Locally resolved stress and strain analysis of sinter-joined micro valves using synchrotron X-ray diffraction and conical slit apertures

Maisenbacher, J.; Gibmeier, Jens; Klimscha, Katharina; Fischer, Torben; Staron, Peter

doi:10.1007/s00542-014-2285-6

Cited by 2 publications

(3 citation statements)

References 13 publications

(11 reference statements)

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“…Considering these conditions, the residual stress gradient in the thickness direction can be evaluated with a depth resolution in the submillimeter range, e.g., realized by using a conical slit cell mounted between the sample and the detector. [49] To validate the applied method, in situ tensile tests were performed to investigate the stability of the experimentally determined strain distribution. Finally, based on the novel approach detailed, the local variation of residual stresses as a function of sample position and the influence of processing parameters were investigated for LPBF IN718.…”

Section: Challenges For Diffraction Experimentsmentioning

confidence: 99%

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A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation

et al. 2021

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Introduction 1.1. Microstructure of Additively Manufactured MaterialsAdditive manufacturing (AM) is the subject of many recent publications. [1][2][3] Typical representatives of AM methods for the processing of metallic metals are mainly divided into three categories: wire feeding, powder feeding, and powder bed fusion systems. [3] The latter technique enables the production of metallic structures by layer-wise melting of a thin metal powder bed only using AM equipment and a sliced model generated by a computeraided design (CAD) program. The application of a powder bed in powder-based AM technology facilitates the selective processing of individual layers in complex geometry. The most commonly used powder bed fusion techniques are selective electron beam powder bed fusion (EPBF) and laser powder bed fusion (LPBF). [3,4] EPBF structures are produced in a vacuum atmosphere and at a high temperature, eventually leading to a relatively low residual stress level. In contrast, LPBF processes usually take place at temperatures up to 200 C. The localized energy input and the small melt pool sizes, respectively, in combination with low build chamber temperatures result in high temperature gradients, whereby residual stresses are favored. [5] Generally, the influence of scan vectors and related strategies is a complex topic, which crucially has to be dealt with. Scan vector lengths, orientations, the order of rotation within a specific layer, and its subsequent layers are variables in every building process. Only a very limited number of comprehensive studies have reported on the effect of the scan strategy on the density, microstructure, mechanical properties, and residual stresses of LPBF parts, as clearly stated in previous studies. [5][6][7][8] Already an increased scan path length, e.g., due to a change of cross-section of a part, can result in a severely decreased relative density as well as fundamentally changed microstructure. [9,10] The influence of parameters on the evolution of residual stresses was already numerously studied. [11,12] The authors showed that the residual stresses are mainly influenced by cooling rates, temperature gradients, and melt pool sizes. Also, a minimization of the temperature gradient by powder bed preheating is an option to reduce process-induced stresses. [1,13] The high influence of the laser power and the effect of scan strategies have been characterized.

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Section: Challenges For Diffraction Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation

et al. 2021

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“…Given that the number of illuminated grains is potentially a controlling consideration for achieving satisfactory lattice strain measurement precision, it is important to understand the associated geometry of the gauge volume, V, and the grain size, D, of the material to be studied. In the monochromatic diffraction experiments covered in this work, depth resolved measurements were not made, which is to say the outgoing beam was not defined (e.g., with the conical slit system) [27]. As such, the gauge length is simply the thickness of the part being measured, z, with the remaining gauge dimensions being defined by the slit size h 1 × h 2 , where in most cases h = h 1 = h 2 , such that V = zh 2 .…”

Section: Measurement Gauge Volume and Illuminated Grainsmentioning

confidence: 99%

Influence of Microstructure on Synchrotron X-ray Diffraction Lattice Strain Measurement Uncertainty

Simpson¹,

Knowles

Mostafavi

2021

Metals

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Accurate residual lattice strain measurements are highly dependent upon the precision of the diffraction peak location and the underlying microstructure suitability. The suitability of the microstructure is related to the requirement for valid powder diffraction sampling statistics and the associated number of appropriately orientated illuminated. In this work, these two sources of uncertainty are separated, and a method given for both the quantification of errors associated with insufficient grain sampling statistics and minimization of the total lattice strain measurement uncertainty. It is possible to reduce the total lattice strain measurement uncertainty by leveraging diffraction peak measurements made at multiple azimuthal angles. Lattice strain measurement data acquired during eight synchrotron X-ray diffraction experiments, monochromatic and energy dispersive, has been assessed as per this approach, with microstructural suitability being seen to dominate total measurement uncertainty when the number of illuminated grains was <106. More than half of the studied experimental data fell into this category, with a severe underestimation of total strain measurement uncertainty being possible when microstructural suitability is not considered. To achieve a strain measurement uncertainty under 10−4, approximately 3×105 grains must be within the sampled gauge volume, with this value varying with the multiplicity of the family of lattice planes under study. Where additional azimuthally arrayed data are available an in-plane lattice strain tensor can be extracted. This improves overall strain measurement accuracy and an uncertainty under 10−4 can then be achieved with just 4×104 grains.

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Locally resolved stress and strain analysis of sinter-joined micro valves using synchrotron X-ray diffraction and conical slit apertures

Cited by 2 publications

References 13 publications

A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation

A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation

Influence of Microstructure on Synchrotron X-ray Diffraction Lattice Strain Measurement Uncertainty

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