Definition of macro- and microstresses and their separation

Hauk, Viktor

doi:10.1016/b978-044482476-9/50007-4

Cited by 6 publications

(2 citation statements)

References 45 publications

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“…[ 20 ]). The residual stresses (RSs) were calculated with the sin 2 ψ method [ 52 ]. Importantly for the application of this method, (i) random crystallographic textures and (ii) negligible residual stresses (RSs) in the surface normal direction (σ yy ≈ 0 MPa, i.e., a planar stress state) have to be assumed.…”

Section: Methodsmentioning

confidence: 99%

Pandora’s Box–Influence of Contour Parameters on Roughness and Subsurface Residual Stresses in Laser Powder Bed Fusion of Ti-6Al-4V

et al. 2020

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The contour scan strategies in laser powder bed fusion (LPBF) of Ti-6Al-4V were studied at the coupon level. These scan strategies determined the surface qualities and subsurface residual stresses. The correlations to these properties were identified for an optimization of the LPBF processing. The surface roughness and the residual stresses in build direction were linked: combining high laser power and high scan velocities with at least two contour lines substantially reduced the surface roughness, expressed by the arithmetic mean height, from values as high as 30 µm to 13 µm, while the residual stresses rose from ~340 to about 800 MPa. At this stress level, manufactured rocket fuel injector components evidenced macroscopic cracking. A scan strategy completing the contour region at 100 W and 1050 mm/s is recommended as a compromise between residual stresses (625 MPa) and surface quality (14.2 µm). The LPBF builds were monitored with an in-line twin-photodiode-based melt pool monitoring (MPM) system, which revealed a correlation between the intensity quotient I2/I1, the surface roughness, and the residual stresses. Thus, this MPM system can provide a predictive estimate of the surface quality of the samples and resulting residual stresses in the material generated during LPBF.

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Section: Methodsmentioning

confidence: 99%

Pandora’s Box–Influence of Contour Parameters on Roughness and Subsurface Residual Stresses in Laser Powder Bed Fusion of Ti-6Al-4V

et al. 2020

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“…Primary slits with an opening of 250 μm × 250 μm and a secondary slit with an opening of 30 μm produced a prismatic gauge volume of ≈1 mm in length. The surface in-plane stress components σ RD (Figure 4a) and σ TD (Figure 4b) were determined in six points along RD and three points along TD (Figure 4c) by the sin 2 ψ technique [16] : diffraction patterns were acquired at nine ψ tilts and four azimuthal directions per measurement point. A biaxial residual stress state in the irradiated surface region was assumed.…”

Section: Determination Of Macro Residual Stress Distribution (Specimentioning

confidence: 99%

Visualisation of deformation gradients in structural steel by macroscopic magnetic domain distribution imaging (Bitter technique)

Sonntag

Cabeza

Kuntner

et al. 2018

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While classically used to visualise the magnetic microstructure of functional materials (e.g., for magnetic applications), in this study, the Bitter technique was applied for the first time to visualise macroscopic deformation gradients in a polycrystalline low-carbon steel. Spherical indentation was chosen to produce a multiaxial elastic-plastic deformation state. After removing the residual imprint, the Bitter technique was applied, and macroscopic contrast differences were captured in optical microscopy. To verify this novel characterisation technique, characteristic "hemispherical" deformation zones evolving during indentation were identified using an analytical model from the field of contact mechanics. In addition, near-surface residual stresses were determined experimentally using synchrotron radiation diffraction. It is established that the magnetic domain distribution contrast provides deformation-related information: regions of different domain wall densities correspond to different "hemispherical" deformation zones (i.e., to hydrostatic core, plastic zone and elastic zone, respectively). Moreover, the transitions between these three zones correlate with characteristic features of the residual stress profiles (sign changes in the radial and local extrema in the hoop stress). These results indicate the potential of magnetic domain distribution imaging: visualising macroscopic deformation gradients in fine-grained ferromagnetic material with a significantly improved spatial resolution as compared to integral, mean value-based measurement methods.

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