Hi,
I'm conducting compressive mechanical tests on jello material on a rheometer HR20 by TA Instruments. The cross hatched top plate is 8mm in diameter and circular in shape.
I'm testing hockey puck shaped jello samples ( 8mm in diameter, 2mm in height) and calculated the area under the curve given by the software.
1. I'm getting results as Pa %. Don't the numbers seem too high for a small soft sample? (I triple checked my input dimensions and down speed).
2. I generated another graph from the same data with um on the x axis instead of %. The numbers make more sense this way but I need help equating between this value and the one from the first graph(as they should be the same when manipulating units).
3 To my understanding, area under the curve is toughness which should be provided in units as J/mm3. Does anyone know how to convert the values from the previous 2 questions to J/mm3?
Please help if you understand this problem, it is greatly appreciated!
- Strain is length/length, %strain is 100*length/length. Given %strain, to get strain you need to compute %strain/100.
- Stress is force/area=force/(length*length). Stress*strain is (force/(length*length))*length/length, or (force*length)/(length*length*length), i.e. energy/volume.
- In your problem, stress in given in Pa=N/m^2 while (it appears) strain in given as mum/mum, i.e. displacements and lengths are given in mum=1e-3mm=1e-6m.
Yousef Ak I believe you'll be able to equate them once you sort out the integration axis ((i) strain % and (ii) extension). Your strength is at 9.6e6 Pa% which means that the strength is 96 KPa. I know you've shown the results in compression but you shouldn't be worried about this being too high a value since gelatin-like films have a tensile strength in the order of 1e2 MPa.
Regarding the 3rd question, the area under curve represents toughness (amount of work done /unit volume) of material specimen, In you case it is 96.1kPa %. The ultimate compressive strength is however (assumed from fig) , ~580.1 kPa = ~ 0.6 MPa.
The Youngs (elastic) modulus is ~ (75.8/58.9)*(100) = 0.128 MPa . The yield seems to have occurred at 58.9 strain %
However, i am not sure if there are direct conversion units from Pa% to J/mm^3 .
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