岩石內部傳遞的超音波除了與組成礦物的彈性模數有關外，與岩石內部裂隙的分佈狀況也有相對關係。為利於層狀材料波速之量測，實有需要針對層狀材料之超音波波速變化加以研究。 本文模式根據Snell’s law，推導多相層狀試體之不同層厚比、波速比於不同角度之超音波波速預測模式。軟體方面使用Tomograph 2D，此程式以Fermat’s principle為基礎，利用離散的方法搜尋最小走時路徑，以此路徑與走時求得層狀材料之波速。本文模式與Tomograph 2D計算結果相當一致。本文模式為解析解，相對於軟體具有計算快速、層狀數量不受限制的優點。 為探討本文模式之正確性，本研究以壓克力、紙張和鋼片堆疊成不同層厚比之層狀試體，進行不同角度之超音波量測。試驗結果於θ=0度之波速為最高，相當接近波速最高材料之波速，且波速隨角度之增加而遞減，至θ=90度時波速達最小值。其餘角度波速可利用鏡射與對稱方式求得。試驗結果顯示與本文模式及Tomograph 2D計算結果相當一致。並以不同厚度之壓克力堆疊成不同界面間距之層狀試體，於相同接觸應力下，界面間距越小，波速異向性越明顯，隨著接觸壓力增加，層狀材料會逐漸趨於等向性。 The ultrasonic transfer within the rock is not only related to the elastic modulus of mineral compostion, but also the cracks distribution of the rock. It is needed to study the change of P-wave velocity. In this paper, predictions are all based on Snell’s law. This study derives different layer thickness ratio of multiphase layered models and different wave velocity ratio at different angle-prediction model. Tomograph 2D is used as computation program. It is based on Fermat’s principle using discrete way to search the minimum travel time path. Therefore, wave velocity is obtained by path and traveltime. The model found in this article is very consistence with the result from Tomograph 2D. Analytical solution is found and its advantages are quick computation and unrestricted by the number of the layers. In order to examine the accuracy of the model, the acrylics, papers and steels are applied to stack into interlayer model of the different layer thickness ratio. In addition the P-wave velocity at different angles is measured. The results showed that the P-wave velocity was fastest at θ=0°, quite close to the velocity of the material which has maximum. The minimum of the P-wave velocity appeared at θ=90°. The velocity at other angles can be obtained from mirroring and symmetric ways. As a result, under the same contact force, the less the layer spacing, the more obvious the velocity anisotropy. With the increasing of contact force, the interlayer material will become more like isotropic material.
