Principal Stress/Strain direction vector
Principal Stress/Strain direction vector
(OP)
Hi Folks,
I'm working on a plan to validate our FEA of a particular prototype with some strain gauge measurements.
In choosing the placement of one or more uniaxial gauges I'm trying to first find the principal stresses and their orientations as predicted by Solidworks Simulation.
I'm able to plot my principal strains as a vector plot, but for the life of me I can't make it tell me which direction the principal stresses are directed. Ideally I'd like the orientations of these vectors at a particular location, or the average direction over a small patch on the surface.
The fact that I can generate the vector plot leads me to believe that SW Simulation has this information somewhere, but all I can get using a list or probe is the magnitude of the principal stresses.
I can pull out the global csys normal and shear stresses and use a stress transformation to determine the orientation of the principal axes, but before I get into that I'd like to see if there's an easier way to pull this info out of Solidworks Simulation directly.
So, is anyone aware of how I might be able to list or probe the orientations of my principal stresses?
Thanks in advance
I'm working on a plan to validate our FEA of a particular prototype with some strain gauge measurements.
In choosing the placement of one or more uniaxial gauges I'm trying to first find the principal stresses and their orientations as predicted by Solidworks Simulation.
I'm able to plot my principal strains as a vector plot, but for the life of me I can't make it tell me which direction the principal stresses are directed. Ideally I'd like the orientations of these vectors at a particular location, or the average direction over a small patch on the surface.
The fact that I can generate the vector plot leads me to believe that SW Simulation has this information somewhere, but all I can get using a list or probe is the magnitude of the principal stresses.
I can pull out the global csys normal and shear stresses and use a stress transformation to determine the orientation of the principal axes, but before I get into that I'd like to see if there's an easier way to pull this info out of Solidworks Simulation directly.
So, is anyone aware of how I might be able to list or probe the orientations of my principal stresses?
Thanks in advance






RE: Principal Stress/Strain direction vector
RE: Principal Stress/Strain direction vector
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."
RE: Principal Stress/Strain direction vector
That's a good point re: stress gradients, thanks.
I'm able to probe a specific location as you suggested, but my issue is that I'm only able to get the magnitude of principal strains, and not the direction in which they point (with respect to the global csys, for example).
My concern is that if I place the strain gauge in an orientation off of the principal axis (P1) at that particular point, I'll be introducing error into my measurement due to the resultant combinations of normal/shear stresses acting on the surface under the gauge.
If I'm wrong here, or I'm way off in my methodology, I'm very open to ideas. I'm doing a bit of "forensic engineering" on a prototype sitting on the shop floor for the purposes of improving the way we use our FEA tools to design our machines.
I can sort of "eyeball" the directions by looking at the vector plot, and come up with a fairly good guess as to which orientation I should place my strain gauge, but I'd like some numbers to back up my decisions regarding placement & orientation.
Thanks again
RE: Principal Stress/Strain direction vector
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."
RE: Principal Stress/Strain direction vector
I'm on a Win7 64 bit machine, running Solidworks 2011 with one floating license of Simulation Professional.
Thanks for the help
RE: Principal Stress/Strain direction vector
It runs in 32bit emulation mode, a virtual machine is not needed.
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."
RE: Principal Stress/Strain direction vector
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."
RE: Principal Stress/Strain direction vector
justkeepgiviner: did you ever figure this out?
RE: Principal Stress/Strain direction vector
Rosettes
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."
RE: Principal Stress/Strain direction vector
An update on this project - I believe I've found a workaround, although I'm working on correlating back to the gauge measurements.
To get a measure of the strain in a particular direction I've created coordinate systems at the centre of a surface patch used to describe where I placed the Strain Gauge, with the X axis aligned with my gauge direction.
I then generated a plot of strains in the "X" direction using the coordinate system as a reference, and then created a probe at my csys location so that I can extract the value of the principal stresses in my known direction.
I also aligned the "Z" axis 90 degrees to my strain normal direction so that I can get an idea of the transverse strain impacting my measurements. In some locations (not all due to I/O limitations) I've applied biaxial gauges to directly check these transverse as well.
Vishay Tech Note TN-511 provides some useful information on the impacts of misaligning the straing gauges.
RE: Principal Stress/Strain direction vector
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."
RE: Principal Stress/Strain direction vector
But, I never did figure out how to get SW to tell me the orientation of the strain vectors. The above method sounds like it will work, but I would sure hope there's an easier way.
RE: Principal Stress/Strain direction vector
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."
RE: Principal Stress/Strain direction vector
So if you stick a csys at the point in question, you can extract this information by probing the approprate normal/shear stresses, and feeding this info into excel to calculate the direction with respect to your csys.
My VAR suggested a visual basic macro if its something that has to be done repeatedly.
It ain't pretty, I know... I've submitted my enhancement request to let us probe this information directly.
RE: Principal Stress/Strain direction vector
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."