In hybrid composites there is more than one reinforcement, I have fabricated Aluminium hybrid composites with SiC and Gr. In this materials when I measured for microvickers hardness at the metal, interface and the reinforcement. The values in the reinforcement and the interface values goes down than the metal in some cases and higher in other cases.
What is the reason for this deviation in values? Or is it better to go for macro hardness. which method is best. Do share the supporting files.
Graphite is a softer phase , so it shows lower hardness. Take number of readings and average it. Microhardness is a better to take hardness of interface along with matrix and reinforcement.
The microhardness method is not suitable with highly heterogeneous materials like composites. The only useful think you can get from mesuring the microhardness in composites would be hardness of matrix .
I would rather go with more interesting characteristics like tensile strength both along and across the fibers, impact toughness and so on.
Dear colleague, the alternative approach may be introduce the nanoindentation of hybrid composite. This scale give the opportunity to study the local variation of stiffness or hardness in heterogeneous materials like that you elaborated. So, valuable results in micromechanics you will obtain using nano-scratching test. First of all, one can study the interface zone for determination of parameters of multiphase mechanical models which including matrix, filler and intermediate (interface) layers. Unfortunately, these data is deficite jet. Good luck!
I am very sceptical with respect to nanoindentation because of elastic restoring the indentation size. At least Oliver and Farr works not well for measuring hardness even on metals.
Dear Manickam
You should use the macrohardess such as Brinell. There are three phase in the hybrid composite. Graphite is the soft phase while SiC is the brittle phase. İf you use the microindentation, this region may not reflect the hybrid composite structure.
your sincerely
Of course, "size have significance'. Macrohardness measurement gives us mechanical characteristics of composite at whole. But when researcher interested in parameters of separate phase? For example, in course of studying the role of interface layer? In this case the possibilities of macroscopic analysis are limited...
I think, performing the nano-indentation on various regions of your hybrid composite would give you a good idea of strength of the composite system. Better perform it in array 6x6, 5x5 or 5x4 indents in array , each indent separated by 20-30 microns. and try to perform multiple array-indents on your sample usually 3-4.
best wishes