INSTRUMENTED PENDULUM FOR IMPACT CHARACTERIZATION OF WHOLE FRUIT AND VEGETABLE SPECIMENS

Abstract

As part of an effort to measure impact damage-related physical properties, a precision 3-m (9.8-ft) instrumented pendulum was developed to record force and contact area profiles for normal impacts of whole fruit or vegetable specimens onto an essentially rigid, flat anvil. The specimen is attached to four adjustable suspending lines (music wire and Kevlar™) to form a pendulum. The anvil against which it strikes is fitted with a force transducer and with a contact area sensor of the authors’ design. Two precisely spaced infrared beams (beams interrupted by sample) allowed approach and rebound velocities to be measured. An accelerometer attached to the trailing end of the commodity measures deceleration during impact and free vibrations during rebound. Impact profile data are typically sampled at 10 kHz per channel, sufficient to capture the required data while conserving data storage space. Operating procedures include single impacts, constant-height multiple-impacts (CHMI) (for determining bruise resistance), increasing-height multiple-impacts (IHMI), and paired increasing-height multiple-impacts (PIHMI) (for determining bruise threshold in apples). These methods are ideally suited for studying impact failure in commodities exhibiting compression failure. Those failing primarily in shear, such as potato tubers, can also be studied. The design, calibration, and operating procedures are described.