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Essays and information on reed making, innovation, pedagogy, and music.

The Hardness Tester

cullen blain

OVERVIEW

The relationship of Density and Hardness of materials is very complex with minimal correlation. However, reed cane is an organic material, and there is a relationship between the material makeup and the material properties. However, the Hardness Tester is obsolete once the density of the reed cane is calculated. A hardness tester, or indentation test, is a very useful materials test for samples of uniform molecular makeup and dimension such as metals and alloys. This apparatus is not effective for measuring the hardness or tensile strength of reed cane.


USING THE HARDNESS TESTER IN REED MAKING

Reed material is a variable organic composite, the convex shape is not conducive to this testing procedure, and there are no direct correlations to the material properties of Density, Stiffness, or Resiliency. The test area is also to localized for the general observations a reed maker and musician need to make.

Though recent testing has found the indentation test has a high correlation to free air space, FAS, this nuanced inferencing still has very low correspondence to other quantifiable material properties. From the indentation test, we can only infer the general resistance strength of the cane to deformation and deflection during active performance as high or low. Many double reed musicians report success using this device. However, this is not true; these musicians are not accounting for material properties that have an actual effect on reed performance and are most likely adjusting the finish scrape in a way that accounts for these divergent qualities.

 

Procedure

  1. Measure (in mm) and record the gouge thickness of the cane (G).
  2. Measure and record the indentation depth (in mm) following the standard procedure for your hardness tester (H).
  3. Calculate the Percent Indentation using the formula below.

OBSERVATIONS FROM INITIAL TESTING

Knowing that the inner cortex of the cane is less dense than the fiber-band and dermis, and there is a correspondence between the radius and density of the tube, the indentation test results will be affected by the sample’s dimensions. Tensile Strength and Density are still independent material properties and an indentation test, for our purposes, will have higher than 20% error. Without conducting further analysis, we can only infer the relative and general resistance to deformation of the sample.

To show the dissimilarity of relative tensile strength and apparent density, as well as the corresponding relationships to an indentation test, find the mass of each sample when working with this materials test.

Using an indentation test in this manner is highly variable, and we cannot calculate the actual density or tensile strength. We can increase the statistical strength of our results by increasing our test population to the point where we can inference our performance preferences of apparent density and relative tensile strength with high accuracy, from a set of roughly 1000 samples. However, we must use a consistent methodology, calibrated equipment, and uniform test samples.

Once we have a large test population and a substantial amount of data, we can calculate the average indentation depth, average percent indentation, percentage of deviation, and chart a normalized distribution. From this data and playtesting the reeds made from this test population, we can identify the relative range of hardness that produces performing reeds. This statistical inferencing of personal preference can be very important to some musicians.