into stress—strain curves. As previously mentioned, the instrument in its usual commercially available form produces curves of force versus linear travel. While linear travel is easily converted to true strain (eq. 11), the stress correction requires a knowledge of the actual shape at any instant during compression. Often this is unknown, or at least unreported. Unless special precautions have been taken, the behavior of the sample will be intermediate between that obtaining in the lubricated and in the bonded situations. For the present purposes the simpler correction applying to the lubricated condition has been used throughout, although it is realized that it will not quite compensate for the barreling which occurs. The values were then read from the transformed curves. The modulus given in the column headed E0 is from the slope at the origin, ie, it refers to the undeformed sample. The entries in the columns headed yield refer to the stress and strain at the peak of the curve.

Table 2 summarizes a number of results which have been obtained by other methods where it has been possible to calculate a modulus from the data. In order to compare the two tables, it will be recalled that Table 1 lists the values of an elastic modulus. It must be most nearly comparable with any quasi-modulus determined by the puncture test or by simple compression. The yield stress measured by a cone penetrometer is more likely to be comparable with the yield value in the force-compression

Table 2. Modulus Measurements Using Various Methods


Modulus (kN/m2)




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