2.06.2.1.2.3 PENDULUM TEST

Swinging beet

The 2023 article “Mechanical Properties of Sugar Beet Roots under Impact Loading Conditions“, by the authors Paweł Kołodziej, Zbigniew Stropek and Krzysztof Gołacki, used a pendulum test. This could be described as a “swinging beet” test; i.e. the root is mobile and the point of impact (which is also a sensor) is fixed.

IMPACT PROPERTIES

Roots were dropped from fixed heights to give impact velocities of 0.5, 1.0, and 1.5 m/s. While this gives fixed velocity, the energy at impact (inertia moment) will be dependent on the mass of the roots, varying with each test. The impact surface could be considered rigid.

CONTACT VOLUME

That is, how large is the point of impact. Given bruising is not as visible on sugar beet as it is for many fruits, an alternative method is needed. In this work, the contact volume was not directly measured, but obtained through a mix of a model and measurements. The approach is somewhat complex, and described in full in section 2.3 of the paper.

CONTACT FORCE

Measured using a force plate, at 10.24 kHz. If I’ve understood this correctly, that is 10 240 measurements per second. I believe that this is the type of resolution that is needed to get accurate measurements of sugar beet impacts under dynamic forces. With impact times of 3 to 5 milliseconds, that is a maximum force at 1.5 to 2.5 milliseconds. If temporal resolution is lower than 10 000 Hz, it will be very easy to miss peak force, or to get enough readings to fit a curve accurately.

DEFORMATION

Measured using a high-speed camera (3413 frames per second). As noted above, this is pushing the limits of temporal resolution to get accurate measurements. I do think it is sufficient. I our own work, at ca. 1000 frames per second, estimates to the nearest half-millisecond seemed feasible. With ca. 10 to 15 frames of impact time (each 0.293 of a millisecond), accuracy to the quarter-millisecond should be possible. The problem with high speed cameras is that they are very very expensive.

Swinging hammer

There is a standard material properties test used to measure “impact toughness”, known as the “notch impact”, or Charpy or Izod test. Here, a sample of the material in fixed dimensions is taken, and a hammer of known weight is released from a known height, giving a known imact force. The hammer swings through the material, which should break, and the height the hammer reaches after impact indicates the impact toughness of the material.

No such test yet described for sugar beet. It would be a little tricky getting consistent samples given the internal structure of roots. It would also be very messy. While this might give good data if comparing varieties / temperature of material, it would be difficult to make some other comparisons like root size.