Fatigue Crack Growth in Bodies with Thermally Sprayed Coating

Kovářík, Ondřej; Haušild, Petr; Medřický, Jan; Tomek, Libor; Mušálek, Radek; Curry, Nicholas; Björklund, Stefan

doi:10.1007/s11666-015-0329-9

Cited by 16 publications

(6 citation statements)

References 27 publications

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“…A value of 1% strain measured by DIC showed good agreement with the surface lengths of the beach marks. This value is in accordance with literature values in Kovárík et al 21 For the tests, the initiation of a macroscopic crack is defined when the strains exceed a value of 1% over a length of 2 mm. This length could reliably be detected in the performed fatigue tests.…”

Section: Fatigue Testssupporting

confidence: 88%

Experimental investigation on the influence of welding residual stresses on fatigue for two different weld geometries

Friedrich

2020

Fatigue Fract Eng Mat Struct

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Fatigue tests on welded small-scale specimens often do not show a distinct residual stress influence. An exception is longitudinal stiffeners, which are therefore frequently used to study the influence of welding residual stresses on fatigue. The results are not directly transferable to other weld geometries because the residual stress distribution depends on the weld geometries. In the presented investigation, fatigue tests on multilayer K-butt weld and longitudinal stiffener specimens were performed. The tests were carried out in the as-welded and stress-relieved conditions at different load ratios. Initiation of macroscopic cracks was detected using digital image correlation. This allowed determining the influence of welding residual stresses on the initiation of macroscopic cracks, crack propagation and total fatigue life for both investigated weld geometries.

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Section: Fatigue Testssupporting

confidence: 88%

Experimental investigation on the influence of welding residual stresses on fatigue for two different weld geometries

Friedrich

2020

Fatigue Fract Eng Mat Struct

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“…Macroscopic cracks are assumed when strains of 1% or more are reached. In a study by Kovárík et al 20 , DIC was applied to detect cracks on thermal spray-coated, unnotched specimens. It was stated that the threshold value for crack detection could be set in the range of 0.5% and 1% without significantly affecting the results.…”

Section: Discussionmentioning

confidence: 99%

“…It should also be applicable to non-welded specimens, as the absence of geometrical notches should facilitate the DIC measurements. A similar procedure has been applied in Kovárík et al 20 on unnotched specimens.…”

Section: Discussionmentioning

confidence: 99%

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Crack Monitoring in Resonance Fatigue Testing of Welded Specimens Using Digital Image Correlation

Friedrich

Ehlers

2019

JoVE

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A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It is intended as a practical and reproducible procedure to identify macroscopic cracks at an early stage and monitor crack propagation during fatigue tests. It consists of strain field measurements at the weld using DIC. Images are taken at fixed load cycle intervals. Cracks become visible in the computed strain field as elevated strains. This way, the whole width of a small-scale specimen can be monitored to detect where and when a crack initiates. Subsequently, it is possible to monitor the development of the crack length. Because the resulting images are saved, the results are verifiable and comparable. The procedure is limited to cracks initiating at the surface and is intended for fatigue tests under laboratory conditions. By visualizing the crack, the presented procedure allows direct observation of macrocracks from their formation until rupture of the specimen. Video Link The video component of this article can be found at https://www.jove.com/video/60390/ With the advance of computational technologies, DIC is becoming more and more popular for industrial and research applications. Several commercial measurement software systems as well as open-source software are available 1. The proposed procedure offers another use of a technology already available in an increasing number of research facilities in mechanical and civil engineering. Compared to visual inspections or dye penetration testing, the proposed procedure is not based on subjective perception, which depends on an operator's experience and the local geometry at the weld toe. Even with high magnification it may be challenging to detect cracks at an early stage (i.e., crack initiation), especially if the exact location is not known in advance. Furthermore, using DIC the results are saved and therefore reproducible and comparable, whereas visual inspection is possible only momentarily. Using a full-field measurement the procedure allows monitoring the whole width of the specimen or length of the weld. Using strain gauges, it would be necessary to apply several gauges over the specimen width, because their measurement is localized. The changes in the strain gauge signal would depend on the distance and the position relative to the crack. The result would depend on whether the crack would initiate in between two gauges or by chance in front of one.

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“…The loadline displacement y was measured using an LVDT sensor, crack opening displacement (COD) was evaluated from DIC. The crack length was measured using DIC by the method described in [11] and also using unloading compliance. The fatigue crack growth rate was measured in resonance bending using the method described in [12].…”

Section: Methodsmentioning

confidence: 99%

Mechanical Properties of Forged Tungsten Heavy Alloys

Kovářík

Čech

Čapek

et al. 2020

APP

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Tungsten heavy alloys are composite materials containing spherical tungsten particles embedded in binder matrix. Their excellent mechanical properties can be further improved by rotary forging. This paper aims to gain deeper understanding of the forging process by investigating the local elastic modulus, hardness, and residual stress of individual phases in W6Ni3Co pseudo-alloy. The resulting global properties of the composite material such as stress-strain behavior, fracture toughness and fatigue crack growth rate behavior are also studied. The results show that sintered and quenched material consists of highly textured matrix containing nearly perfect single crystal spheres of pure W. The rotary forging leads to significant lattice deformations destroying the texture and significantly increasing the hardness of both WNiCo matrix and W particles and making residual stresses in W particles anisotropic with increased compression along the longitudinal axis of the forged part.

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Fatigue Crack Growth in Bodies with Thermally Sprayed Coating

Cited by 16 publications

References 27 publications

Experimental investigation on the influence of welding residual stresses on fatigue for two different weld geometries

Experimental investigation on the influence of welding residual stresses on fatigue for two different weld geometries

Crack Monitoring in Resonance Fatigue Testing of Welded Specimens Using Digital Image Correlation

Mechanical Properties of Forged Tungsten Heavy Alloys

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