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.
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,
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?
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,
Maybe the following open access article in Materials 2017, 10(1), 88 is of interest to modellers wanting to use experimental microstructures in their simulations:
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.
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.
