Learning Forum

[Yadukrishnan Satheesan]

Hi, I am looking to simulate uniaxial cyclic loading on a specimen to generate the stress-strain hysteris loop through the loading and unloading phase. I am considering multi-linear hardening for plasticity. Is it possible to achieve this graph using Mechanical APDL? 

[John Doyle]

What is the source of the hysteresis?  Is it rate dependent?  Is it large strain or small strain?  Is it like ratchetting and shakedown?  If so, perhaps you need a Chaboche plasticity model.  Please refer to Section 4.4.4.2.3 of the MAPDL Material Reference Guide for more details.

[Bill Bulat]

If you don't intend to mimic the shakedown of ratcheting phenomena that John mentioned...

if you're content to model material response that does not change each cycle, then the input below might suffice your needs:

 

fini

/cle

 

/vie,1,1,1,1

/vup,1,z

/pbc,u,,1

 

/sys,del file*.png

 

 

C******************************************

C*** PARAMETERS

C******************************************

l=0.100 ! LENGTH

w=0.015 ! WIDTH

t=0.005 ! THICKNESS

 

E=2e11 ! ELASTIC MODULUS

Sy=2.5e8 ! YIELD STRESS

 

P=23e5 ! APPLIED PRESSURE

 

 

 

C******************************************

C*** MODEL

C******************************************

/prep7

 

bloc,,l,,w,,t ! GEOMETRY

 

et,1,185 ! ELEMENT TYPE, MESH

vmes,all

 

nsel,s,loc,x ! CONSTRAINTS

nsel,a,loc,x,l

nsel,r,loc,z

d,all,uz

nsel,r,loc,y

d,all,uy

nsel,r,loc,x

d,all,ux

 

 

mp,ex,1,E ! DEFINE ELASTIC MODULUS

TB, PLASTIC,1,,4,MISO ! DEFINE MULTILINEAR ISOTROPIC HARDENING

TBPT, ,0,1.00*Sy ! YIELD STRESS

TBPT, ,0.00005,1.10*Sy ! FIRST STRAIN, STRESS POINT

TBPT, ,0.00105,1.20*Sy ! SECOND STRAIN, STRESS POINT

TBPT, ,0.00305,1.25*Sy ! THIRD STRAIN, STRESS POINT

 

tbli,all,all

 

fini

 

 

C******************************************

C*** SOLVE

C******************************************

/solu

 

autots,off

nsub,250

outr,all,all

nlge,on

 

/title,STEP 1: Apply Pressure

nsel,s,loc,z,t,

sf,all,pres,P

alls

save

solve

 

/title,STEP 2: Ramp Pressure to Zero

nsel,s,loc,z,t,

sf,all,pres,0

alls

save

solve

 

/title,STEP 3: Reverse Pressure

nsel,s,loc,z,t,

sf,all,pres,-P

alls

save

solve

 

/title,STEP 4: Ramp Pressure to Zero

nsel,s,loc,z,t,

sf,all,pres,0

alls

save

solve

 

/title,STEP 5: Apply Pressure

nsel,s,loc,z,t,

sf,all,pres,P

alls

save

solve

fini

 

 

C******************************************

C*** POSTPROCESS

C******************************************

/post1

plns,eppl,eqv

/sho,png $plns,eppl,eqv $/sho,close $/wait,2

fini

 

/post26 ! PLOT STRESS VERSUS STRAIN HYTERESIS LOOP

 

ansol,2,node(l/2,,-t),s,x ! SX: X COMPONENT ELASTIC STRESS

ansol,3,node(l/2,,-t),eppl,x ! EPPLX: X COMPONENT PLASTIC STRAIN

add,4,2,3,,eptot,,,1/E,1 ! TOTAL X COMPONENT STRAIN = SX/E + EPPLX

 

/axl,x,Total Strain

/axl,y,X Component Stress

xvar,4

plva,2

 

/sho,png $plva,2 $/sho,close

 

/eof

 

[Yadukrishnan Satheesan]

Hi Biil, 

I am bit confused in implementing the cyclic load. Instead of ramping pressure up and down at each step, I want to used cyclic load with ratcheting phenomena, for example, 100 cycles of stress ratio -1 with frequency of 2. I had a look at Chaboche plasticity model, I will be alright to simulate it but I am not sure to implement the cyclic load. 

[Yadukrishnan Satheesan]

 

Thank you Bill. I want to mimic ratcheting on my model as well but this would really help me to kick start my modelling. 

Kind regards, 

Yadu