Fatigue crack growth behaviour of wire and arc additively manufactured ER70S-6 low carbon steel components

Abstract

The new emerging Wire and Arc Additive Manufacturing (WAAM) technology has significant potential to improve material design and efficiency for structural components as well as reducing manufacturing costs. Due to repeated and periodic melting, solidification and reheating of the layers, the WAAM deposition technique results in some elastic, plastic and viscous deformations that can affect material degradation and crack propagation behaviour in additively manufactured components. Therefore, it is crucial to characterise the cracking behaviour in WAAM built components for structural design and integrity assessment purposes. In this work, fatigue crack growth tests have been conducted on compact tension specimens extracted from ER70S-6 steel WAAM built components. The crack propagation behaviour of the specimens extracted with different orientations (i.e. horizontal and vertical with respect to the deposition direction) has been characterised under two different cyclic load levels. The obtained fatigue crack growth rate data have been correlated with the linear elastic fracture mechanics parameter $$\varDelta K$$ Δ K and the results are compared with the literature data available for corresponding wrought structural steels and the recommended fatigue crack growth trends in the BS7910 standard. The obtained results have been found to fall below the recommended trends in the BS7910 standard and above the data points obtained from S355 wrought material. The obtained fatigue growth trends and Paris law constants from this study contribute to the overall understanding of the design requirements for the new optimised functionally graded structures fabricated using the WAAM technique.

Assessment of mechanical and fatigue crack growth properties of wire + arc additively manufactured mild steel components

“…It was noted that the material constant, m, calculated in this study lies within the range of 2 to 4 which is typically observed in the wrought material counterparts tested in the absence of corrosive media. 15 From the results presented in Figure 8B and Table 3, it has been observed that the location and orientation of the C(T) samples do not have a major influence on the FCG behavior of the ER70S-6 WAAM specimen with parallel-built deposition strategy.…”

“…The FCG rates obtained from the present study were further compared with an oscillation-built deposition strategy on the same material from the literature. 15 The C(T) samples in Ermakova et al 15 were tested in air at the same load ratio and P max . The comparison of the parallel-built and oscillation-built strategies has been presented in Figure 8 and Table 3.…”

“…Overall, the crack growth rate has been found to be unaffected for both deposition strategies at different locations and orientations for ER70S-6. For further comparison, the crack growth rate T A B L E 3 Paris law constants for the fatigue test results for the parallel-built strategy from the present study, compared to the ones obtained from the literature for the oscillation-built strategy 15 of S355 is also included in Figure 8. It can be observed FCG were slower in the base material.…”

“…There is limited literature available on the fatigue behavior of WAAM-built low-carbon steels such as ER70S-6. [13][14][15] A recent study by Ermakova et al 14,15 was conducted on WAAM-built components made of ER70S-6 using an oscillation-built strategy while Dirisu et al 16 compared mechanical properties of oscillation and single-pass WAAM ER70S-6. They demonstrated comparable mechanical properties to the conventionally manufactured counterparts.…”

“…(the corresponding values for da/dN are in mm/cycle and ΔK in MPa√m) Comparison of FCG rates for the parallel-built strategy from the present study and the oscillation-built strategy from the lietrature15 [Colour figure can be viewed at wileyonlinelibrary.com]…”