Material properties around a punched hole in steel.

[cpjcoe]

I am working on a FEA model of a steel structure under a high impact load. Several areas of the structure undergoes plastic deformation. I am getting good correlation with physical test with one exception. Material around a punched hole is just beginning to yield in the FEA model but has significant deformation in the physical model. A larger burned hole in the model, on the opposite side of the nearly symmetric model, matches closely with the physical test. Could the punching process have an effect on the material properties around the punched hole?

 

[BillPSU]

Are you taking into account the breakout diameter of the punched hole. The hole diameter is controlled at the entry side of a punched hole by the punch diameter the exit side is controlled by the die size. Typical die clearance is 8-15% of the material thickness. I believe the stress concentration factors assume a consisten diameter through the part. the tapered hole will porbably put higher stresses at the entry side of the hole.

 

[CdotS]

We also have square holes punched out in steel plates and often observed cracking emanating from the corners of the hole when 0.30%C steel is tempered to higher hardness ranges. A close observation of the inside surfaces of the holes revealed very rough surface at the exit side. There is clear evidence for severe plastic deformation and gouging (ripping) of surface due to poor lubrication. There should be microcracks (we however have not done any cross sectional microscopy yet). We are going to try to cut using water jet and laser to see whether these less damaging techniques make any difference in the quality of surface of the holes.