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[Jérôme Duriez <question698058@xxxxxxxxxxxxxxxxxxxxx>]

Question #698058 on Yade changed:
https://answers.launchpad.net/yade/+question/698058

Jérôme Duriez posted a new comment:
Regarding the sign convention of UniaxialStrainer, it seems to be as
usual, conforming the continuum mechanics convention (which you
exposed). See the following MWE:

#### UniaxialStrainer for compressing a 2 spheres example
for z in [0,1.99]:
    O.bodies.append(sphere((0,0,z),1,dynamic=False))
O.dt = 1.e-3
O.dynDt = False
O.engines = O.engines + [UniaxialStrainer(strainRate = -1,negIds=[0],posIds= [1],crossSectionArea=1,blockDisplacements=True,label='uas')]

O.run(100,True)

signStrR = 'positive' if uas.strainRate > 0 else 'negative'
lengthVar = 'increasing' if O.bodies[uas.posIds[0]].state.pos[2]-O.bodies[uas.negIds[0]].state.pos[1] > uas.originalLength else 'decreasing'
print('With a',signStrR,'strain rate, length is',lengthVar,'and stress - strain are',uas.avgStress,uas.strain)
##########

With Yade 2021-06-21.git-c1be24c, I do get all negative values for that
compressive example:

"With a negative strain rate, length is decreasing and stress - strain
are -1871100.0000000698 -0.09900000000000386"

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