Fatigue Failure of a Pressing Machine

This article presents an analysis of the causes of a fatigue crack in the guide bar of a pressing device. The detailed analysis included the analysis of a material’s microstructure and its cyclic properties. Direct measurements of the strains during operation allowed the nominal loading process in the critical cross-section of the press subassembly to be obtained. The notch effect of the inner thread of the guide bar was analyzed using a precision FEM (finite element method) model and was followed by the transformation of the nominal loading into the notch root. A methodological approach was formulated based on the analyses made, which lay in the statistical interpretation of the factors leading to an identification of the cause of an early fracture.

Analysis of Notch Effect in 3D-Printed ABS Fracture Specimens Containing U-Notches

In this paper a fracture assessment in additive manufactured acrylonitrile butadiene styrene (ABS) fracture specimens containing U-notches is performed. We performed 33 fracture tests and 9 tensile tests, combining five different notch radii (0 mm, 0.25 mm, 0.50 mm, 1 mm and 2 mm) and three different raster orientations: 0/90, 30/−60 and 45/−45. The theory of critical distances (TCD) was then used in the analysis of fracture test results, obtaining additional validation of this theoretical framework. Different versions of TCD provided suitable results contrasting with the experimental tests performed. Moreover, the fracture mechanisms were evaluated using scanning electron microscopy in order to establish relationships with the behaviour observed. It was demonstrated that 3D-printed ABS material presents a clear notch effect, and also that the TCD, through both the point method and the line method, captured the physics of the notch effect in 3D-printed ABS. Finally, it was observed that the change in the fracture mechanisms when introducing a finite notch radius was limited to a narrow band behind the original defect, which appeared in cracked specimens but not in notched specimens.