Indentation is seen by researchers and industry to be an attractive alternative to uniaxial testing when viewed as an experimental procedure. Multiple tests can be performed on a single specimen, far less material needs to be used to characterize the mechanical properties, and less time is required to perform what would be equivalent uniaxial tests. For example, testing for creep properties using traditional bulk testing requires up to hundreds of hours but indentation methods can reduce this by a factor of at least ten.
Unfortunately, unlike tensile tests, indentation produces non uniform stress and strain around the indenter. This is in addition to the fact that the indented material is under hydrostatic compressive stress and has localized constrained deformation fields. Thus, methods to extract material properties from indentation tests have to take all of these factors into account that are not present in uniaxial tests, so numerical simulation is commonly used in conjunction to the empirical methods or by itself to model the indentation.
The material used in this study is a family of porous sintered silver materials used for interconnects and die-attach in high-temperature electronics and in printed electronics. The objective of this research is to develop hybrid testing-modeling approaches to estimate mechanical properties of porous materials including creep properties. The modeling will range from closed-form empirical models to an implementation of a varied density model to capture the effects of the material’s initial porosity due to different sintering conditions and of the changing porosity during the indentation, due to densification under the indenter. The material properties extracted from each modeling approach will be compared to those estimated from uniaxial compression test results.
This study will not only provide a procedure to estimate creep properties for any porous materials using indentation, but a gives a guideline for using a similar procedure with any other material that has an additional varying material parameter (such as a composite). An example of the work, including the type of material, experimental work, and initial finite element analysis can be seen in ‘Viscoplastic properties of pressure-less sintered silver materials using indentation.'
To know more on the research, contact Prof. Abhijit Dasgupta.
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