本研究利用上下施力之載重系統建立一套平板彎曲試驗以求取石材之III型破裂韌度。本試驗選用花崗岩平板為試驗材料，觀察不同裂縫邊長比試體對試驗之影響，高溫燒結後III型破裂韌度之改變，並以ANSYS數值軟體模擬驗證本試驗所得數據後，做出以下結論：提高試體之裂縫邊長比(S/L)至2/5時可獲得III型破裂模式。花崗岩III型破裂韌度為 2.29～2.96 。試體歷經高溫燒結後之III型破裂韌度有明顯下降趨勢。ANSYS數值解與公式解誤差在5%以下。
在本研究建議尺寸下，試體均穩定呈現III型破裂模式，試驗成功率為100%。在本研究的加載方式下所引起I型、II型破裂甚小，故可視本試驗為成功之III型破裂韌度試驗。

A plate bending test based on a vertical loading system was built in this study to measure the Mode III fracture toughness of rock material. Granite plates are selected as the testing materials. The topics to be investigated in this study include the crack-width ratio and temperature.
This study finds that: The plate bending test can result in the Mode III fracture when the crack-width ratio is 2/5 .Mode III fracture toughness of granite is 2.29 to 2.96 .Mode III fracture toughness decreases when the temperature increases. The formula derived by Farshad is compared with the numerical solution by ANSYS. The deviation is less than 5%.

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