Punch Indentation (MPM2D)

Example Application

The project file for this example may be viewed/run in MPoint.[1] The main data file used is shown at the end of this example.

How To Read and Use Examples

A rigid punch is driven at a constant velocity into a cohesive, frictionless material. When run in large-strain calculation mode in FLAC2D, a “bad geometry” error will occur when deformation becomes excessive, such that the model run cannot continue. The MPM approach overcomes this problem.

The model is 55 m wide and 30 m deep. It is created by first specifying a background grid that is larger than the desired sample. The material points are created to make a 55 x 30 m box. A thin strip of material points 5 m wide are assigned the group name “punch” (Figure 1).

Figure 1: Punch model geometry.

The left and right boundaries (background nodes) are fixed in the x direction and the bottom boundary is fixed in all directions. Note that the material point nodes do not lie exactly on the boundary (see Figure 1), so to fix the material point nodes, a range needs to be given that encompases them.

The punch material points are assigned a y-velocity of -2e-4 m/s and the model is run for 100,000 steps. Since the model is not being run in dynamic mode, the timestep is 1, so the total displacement of the punch will be 20 m.

Figure 2 shows the final model deformation. The points are contoured by x-displacement.

Figure 2: Punch model results after 100000 steps.

The model datafile is shown below.

model new
model large-strain on

; make domain and create background mesh
model domain extent -5 60 -5 35
mpoint node spacing 1 

mpoint generate range position-x 0 55 position-y 0 30

; assign constitutive model
mpoint cmodel assign mohr-coulomb
mpoint property density 1000 bulk 2e8 shear 1e8 cohesion 1e5 tension 1e10

; boundary conditions
mpoint node fix velocity range position-y -5 1
mpoint node fix velocity-x range position-x -5 1
mpoint node fix velocity-x range position-x 54 60

;simulate punch
mpoint group 'punch' range position-x 25 30 position-y 29 35
mpoint initialize velocity-y -2e-4 range group 'punch'
mpoint fix velocity-y range group 'punch'

model cycle 100000

model save 'punch'

Endnote

[1]

This example is listed under the present document title in the i Examples dialog (use the menu command Help -> Examples… to access).