PSTRESS (Initial Stress Definition)

Description

This option sets the stress values in a part to the specified values. An amplitude function may be provided on the optional second line. This amplitude is typically used to ramp-up the stresses from zero to the desired values over some time to mitigate dynamic effects that would occur if the stresses were to be applied instantaneously at the beginning of time. If no amplitude function TID is provided, the initial stresses are applied instantaneously. If an amplitude function is provided, the elements to which this pre-stress is applied will not compute stress increments from the strain increments using the material model while the amplitude is active.

A release time is typically specified on the optional second line when an amplitude is applied. The release time defines the time at which the amplitude is no longer applied and the material model is released to begin computing stress increments from the strain increments using the material model. The default value of release time is zero which implies the amplitude function is used throughout the analysis.

Format

1	2	3	4	5	6	7	8	9	10
PSTRESS	SID	PID	SIGX	SIGY	SIGZ	TAUXY	TAUYZ	TAUZX
	TID	RT

Example: Initial stress in a 3D solid part

PSTRESS	10	99	1882	-662	512	118.5	331	-18
	19	0.001

Example: Initial stress in a beam part

PSTRESS

10

18

562

Example: Initial stress in a shell part

PSTRESS

10

33

118

77.5

-27.6

Field	Definition	Type	Default
SID	Identification number.	Integer > 0	Required See Remark 1
PID	Part identification number.	Integer > 0	Required See Remark 2
SIGX	XX component of stress.	Real	0.0 See Remark 3
SIGY	YY component of stress.	Real	0.0 See Remark 3
SIGZ	ZZ component of stress.	Real	0.0 See Remark 3
TAUXY	XY component of stress.	Real	0.0 See Remark 3
TAUYZ	YZ component of stress.	Real	0.0 See Remark 3
TAUZX	ZX component of stress.	Real	0.0 See Remark 3
TID	Identification number.	Integer ≥ 0	0 See Remark 4
RT	Release time.	Real ≥ 0.0	0.0 See Remark 5

Remarks

1. The SID must reference a DLOAD ID in the Case control.
2. The PID must reference a valid PSOLID, PSHELL, PBEAM, or PROD property ID. All elements connected to the PID specified will have the initial strain applied to them.
3. The number of stress components specified in this option depends upon the property type of the referenced property ID.
4. The amplitude function is applied to the stress values defined upon the first line as:

   σ(t) = A(t)σ₀

   If no amplitude TID is supplied, the specified initial stresses are applied instantaneously at the beginning of time.

5. If no release time is supplied, the stresses are applied according to the amplitude specification and not released.