Failure Mechanisms of Mechanically and Thermally Produced Holes in High-Strength Low-Alloy Steel Plates Subjected to Fatigue Loading

Abstract

High-strength low-alloy steels (HSLA) are gaining popularity in structural applications in which weight reduction is of interest, such as heavy duty machinery, bridges, and offshore structures. Since the fatigue behavior of welds appears to be almost independent of the base material and displays little improvement when more resistant steel grades are employed, the use of bolted joints is an alternative joining technique which can lead to an increased fatigue performance of HSLA connections. Manufacturing a hole to allocate the fastener elements is an unavoidable step in bolted elements and it might induce defects and tensile residual stresses that could affect its fatigue behavior. This paper studies and compares several mechanical (punching, drilling, and waterjet-cut) and thermal (plasma and laser-cut) hole-making procedures in HSLA structural plates. A series of 63 uniaxial fatigue tests was completed, covering three HSLA grades produced by thermomechanically controlled process (TMCP) with yield strength ranging from 500 to 960 MPa. Samples were tested at single load level, which was considered representative in HSLA typical applications, according to the input received from end users. The manufactured holes were examined by means of optical and electron microscopy, 3D point measurement, micro hardness tests, X-ray diffraction, and electron backscatter diffraction (EBSD). The results give insight on cutting processes in HSLA and indicate how the fatigue failure is dominated by macro defects rather than by the steel grade. It was shown that the higher yield strength of the HSLA grades did not lead to a higher fatigue life. Best fatigue results were achieved with laser-cut specimens while punched samples withstood the lowest amount of cycles.

Experimental Investigation of Industrial Laser Cutting: The Effect of the Material Selection and the Process Parameters on the Kerf Quality

“…Compared to plasma cutting, laser machining offers several benefits such as automation capability and reduced production costs, and it provides higher-quality kerfs [3], even though it allows cutting thinner sections.…”

High-Strength Low-Alloy Steels

“…This means that engineering design must be able to account for the loading history, the geometrical effects, the environmental effects, and the processing variables, among others. Jiménez-Peña et al [15] compared the fatigue response of high-strength low-alloy plates with holes manufactured by five processes, namely punching, drilling, waterjet-cut, plasma, and laser-cut. Guo et al [16] evaluated the variability in the mechanical properties of pipeline steel associated with the centreline segregation in continuously cast slab to meet the requirements of strain-based design.Ślęzak [17] studied the fatigue crack initiation and fatigue crack growth in welded joints made of S960QL high-strength low-alloy steel subjected to straincontrolled conditions.…”

Fracture Areas Quantitative Investigating of Bending-Torsion Fatigued Low-Alloy High-Strength Steel

“…Therefore, Cruces et al [3] as well as Pawliczek and Rozumek [4] studied multiaxial fatigue and fracture of this type of steel in their research. The importance of this issue is indicated by a large number of publications on fatigue and fracture of HSLA steels subjected to various kind treatments [5,6].…”