scholarly journals Inter-Granular Residual Stresses in Polycrystalline Aggregates: Finite Element Modelling and Diffraction Post-Processing

2008 ◽  
Vol 571-572 ◽  
pp. 271-276 ◽  
Author(s):  
Xu Song ◽  
Shu Yan Zhang ◽  
Daniele Dini ◽  
Alexander M. Korsunsky
Keyword(s):  
Stress State ◽  
Residual Stresses ◽  
Elastic Anisotropy ◽  
Fatigue Crack Initiation ◽  
Grain Morphology ◽  
High Energy ◽  
External Loading ◽  
X Rays ◽  
Micro Scale ◽  
Residual Strains

Most models based on continuum mechanics do not account for inhomogeneities at the micro-scale. This can be achieved by considering a representative volume of material and using (poly)crystal elasto-plastic deformation theory to model the effects of grain morphology and crystallographic orientation. In this way, the relationship between the macroscopic stress state and the stress state at the grain level can be investigated in detail. In addition, this approach enables the determination of the inhomogeneous fields of plastic strain, the identification of regions of localised plasticity (persistent slip bands), grain level shakedown, and the prediction of fatigue crack initiation using energy dissipation at the micro-scale. Elastic anisotropy is known to promote earlier onset of yielding, and to increase the magnitude of intergranular residual stresses. The effect of hardening behaviour of different slip systems on intergranular residual stresses is more subtle, as discussed in the text. The present study focuses on the analysis average intergranular residual strains and stresses that arise within the polycrystal aggregate following the application of single or cyclic external loading. These residual strains can also be evaluated experimentally using diffraction of penetrating radiation, e.g. neutrons or high energy X-rays, allowing comparisons with the model predictions to be made.

Temperature Dependence of Residual Stresses and Stress Relaxation in Blanket Films of Various Thicknesses

1994 ◽  
Vol 356 ◽  
Author(s):  
A. P. Clarke ◽  
G. Langelaan ◽  
S. Saimoto
Keyword(s):  
Residual Stress ◽  
Stress Relaxation ◽  
Residual Stresses ◽  
Back Stress ◽  
Temperature Cycling ◽  
Misfit Dislocations ◽  
X Rays ◽  
Heating Rates ◽  
Residual Strains ◽  
Continuous Temperature

AbstractA rapid method to measure residual strains using x-rays during continuous temperature ramping has been developed whereby resolution of ±5xl0-5 can be attained with 2θ scans of about one minute using low index reflections. The method was used to make residual stress measurements during temperature cycling at heating rates of 2 to 15°C/min with interrupted stress relaxations at 235°C and 130°C on pure Al blanket films of 0.24μm, 0.58μm and 1.01 μm thicknesses. The results are consistent with the notion that surface sources are activated by the back stress of misfit dislocations.

Preferred orientation and elastic anisotropy of illite-rich shale

Geophysics ◽  
2007 ◽  
Vol 72 (2) ◽  
pp. E69-E75 ◽  
Author(s):  
Hans-Rudolf Wenk ◽  
Ivan Lonardelli ◽  
Hermann Franz ◽  
Kurt Nihei ◽  
Seiji Nakagawa
Keyword(s):  
Grain Size ◽  
Seismic Anisotropy ◽  
Elastic Anisotropy ◽  
Rietveld Method ◽  
Transverse Isotropy ◽  
Orientation Distribution ◽  
High Energy ◽  
Quantitative Information ◽  
Preferred Orientation ◽  
X Rays

Shales display significant seismic anisotropy that is attributed in part to preferred orientation of constituent minerals. This orientation pattern has been difficult to quantify because of the poor crystallinity and small grain size of clay minerals. A new method is introduced that uses high-energy synchrotron X-rays to obtain diffraction images in transmission geometry and applies it to an illite-rich shale. The images are analyzed with the crystallographic Rietveld method to obtain quantitative information about phase proportions, crystal structure, grain size, and preferred orientation (texture) that is the focus of the study. Textures for illite are extremely strong, with a maximum of 10 multiples of a random distribution for (001) pole figures. From the three-dimensional orientation distribution of crystallites, and single-crystal elastic properties, the intrinsic anisotropic elastic constants of the illite aggregate (excluding contribution from aligned micropores) can be calculated by appropriate medium averaging. The illitic shale displays roughly transverse isotropy with [Formula: see text] close to [Formula: see text] and more than twice as strong as [Formula: see text]. This method will lend itself to investigate complex polymineralic shales and quantify the contribution of preferred orientation to macroscopic anisotropy.

Evaluation by Synchrotron Radiation of Shape Factor Effects on Residual Stress in Nitrided Layers

2006 ◽  
Vol 524-525 ◽  
pp. 285-290 ◽  
Author(s):  
Vincent Goret ◽  
Agnès Fabre ◽  
Laurent Barrallier ◽  
Patrick Vardon
Keyword(s):  
Residual Stresses ◽  
Stress Tensor ◽  
Plane Surface ◽  
Depth Map ◽  
High Energy ◽  
Great Accuracy ◽  
Stress Profile ◽  
X Rays ◽  
Nitrogen Diffusion ◽  
Stress Gradients

Nitriding is a thermo-chemical treatment to improve fatigue life of steel parts what are exposed to high cyclic loading on and close to the surface like gears for example. During the nitrogen diffusion, the precipitation of nitrides and carbides generates residual stresses and increases the superficial hardness. These residual stresses are function of the conditions of the nitriding process but also critically depend on the geometry of the steel components. Indeed, the result of the diffusion process is different for a plane geometry or a curvilinear one. In this present work, the sample is a part of a gear, composed by two teeth. Between two teeth of gear, the determination of in-depth stress gradients by classical X-rays diffraction cannot be done with a great accuracy: the spatial resolution is not sufficient because the irradiated area has the same dimension than the surface curvature of the component. Furthermore, it is very difficult to take into account the removal of matter that is required to determine in-depth stress profile because of the particular geometry. The synchrotron diffraction technique is a well-adapted method to determine such stress gradients in strongly absorbing materials due to the capability of penetration power of high energy X-rays. The removal of matter is not required and it is possible to determine an in-depth map of the stress tensor. After measurements on the ESRF ID15 beam line, stress profile has been calculated without the σ33 equal to zero hypothesis. The results are as following: compressive residual stresses were found close to the surface, and the calculated σ33 component of stress tensor is really not equal to zero. This important result seems to show the geometrical effect on stress state near non-plane surface.

In Situ Synchrotron Measurements of Oxide Growth Strains

2005 ◽  
Vol 490-491 ◽  
pp. 287-293 ◽  
Author(s):  
Jonathan Almer ◽  
Geoffrey A. Swift ◽  
John A. Nychka ◽  
Ersan Üstündag ◽  
David R. Clarke
Keyword(s):  
Strain Relaxation ◽  
Relaxation Mechanism ◽  
High Energy ◽  
Oxide Growth ◽  
X Rays ◽  
Pure Alumina ◽  
Transmission Geometry ◽  
Residual Strains

Synchrotron x-rays are used for in situ determination of oxide strain, during oxide formation on a Kanthal A1 FeCrAlZr substrate at 1160°C. The measurements rely on use of high-energy (~80keV) x-rays and transmission geometry, and the methodology of the strain measurements is presented. Oxide growth strains at elevated temperature, relative to pure alumina, were seen to be small, while temperature excursions induced significant strains. Furthermore, significant strain relaxation was observed during isothermal holds, suggesting oxide creep as a major relaxation mechanism. Upon cooling to room temperature, significant residual strains developed, with a corresponding in-plane residual stress of -3.7 GPa.

Investigation of Plastic Instability in TWIP Steels by In Situ Diffraction of High Energy X-Rays

2014 ◽  
Vol 783-786 ◽  
pp. 1105-1110
Author(s):  
Jean Philippe Chateau-Cornu ◽  
Alain Jacques ◽  
Jean Philippe Tinnes ◽  
Thomas Schenk
Keyword(s):  
Plastic Strain ◽  
Elastic Anisotropy ◽  
Tensile Tests ◽  
Plastic Instability ◽  
High Energy ◽  
Nucleation Site ◽  
X Rays ◽  
Cubic Crystal ◽  
Twip Steels

We investigate the non uniform plastic deformation of a TWIP FeMnC steel by diffraction of high energy synchrotron X-rays. In particular, we observe the propagation of bands of plastic strain localisation. Debye-Scherrer rings are recorded in situ during tensile tests at two different strain rates. Discontinuous initial rings characteristic of unstrained polycristals with no texture become rapidly continuous after several percents of plastic strain due to strain gradients within the grains and a strong texture develops. The crystallographic dependence of the Young’s modulus is estimated and is consistent with the elastic anisotropy of a cubic crystal. A delay between the serrations on the macroscopic tensile curve and the stepwise variations of the diffracted peak’s position and width are consistent with propagating bands nucleating outside the X-ray beam. Slower and thinner bands are observed at the lowest strain rate. A tensile test interrupted to perform a few minute relaxation leads to a displacement of the nucleation site of the bands from one end to the middle of the gauge part.

Neutron Surface Residual Stress Scanning Using Optimisation of a Si Bent Perfect Crystal Monochromator for Minimising Spurious Strains

2011 ◽  
Vol 681 ◽  
pp. 399-404 ◽  
Author(s):  
Joana Rebelo-Kornmeier ◽  
Jens Gibmeier ◽  
Michael Hofmann ◽  
Robert C. Wimpory
Keyword(s):  
Residual Stress ◽  
Stress Analysis ◽  
Surface Effect ◽  
Stress Gradient ◽  
High Energy ◽  
Surface Strain ◽  
X Rays ◽  
Surface Residual Stress ◽  
Gauge Volume ◽  
Residual Strains

For non destructive stress analysis of surface treated steel samples the application of laboratory X rays or high energy synchrotron radiation in reflection mode covers the region from some micrometers up to a depth of about 150 - 200 µm. To access depth regions deeper than 200 µm the incremental layer removal technique in combination with the repeated application of X‑ray stress analysis for the newly generated surfaces can be used. However, this procedure is destructive, laborious and furthermore, it has to be checked whether corrections have to be applied due to stress relaxation. By using neutron radiation penetration depths generally up to several millimetres can be achieved non destructively [1]. However neutron measurements are critical at the surface. When scanning a sample surface, aberration peak shifts caused by so called spurious strains arise due to the fact that the gauge volume defined by the primary and secondary optics is partially outside of the sample. These aberration peak shifts can be of the same order of magnitude as the peak shifts related to residual strains [2-6]. In this exemplary study it will be demonstrated that, by optimising the bending radius of a Si (400) monochromator, the spurious surface strains can be strongly reduced when compared to the values obtained with a traditional Ge (311) mosaic monochromator, even when the gauge volume is mainly out of the surface. The objective of the experiments is to find the optimal monochromator settings for the Si (400) monochromator at the STRESS-SPEC instrument at the research reactor FRM II, Munich, Germany. For the parametric studies a stress free steel sample of the fine grained construction steel, S690QL was used. The optimised conditions for the Si (400) monochromator that resulted from the systematic studies were applied to a shot peened plate of steel SAE 4140. The residual stress distribution is analysed by means of through surface strain scanning. The residual stress gradient obtained is in very good agreement with the well characterised residual stress depth profile obtained within a round robin test in the scope of the BRITE-EURAM-project ENSPED (European Network of Surface and Prestress Engineering and Design) [7]. The results indicated that surface residual stress profiles can be measured with neutrons up to 200 µm underneath the surface without time consuming and laborious surface effect corrections.

Hydrogen Interaction with Residual Stresses in Steel Studied by Synchrotron X-Ray Diffraction

2013 ◽  
Vol 772 ◽  
pp. 91-95 ◽  
Author(s):  
Eitan Dabah ◽  
Thomas Kannengiesser ◽  
Dan Eliezer ◽  
Thomas Boellinghaus
Keyword(s):  
Residual Stress ◽  
Stress State ◽  
Residual Stresses ◽  
High Energy ◽  
Steel Sample ◽  
Stainless Steel Sample ◽  
X Ray Diffraction ◽  
High Hydrogen ◽  
X Ray ◽  
Residual Stress State

The residual stress state in a material has an important role in the mechanism of cracking, induced or assisted by hydrogen. In this contribution, the beamline EDDI in BESSY II instrument in Berlin was used in order to investigate the influence of hydrogen upon the residual stresses state existing in a Supermartensitic stainless steel sample. The method used for investigating the residual stresses is the “sinus square ψ” method. This method involves the usage of high energy X-ray diffraction in order to measure the residual stress state and magnitude. It was found that hydrogen presence has a significant influence upon the magnitude of the residual stresses, as its value decreases with high hydrogen content. This effect is reversible, as hydrogen desorbs from the sample the residual stress magnitude gains its initial value before hydrogen charging.

Characterisation of the Residual Stresses in HVOF WC-Co Coatings and Substrates

2013 ◽  
Vol 768-769 ◽  
pp. 280-285
Author(s):  
Andrew M. Venter ◽  
O. Philip Oladijo ◽  
L.A. Cornish ◽  
Natasha Sacks
Keyword(s):  
High Energy ◽  
Substrate Material ◽  
X Rays ◽  
Hvof Thermal Spray ◽  
Residual Strains ◽  
Strain Stress ◽  
Oxygen Fuel ◽  
Processing Steps ◽  
Deformation Approach

Residual strains and stresses associated with the processing steps of the industrial high-velocity oxygen-fuel (HVOF) thermal spray technique, was non-destructively characterised in both the coatings and substrates. A range of substrates, having coefficients of thermal expansion different to that of the as-coated WC-Co material, have been considered to assess the potential role of the thermal misfit associated with the coating procedure. Surface and depth resolved studies of the in-plane and normal components of residual strains have been investigated by exploiting the penetrating capabilities of high energy synchrotron X-rays in conjunction with micron sized gauge volumes to enable strain gradient determination with high positional resolution. Results reveal the presence of large residual strain/stress mismatches at the interface region in all the substrate materials, whereas the strains/stresses in the as-coated material are small, seemingly independent of the substrate material. The different contributions due to the HVOF process are qualitatively assessed in terms of an eigenstrains (plastic deformation) approach.

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