Learning Forum

[NUR ZUMIRAH AHMAD KAMAL]

greeting everyone,

i'm a final year students of mechanical engineering and currently working on developing my samples via ANSYS WORKBENCH. i'm currently setting up a proper methodology for test with standard ASTM D1599-99 which is a hydrostatic pressure test for thermoplastic material. 

summary of experiment : a 1m pvc pipe with 3mm thickness and 20mm hole in the middle was repaired with fiber reinforced polymer composite. The fibers will varies more than 5 type while the resin is polyurethane thermoplastic (poly silicate isocyante - WILLKAT). the repaired pipe was put under hydrostatic pressure from 0 to 15MPa and usually the pipe will burst.

the pipe was designed in design modeler but for the testing part i was a bit confuse. i already applied the pipe with both hydrostatic pressure and pressure. my concern is if i want to build exact test in simulation, which applied pressure are more suitable? hydrostatic pressure does not allowed me to put the exact applied pressure however i used it bcause my project was based on hydrostatic pressure. while pressure allowed me to applied desired pressure but i'm affaid it will include atmosphere pressure. 

result that i obtain from both pressure in simulation:
hydrostatic pressure : run well but the maximum stress and strain are not same with the experiment
pressure : ANSYS state the step size are too small and few random hole was appear on the pipe surface after pressure applied. i dont know if this mean the pipe had burst or else).

can somebody help me ??

[peteroznewman]

To model the experiment where water pressure was increased from 0 to 15 MPa in Ansys, just use Pressure, which will put the same load over the surfaces selected in your model.

Do not use Hydrostatic Pressure, which assumes that only the weight of the water, pulled down by gravity has a pressure that starts at 0 at the free surface and increases linearly with depth below the free surface. That is not what you have in this experiment.

 

[NUR ZUMIRAH AHMAD KAMAL]

thank you for your reply. however i'm getting new error from the system 
note that i had assign supplied pressure at 10 MPa and fixed support at closed end. 

first error : Solver error - time step too small. current number of step is 10.(had do some reserach it says that it because material thickness is too small - it is true?)

second error : Some of the elements on the problematic bodies can't meet the specified target metrics. Please check the elements and try changing the mesh size settings to achieve the needed mesh quality. (I've been getting same error even after changed few setting on mesh setting - as display in pic below)



third error : 94.2  % of total volume of Flexible Parts filled with elements with Characteristic Length (LS-DYNA) lower than target value 2.5078 mm. (does this mean i need to run my simulation using LS-DYNA?)



can you help?

[peteroznewman]

What is the OD of this pipe?

Go back to DesignModeler or SpaceClaim and use the Midsurface tool to replace the solid pipe with a surface. This will make it much easier to mesh with larger shell elements that will have good element quality and speed up the solution time.

A Fixed Support introduces higher stress, replace the Fixed Support with a Remote Displacement, Behavior = Deformable and set all six values to 0.

Please describe the real method of end closure. You may want to put a cap surface in the CAD and apply pressure to that as well to have some axial load in the pipe. A dome end will introduce the smallest stress rise if you want to avoid element failure near the cap to focus on the element failure near the repair.