三次元光弾性実験法による鼓室小骨の応力解析
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概要
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When sound waves impinge upon the tympanic membrane, the manubrium of the malleus yields mechanical forces.Those forces are conducted by way of the auditory ossicular chain to the inner ear and cause consequently movements of the intralaby- rinthine fluid.Conducting the force from the manubrium to the cochlea, the auditory ossicles produce stresses in themselves.The author has investigated this stress systems in the ossicles. A method of stress analysis adopted for the purpose was three-dimensional pho- toelastic experiment, using models of diallylphthalate that were 15 times as large as the human ossicles and had accurate similarity to them. Three pieces of such model were constructed in the following manner; the long process of the malleus and the short process of the incus were respectively fixed through an attachment of bakelite to a metal frame, and the footplate of the stapes was set on a flat plate (Fig.2).External force was applied on the set of the models by weighing a weight (3.5 Kg)at the lower end of the manubrium in the direction of the stapes.This procedure was carried out inside a closed box, equipped with electric heaters, under the condition of a high temperature (170- C), After applying external force the models were cooled as slowly as possible, and thus the stress produced inside the models could be frozen perfectly.Then each of the models was sliced off in a proper direction.Stress systems in those slices were examined by passing polarized light vertically through the faces of the slice, or more minutely speaking, stress intensities were measured by circularly polarized light and directions of stress by plane polarized one (Fig.4). From the results of such optical examination it was able to know conditions of st- ress distribution in the ossicles. It is a most remarkable fact that boundary stress concentrated in the inner side of the neck of the malleus, from which to the head of the malleus the stress decreased gra- dually, but to the manbrium very steeply (Fig.5) Stress intensities in the manubrium were truely lower than that in the other parts of the malleus.From the line of prin- cipal stress it was recognized that the bending action took place at the neck of the malleus so that the inner side of the malleus produced compressive stress and the out- side produced tensile one (Fig.10). In the incus the distribution of boundary stress was almost uniform against in the malleus, and particularly inside the body of the incus, the lines of principal stress were without definite directions (Fig.7). Stapes indicated such a mode of stress distribution that both the lines of principal stress and the intensities of boundary stress were almost symmetrical in its anterior and" posterior part, involving the head, neck and the foot (Fig.8, 15). Comparing the experimentally measured stress distribution with the real structure of the human ossicles, it is found to exist an intimate relationship between the inten- sity of boundary stress and the thickness of the bony cortex.
- 社団法人 日本耳鼻咽喉科学会の論文