Abstract: Based on the triangle irregular net(TIN) reconstruction theory， a 3D software about the fracture surface reconstruction of connecting rods was developed by combining the image processing with the reverse engineering technique， which realized the morphology reproduction of the fracture surface and the calculation of the real surface area. Then the permit range of the area defect of the fracture surface for the fracture splitting connecting rods was determined， and the surface roughness (RS) and line roughness (RL) of the fracture surface were calculated and analyzed. The results showed that the fracture surface area of C70S6 connecting rods in a car produced by the fracture splitting method was 130% larger than that produced by the machining method. It represented that the tolerance range of fracture surface defect dimension was improved compared to the empirical value without reducing the carrying capacity and usability. Furthermore， the relationship between RS and RL was linear， and the mathematical model of these two was established which simplified the calculation procedure of the true area of the interaction surface of the fracture splitting connecting rods， and was beneficial for quantitatively describing the fracture surface.

Key words: connecting rod, fracture splitting, fracture surface reconstruction, roughness, area defect