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    Title: 受剪節理面之接觸應力量測
    Other Titles: Measuring the contact stress of joint surface during shear
    Authors: 邱偉杰;Chiu, Wei-Chieh
    Contributors: 淡江大學土木工程學系碩士班
    楊長義
    Keywords: 節理面;接觸應力;富士感壓紙;張力裂縫;Joint Surface;contact stress;Prescale film;Tension cracks
    Date: 2016
    Issue Date: 2017-08-24 23:48:48 (UTC+8)
    Abstract: 在節理剪力試驗研究上,一般是以外部施加的正向力(N)或剪力(T),除以試體整體受剪面積(A)而計算得作用在節理面間的平均正向應力及平均剪應力。但實際上,因真正受力接觸面積僅發生在少數節瘤面上,故作用於節理面間真實的接觸正向應力及剪應力,可能大於其平均應力計算值。本文是嘗試以富士感壓紙薄膜為量測介質,借感壓紙在受不同壓力作用後,會顯示出不同顏色深淺印痕反應。試驗時,特將感壓紙放置於兩節理平面間,透由內部之應力量測值與外部應力衡盒量測得正向應力及剪應力之關係,期望了解比較剪動過程中,在不同剪動情況下,探討實際的接觸應力與平均應力計算值兩者的差異。
    本文主要獲致結論如下:在平面型節理:(1) 其尖峰剪力強度值,只受施加正向應力的大小影響,不受分段剪位移量多寡之影響。(2) 富士感壓紙之印痕,會受不同正向應力及剪動量,造成印痕顏色發生深淺變化及印痕接觸面積的改變。未剪動時,接觸印痕面積為41%~75%;受剪後,會提升至約85~90%。(3) 因分佈接觸應力值與感壓紙印痕深淺分佈有相關,進而可藉以分析接觸應力值的改變。(4) 外部量測剪應力與內部實測接觸剪應力,於受不同分段剪位移量下,在低正向應力時,內部量測接觸剪應力值約為外部剪應力值的1.1~1.4倍間;中度正向應力時,隨分段剪位移量增加,其比值由0.96倍逐漸提升至2.5倍;高正向應力時,比值由0.66倍提升至1.46倍,顯示較高正向應力中,分段剪位移量的增加,會影響實際作用於內部節理面之應力值。
    在45°鋸齒型節理:(1) 外加正向應力較高時,使鋸齒,產生張力裂縫所需施加之剪應力較少,所需驅動剪動距離較短。(2) 上坡面出現張力裂縫的位置,不因外加正向應力高低而有所變化,均出現在上坡面受力區之下緣部位。(3)其接觸應力分佈型態,亦不因正向應力高低或錯開位移量不同而有所變化,均為梯型分佈型態,僅在應力最大值分佈位置有所差別。(4)經比較發現透由兩量測方式所量得作用於上坡面之應力值(外部正向分量之應力值6.14±0.36MPa,內部量測接觸應力值5.18±0.08MPa),均與單壓強度值(UCS=5.98±0.56MPa)相近,並與外部正向力與剪力Loadcell量測值之正向分量應力值最為接近,顯示受剪鋸齒節理上坡面之張裂行為與節理壁材單軸抗壓行為有關。
    In general joint shear tests, external normal forces (N) or shear forces (T) are divided by the overall area of a specimen under shear forces (A) to calculate the average normal stress and shear stress applied on joint surfaces. However, the actual contact area under force merely occurs on several asperities. Therefore, the actual contact normal stress and shear stress between joint surfaces may be higher than the calculated average stress values. In this study, Prescale films developed by Fujifilm were used as the measurement material, which displays imprint of varying color shades corresponding to different pressure levels applied. During the test, a Prescale film was placed between two joint surfaces. The relationship between normal stress and shear stress was determined through the measurement value of internal stress and external stress measured using a load cell. Different shearing processes were compared to explore the difference between the actual contact stress and the calculated average stress.
    The primary findings are as follows.In a planar joint:(1)The peak shear strength is affected by the applied normal stress, rather than by segmentation shear displacement.(2)The imprint on Fuji Prescale film shows varying color shades and contact areas in accordance with different normal stress and shear displacement applied. The imprint contact area was 41%-75% before shearing and 85%-90% after shear stress was applied.(3)Because distributed contact stress is related to the imprint color distribution of Prescale films, changes in contact stress can be analyzed.(4)The externally measured shear stress and the internal contact shear stress measured differ under shear displacements within different segmentations. Under low normal stress, the internal contact shear stress was approximately 1.1 to 1.4 folds that of the external shear stress. When an intermediate level of normal stress was applied, the ratio of internal to external shear stresses increased from 0.96 to 2.5 folds gradually as the segmentation shear displacement increases. When a high level of normal stress was applied, the ratio was increased from 0.66 to 1.46 folds in accordance with increasing segmentation shear displacements. These results revealed that increase in segmentation shear displacements affects the stress actually applied on internal joint surfaces.
    In a 45° saw-tooth joint:(1)Low shear stress is required to be applied on the joint to create tension cracks when the externally applied normal stress is high, thereby reducing the distance for driving shearing.(2)The position of tension cracks on the uphill plane consistently locates at the lower edge of the region under force and does not vary with the external normal stress applied.(3)The contact stress distribution patterns are consistently trapezoidal regardless of the applied normal stress and displacement. The distribution patterns differ only at the distribution of maximal stress.(4)Comparison results of external and internal stresses applied on the uphill plane (6.14±0.36MPa for external normal stress and 5.18±0.08MPa for internal contact stress) were close to the uniaxial compressive strength (UCS= 5.98±0.56MPa). It is also close to the external normal stress and shear measured in the load cell. The result indicated that the tension crack behavior on the uphill plane of saw-tooth joint under shear is related to uniaxial compressive behavior of joint wall material.
    Appears in Collections:[土木工程學系暨研究所] 學位論文

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