Stress Triaxiality is the ratio of Hydrostatic stress and the von-Mises stress and is known to have a great influence on the plastic deformation.
You can view this factor in LS-PrePost now as shown below.
Its been a while since my last post. I wanted to take the time to share that I will be teaching an LS-DYNA Class in Detroit, Michigan. You can visit Registration for more information. FEA Information will be including more information on this in its next publication.
LS-PrePost development version 3.2 is now released for Macs. Below is a screenshot of LS-PrePost running on a MacBook Pro.
You can download it Here
Click to Enlarge:
I will be attending the upcoming LS-DYNA Update meeting in Pune (May 3, 2011) and Bangalore (May 5, 2011). You can find more information at LS-DYNA Update meeting . If you are in Pune or Bangalore, it will be great to see you there.
When modeling low-density foams, it is important to consider potential failure under tensile loading. In LS-DYNA, the most popular constitutive material model is MAT_LOW_DENSITY_FOAM (MAT_057), in which the default treatment of foams under tensile loading is linear with no failure. The Elastic Modulus (Emax) in tension is computed to be the max( max(slope of the stress-strain curve in compression), E). With this treatment, the element does not fail and its stiffness in tension is based on Emax.
One option provided by LS-DYNA is to input a limiting stress in the form of TC (Tensile cut-off stress) which essentially models a elastic-perfectly plastic behavior in tension. Under tensile loading, when the tensile stress reaches the value of TC, the stress is min( tensile_stress, TC) for any further loading.
In addition to TC, we can also specify FAIL = 1, to reset the tensile stress to zero for any tensile loading beyond TC thereby eliminating the element’s capacity to offer any further resistance under further tensile loading. It must be noted that when tensile stress reaches TC with FAIL =1, the element is NOT eroded but simply loses resistance along tensile direction. Upon unloading, the element continues to have zero stress until it reaches a relative volume of 1 (original volume) after which the stress is governed by the compressive behavior.
When friction is enabled in contact treatment using static or dynamic fricition coefficients (FS, FD in *CONTACT), the energy dissipated due to friction can be recorded and visualized. The parameter that tells LS-DYNA to ouput the frictional energy is FRCENG in *CONTROL_CONTACT. FRCENG by default is set to 0 to ignore the recording and output of the frictional energy. When FRCENG is set to 1, LS-DYNA outputs the frictional energy as “Surface Energy Density” into a binary database name “INTerface FORce” (INTFOR) file. The INTFOR file is not output by default and hence to request the output, you must use the keyword *DATABASE_BINARY_INTFOR with a frequency of output time (DT) AND provide a command line argument “s=Intforc_file_name”. Upon completion of the simulation, you can read the INTFOR file using LS-PrePost using File/Open/Interface Force File option and use FCOMP button to fringe the frictionaly energy.
If you are perfoming a coupled thermal-mechanical analysis using the option SOLN =2 in *CONTROL_SOLUTION, then this frictional energy can be converted to heat energy to be included by the thermal solver.
Summary of the steps to output and view frictionaly energy are included here.
1. Set FRCENG = 1i n Card 4 of *CONTROL_CONTACT
2. Use *DATABASE_BINARY_INTFOR with desired output time interval DT
3. Use “s=intforce_file_name” as one of the command line arguments when invoking LS-DYNA
4. View the results in LS-PrePost/File/Open/Interface Force File and FCOMP/SurfaceEnergyDensity to contour the results
With the recent growth of multi-core chips, scalibility of pure MPP LS-DYNA beyond 128 cores has shown degration due to several factors including latency and network communications. LSTC has recently developed a new code named “Hybrid LS-DYNA” that provides sustained scalibility for large number of cores and also yields digit-2-digit repeatibility when changing the number of cores per job. Both these offer tremendous advantages as we move forward to take advantage of multi-core chips. A surpise advantage that we recently saw is the ability to run IMPLICIT jobs in Hybrid LS-DYNA on comptuers with substantially less memory.
Hybrid MPP LS-DYNA is a very promising solver version that is very easy to run and set up. Below is a picture that illustrates the difference between pure MPP-LSDYNA and Hybrid LS-DYNA.
How Hybrid LS-DYNA Works [ click the image to enlarge]
How to use Hybrid LS-DYNA. [click the image to enlarge]
Thanks to Dr. Jason Wang, whose presentation at the recently concluded Dynamore LS-DYNA Conference in Germany, was helpful for this post.
Several of you requested the manual pages for the newly developed tabulated Johnson-Cook constitutive law now labeled as MAT_224.
Here are the three pages of the keyword manual.
MAT224 All Pages [ Click the image to enlarge]
MAT224 Page 1 [ Click the image to enlarge]
MAT224 Page 2 [ Click the image to enlarge]
MAT224 Page 4 [ Click the image to enlarge]
Most orthotropic material rely on the parameter AOPT to define the change/update the default material axes defined by LS-DYNA. The default axis for every shell element is based on the order of the node numbers if INN=0 which is then based on N1-N2 and the cross-product of N1-N2 and N1-N4. The default material axes may not necessarily coincide with the direction of the intended axes for a given material. To help reorient the default material axes, LS-DYNA provides the parameter AOPT to reorient and further rotate the reoriented axes by using the BETA parameter in *SECTION_SHELL and/or *ELEMENT_SHELL_BETA. The following table attempts to illustrate this. I have ignored AOPT = 3, as I am yet to find a better way to illustrate it in a easier way but I will update it when its done.
Click to Enlarge
Finding a good material law can sometimes be a daunting task even for experienced users. To facilitate a quick review of possible material laws for a given material criteria, a LS-DYNA Material Law Browser was created for personal use and I hope its useful for others.
Please send any feedback you may have at info at d3view dot com