The Systems Development Of Strain Measurent And Data Processing In The Sheet Metal Forming Experiment

In modern stamping industry, sheet metal forming is an important plastic processing method. Itwas widely used in the aerospace, automotive, and other fields. As the stress distribution was different,which resulted in sheet surface rupture, wrinkling and other defects in the sheet metal processing. Ithas practical significance to calculate the stress and strain values of forming regions to avoid theemergence of defects. Coordinate grid method is the mainly method to study the plastic deformationof metal. Through printed coordinate grids in the sheet metal surface, Analysis the change of grid sizebefore and after deformation, then you can get the size and distribution of sheet metal strain.In the experiment of sheet metal form-ability, the stress measurement was difficult, we needed toanalysis the material forming situation from the strain. During the measurement of strain, the accuracyof forming limit was determined by the measurement accuracy of the grid deformation amount. Thetraditional grid strain measurement methods and a lot of discrete data processing methods were usedby the hand, so the measurement and calculation workload were great, accuracy was also low. Therewere many companies and institution having developed strain automatic measurement system, whichbased on computer vision technology. However, because the price is high, cannot be popular in thelaboratory. Therefore, we developed a lower cost and practical system for sheet metal strainmeasurement, which had great practical value.This Paper used the image measurement for images collection and preprocessing. We had builthardware systems, which took the CCD camera, the image acquisition card and computer as the core.Experiment proved that the system can capture images accurately, complete image processing andstrain measurement calibration. Then we used Visual C++6.0for development, It included obtainingthe coordinates of the grid before and after deformation, the method of grid strain calculation, thethickness of the curvature correction and fitting three-dimensional approximately, the output of thestrain calculations. Finally, draw the strain distribution curve and FLD which is based on ISO12004.The results show that the system can accomplish the strain measurement accurately andconveniently, and the experiment data can be easily handle in accordance with the latest internationalstandards. And we can handle test data easily according to the latest international standard. Thesystem provided an important research tool for strain measurement and analysis.