On the fatigue crack growth behaviour of selective laser melting fabricated Inconel 625: Effects of build orientation and stress ratio

This paper discusses two approaches that have been proposed to account for the data scatter observed in delamination growth tests under cyclic-fatigue loading and thereby enable an estimate of a worst-case delamination growth curve for use in the damage tolerance and durability assessment of composite and adhesively-bonded airframes. The two approaches discussed are: (a) the normalisation approach, whereby the energy release rate is divided by the resistance to delamination growth, GR(a), and (b) the Hartman-Schijve approach to delamination growth. It is shown that for the cases considered this normalisation approach can be used to yield curves that are similar to the 'mean-3σ', "worst-case", i.e. upper-bound, curve obtained using the Hartman-Schijve equation. However, despite the reduction in the scatter that arises if this particular normalisation approach is adopted, there is still considerable scatter in the important "near-threshold" region. In this region the normalised curves are bounded above by the 'mean-3σ' curve obtained using the Hartman-Schijve equation. To address this issue, an alternative normalisation approach is then proposed. This alternative normalisation approach has the advantage of having reduced scatter in the near-threshold region but elsewhere is significantly more conservative than the Hartman-Schijve approach.

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“…Figure 19. The test data presented in [71] replotted as da/dN versus ΔK/ΔKth curves. 3) and the 'mean-3σ' threshold, from [18].…”

Section: Discussionmentioning

confidence: 99%

Thoughts on two approaches for accounting for the scatter in fatigue delamination growth curves

Jones

Peng

Kinloch

et al. 2021

Composite Structures

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“…1 Selective laser melting (SLM) is one of the most popular AM techniques, which is capable of medium build rates, good repeatability, and medium to high surface quality. 2,3 To date, many metal materials like titanium alloys, 4 superalloys, 5,6 and aluminum alloys 7 have been successfully printed by AM methods and studied for fatigue behavior. Hu et al 6 studied on the fatigue crack growth behavior of SLM Inconel 625.…”

Section: Introductionmentioning

confidence: 99%

“…2,3 To date, many metal materials like titanium alloys, 4 superalloys, 5,6 and aluminum alloys 7 have been successfully printed by AM methods and studied for fatigue behavior. Hu et al 6 studied on the fatigue crack growth behavior of SLM Inconel 625. Caivano et al 7 compared and analyzed the main factors affecting the very high cycle fatigue response of AM materials, including aluminum alloy, Inconel718, and Ti6Al4V.…”

Section: Introductionmentioning

confidence: 99%

Study on fatigue crack growth behavior of selective laser‐melted Ti6Al4V under different build directions, stress ratios, and temperatures

Jiao

2022

Fatigue Fract Eng Mat Struct

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The experimental study of fatigue crack growth (FCG) behavior in Ti6Al4V alloy manufactured by selective laser melting (SLM) was carried out on an in situ fatigue testing machine. Two specimen orientations relative to the build direction (horizontal and vertical), two temperatures (room temperature, RT, and 400 C), and two stress ratios (0.1 and 0.5) were considered, and the FCG curves with the threshold values were determined. The results showed that the FCG properties were affected by the stress ratio due to different degree of crack closure and temperature with grain softening at 400 C in threshold and Paris region. The threshold value is highly dependent on the build direction of the alloy, which was caused by the anisotropic microstructure, while in the Paris region, the effect of material direction can be negligible and FCG rate tends to be consistent. The fracture mechanism at different stages was discussed and revealed by the fracture morphology observation using scanning electron microscopy.

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“…The stress intensity factor K in Paris model does not directly reflect the relationship between the material direction and the stress ratio and da/dN. Therefore, a driving force parameter (DFP) proposed by Hu et al [25] was adopted to replace K, and the traditional Paris model was modified by considering the influence of material direction and stress ratio. The construction of the DFP model combined the cyclic crack tip opening displacement (CCTOD, ∆δ) with the stress ratio and elastic strain energy release rate criteria proposed by Griffith, which can converge the FCG data of the same material into a narrow band.…”

Section: Discussionmentioning

confidence: 99%

Fatigue Crack Growth Characteristics of 34CrMo4 Steel for Gas Cylinders by Cold Flow Forming after Hot Drawing

et al. 2021

Metals

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The fatigue crack growth (FCG) behavior of 34CrMo4 steel, a typical material for gas cylinders, has been investigated. Specimens were taken from the base material (BM) as well as the hot-drawn (HD) cylinder and cold-flow (CF) formed cylinder along the longitudinal and transverse directions. The FCG tests were conducted under different stress ratios for different materials and directions. The main purpose of this research was to explore the influences of the mechanical and thermal processes, sampling direction and stress ratio on the FCG behavior of 34CrMo4 steel. To further reveal the mechanism of crack propagation at different stages, the microstructures and fracture modes of FCG specimens were analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), respectively. The results showed that HD and CF materials exhibited better resistance to fatigue crack propagation than BM. The FCG rates of investigated materials can be accelerated by the increase in stress ratio. However, the sampling direction had little effect on the FCG rate. Finally, a driving force parameter (DFP) model was used to fit the experimental FCG data of three materials with different mechanical and thermal processes. A unified transition stage between the stable and unstable FCG stages of three materials under various experimental conditions was revealed by DFP model, playing an important role on the early warning of fatigue fracture for different types of 34CrMo4 steel.

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On the fatigue crack growth behaviour of selective laser melting fabricated Inconel 625: Effects of build orientation and stress ratio

Cited by 32 publications

References 46 publications

Thoughts on two approaches for accounting for the scatter in fatigue delamination growth curves

Thoughts on two approaches for accounting for the scatter in fatigue delamination growth curves

Study on fatigue crack growth behavior of selective laser‐melted Ti6Al4V under different build directions, stress ratios, and temperatures

Fatigue Crack Growth Characteristics of 34CrMo4 Steel for Gas Cylinders by Cold Flow Forming after Hot Drawing

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