Learning Forum

[Ken Ng]

Hi,

I am trying to make a simulation to match the experimental result with some data from another program

This is my model, a 4.5 × 50 mm screw (modelled as smooth surface) inserted into a predrilled orthotropic block is the hole diameter slightly smaller than the screw's diameter (overlapping diameter from another program's data is 1mm) to create the friction contract (the blue part is the surface of the hole, the red part is the surface of the screw).

The table is the orthotropic block material:

Density (kg/m3)	500
Young's Modulus X direction (MPa)	14700
Young's Modulus Y direction (MPa)	737
Young's Modulus Z direction (MPa)	1000
Poisson's Ratio XY	0.449
Poisson's Ratio YZ	0.292
Poisson's Ratio XZ	0.374
Shear Modulus XY (MPa)	1150
Shear Modulus YZ (MPa)	942
Shear Modulus XZ (MPa)	103

The following are the screw material changed properties, other properties remain unchanged of the default structure steel material

Density (kg/m3)	8000
Young's Modulus (MPa)	200000
Yield strength (MPa)	215
Ultimate strength (MPa)	450
Poisson's Ratio	0.29

The graph of force reaction for the displacement vs the displacement is plotted to do the comparison. 

the frictional contact is set as mu = 0.3 and with the command

et ,cid, 174
RMODIF,cid,21, 5.3
RMODIF,cid,22, 4

but I am encountering some problems:

1. I wonder why the simulation failed to run the overlapping diameter is 1mm.

When I set the hole diameter is 3.5mm (overlapping diameter is 1mm), the simulation goes error and gives me these messages. Why would this happen?

2.  The DC coefficient failed to function or function weirdly

So as the 1mm overlapping diameter can't work, I changed the overlapping diameter to a smaller value. but the DC coefficient would either cause errors like that shown in the previous image or give out a strange result that does not decay exponentially. What do I miss for the dynamic friction formula to work properly?

3. How to insert the Hashin failure criterion into the model?

I have checked this post (/forum/forums/topic/hashin-failure-results/) and the guide but I am still confused about where and how to input the Hashin failure criterion into the material. These are the data I have for the Hashin failure criterion

Failure criteria:
Parallel tension = 108 MPa
Parallel compression = 29.8 MPa
Matrix tension = 2.3 MPa
Matrix compression = 5.5 MPa
Longitudinal shear = 7.8 MPa
Transverse shear  = 7.8 MPa
Fracture energy 
Longitudinal tension = 1.6 N/mm
Longitudinal compression = 60 N/mm
Transverse tension = 0.06 N/mm
Transverse compression = 0.2 N/mm

Thanks

 

 

 

 

[Ashish Khemka]

Hi,

The error message indicates rigid body motion. What if you perform a modal analysis and see if any of the part seem to be unconstrained?

Regards,

Ashish Khemka