$ , if fct_ID₁ = 0

4. If slide length $D_1$ is defined, then the pretension force is set to zero and spring is locked when the spring shortens in length by the slide length $D_1$ .
5. If Ilock = 1, the spring is locked when the spring shortens by the slide length $D_1$ or the pretension force is zero as defined by the force functions fct_ID₁ or fct_ID₂:
6. If Ilock=2, the spring is locked after any unloading.
   Lock examples for force versus displacement, fct_ID₁ but also valid for force versus time fct_ID₂

   • 
     
     Figure 2. Ilock= 1, spring locks when force = 0

   • 
     
     Figure 3. Spring locks when $D_1$ is reached

   • 
     
     Figure 4. Ilock= 2, Spring locks due to unloading

7. After the spring is locked, the spring stiffness is $Sti{f}_0$ .
8. The pretension spring can become unstable if the length of the spring approaches zero.
9. Elongation output, LX, LY, LZ from /TH/SPRING is elongation velocity.
10. If used for bolt pretensioning:
    • A duplicate spring with /PROP/SPR_BEAM should be used to model 2 – 6 degrees of freedom of the bolt.
    • Use Ilock=1, and define force versus time function fct_ID₂ with a force=0 at the time required for the pretension spring to lock. In Figure 5 the spring is locked at t=5.5.

      
      
      Figure 5.