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Eingeladener Vortrag
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Characterization of multiphase metal matrix composites by means of CT and neutron diffraction
(2016)
The present study examines the relationship between the microstructure of multiphase MMC and their damage mechanisms. The matrix AlSi12CuMgNi was combined with 15% vol. Al2O3 (short fibres) and with 7% vol. Al2O3 + 15% vol. SiC (short fibres and whiskers, respectively). The experimental approach encompasses 3D microstructure characterization by means of computed tomography of samples (a) as-received, (b) after heat treatment, and (c) after compression tests at room temperature. The volume fraction of different phases, their distribution, their orientation and the presence of defects and damage are studied.
Influence of addition of SiC whiskers on mechanical properties of composite was investigated. Phase-specific load partition analysis for samples with fibre plane parallel to load was perform by using neutron diffraction measurements during in-situ compression. It shows damage in the Si phase, while Al2O3 short fibres carry load without damage until failure. The computed tomography observations confirm the load partition analysis.
Neutron diffraction: the forgotten non-destructive technique for residual stress analysis … and more
(2016)
3-D Stress Analysis
(Bulk) Stress mapping
Thick (and thin) films & Interfaces
Bulk high temperature
Real time
In-situ testing: Large sample environment (Stress rigs, Furnaces, …)
Neutrons and Synchrotron Radiation allow all this because they are FASTER , DEEPER and MORE PRECISE than lab equipment
(Flux)(Energy)(Parallel Beam)
The load partition in Mg-Y-Zn system is studied by means of synchrotron diffraction. in-situ tensile tests disclose LPSO phases were for the first time proved to behave as an efficient reinforcement in Mg-Y-Zn alloys, therefore they could be treated as “short-fibre composite” for the modeling of mechanical behaviour.
The residual stress distribution of IN718 parts produced by Selective Laser Melting (SLM) technique was studied by means of neutron diffraction.
Two deposition hatching lengths were considered in the fabrication. Both lateral (building direction) and top (finishing) near-surface regions were characterized. Measurements on samples in as-built condition and after release from the plate proved the presence of stress gradients both in-plane and along the building direction.
As-built samples presented in top region a longitudinal stress relief for large hatching, whereas small one showed tensile stresses around (200MPa) in the middle, evolving towards compression at the tip of the sample (down to -300MPa). Towards the lateral edge, longitudinal stresses shifted also to compression. The transverse stresses for large hatching were relief in the middle, whereas for small hatching shifted to compression at the edge. As for the normal component, this was more homogenous: stress-relief was proved for large hatching and, in contrast, was in compression (-200MPa) for small hatching. In the building direction (lateral region from base plate to top) of the sample with large hatching all stress components showed tensile values near the base plate (particularly high for normal component around 300MPa), decreasing towards compression to the top, where they were almost released.
After release, in the top region, the longitudinal stress component for small hatching showed high compressive stresses in the central part (down to -250MPa). In contrast, for large hatching a stress relief was found. In the transversal direction, this behavior was inverted: a small hatching released stresses more effectively, while a large hatching presented high tensile stresses (around 200MPa). As for the normal component (i.e., building direction), the sample with small hatching was found in compression, while that with large hatching was stress-released or slightly in tension (around 100MPa). In the lateral surface region, all components showed similar behavior: a small hatching promoted high compressive stresses along the building direction, whereas a large hatching showed small tensile values at the bottom, which balance towards the top region. There is an overall shift of stresses in 3 directions towards tension when compared with as-built condition for top region. In contrast, the lateral region is stress-relief or shifted towards compression after cutting from baseplate.
In conclusion, hatching length parameter strongly influenced the 3D distribution of residual stress in SLM produced parts.