Plastic zones around fatigue cracks studied by ultra-low-load indentation technique

Nyström, Magda; Söderlund, E.; Karlsson, Birger

doi:10.1016/0142-1123(95)95894-m

Cited by 6 publications

(5 citation statements)

References 5 publications

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“…This is due to the easier surface penetration of the indenter due to less surface irregularities existing in the surface. Such behaviour is in agreement with previous works where higher scattering was recorded for smaller loads of the indenter [ 19 ]. The fact that larger indenter loads produce overall lower HV values has also been observed in previous repeatability studies [ 30 ].…”

Section: Micro-indentation Techniquesupporting

confidence: 93%

“…One method to characterise experimentally the plastic zone is to measure the hardness at different locations around the crack tip [ 19 ]. The volume of material within the plastic zone has been plastically deformed and thus has hardened.…”

Section: Introductionmentioning

confidence: 99%

“…Such works employed around 20 measurement points to characterise the crack tip. Subsequent works focused on a number of issues both related to the material and the techniques, such as the effect of using a very low load, the effect of the microstructure [ 19 ], the effect of high temperatures on the plastic zone [ 23 ] or the influence of the specimen geometry on the plastic zone [ 24 ]. Nevertheless, their plastic zone characterisation was based on measuring the hardness along single directions.…”

Section: Introductionmentioning

confidence: 99%

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Estimation of the Plastic Zone in Fatigue via Micro-Indentation

et al. 2021

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Accurate knowledge of the plastic zone of fatigue cracks is a very direct and effective way to quantify the damage of components subjected to cyclic loads. In this work, we propose an ultra-fine experimental characterisation of the plastic zone based on Vickers micro-indentations. The methodology is applied to different compact tension (CT) specimens made of aluminium alloy 2024-T351 subjected to increasing stress intensity factors. The experimental work and sensitivity analysis showed that polishing the surface to #3 μm surface finish and applying a 25 g-force load for 15 s produced the best results in terms of resolution and quality of the data. The methodology allowed the size and shape of both the cyclic and the monotonic plastic zones to be visualised through 2D contour maps. Comparison with Westergaard’s analytical model indicates that the methodology, in general, overestimates the plastic zone. Comparison with S355 low carbon steel suggests that the methodology works best for alloys exhibiting a high strain hardening ratio.

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Section: Micro-indentation Techniquesupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Estimation of the Plastic Zone in Fatigue via Micro-Indentation

et al. 2021

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“…They are capable of effectively resisting stress and strain and ensure safe operation of equipment by means of nondestructive testing (NDT) techniques and equipment [1,2,3,4,5,6,7]. There are a number of investigations on crack failure prediction in metallic materials using different fatigue approaches to predict failure as well as measurement by employing different techniques and scanning methods with different tools [8,9,10,11]. The studies mentioned are related to crack propagation in metallic materials, but so far, we have not seen any study that estimates the crack direction using experimental measures from the top view.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Depth Direction of Crack by measuring the Residual Magnetic Vector Flux Density around Grains

Berkache¹,

Lee²,

Dubin³

2022

eJNDT

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We suggests an algorithm to estimate the depth direction of fatigue cracks. This algorithm uses the distribution of residual magnetic vector flux density (RMVFD) on the specimen. Magnetic domains are the region with a magnetic moment in the same direction. A grain has several magnetic domains. Domain wall is the boundary of the magnetic domain. Magnetic energy stabilized when no external magnetic field applied. That is, the sum of the total magnetic moments is close to zero. It is because that the magnetic flux densities are canceling each other at both ends of the domain wall. The domain wall moves when an external magnetic field applied. As a result, the magnetic domain, which has the same direction with the external magnetic field, enlarged. This phenomenon is magnetization. The domain wall stops moving when it meets with factors that limit the domain wall movement (FLWM). Here FLWM are dislocations, defects, and crystal boundaries. The magnetic energy is unstable at the end of FLWM in the magnetic hysteresis phenomenon. Other end of FLWM has to have the opposite direction of RMVFD to stabilize the magnetic energy. Thus, there are opposite direction of RMVFD each other around crack or grain boundaries. Three dimensional RMVFD (3-RMVFD) can indicates crack existence and depth direction of crack. To verify this theorem, we prepared fatigue crack specimens with different depth direction. The three dimensional shapes of grains reconstructs at the crack. The RMVFD measured by scanning a 3-axis magnetic sensor. And the 3-RMVFD indicated in each grains around crack. The depth directions of crack and grains could estimated by using the 3-RMVFD.

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“…The techniques of indentation hardness measurements such as Vickers microhardness [6,7] and nano-hardness [8] measurements have also been utilized to analyze the development of plastic deformation at the crack tip during fatigue loading. Their application to the assessment of fatigue behavior is based on the assumption that the progress of plastic strain can be reflected in the measured hardness.…”

Section: Introductionmentioning

confidence: 99%