Correlating Surface Hardness to Shear Strength of Driven Rivets and Distribution of In Situ Rivet Hardness

Abstract

Measuring surface hardness and correlating it to shear strength is a nondestructive test method that can be used when a more accurate estimate of rivet strength is necessary. The objectives of this research were to (1) correlate the surface hardness to shear strength of driven rivets, and (2) determine if a subset of rivets could be tested to estimate the hardness of all rivets on a structure. Modern rivets were driven with a pneumatic rivet hammer and tested with a portable hardness tester. The shear strength was then estimated using the approximate tensile strength and two factors, 0.58 and 0.85, from previous research. When using the 0.85 factor, the difference between estimated and actual shear strengths was as low as 1%–6%, compared with 28%–34% when using the 0.58 factor. A factor of 4.8 MPa/hardness Rockwell B (HRB) (0.7 ksi/HRB) was then proposed as a direct correlation between surface hardness and shear strength. The range of rivet hardness measurements was approximately 30 HRB for each of the three bridges tested. Thus, it would be inappropriate to estimate the hardness of all rivets from a small subset of tested rivets. A proposed method is to test a subset of rivets on a member or connection of interest and use those measurements to estimate the hardness of rivets only on that member or connection.