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Finding the principal strain along the direction of the force applied
Posted Feb 16, 2022, 9:11 p.m. EST Structural & Acoustics, Results & Visualization Version 5.6 4 Replies
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For a stationary static study, I apply a body load to the model. I then want to find the max strain at a point with respect to the direction of the force application. Exporting the data for solid.ep1, solid.ep2, solid.ep3, and its respective component directions (solid.ep1X, etc.), I am thinking I can create the vector of the principal strains and then use external math for solving the component of one vector along another to find the amount of strain along the direction of force applied. My question is whether solid.ep1, and the other principal strains are with resepect to the global axes of x, y, and z in COMSOL?
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The orientation vectors, (solid.ep1X, etc.) are expressed in the global directions, yes.
However, there is something strange with the question, or at least the terminology. The three principal strains have certain orientations, computed from the full strain tensor. There cannot be anything like "principal strain along the direction of the force applied", unless by some coincidence, one of the principal strains happen to be oriented in the load direction.
If you are interested in the direct (or normal) strain (as opposed to shear strain) in a certain direction, the easiest option is to select a coordinate system coinciding with the load in the Linear Elastic Material. Then the local strain tensor has the orientations you are looking for.
You can also use the Matrix Transform feature under Definitions, to perform arbitrary rotations of tensors.
-------------------Henrik Sönnerlind
COMSOL
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Henrik, Thanks for the answer. I am intersted in the strain in a certain direction (that being the direction the force is applied). Can you give me a little more instruction on how to "select a coordinate system coinciding with the load" so the strain values I attain for the strain tensor has the orientation along that direction? I appreciate the help.
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The orientation vectors, (solid.ep1X, etc.) are expressed in the global directions, yes.
However, there is something strange with the question, or at least the terminology. The three principal strains have certain orientations, computed from the full strain tensor. There cannot be anything like "principal strain along the direction of the force applied", unless by some coincidence, one of the principal strains happen to be oriented in the load direction.
If you are interested in the direct (or normal) strain (as opposed to shear strain) in a certain direction, the easiest option is to select a coordinate system coinciding with the load in the Linear Elastic Material. Then the local strain tensor has the orientations you are looking for.
You can also use the Matrix Transform feature under Definitions, to perform arbitrary rotations of tensors.
Henrik,
Any chance you could provide some information on how to use the Matrix Transform feature under Definitions? My thought would be to transform the strain matrix to the system that aligns with my force vector. However, I don't understand where in the Matrix Transform feature I input a transform matrix or some "transform rule"
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Hello Coleman,
To request support from COMSOL staff, please use www.comsol.com/support/ .
Best regards,
Jeff
-------------------Jeff Hiller