{"id":305166,"date":"2023-09-06T15:41:19","date_gmt":"2023-09-06T15:41:19","guid":{"rendered":"\/forum\/forums\/topic\/material-coordinate-system\/"},"modified":"2024-01-10T18:16:43","modified_gmt":"2024-01-10T18:16:43","slug":"material-coordinate-system","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/material-coordinate-system\/","title":{"rendered":"Material Coordinate System"},"content":{"rendered":"

Hello,<\/span><\/p>\n

I have modeled a timber beam in LS-DYNA. In this regard, I used *MAT_WOOD which is a transversely isotropic materia<\/span>l. I intend to define a proper material coordinate system so that the model can realistically behave. I have read LS-DYNA Manual <\/span>regarding <\/span>*MAT_WOOD, ELEMENT_SOLID_ORTHO, and other relevant sections. I will describe the steps I went through to define the proper material coordinate system for the model. <\/span><\/p>\n

I would appreciate it if you could give me some advice.<\/span><\/p>\n

Thanks in advance.<\/span><\/p>\n

Regards, <\/span><\/p>\n

Mehdi<\/span><\/p>\n

Step 0: FEM Model <\/span><\/strong><\/p>\n

Wood is an orthotropic material<\/strong> because it possesses different properties in three directions\u2015l<\/strong>ongitudinal, t<\/strong>angential, and r<\/strong>adial. A common assumption is that wood is transversely isotropic<\/strong> which means the properties in the t<\/strong>angential and r<\/strong>adial directions are modeled the same (*<\/strong>MAT_WOOD). The parallel direction<\/strong> refers to the l<\/strong>ongitudinal direction (<\/span>L<\/span><\/strong>) and the perpendicular direction<\/strong> refers to the r<\/strong>adial or t<\/strong>angential direction (<\/span>T<\/span><\/strong>). <\/span><\/p>\n

For my FE Model, l<\/strong>ongitudinal direction (<\/span>L<\/span><\/strong>) is along the global <\/span>Z<\/span><\/strong> axis and transverse directions (<\/span>T<\/span><\/strong>) are along the global <\/span>X<\/span><\/strong> and <\/span>Y<\/span><\/strong> axes. Therefore, longitudinal stiffness and strength properties (<\/span>EL<\/span><\/strong>, <\/span>XT<\/span><\/strong>, <\/span>XC<\/span><\/strong>, …) should be assigned to the global <\/span>Z<\/span><\/strong> axis of the specimen and perpendicular stiffness and strength properties (<\/span>ET<\/span><\/strong>, <\/span>YT<\/span><\/strong>, <\/span>YC<\/span><\/strong>, …) should be assigned to the global <\/span>X<\/span><\/strong> and <\/span>Y<\/span><\/strong> axes of the specimen (see the picture 1<\/strong>).<\/span><\/p>\n

Picture 1: The timber beam and global coordinate system (x, y, and Z)<\/span><\/p>\n

 <\/p>\n

\"\"<\/a><\/span><\/p>\n

 <\/p>\n

Step 1: Material Directions for the Wood Material Model (AOPT=2.0)<\/span><\/strong><\/p>\n

I used the AOPT material axes option (AOPT = 2) and defined vectors a<\/strong> and d<\/strong>. The vector a is the parallel-to-the-grain direction (<\/span>L<\/span><\/strong>) and d is one of the perpendicular-to-the-grain directions (<\/span>T<\/span><\/strong>). Then, a x d = c and c x a = b, where a, b, and c<\/strong> are the principal material axes<\/strong>. Please see the following pictures. Please note that we have solid elements<\/strong> so far (see picture 5<\/strong>).<\/span><\/p>\n

 <\/span><\/p>\n

Picture 2:<\/span><\/strong> AOPT material axes option (AOPT = 2)<\/span><\/p>\n

<\/a><\/span><\/p>\n

Picture 3:<\/span><\/strong> Display the material coordinate system for solid elements (Mat Dir: shows the material direction orthotropy defined by the AOPT)<\/span><\/p>\n

<\/a><\/span><\/p>\n

Picture 4:<\/span><\/strong> Display the local element coordinate system<\/span><\/p>\n

<\/a><\/span><\/p>\n

Picture 5:<\/span><\/strong> Solid elements for timber beam<\/span><\/p>\n

<\/a><\/span><\/p>\n

 <\/p>\n

Step 2: Setting the direction of orthotropy axis 1 of the material<\/span><\/strong><\/p>\n

On the following page of your website, it is mentioned that “In Element Tools > Element Editing, the Direction option sets the direction of orthotropy axis 1 of the material.” <\/span><\/p>\n

\/forum\/forums\/topic\/element-direction-in-ls-prepost\/<\/span><\/a> <\/span><\/p>\n

As you can see in picture 6, it seems that this direction is wrong and should be along the global <\/span>Z<\/span><\/strong> axis. Therefore, I changed the direction and set it along the global <\/span>Z<\/span><\/strong> axis (Picture 7). After that, the elements for the beam changed to ELEMENT_SOLID_ORTHO <\/strong>as you can see in picture 8. It is also noteworthy to mention that the element direction does not change according to picture 9. <\/span><\/p>\n

Picture 6:<\/span><\/strong> The direction of orthotropy axis 1 of the material<\/span><\/p>\n

<\/a><\/span><\/p>\n

Picture 7:<\/span><\/strong> Setting the direction of orthotropy axis 1 of the material along Z axis <\/span><\/p>\n

<\/a><\/span><\/p>\n

Picture 8:<\/span><\/strong> Solid_Ortho elements for timber beam<\/span><\/p>\n

<\/a><\/span><\/p>\n

Picture 9:<\/span><\/strong> Display the local element coordinate system<\/span><\/p>\n

<\/a><\/span><\/p>\n","protected":false},"template":"","class_list":["post-305166","topic","type-topic","status-closed","hentry","topic-tag-ls-dyna"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t