Mechanical Loads

MechanicalLoads schedules time-varying mechanical loads on top of the static boundary conditions supplied by ElasticProperties. Each entry in the list is one load step: a set of applied stresses / strains / strain rates on the six Voigt axes, an ON trigger, an OFF trigger, and a repeat count. Use it for cyclic loading, time-staged tests, or chained experiments within a single simulation.

Key Classes and Concepts

• MechanicalLoads : public OPObject: owns the ordered list of MechanicalLoadStructure records read from the input file.
• MechanicalLoadStructure: one load step. Records the per-axis applied values and masks, its ON/OFF triggers, and repeat count.
• EventTriggers: enum used for both ON and OFF triggers. Accepted values: USER, TIME, TIMESTEP, STRESS, STRAIN.

Axis components

When TriggerON = STRESS or STRAIN, the trigger must also name which tensor component to monitor via $ONindex_<n>. The same applies to $OFFindex_<n>. Accepted strings:

$ONindex_<n> value	Voigt index
XX	0
YY	1
ZZ	2
YZ / ZY	3
XZ / ZX	4
XY / YX	5

Per-axis loading within a load step

The same six-axis grid used by ElasticProperties is re-used here, with a trailing _<n> to name the load step:

Token	Voigt axis
$BCX_<n>	$xx$
$BCY_<n>	$yy$
$BCZ_<n>	$zz$
$BCYZ_<n>	$yz$
$BCXZ_<n>	$xz$
$BCXY_<n>	$xy$

Each axis accepts STRAIN, STRAINRATE, or STRESS; the corresponding value is supplied as $BCValueX_<n> … $BCValueXY_<n>.

Usage

Input

@MechanicalLoads

# Load step 0: apply a 1% tensile strain along Y when t > 0 and hold {#load-step-0-apply-a-1-tensile-strain-along-y-when-t-0-and-hold}
$Load_0              Enable load 0                        : Yes
$TriggerON_0         ON trigger                           : TIME
$TriggerONvalue_0    Activate at simulation time          : 0.0
$TriggerOFF_0        OFF trigger                          : TIME
$TriggerOFFvalue_0   Deactivate at simulation time        : 10.0
$Repeat_0            Repeat count                         : 1

$BCY_0               Y-axis loading mode                  : STRAIN
$BCValueY_0          Y-axis applied strain                : 0.01

# Load step 1: release when σ_yy drops below threshold {#load-step-1-release-when-_yy-drops-below-threshold}
$Load_1              Enable load 1                        : Yes
$TriggerON_1         ON trigger                           : STRESS
$ONindex_1           Monitored stress component           : YY
$TriggerONvalue_1    Activate when σ_yy exceeds           : 5.0e8
$TriggerOFF_1        OFF trigger                          : USER
$Repeat_1            Repeat count                         : 1

$BCY_1               Y-axis loading mode                  : STRAINRATE
$BCValueY_1          Y-axis strain rate                   : -1.0e-3

$TriggerONvalue_<n> is required unless the ON trigger is USER. $ONindex_<n> / $OFFindex_<n> are required only when the corresponding trigger is STRESS or STRAIN.

Output

MechanicalLoads does not produce its own output file; the loads it activates are applied to ElasticProperties, whose stress / strain fields carry the result.

Example

#include "MechanicalLoads.h"

MechanicalLoads         ML(OPSettings, InputFile);
ElasticProperties       EP(OPSettings, InputFile);
ElasticitySolverSpectral ES(OPSettings, InputFile);

for(RTC.tStep = RTC.tStart; RTC.tStep <= RTC.nSteps; RTC.IncrementTimeStep())
{
    ML.Apply(EP, RTC);        // activate / deactivate loads, then push into EP
    ES.Solve(EP, BC, RTC.dt);
}

Dependencies

• ElasticProperties — where per-axis applied values end up.
• ElasticitySolverSpectral — consumes the updated state.
• RunTimeControl — triggers TIME and TIMESTEP reference its time and step counters.