Errors using custom orthotropic materials

[marcus_newleaf]

I'm doing a bending analysis to find the neutral axis of a part in Static Stress with Linear Material Models mode. Initially all the components of the part had isotropic material properties. These were custom materials and the properties I defined were density, modulus of elasticity & poisson's ratio. I believe during the analysis the shear modulus of elasticity gets calculated using modulus of elasticity and poisson's ration, ie. G = E/(2*(1+v)). When all the components had isotropic properties the analysis was done fine and I was able to find the neutral axis.

But once I changed one of the components to orthotropic material and did the check model test, I started getting this error msg: "Invalid material properties defined" for the component that had orthotropic material properties. The Element Type was set to Brick, Element Definition was set to Orthotropic, Material Axis Direction was in the Global Z-direction and meshed using Bricks and Tetrahedra.

I have attached a screenshot to see how the part is orientated. The force is applied in the Y-axis, half way along the Z-axis and X-axis. It is an iterative process to find the neutal axis by moving the force along the X-axis and see if the front side bends the same amount as the back side.

[ilyas_drawbridge]

Hi,

When you change from Isotropic to Orthotropic, additional material properties are required to define the stiffness of the material. The problem might have occured because some of the input to the material properties are empty or invalid. Check your material properties. Material input should best come after defining the element type and material model.

Regards

Ilyas

[marcus_newleaf]

Yes the material input was done after defining the element type and material model. I was able to get it to solve without any errors by defining shear modulus in the material properties. But the equation to calculate shear modulus for an isotropic material, ie. G=E/2(1+v) does not apply for an orthotropic material. I guess now its more of a physics problem rather than the software.

Thanks Ilyas.

[ilyas_drawbridge]

If your material is orthotropic, I suggest you use plate/shell elements. The properties that you need to input should be minimal then. And if I'm not mistaken, the shear modulus is calculated by the software as well. I'm not particularly sure about this. It would be very helpful if someone else could verify this.

Regards

Ilyas 

[AstroJohnPE]

I know that the software does not calculate the shear modulus of elasticity for an orthotropic material. Marcus is correct when he stated that their is no straight forward formula to calculate the shear modulus of an orthotropic. If I remember correctly, there are formulas (probably matrix operations) that will indicate the allowable limit, but I do not know whether those give the upper and lower limit, just the upper, and so on.