Gaussian specimens for VHCF tests: Analytical prediction of damping effects

Biffi

Fiocchi

et al. 2018

Self Cite

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.

Section: Resultsmentioning

confidence: 99%

Section: Ultrasonic Testing Configurationmentioning

confidence: 99%

Section: Defect Analysismentioning

confidence: 99%

See 1 more Smart Citation

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

Biffi

Fiocchi

et al. 2018

Self Cite

“…Hysteretic damping was also considered in the analysis to take into account internal dissipations. 29 Figure 3 shows the FEM and the real part of stress amplitude along the horn and the bar. The stress amplitude, σ real , is normalized with respect to the maximum real stress amplitude, σ real, max , along the bar.…”

Section: Feas: Design Of the Cyanoacrylate Butt-jointmentioning

confidence: 99%

An innovative testing technique for assessing the VHCF response of adhesively bonded joints

Paolino

Chiandussi

et al. 2018

Self Cite

In the last few years, the use of adhesive joints for structural applications has rapidly increased and adhesives are more often subject to fatigue loads during their in‐service life. In presence of a rapidly varying load, such as a high‐frequency vibration, adhesively bonded joints may undergo fatigue lives in the Very High Cycle Fatigue (VHCF) region that are significantly larger than those investigated in usual high‐cycle fatigue tests. The present paper proposes an innovative testing technique for performing accelerated fully reversed tension‐compression VHCF tests on adhesive butt‐joints. The procedure for the design of the adherends is described and then experimentally validated. Ultrasonic VHCF tests are finally carried out on a cyanoacrylate butt‐joint up to 109 cycles: experimental results show that the proposed testing equipment permits an effective assessment of the VHCF response of the adhesive in a limited testing time.

“…Intermittent tests are carried out 28,29 in order to limit the temperature increment due to the specimen selfheating. 30 Pulse and pause phases are continuously alternated in order to keep the specimen temperature below 323 K. A control system developed in the NI LabView environment automatically stops the test if the detected temperature exceeds the maximum allowable value. The test restarts when the specimen temperature falls below the lower limit temperature, set at 303 K. The real frequency of the test (load frequency evaluated by considering also the pause time) is above 10 kHz.…”

Section: Experimental Set-upmentioning

confidence: 99%

VHCF response of Gaussian specimens made of high‐strength steels: comparison between unrefined and refined AISI H13

2017

Self Cite

It is well‐known in the literature that the characteristic defect size of high‐strength steels strongly influences their Very‐High‐Cycle Fatigue (VHCF) response. Currently, several refining processes permit to reduce the characteristic defect size and permit to remove large defects in high‐strength steels, thus inducing a possible significant enhancement of the VHCF response. The present paper investigates the effects of a specific refinement process, the Electro‐Slag Remelting (ESR), on the VHCF response of an AISI H13 steel. Ultrasonic VHCF tests are carried out on large Gaussian specimens made of unrefined and refined AISI H13 steels. Fracture surfaces are investigated to compare inclusion populations before and after the ESR process. Finally, the fatigue limit and the design S‐N curves are statistically estimated to quantify the beneficial effects induced by the ESR process.