mechanical properties
Investigation of the mechanical behaviour of thin metal sheets using the hydraulic bulge test
A. Diehl, D. Staud, U. Engel
Chair of Manufacturing Technology, University of Erlangen-Nuremberg Egerlandstr. 11, D-91058 Erlangen / Germany
Abstract
Ongoing miniaturisation leads to increasing complexity of micro parts linked with continuously decreasing development time. Hence, the demand for reliable material data and means to collect these data in a most efficient way is rising. Since the mechanical properties and thus material forming behaviour are dependent on the stress and strain conditions, the test methods have to be as close as possible to real conditions. Further, due to the so called size effects, data gathered from conventional length scale experiments cannot be used for the description of material used for parts with feature sizes in the micrometer range. In the present paper, the hydraulic bulge test as a means for the mechanical characterisation of thin metal sheets with thicknesses in the range of 25 μm to 500 μm is discussed and compared to data obtained by conventional tensile testing. Challenges due to the small sheet thickness are emphasized and the effect of strain rate on the flow curve is shown. The influence of geometric dimensions on the evaluation of the experiments is investigated by downscaling of the hydraulic bulge test. The material flow curves, as well as the forming limits are discussed in dependence of the sheet thickness.
| 141 reads | Low-Pressure Injection Molding of Ceramic Micro Devices Using Sub-Micron and Nano Scaled Powders
M. Müller, W. Bauer, H.-J. Ritzhaupt-Kleissl
Institut für Materialforschung 3, Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, D
Abstract
The requirements for the manufacturing of ceramic micro parts are considered when applying the processing technology of low-pressure injection molding (LPIM). For the preparation of the feedstocks 3 mol% yttria stabilized zirconia (3YSZ) powders with different particle size were employed, ranging from the sub-μ (0.2-0.4 μm) to the nano scale (10-100 nm). Resulting from the varying powder characteristics, significant changes in feedstock properties, debinding, and sintering behavior were observed. Due to an increasing specific surface area the achievable feedstock solid loading decreased from 52 vol.% for the sub-μ powder to 45 vol.% for the nano scaled material. Correspondingly higher sintering shrinkages occurred for the feedstocks with lower solid loading, and owing to a higher binder content, during debinding the tendency to shape deviation is enlarged. On the other hand smaller particle size allows reduced sintering temperatures and leads to a smaller grain size. With nano scaled 3YSZ powder (synthesized by laser evaporation) dense samples with an average grain size of 0,26 μm were obtained at a sintering temperature of just 1300°C. In spite of a promising microstructure, samples from the nano scaled powder do not exhibit the same level of mechanical strength, yet. Depending on surface roughness and edge geometry 3 point-micro-bending tests of the standard sub-μ powder show characteristic strength values σ0 of 2700 MPa and more. For specimen with the nano scaled powder not more than 1780 MPa were detected. In the present state of research inhomogeneities, especially agglomerates, which are closely connected to the synthesis of the nano scaled powders, are considered to be the limitation for improved mechanical properties.
categories
3YSZ | ceramics | Injection moulding | low-pressure injection molding | mechanical properties | nano scaled ceramic powder
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