A comparison of fatigue strength sensitivity to defects for materials manufactured by AM or traditional processes

Tension‐compression fatigue tests were performed on two types of Ni‐based superalloy 718 with different microstructures in which small artificial defects of various sizes and shapes were introduced. The susceptibility of the fatigue strength to the defects varied significantly with the microstructure morphology, ie, a smaller grain size made the alloy more susceptible to defects. The fatigue limit as a small‐crack threshold was successfully predicted using the area parameter model. The evaluation of the fatigue limit was classified into the following three stages depending on the defect size: (a) harmless defect regime, (b) small‐crack regime, and (c) large‐crack regime. Such a classification enabled comprehensive evaluation of the fatigue limit in a wide range of defect size, considering (a) defect size over a range of small crack to large crack and (b) characteristics of matrix represented by grain size and hardness.

\sqrt{area}

) parameter model proposed by Murakami and Endo . Beretta et al also confirmed that the model is also applicable to AMed materials …”

Section: Introductionmentioning

confidence: 80%

Effect of defects on the fatigue limit of Ni‐based superalloy 718 with different grain sizes

Kevinsanny

Okazaki

Takakuwa

et al. 2019

“…The process‐driven thermal history inherent to parts processed via metal AM (eg, melt pool temperature, thermal gradient, and cyclic reheating) is highly dynamic and nonuniform, which impacts microstructure evolution, crystallographic texture, residual stress, etc . Additionally, this variability in thermal history can result in parts exhibiting inadvertent anomalies (eg, porosity, lack‐of‐fusion [LOF] defect, and microcracking) and lacking certifiable mechanical properties and/or sufficient quality for engineering applications . Furthermore, variations in commercial powder characteristics, building procedure, and AM systems exacerbate the variability in the thermal history .…”

Section: Introductionmentioning

confidence: 99%

Fatigue‐life prediction of additively manufactured material: Effects of heat treatment and build orientation

Yadollahi

Elwany

Doude

et al. 2020

In this study, the crack‐growth approach is used to predict the fatigue life of 17‐4 precipitation hardening (PH) stainless steel (SS) fabricated via an additive manufacturing (AM) system in different orientations (ie, vertical and horizontal) before and after heat treatment. To perform fatigue‐life calculations, the effective stress intensity factor as a function of crack‐growth rate was obtained from testing modified compact specimens with different crack orientations in as‐built and heat‐treated conditions. The plasticity‐induced crack closure model, FASTRAN, was used to calculate fatigue lives based on the size of process‐induced defects. Results indicated that in the presence of large voids (ie, lack‐of‐fusion defects), the total fatigue life of AM 17‐4 PH SS in as‐built and heat‐treated conditions is dominated by crack growth. Effect of build orientation on fatigue life of AM 17‐4 PH SS was also captured based on the size of defects projected on a plane perpendicular to the loading direction.

“…The SLM process permits to manufacture parts characterized by promising quasi‐static mechanical properties but fatigue strength can be critical for SLM parts . During the SLM building process, many defects originate within AM parts, such as porosities induced by vaporization of light elements, sintered powders, and residual oxide layers.…”

Section: Introductionmentioning

confidence: 99%

“…These AM defects are extremely dangerous for components subject to fatigue because they represent a critical initiation site for the fatigue crack and could lead to unexpected failures in the High Cycle Fatigue (HCF) and in the Very High Cycle (VHCF) regimes. In the literature, the HCF response of SLM parts has been extensively investigated . However, there are still very few results on the VHCF behavior of SLM parts, even if the number of machinery components that may sustain VHCF is rapidly increasing in the last years (see, e.g., the numerous applications where high frequency vibrations are present) .…”

Section: Introductionmentioning

confidence: 99%

VHCF response of as‐built SLM AlSi10Mg specimens with large loaded volume

Tridello

Biffi

Fiocchi

et al. 2018

It is well known in the literature that fatigue is particularly critical for Additive Manufacturing (AM) parts, because internal defects originating during the AM process represent a critical site for crack initiation. In the literature, the High‐Cycle‐Fatigue (HCF) response of AM parts has been extensively investigated; however, there are few results on the Very‐High‐Cycle‐Fatigue (VHCF) behavior of AM parts, even if the number of machinery components that may sustain VHCF is rapidly increasing in the last years. The present paper investigates the VHCF response of an AlSi10Mg alloy produced through Selective Laser Melting. Ultrasonic tests are carried out on Gaussian specimens with a large loaded volume and show that fatigue failures in VHCF originate from surface and sub‐surface defects with the same mechanism of HCF failures. P‐S‐N curves and fatigue strength at 109 cycles are finally estimated to show the effect of defect size on the VHCF strength. Research highlights Ultrasonic VHCF tests on AlSi10Mg Gaussian specimens produced through SLM. Identification and analysis of critical AM defects inducing VHCF failure. Statistical estimation of models for the prediction of the VHCF response of AM parts. Statistical prediction of effect of defect size on the VHCF response of AM parts.