Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Eingeladener Vortrag
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In the present study, Ti-6Al-4V bridge-like specimens were manufactured additively by selective laser melting (SLM) under different laser scanning speed conditions in order to compare the effect of process energy density on the residual stress state. Subsurface residual stress analysis was conducted by means of synchrotron diffraction in energy dispersive mode for three conditions: as-built on base plate, released from base plate, and after heat treatment on the base plate. The quantitative residual stress characterization shows a correlation with the qualitative bridge curvature method. Computed tomography (CT) was carried out to ensure that no stress relief took place owing to the presence of porosity. CT allows obtaining spatial and size pores distribution which helps in optimization of the SLM process.
High tensile residual stresses were found at the lateral surface for samples in the as-built conditions. We observed that higher laser energy density during fabrication leads to lower residual stresses. Samples in released condition showed redistribution of the stresses due to distortion. A method for the calculation of the stress associated to distortion of the parts after cutting from base plate is proposed. The distortion measurements were used as input for FEM simulations.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread equally holds for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated.
I will show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. Examples of micro-structured inhomogeneous materials will be given, such as Composites, Ceramics, Concrete, and Additively manufactured parts. I will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Additionally, I will present a new technique in our portfolio, Neutron Diffraction, which is extremely well suited to the study of internal stresses, both residual and under external load.
Complex materials (e.g., porous ceramics) need high resolution techniques at multi-scale levels. Microstructure is intimately linked to properties and performance. One technique (or even a few techniques) is not enough. X-ray refraction and CT are very powerful tools. Non-destructive characterisation and quantitative image analysis techniques (2D and 3D) are necessary to understand the anisotropy.
The evolution of the microstructure of multiphase metal matrix composite AlSi12CuNiMg with 7% vol. Al2O3 + 15% vol. SiC (short fibers and whiskers, respectively) was studied by synchrotron computed tomography. It comprehended as cast and after heat treatment conditions, as well as damage evaluation after ex-situ compression tests at room temperature. The volume fraction of different phases, their distribution, their orientation, and damage events are studied.
The influence on mechanical properties of the orientation of the planar random short fibres Al2O3 towards loading was investigated. Phase-specific load partition analysis for samples with fiber plane parallel and orthogonal to load, respectively, was performed by means of neutron diffraction (ND) during in-situ compression tests at room temperature. ND results proved that damage occurrence in the fillers strongly depends on the preferential orientation of those, playing a crucial role in the failure of the sample. The computed tomography observations confirm the damage observations from curves of load partition analysis of each phase.
This paper focuses on the aspect on how damage evolution processes in composite materials and structures including matrix fracture, delamination, fibre-matrix debonding, and fibre fracture can be detected by taking advantage of the material’s inherit mechanical properties. These properties can be described on the basis of non-linear mechanical phenomena measurable as an inert frequency response signal. The approach is proposed as a means for residual life structural assessment specifically in the context of VHCF.
X-ray refraction techniques represent a very promising, yet not so wide-spread, set of X-ray techniques
based on refraction effects. They allow determining internal specific surface (surface per unit volume) in a non-destructive fashion, position and orientation sensitive, and with nanometric detectability. While they are limited by the X-ray absorption of the material under investigation, we demonstrate showcases of ceramics and composite materials, where understanding of microstructural features could be achieved in a way unrivalled even by high-resolution techniques such as electron microscopy or computed tomography.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread equally holds for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated.
I will show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. Examples of micro-structured inhomogeneous materials will be given, such as Composites, Ceramics, Concrete, and Additively manufactured parts. I will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Additionally, I will present a new technique in our portfolio, Neutron Diffraction, which is extremely well suited to the study of internal stresses, both residual and under external load.
Applications of X-ray refraction to non-destructive characterization of ceramics and composites
(2017)
X-ray refraction is analogous to visible light deflection by matter, with two main differences: 1- convex objects cause divergence (i.e., the refraction index n is smaller than 1), and 2- deflection angles are very small, from a few seconds to a few minutes of arc (i.e., n is near to 1). Trivially but importantly, deflection of X-rays is also sensitive to the orientation of the object boundaries. These features make X-ray refraction techniques extremely suitable to a) detect defects such as pores and microcracks, and quantify their densities in bulk (light) materials, and b) evaluate porosity and particle properties such as orientation, size, and spatial distribution (by mapping). While X-ray refraction techniques cannot in general image single defects, their detectability is simply limited by the wavelength of the radiation.
We will thereby show the application of X-ray refraction 2D mapping (topography) and tomography to different sorts of problems in ceramic science and technology: 1) Sintering of SiC green bodies; 2) Porosity analysis in diesel particulate filter silicates; 3) fiber de-bonding in metal and polymer matrix composites; 4) micro-cracking of glass-precursor -eucryptite. We will see that the use of X-ray refraction analysis yields quantitative results, also directly usable in available models.
Quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. I will show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing, with particular focus on additively manufactured materials. I will also show how X-ray refraction computed tomography (CT) and Neutron diffraction can be highly complementary to classic absorption CT, being sensitive to internal interfaces and residual stress analysis, respectively.
Shock tube systems are non-electric explosive fuses employed in blasting and demolition applications to trigger the detonation of explosive charges. Their working principle is based on the explosive reaction of a fine explosive powder on the tubing's inner surface, generating a shock wave traveling at a velocity of 2,100 m/s along the length of the tube, without destroying it. One of
the key aspects of the manufacturing process of these shock tubes is the size and morphology of the explosive powder grains and their distribution on the inner wall of the tube, in order to propagate the shockwave efficiently and reliably. For the first time, synchrotron X-ray computed tomography has been used to characterize non-destructively the explosive powder grains, typically Al/HMX between 10 and 20 μm in size, in terms of morphology and 3D distribution but also to characterise the presence and location of defects
within the shock tube walls.