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Journal of Applied Sciences

Year: 2008 | Volume: 8 | Issue: 5 | Page No.: 886-890
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Authors

Faroogh Sharifian

Mohammadali Haddad Derafshi

Keywords

Research Article

Mechanical Behavior of Walnut under Cracking Conditions

Faroogh Sharifian and Mohammadali Haddad Derafshi
The main objective of this study was to determine the effects of the moisture content, loading velocity and compression position on the force, specific deformation, absorbed energy and required power to achieve the initial rupture of the walnut shell. Iran is the third walnut producing country in the world. Separation of walnut kernel from the shell is a very time consuming and costly task. A proper cracking machine for walnut has not yet been manufactured. It seems that the determination of mechanical properties of different walnut varieties is the pre-requisite step for this purpose. Thus, 108 local walnut samples, (a local cultivar) obtained from the seedling trees of Urmia district, with almost equal dimensions were selected. These samples were compression loaded by an Instron test machine until the shell rupture was initiated. During this experiment, rupture force, specific deformation, required energy and power for shell rupture, in 9, 21 and 27% (w.b.) walnut moisture levels, 50, 200 and 500 mm min-1 loading velocities and at 3 major compression directions namely, length (X), suture (Z) and width (Y), were determined. The results of this experiment indicated that, the highest force, energy and power values, required for walnut rupture, occur when the force is applied at the length direction of the fruit and the lowest of these values were required at either width or suture line. Specific deformation of walnut shell increased with increasing loading velocity, regardless of its moisture content and loading direction. Furthermore, moisture content of walnut shell increased the specific deformation for 21% moisture, but did not cause further changes at the higher level of 27% of moisture. However, the strain values (specific deformation) appeared to be the same at all loading position. Increasing the loading velocity, although increased the required rupture energy and power, but reduced the fracture force. Furthermore, in higher loading velocities (about 500 mm min-1), the specific deformation increased which indicates more flexibility in walnut shell. Flexible shell may protect the fruit against fracture in the walnut cracking process.
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