Monterey Bay Aquarium Research Institute
Marine Botany


Under the supervision of Ben Hale of Hopkins Marine Station, the following strength tests were performed on a  Macrocystis pyrifera stipe.  

plot of Macrocysis strength tests

This data was obtained from putting a 18.5 cm section of stipe of mass 5.135g and 2.76E-5 m2 cross sectional area through a machine that applies a force on the sample.

With the following information, some interesting concepts can be drawn from the data.

Strain = dx/x       Stiffness = Stress/Strain

Stress = Force/Area = Stiffness * Strain

Strength = breaking Stress

Interesting aspects of the data are strength, breaking strain, and stiffness.  Strength is the highest stress in the stipe before it broke.  Breaking strain is the strain at which the sample breaks, and stiffness is the slope of the stress/strain curve.

The highest stress in the stipe before it broke, and thus the strength of the sample, was 4.064707301 MN/m2. The breaking strain for this sample was 0.257738196. This value is unit less because of the equation for strain, see above.  The stiffness from the slope of the average slope of the plots was 13.513 MN/m2See average slope plotted. However, the stiffness changed over time as is evident by the change in slope.  

All of the data from the stress/strain test: (7KB)

Copyright 2001:  James Lopez

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