Crack Growth analysis at a cold worked bore
The workflow for a crack growth assessment of a cold worked bore in LIFING is as follows.
Step 1.
Import/solve a Quick2DFEM representative a patch with a bore.
The material must be defined with plastic stress-strain curve.
An example is shown below:
extrude-circ -2 2.75
material 70000 0.33
matplast 3 100 .02 200 .07 500 .12
point 1 0 0
point 2 5.5 0
point 3 5.5 3
point 4 0 3
edge 1 0 1 2 6
edge 2 0 2 3 3
edge 3 0 3 4 6
edge 4 0 4 1 3
dbore 2 0.01 0
constrain-back 2 Z
constrain-backleft 2 X
constrain-backbottom 2 Y
unload 3
constrain-back 3 Z
constrain-backleft 3 X
constrain-backbottom 3 Y
The extruce-circ card is needed to generate the patch with a bore.
The matplast card defines the stress-strain curve (in this case made of three points only: sigma(1)=100, epsilon(1)=0.02, sigma(2)=200, epsilon(2)=0.07, sigma(3)=500, epsilon(3)=0.12).
The dbore card defines how much the bore is expanded (by the mandrel) during cold-working.
The unload card defines the unload condition after expansion.
The picture below shows the solution (min principal stresses) resulting after the unload event.
Step 2.
Import/solve a Quick2DFEM representative of the same patch with a bore, including a pin (if applicable), with operative load conditions (e.g. far field tension and/or pin bearing).
This second model SHALL NOT have material plasticity defined.
An example is shown below:
extrude-circ -2 2.75
material 70000 0.33
point 1 0 0
point 2 5.5 0
point 3 5.5 3
point 4 0 3
edge 1 0 1 2 6
edge 2 0 2 3 3
edge 3 0 3 4 6
edge 4 0 4 1 3
pinbore 0 70000 0.33 1000000 0
tension 10 100
constrain-back 10 Z
constrain-backleft 10 X
constrain-backbottom 10 Y
Step 3.
Import in the LIFING database of this second model, the 'unload' solution from the database resulting at Step 1.
At this point the database contains the solution of the operative load (in this case a tension case LC 10) and the solution related to the unload event (from cold-working).
Step 4.
Introduce the initial crack (it can be defined in the Quick2DFEM file with the dedicated card split).
Step 5.
Define the residual stress LC from the unload LC and all other parameters (material data, sequence file, etc.).
Step 6.
Run the crack propagation simulation automatically, with button Calculate New Fronts.
The user must first define the number of fronts, extension in both directions X and Y and the crack front template geometrical parameters.
LIFING will calculate the new crack fronts with a predictor-corrector approach by setting at beginning the next step at the defined distances, then the crack growth analysis will define the ne correct aspect ratio of the crack front and the crack will be updated accordingly.
