Axial Force Measurement Method Using Digital Image Correlation

As a simple and highly accurate axial force management method during manufacturing and maintenance of bolt-fastened structures, we examined a method to calculate the axial force from the image of the bolt head. In this method, the axial force is calculated using the strain on the bolt head measured by digital image correlation (DIC) technique from the image of the bolt head and strain results database by finite element analysis (FEA) that organizes the relationship between the strain and the axial force. We examined this method through two comparisons. The first was to compare the strain on the bolt head measured by DIC with data by strain gauges on the bolt head. The second was to compare the axial force calculated by using the relation database with data by strain gauges on the bolt side. As a result of comparing measured strain by DIC on M10 bolt head with data by strain gauges, the higher the axial force, the smaller the error between the two, and the error was less than 10% at the proof load 18kN in strength category 4.8. We confirmed that the strain on the bolt head generated its fastening can be measured with high accuracy using DIC. Axial force was calculated by using the relation database value of case in which the strain by FEA was being equal as the strain by DIC. The axial force calculation based on DIC measurement for a M10 bolt with 15.4kN fastening force showed 16.5kN, thus the error was 6.9%. We confirmed that the axial force calculation result based on the measurement strain on bolt head by DIC indicated much better accuracy than 30% in error by typical conventional torque management method.