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ahmedettaf's picture

Localization and instability in sheared granular materials: Role of friction and vibration

Shear banding and stick-slip instabilities have been long observed in sheared granular materials. Yet, their microscopic underpinnings, interdependencies and variability under different loading conditions have not been fully explored. Here, we use a non-equilibrium thermodynamics model, the Shear Transformation Zone theory, to investigate the dynamics of strain localization and its connection to stability of sliding in sheared, dry, granular materials. We consider frictional and frictionless grains as well as presence and absence of acoustic vibrations.

Bin Liu's picture

Objective Fracture Parameters and a Paradox for Interface Cracks

Due to the oscillatory singular stress field around a crack tip, interface fracture has some peculiar features. This paper is focused on two of them. One can be reflected by a proposed paradox that geometrically similar structures with interface cracks under similar loadings may have different failure behaviors. The other one is that the existing fracture parameters of the oscillatory singular stress field, such as a complex stress intensity factor, exhibit some nonobjectivity because their phase angle depends on an arbitrarily chosen length.

Antonio Papangelo's picture

A note on the pull-off force for a pattern of contacts distributed over a halfspace

ArticleinMeccanica · March 2017 --- We found a very simple formula for pull-off force for a pattern of contacts distributed over an halfspace which could be very useful in predicting the adhesive propreties of structured surfaces, as bioinspired surfaces.  

Mike Ciavarella's picture

A simple finding on variable amplitude (Gassner) fatigue SN curves obtained using Miner’s rule for unnotched or notched specimen

We provide a very simple result for a problem which has been often neglected (variable amplitude loading) in academia, but which is of paramount importance in real engineering situations, where fatigue is almost never "constant amplitude".

We found few cases where we could check this extremely simple result, but it worked very well.  We would welcome further verifications.

The paper is in press here.

Giorgio Carta's picture

A phononic band gap model for long bridges. The ‘Brabau’ bridge case

In this paper, we study the dynamic flexural behaviour of a long bridge, modelled as an infinite periodic structure. The analysis is applied to the ‘Brabau’ bridge across the river Tirso in Italy. The approach reduces to a spectral problem leading to the analytical expression of the dispersion relation, which provides the ranges of frequencies for which waves do and do not propagate. The contributions of the bridge structural elements on the dispersive properties of the structure are investigated in detail.

Why CVOL increases?

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Hello,

Abaqus VUMAT for hypoplastic law

Please, I’m investing about the hypoplastic model for granular materials to study the behavior of sand under a dynamic excitation. I try to use the UMAT – VUMAT interface, Interface between UMAT (Abaqus/Standard) and VUMAT (Abaqus/Explicit) from http://www.soilmodels.info/ node17.html website.

zichen's picture

Shape formation of helical ribbons induced by material anisotropy

Helices are ubiquitous building blocks in natural and engineered systems. Previous studies showed that helical ribbon morphology can result from anisotropic driving forces and geometric misorientation between the principal axes of the driving forces and the geometric axes. However, helical ribbon shapes induced by elastic modulus anisotropy have not been systematically examined even though most natural and engineered structures are made of composite materials with anisotropic mechanical properties.

cohesive model of Needleman was input into abaqus, but wrong???

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 I have written  vumat codes of a cohesive model of Needleman (whose paper entilted "Numerical simulations of fast crack growth in brittle solids"), and I have implemented it into ABAQUS/Explicit, but the predicted result is wrong. I don't know why. The corresponding fortran file is as follows:

      subroutine vumat(

C Read only (unmodifiable)variables -

     1  nblock, ndir, nshr, nstatev, nfieldv, nprops, lanneal,

     2  stepTime, totalTime, dt, cmname, coordMp, charLength,

     3  props, density, strainInc, relSpinInc,

Ballistic impact simulation of composite targets in AUTODYN?

In general we use Johnson-Cook model for bullet, which accounts for strain-rate effects, while for the target (Composites), the we use orthotropic constitutive model. Does it mean that strain-rate effects are not important for composites? The Johnson-Cook model cannot be readily used for composites. How does the AUTODYN considers strain rate effects for composites in ballistic impact simulations? 

UMAT for Kinematic hardening

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I just followed the code that ABAQUS presented (Copied below), but I'm getting very strange results comparing with ABAQUS GUI, what's wrong with that? 

Please help if you have experience 

 

 

      SUBROUTINE UMAT(STRESS, STATEV, DDSDDE, SSE, SPD, SCD, RPL,

     1 DDSDDT, DRPLDE, DRPLDT, STRAN, DSTRAN, TIME, DTIME, TEMP, DTEMP,

     2 PREDEF, DPRED, CMNAME, NDI, NSHR, NTENS, NSTATV, PROPS, NPROPS,

     3 COORDS, DROT, PNEWDT, CELENT, DFGRD0, DFGRD1, NOEL, NPT, LAYER,

     4 KSPT, KSTEP, KINC)

C

saberelarem's picture

On a systematic approach for cracked rotating shaft study: breathing mechanism, dynamics and instability

We present a systematic approach to deal with the modelling and analysis of the cracked rotating shafts behaviour. We begin by revisiting the problem of modelling the breathing mechanism of the crack. Here we consider an original approach based on the form we give to the energy of the system and then identify the mechanism parameters using 3D computations with unilateral contact conditions on the crack lips. A dimensionless flexibility is identified which makes the application of the approach to similar problems straightforward.

Shailendra's picture

Post-doctoral position in Failure of Brittle Materials at National University of Singapore

We anticipate an opening for a post-doctoral fellow position in micromechanics based failure modeling of heterogeneous brittle materials. The focus will be on characterizing the roles of flaw distributions on rate-dependent failure in materials such as concrete. The objective is to develop an understanding of failure processes with the aim of designing high performance brittle materials.

Shailendra's picture

Post-doctoral position in Failure of Brittle Materials at National University of Singapore

We anticipate an opening for a post-doctoral fellow position in micromechanics based failure modeling of heterogeneous brittle materials. The focus will be on characterizing the roles of flaw distributions on rate-dependent failure in materials such as concrete. The objective is to develop an understanding of failure processes with the aim of designing high performance brittle materials.

constitutive model of polymers

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I have been studying constitutive models of polymers for four years, and I have written vumat codes of several constitutive models, such as BPA, Arruda-Boyce, Mulliken-Boyce, Johnson-Cook, DSGZ and G’Sell-Jonas, but I don't understand the theory of anand constitutive model. If anybody share the corresponding the vumat codes of anand constitutive model, I will appreciate his or her help very much, and I am also willing to help him or her by sharing my codes with  him or her. My mailbox is wanghaitao@hust.edu.cn.

ABAQUS: Access stress of integration point of elements during calculation

Hi all,

I'm using ABAQUS and UMAT for structural simulation. I used quadratic element (CPS4) with 4 integration points (IP).

During the calculation (which calling my UMAT), at each time step, for each element, I need to calculate the average stress of these IPs and produce a state variable for these IPs from this average stress. Then, I would need to update this state variable back to these IPs in that element. But as far as I know, the ABAQUS call UMAT for every IP and calculate everything within this current IP.

Prony series with temperature dependent stiffness

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Hello,

I have implemented a viscoelastic model (Simo/Hughes approach: Prony series for small strain)

in Abaqus using Umat and it works fine for dynamic isothermal simulations (I validated with the Prony series implemented in Abaqus).

Now, I want to consider thermal loads (I have temperature dependent stiffnesses from a DMA experiment).

How should I use these temperature dependent stiffnesses in the model?

saberelarem's picture

On a systematic approach for cracked rotating shaft study: breathing mechanism, dynamics and instability

We present a systematic approach to deal with the modelling and analysis of the cracked rotating shafts behaviour. We begin by revisiting

the problem of modelling the breathing mechanism of the crack. Here we consider an original approach based on the form we give to the energy of the system and then identify

the mechanism parameters using 3D computations with unilateral contact conditions on the crack lips. A dimensionless flexibility is identified which makes the application

Drucker Prager Plasticity model

Hi All,

I am trying to code the Drucker prager plasticity model for the 2D plane strain case using consistent tangent modulus. I am using C++, therefore I would appreciate if anyone could share relevant materials which I could use and preferrably for the 2D case so it is not unnecessarily complicated.

 

Mike Ciavarella's picture

3D Printing Grand Challenge

Abstract Submission Extended to March 1st 2017

More information

Issues with the implementation of Strain gradient plasticity framework of Niordson and Hutchinson (2003) in ABAQUS UEL

I have implemented the rate-independent strain gradient plasticity framework of Niordson and Hutchinson (2003) in UEL. I was able to validate the results of the shear of infinitely wide thin layer between two rigid surfaces (Niordson and Hutchinson, 2003). However, the UEL subroutine fails to converge for the more complex problem of the shear of finite width slab. I suspect the convergence issues are arising out of internal elastic-plastic boundary conditions and the yield criteria. I have few doubts in this regard.

 

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