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Plasticity model in Abaqus to capture the continues plastic strain of granular material under triaxial cyclic loading?

Submitted by navaratnarajah on Thu, 08/25/2016 - 02:49

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I am working on modelling ballast aggregates under triaxial loading. Confining pressure applied in the intermediate and minor principal direction and cyclic compression load applied in the major principal axis direction. I wanted to capture the continues plastic strain (PS) with cycles (N). My test results show that the PS increase with N up to about 10,000 cycles and the rate of strain slowly diminish for later cycles and almost stay constant after N=100,000. What available model in Abaqus can be used to get this behaviour. I have to run my analysis at least for 10,000 cycles.

Could you give me a basic explanation for lattice incompatibilty in the crystal plasticity framework ?

Submitted by rajan_prithivi on Wed, 08/17/2016 - 16:43

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I read a few papers wherein the lattice incompatibility is defined mathematically, taking the route of the non closure of the loop in the intermediate configuration and finally arriving at the Nye tensor as curl (Fp) or curl (Fe) . These are related to GND density/lattice curvatures and they are used in the non local formulations. but i am unable to comprehend the basic things -

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What is the basis for the kinematic relation between the plastic velocity gradient and slip rate in crystal plasticity framework

Submitted by rajan_prithivi on Fri, 08/12/2016 - 00:16

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One of the fundamental kinematic equation in crystal plasticity is the relation between the velocity gradient and slip rate.

[ Please find the equation in the attached figure ]

In general terms, L is the spatial velocity gradient ( partial _v / partial_x ) which is a continuum quantity

Lp is a portion of L

Now, the RHS of the equation - gamma_dot, s and m are the slip level quantities essentially at the length scale of lattice

Questions :

Localization of damage

Submitted by SDutta on Mon, 08/08/2016 - 21:19

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Hi,

Is it possible to use micromechanical homogenization to simulate damage localization? The analytical procedures that I have come across, mostly gives a homogenized behavior of the composite and is suitable as long as the damage is diffused. Is there a way to obtain the behavior when the defects (for example microcracks) localize into a damage zone? Some lead or suggestions of reference materials would be of great help.

Thanks.

Does a single crystal have a net rotation after you load and then unload it ?

Submitted by rajan_prithivi on Wed, 08/03/2016 - 21:49

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To detail out,

My understanding of multiplicative decomposition of deformation gradient F =F_eF_p (see the attached figure) is

F_p indicates the shape change without inducing any stress
F_eleads to elastic stretching and rotation

Discrete Element Method

Submitted by ntuecd on Tue, 08/02/2016 - 16:13

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Hallo,

from this month i am going to start my work on Discrete Element Method. I am totally new to this field. Therefore, i am looking for some material which can help me not only to understand the theoretical concept but as well as the programming concept in this field.

I will be very thankful if someone have materials related to DEM.

Regrads

Braj Bhushan Prasad

UMAT for uniaxial compression (plasticity)test is not converge

Submitted by PK on Wed, 07/20/2016 - 11:43

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Hello everyone,

I am beginner of UMAT.

I am now modeling the model for uniaxial compression of shape memory alloys based on plasticity model and backward euler method.

My material is in cubic 1*1*1. It seems to be simple problem.

Anyway, I am still not familiar with UMAT and Abaqus.

The problem is I apply load just only in Y-axis and specify the boundary condition as in attached file

I think that it passed the plastic deformation zone and abaqus try to calculate...

defining a time dependent elastic modulus

Submitted by gna on Mon, 07/18/2016 - 07:55

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Hi,

I'm working on a model with Abaqus and I face a problem. One of my materials has an elastic modulus which isn't constant according to time. As I search I found out that this should be done by USDFLD subroutine. I'm not familiar with subroutins and how to write them and all the resourses that I've found just confused me more. I would be grateful if someone helps me.....

Direct Cyclic Periodic Pressure Load

Submitted by navaratnarajah on Tue, 07/12/2016 - 12:20

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Could you please anyone help me to input Direct Cyclic Periodic Pressure Load.

I have a sine load of amplitude 50 kPa and frequency 5 Hz (ang. freq 31.42 rad/s).

I need to ramp my load to 100 kPa for 5 seconds and then to run the sine load of above amplitude with its mean load on 100 kPa. The sine load go for 10 seconds.

I try with Direct cyclic periodic pressure, but when I check the pressure on applied surface, the pressure not seems what I am applying.