New question #699998 on Yade: https://answers.launchpad.net/yade/+question/699998
Hi, I'd like to ask that how to simulate a drained triaxial compression test within a small-strain level. The goal of this simulation is to get the small strain stiffness G0. A typical way is (1) generating a sand packing and isotropically load it to target confining pressure, e.g., 100 kPa. (2) a small axial strain increment deps1 is applied on the top wall, while the lateral stresses sigma2 and sigma3 keep constant. (3) the simulation finishes when the shear strain, gamma = deps1-deps2, reaches 10e-6. (4) then G0 can be calculated by G0 = dsigma1/(2*gamma) What I have done is using the example code provided by Bruno[1]. I set the loading rate to a very small value (1e-20), and the simulations finished in one second. I thought this process is too quick to generate accurate results, actually the lateral confining pressure changes (i.e., not constant). I know this script works well for a classic triaxial compression test because usually we look at a large strain level (like 20% of axial strain), thereby a small amout of fluctuation on lateral stress is acceptable. But when we look at such a small range and in such a short time, this will lead to inaccurate results. So my question is how can we make the simulation of triaxial compression test within a small-strain level. Thanks, Leonard [1]https://gitlab.com/yade-dev/trunk/blob/master/examples/triax-tutorial/script-session1.py The MWE is as follow if the question is not clearly described. from yade import pack nRead=readParamsFromTable( num_spheres=1000,# number of spheres compFricDegree = 30, # contact friction during the confining phase key='_triax_base_', # put you simulation's name here unknownOk=True ) from yade.params import table num_spheres=table.num_spheres# number of spheres key=table.key targetPorosity = 0.43 #the porosity we want for the packing compFricDegree = table.compFricDegree # initial contact friction during the confining phase (will be decreased during the REFD compaction process) finalFricDegree = 30 # contact friction during the deviatoric loading rate=-1e-20 # loading rate (strain rate) damp=0.2 # damping coefficient stabilityThreshold=0.01 # we test unbalancedForce against this value in different loops (see below) young=5e6 # contact stiffness mn,mx=Vector3(0,0,0),Vector3(1,1,1) # corners of the initial packing O.materials.append(FrictMat(young=young,poisson=0.5,frictionAngle=radians(compFricDegree),density=2600,label='spheres')) O.materials.append(FrictMat(young=young,poisson=0.5,frictionAngle=0,density=0,label='walls')) walls=aabbWalls([mn,mx],thickness=0,material='walls') wallIds=O.bodies.append(walls) sp=pack.SpherePack() sp.makeCloud(mn,mx,-1,0.3333,num_spheres,False, 0.95,seed=1) #"seed" make the "random" generation always the same O.bodies.append([sphere(center,rad,material='spheres') for center,rad in sp]) triax=TriaxialStressController( maxMultiplier=1.+2e4/young, # spheres growing factor (fast growth) finalMaxMultiplier=1.+2e3/young, # spheres growing factor (slow growth) thickness = 0, stressMask = 7, internalCompaction=True, # If true the confining pressure is generated by growing particles ) newton=NewtonIntegrator(damping=damp) O.engines=[ ForceResetter(), InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Box_Aabb()]), InteractionLoop( [Ig2_Sphere_Sphere_ScGeom(),Ig2_Box_Sphere_ScGeom()], [Ip2_FrictMat_FrictMat_FrictPhys()], [Law2_ScGeom_FrictPhys_CundallStrack()] ), GlobalStiffnessTimeStepper(active=1,timeStepUpdateInterval=100,timestepSafetyCoefficient=0.8), triax, TriaxialStateRecorder(iterPeriod=100,file='WallStresses'+table.key), newton, ] Gl1_Sphere.stripes=0 if nRead==0: yade.qt.Controller(), yade.qt.View() triax.goal1=triax.goal2=triax.goal3=-100000 while 1: O.run(1000, True) unb=unbalancedForce() print 'unbalanced force:',unb,' mean stress: ',triax.meanStress if unb<stabilityThreshold and abs(-100000-triax.meanStress)/100000<0.001: break print "### Isotropic state saved ###" import sys #this is only for the flush() below while triax.porosity>targetPorosity: # we decrease friction value and apply it to all the bodies and contacts compFricDegree = 0.95*compFricDegree setContactFriction(radians(compFricDegree)) print "\r Friction: ",compFricDegree," porosity:",triax.porosity, sys.stdout.flush() O.run(500,1) O.save('compactedState'+key+'.yade.gz') print "### Compacted state saved ###" triax.internalCompaction=False setContactFriction(radians(finalFricDegree)) triax.stressMask = 5 triax.goal2=rate triax.goal1=-100000 triax.goal3=-100000 newton.damping=0.1 print "gamma before deviatoric loading is", abs(triax.strain[1]-triax.strain[0]) print "click run to start small-strain deviatoric loading" from yade import plot def history(): plot.addData(e11=-triax.strain[0], e22=-triax.strain[1], e33=-triax.strain[2], ev=-triax.strain[0]-triax.strain[1]-triax.strain[2], s11=-triax.stress(triax.wall_right_id)[0], s22=-triax.stress(triax.wall_top_id)[1], s33=-triax.stress(triax.wall_front_id)[2], i=O.iter) def stop(): if abs(triax.strain[1]-triax.strain[0])>1e-6: O.pause() print "gamma after deviatoric loading is", abs(triax.strain[1]-triax.strain[0]) O.engines=O.engines+[PyRunner(iterPeriod=20,command='history()',label='recorder')] O.engines=O.engines+[PyRunner(iterPeriod=1,command='stop()',label='stop')] ### declare what is to plot. "None" is for separating y and y2 axis # plot.plots={'i':('e11','e22','e33',None,'s11','s22','s33')} ## the traditional triaxial curves would be more like this: #plot.plots={'e22':('s11','s22','s33',None,'ev')} # display on the screen (doesn't work on VMware image it seems) # plot.plot() -- You received this question notification because your team yade-users is an answer contact for Yade. _______________________________________________ Mailing list: https://launchpad.net/~yade-users Post to : yade-users@lists.launchpad.net Unsubscribe : https://launchpad.net/~yade-users More help : https://help.launchpad.net/ListHelp