Abstract: The article analyses theoretically three kinds of jaw shapes(horizontal ellipse, circle, verticle ellipse jew shapes) widely used in forest areas of China based on mechanics. Then, using the technology of resistance strain gage and three kinds of jaw shapes same as theoretical jaw shapes, it tests the effects of log grapple's jaw shapes on the grabbing properties under the working condition of grabbing compact pila; the testing items include grabbing force, log volume grabbed, grabbing force/log volume grabbed and "the number of logs blocked" duzing grabbing. The theoretical results correspond with the testing results. The results show that the property of horizontal ellipse jaw shape is better, circle jaw shape's takes second place and vertical ellipse jaw shape's is worse.

Key words: Log grabble, Jaw of grapple, Jaw shape, Operations in log yard