Uncertainty Evaluation on Measurement of Plastic Yield Stress

The yield stress of polypropylene plastic was measured by electronic tensile universal testing machine. The uncertainty components caused by measurement repeatability, yield load measurement of electronic tensile universal testing machine, width measurement of vernier caliper and thickness measurement of vernier caliper were discussed. The combined standard uncertainty and expanded uncertainty of measuring plastic yield stress were calculated. The results show that the expanded uncertainty of yield stress measurement was 0. 16 MPa when the inclusion factor k=2 and the confidence probability p=95%.