CQUAD4 and CQUAD 8 1

[caemagic]

Hey guys , I would like to know the difference between these two elements , as a guideline it's preferable to use CQUAD8 , do we always use CQUAD8 when ever we mesh and analyse ? thank you

caemagic

 

[BlasMolero]

Hello!,
The CQUAD8 have the same features as the CQUAD4 elements, but are not used as frequently. The CQUAD8 are higher-order elements that let you use mid-side nodes in addition to corner nodes. Mid-side nodes increase the accuracy of the element but can make meshing more difficult. CQUAD8 is an isoparametric element with four corner and four mid-side grid points. Although they are useful for modeling singly-curved shells like a cylinder, CQUAD4 elements perform better on doubly-curved shells like a sphere.

I only use CQUAD8 elements for highly nonlinear problems, CQUAD4 is my preferred element for linear static analysis, in general I prefer to split elements (using the H-Method approach) to improve accuracy instead to use parabolid high-order Shell CQUAD8 elements.

The principal advantage of CQUAD8 elements is that they may be more accurate in curved shell applications for the same number of degrees of freedom. The disadvantage is that with the addition of the mid-side node, they are more difficult to mesh for irregular shape structures, but this is not a problem with currently powerful preprocessings FE programas like NX AdvSim & FEMAP.

In summary, my suggestion in general for linear structural problems (critical for dynamic problems!!, forget CQUAD8, you will arrive with GBs & GBs of database size results!!) is to use CQUAD4 elements instead CQUAD8. Check mesh quality using general shell recomendations of minimum mesh size requirement & mesh distortion and you are done!. Take a look to

http://www.iberisa.com/soporte/femap/shell.htm

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[caemagic]

Dear Blas , this was very helpful , thank you so much