Dear All,
I have plotted force vs deflection and stress vs strain curves.
Now I want to determine the stiffness of polymer composite.
I have two options and I am not sure which one to use.
1. Determine the stiffness by considering the load vs deflection value within elastic limit, i.e. k (stiffness) = f (load)/x (deflection)
2. k = Area of composite specimen x young's modulus / gauge length
Now please help me which one I must consider and why.
Thank you for the support.
It depends on your specimen/test configuration. If you are testing by a 3 point bending method or a cantilever beam method, then the slope of the force versus deflection plot will give you the stiffness. If you are using a dog-bone shaped tensile specimen, then the second method will be appropriate. If you are using an extensometer, you get more reliable data. Mathematically both equations lead to the same result.
For tensile tests, you can refer to ASTM D3039. You must calculate the slope between two strain values, as explained in the ASTM. For flexion, you can refer to the ASTM D709.
Dear Gangadhar M Kanaginahal,
The elevated question is innate, and many studies are being explored on composites. Part of the composite materials show improvement of the technological shifts. Others, however, deteriorate under certain working conditions. The purpose of the composites is to obtain a material with complex mechanical properties such as strength, toughness, plasticity, lightness, and the like, which are close to the mechanical properties of the replaced base material. The results obtained from the tensile, compression, bending tests are complex of the composite. When measuring hardness, the results may differ from theoretical calculations due to the different properties of the input materials. Regards Emil Yankov
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