Short beam shear strength of carbon fiber..

[Rinos]

I am doing simple buckling analysis on a carbon fiber tublar product subject to compressive load. I use NE nastran. My model contain PCOMP card and MAT8 card. I have the material property for the carbon prepreg from the supplier from which I am pluging in all the values in MAT8 card. In MAT8 card, there is a coloumn for shear strenth value in XY plane of fiber. The material data what I have contain short beam shear stress in 0 degree and 90 degree as per ASTM std. Which one is the right value to be pluged in for this shear stress value? I am interested in seeing failure critria of all the plies in the laminate.

Thanks

 

[sdm919]

The MAT8 card does not define transverse shear strength. It defines in-plane stiffness (E1, E2, nu12, G12), transverse shear stiffness (G1z, G2z), and in-plane strength (Xt, Xc, Yt, Yc, S).

But you can input the “allowable interlaminar shear stress” on the PCOMP card in the SB field. Since there is only one value, it does not account for different strengths in the xz (0 degree) and yz (90 degree) directions. Therefore, you should probably input the smaller of the two shear strengths you have for SB. Then check that all the failure indices are greater than 1.0.

By the way, the Short Beam Shear test (ASTM D 2344) is considered obsolete and the currently recommended transverse shear test is the V-Notched Beam test (ASTM D 5379) which gives both transverse shear strength and stiffness.

For your buckling analysis, you may get global buckling of the tube as a column or local buckling of the shell wall if it’s thin. For local buckling the mesh needs to be fine enough to capture these modes.

Also note that for columns, it’s typical to assume an initial eccentricity in the axial load or a specified bow along the length of the column, so that you get some bending rather than pure axial load. This accounts for the unavoidable imperfections that occur in reality.