Fracture mechanics analysis of a fatigue failure of a parabolic spring

Abstract

This study analyzed the fatigue failure of a parabolic spring made of 51CrV4 steel. A fracture mechanics approach was used to quantify the driving force and resistance for different loading configurations, inclusion sizes, and residual stresses. The analysis considered surface and internal initiation processes, including the impact of residual stresses introduced by shot peening. Key findings include the ability of the methodology to analyze the variables influencing fatigue resistance and failure configuration, the competition between surface and internal fracture processes, the limitation of residual stresses, the importance of minimizing the maximum inclusion size, and the potential for enhancing the propagation threshold for long cracks. The employed methodology facilitates not only the quantification but also the comprehension of the influence of the intrinsic material resistance on the fracture process.

Fatigue Crack Propagation of 51CrV4 Steels for Leaf Spring Suspensions of Railway Freight Wagons

“…The procedure for the determination of ∆K th is illustrated in Figure 8. According to the gathered data presented in Figure 8, ∆K th is the value of ∆K when N/N th = 1, which corresponds to the crack length that stops to propagate; this resulted in a ∆K th of 6.92 MPa √ m for σ = 0.1 (very close to the value observed in [40] of 5 MPa √ m), 5.78, and 5.39 MPa √ m for R σ = 0.1, 0.3, and 0.5, respectively. In [41,42], the same steel grade was tested for R σ = 0.1 (with a 10 mm thick specimen), for a martensitic material (without tempering) and for a steel grade with a ferrite/pearlitic microstructure.…”

Fatigue Crack Propagation of 51CrV4 Steels for Leaf Springs Suspensions of Railway Freight Wagons

“…The average value found for K c was 138.37 ± 2.61 MPa √ m (see The procedure for the determination of ∆K th is illustrated in Figure 8. According to the gathered data presented in Figure 8, ∆K th is the value of ∆K for the moment that N/N th = 1, which corresponds to the crack length that stops to propagate, which results in a ∆K th of 6.92 MPa √ m for R σ = 0.1 (very close to the observed in [40] (5 MPa √ m)), 5.78, and 5.39 MPa √ m for R σ = 0.1, 0.3, and 0.5, respectively.…”