梁和实体结合的结构分析

hxwgter

file:///C:/Users/HUIHUI~1/AppData/Local/Temp/msohtml1/01/clip_image001.gifThis is ¼ ofmy model，see Fig.1. The top view is shown in Fig.2. There are 8 beams. I cut the wholebody along the red lines.
Plane 1 and 2in Fig.1 are symmetric ones and force is given to the node in the red circle.The constrains at the ends of two beams are All DOF =0. For plane 1, the UX=0and UY=0 for plane 2. I give FZ=-1mN to the node point in the red circle. Theforce is perpendicular to the bottom plane.
My question is that the force and displacement relationship is linear. Well,based on my FEA knowledge, the behavior will be nonlinear when the displacementis at 10 times bigger than the thickness of the cross section. We also have theexperiment results from the nanoindenter indicating the nonlinear results too.No matter I treat the central square mass as a rigid body or not, the resultsare linear. I do not know what the problems are. Could you give me somesuggestions?

BTW: The central square bulk is 2mm*2mm*100um. Each beam of those 8ones are the same and its dimension is 250um*30um*3um. The force is given onthe bottom plane of the central square mass.

Fig.1

Fig1

Fig.2

Fig2