/PROP/TYPE32 (SPR_PRE)

Block Format Keyword This property describes the pretension spring property set that can be used to model seat belt pretensioners or apply pretension to a bolt.

Format

(1)	(2)	(3)	(5)	(6)	(7)	(9)
/PROP/TYPE32/`prop_ID`/`unit_ID` or /PROP/SPR_PRE/`prop_ID`/`unit_ID`
`prop_title`
`M`				`sens_ID`	`Ilock`
$S t i f_{0}$		$F_{1}$	$D_{1}$		$E_{1}$	$S t i f_{1}$
`fct_ID`₁	`fct_ID`₂

Definitions

Field	Contents	SI Unit Example
`prop_ID`	Property identifier (Integer, maximum 10 digits)
`unit_ID`	Unit Identifier (Integer, maximum 10 digits)
`prop_title`	Property title (Character, maximum 100 characters)
`M`	Spring mass (Real)	$[kg]$
`sens_ID`	Sensor identifier (Integer)
`Ilock`	Lock feature flag. = 1 (Default) 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_ID`₁ or `fct_ID`₂. = 2 Spring is locked after any unloading. (Integer)
$S t i f_{0}$	Spring stiffness before sensor activation, unloading stiffness after sensor activation, and spring stiffness after the spring has locked. (Real)	$[\frac{N}{m}]$
$F_{1}$	Force at sensor activation (Real)	$[N]$
$D_{1}$	Piston's slide length (Real)	$[m]$
$E_{1}$	Initial internal energy at sensor activation (Real)	$[J]$
$S t i f_{1}$	Loading stiffness after sensor activation. (Real)	$[\frac{N}{m}]$
`fct_ID`₁	Loading force function vs displacement after sensor activation $F=f (x - x_{0})$ . (Integer)
`fct_ID`₂	Loading force function vs time after sensor activation $F=g (t - t_{0})$ . (Integer)

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
PRETENSIONER
#                  M                                 sens_ID     Ilock
                 .05                                       1         0
#              Stif0                  F1                  D1                  E1               Stif1
              100000                   0                 .25                   0                   0
#  fct_ID1   fct_ID2
         1         0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/SENSOR/TIME/1
pretentioner
#            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

Pretension elements are /SPRING elements with two nodes. These elements can be used to model seat belt pretensioners or apply pretension to a bolt.
The pretension element can be visualized as a piston with slide length $D_{1}$ that moves to create the pretension force.

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 ( $S t i f_{1}$ )
The other two parameters are calculated using:

$E_{1} = - \frac{1}{2} D_{1} F_{1}$ and $S t i f_{1} = - \frac{F_{1}}{D_{1}}$ (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

S t i f_{1}

are ignored. The pretension force is then defined as:

$F = f (x - x_{0}) \cdot g (t - t_{0})$	$f (x) \cdot g (t) \geq 0$

$t_{0}$: Time at sensor activation
$x_{0}$: Length at sensor activation with; $g (t) = 1$ , if fct_ID₂ = 0; $f (x) = 1$ , if fct_ID₁ = 0

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 $D_{1}$ .
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:
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 1. Ilock= 1, spring locks when force = 0
- Figure 2. Spring locks when $D_{1}$ is reached
- Figure 3. Ilock= 2, Spring locks due to unloading
After the spring is locked, the spring stiffness is $S t i f_{0}$ .
The pretension spring can become unstable if the length of the spring approaches zero.
Elongation output, LX, LY, LZ from /TH/SPRING is elongation velocity.
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 fct_ID₂ with zero force at the end of the pretensioning time to lock the spring.
Figure 4. Pre-tension Force vs. Time