Published in Scientific Papers. Series "Management, Economic Engineering in Agriculture and rural development", Vol. 15 ISSUE 3
Written by Małgorzata MŁOTEK, Roman STOPA, Piotr KOMARNICKI, Daniel SZYJEWICZ, Łukasz KUTA

The paper presents the results of surface pressure measurements for pears subjected to creep testing. The study was conducted in the Laboratory of Agrophysics at the Agricultural Engineering Institute of Wrocław University of Environmental and Life Sciences. The load was applied using an Instron 5566 testing machine equipped with a strain gauge head of a measuring range up to 1 kN that allowed measuring the strength with an accuracy of 1 N, and the offset with an accuracy of 0.05 mm. The machine was controlled by a computer with BlueHill software which enabled the recording and analysis of test results. The head feed speed until it reached the predetermined value of preload was 1.8 mm∙min-1. A sensor of the Tekscan system with number 5076 was fitted in the testing machine working area to enable continuous observation of the contact surface of the tested fruit with the working element of the testing machine as well as measurement of the surface pressures. The contours and distributions of surface pressures were determined at subsequent stages of the creep test. The maximum and the average values of surface pressures were found to be markedly reduced in the course of the test. The surface pressures distribution in the tested load range was found to take shape typical of contact cases of an elastic character, with the maximum value measured in the central contact zone. At the end of the test there was a slight equalization of pressure distribution on the contact surface of the fruit with the working element of the testing machine. The contact surface area of the maximum surface pressure values clearly increased. The measurements were carried out at three initial load values for 5 repetitions. After initial studies the measuring time at constant load was set at 1200 seconds.

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