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- 2016 (8) (entfernen)
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- CT (1)
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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 metal matrix composites and their damage mechanisms. The matrix AlSi12CuMgNi was combined with 15% vol. Al₂O₃ (short fibers), and with 7% vol. Al₂O₃ + 15% vol. SiC (short fibers and whiskers, respectively). The experimental approach encompasses 3D microstructure characterization by means of computed tomography of samples (a) as-cast, (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.
The influence of the addition of SiC particles on mechanical properties of composite was investigated. Phase-specific load partition analysis for samples with fiber plane parallel to load was performed by using neutron diffraction (ND) during in-situ compression. ND results show damage in the Si phase, while Al₂O₃ short fibers carry load without damage until failure. The computed tomography observations confirm the load partition analysis.
Internal damage of an AlSi12CuMgNi alloy reinforced with planar random short fibres has been investigated after compression. This damage strongly influences the load partition between matrix and reinforcement. For fibres perpendicular to the applied load, breakage and interconnected cracks appear in significantly higher volume fraction than with fibres parallel to load.
The influence of second phase arrangements on the corrosion resistance of extruded Mg97Y2Zn1 alloy has been evaluated in a 0.1 M NaCl solution. The microstructure of the alloy consists of a high volume fraction of coarse elongated particles of a long period stacking ordered phase aligned along the extrusion direction. Corrosion rate of transversal sections is lower than that of longitudinal sections. Such difference is attributed to the different orientation of second phases in longitudinal and transversal sections. The corrosion front advances mainly perpendicular to the surface in transversal samples while perpendicular and lateral growth occur in longitudinal samples
Internal damage of an AlSi12CuMgNi alloy reinforced with planar randomshort fibres has been investigated after compression. This damage strongly influences the load partition between matrix and reinforcement. For fibres perpendicular to the applied load, breakage and interconnected cracks appear in significantly higher volume fraction than with fibres parallel to load.
Average phase stress concentrations in multiphase metal matrix composites under compressive loading
(2016)
We develop a model to predict average over individual phases stress concentrations in a multiphase metal matrix composite under compressive loading. The model accounts for matrix plasticity through variation of the shear modulus with applied stress and for frac- ture of filler through change in the shape of the particles. Three micromechanical models are compared –non interaction approximation, Mori–Tanaka–Benveniste (MTB) scheme, and Maxwell scheme. Comparison with the experimental measurements of Cabeza et al. (2016) shows that Maxwell scheme generally predicts the stress concentration with satis- factory accuracy. Results of MTB scheme vary depending on the loading case and ignoring of the interaction leads to substantial overestimation of the stresses.
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)
Additive Manufacturing (AM) by Selective Laser Melting (SLM) offers ample scope for producing geometrically complex parts as compared to the traditional subtractive manufacturing strategies. However, the residual stresses developed during the processing can reduce the load bearing capacity as well as induce unwanted distortion, limiting the application of SLM parts.
IN718 manufactured by SLM process can show high tensile residual stresses in the surface as high as the yield strength of the wrought alloy. On the other hand, residual stresses in the bulk Show considerably lower stress values, even in compression, indicating a stress re-distribution during deposition of the SLM layers.