高溫超導塊材在高磁場環境下冷卻至低溫後具有擄獲磁場的能力，但擄獲磁場與塊材內部感應的超導永久電流相互作用而產生拉伸之電磁應力。當此應力大於塊材的破壞強度時，內部裂縫成長進而造成塊材的破壞。因此，對於高溫超導塊材的發展與應用而言，高磁場應用時的機械穩定性比往日所注重的高臨界密度與大晶粒等性質的重要性相同。本研究目的在於探討單晶粒Y-Ba-Cu-O超導塊材的破壞強度與破壞韌性等機械性質，再經由破壞強度與韌性來計算出試片內部裂縫的長度，並用SEM實際觀察加以應證。
本研究使用的試片為實驗室自製之單晶粒Y-Ba-Cu-O超導試片，並將試片尺寸磨成直徑為16mm厚4mm。在試片邊緣包覆碳纖維布，並使用具流動性的環氧樹脂填入試片開放性裂縫及塊材與碳纖維布的空隙中，來增加超導試片的機械性質。我們利用微硬度試驗量測超導試片之破壞韌性，未經披覆處理與經過披覆處理的超導試片之破壞韌性分別為0.654MPa×m1/2與0.7MPa×m1/2。
我們使用物理性質量測系統(PPMS)來量測Y-Ba-Cu-O超導體於低溫與高磁場環境中的機械性質與擄獲磁場能力。經由線性回歸結果，我們得知超導試片於15K的最大擄獲磁場為4.916T。我們觀察到未經披覆處理之超導試片承受7.22MPa之應力後導致試片破裂。而藉由二維擄獲磁場掃瞄量測，我們亦觀察到經過披覆處理之超導試片，在承受13MPa之應力後試片內部有裂縫的出現。因此得知經披覆處理試片的破壞強度大約為無披覆試片的兩倍。藉由無披覆試片的破壞韌性(0.654MPa×m1/2)與破壞強度(7MPa)，我們可以算出試片內部之裂縫長度約為1.75mm。實際以SEM所觀察到試片內部(001)面上的裂縫長度範圍介於1~3mm。
最後我們欲以已知裂縫長度與破壞強度來計算破壞韌性，來印證使用微硬度試驗量測之結果。因此我們藉由CO2雷射在試片切割出特定長度之裂縫。但由於試片經過雷射切割過後，擄獲磁場能力被大幅破壞，並且在低溫環境下易產生磁束跳躍，故無法獲得足夠大之應力造成試片破裂，因此無法得到預期之結果。

The melt-textured high-temperature supercondutor (HTSC) bulk can trap multi-tesla field via cooling to low temperature under high magnetic field. Howerver, the interaction of the trapped field and the internal current causes the outward electromagnetic stress. When this stress is larger than the fracture strength of the superconductor, the cracks or fracture will be observed. Therefore, the development of HTSC bulks and their applications have come to a point where the mechanical response to high magnetic fields is equally important to their critical-current density and large grain properties. The purpose of this experiment is to calculate the fracture strength and fracture toughness of Y-Ba-Cu-O superconductor. It is permitted to estimate the length of internal crack of Y-Ba-Cu-O bulk with fracture strength and toughness.
The single grained Y-Ba-Cu-O superconductor bulk were prepared and grinded to 16 mm in diameter and 4 mm in thickness. The improvement of the mechanical properties of Y-Ba-Cu-O superconductor bulk is commerial resin and carbon fiber impregnation.
We measure the fracture tougness by micro-hardness test. The fracture toughness of Y-Ba-Cu-O bulks with and without resin and carbon fiber impregnation are 0.654MPa×m1/2 and 0.7MPa×m1/2, respectively.
For trapped-field measurement, we used PPMS model 9000 (maximum field is 9 tesla) at Institute of Physics, Academia Sinica as magnetic source. The maximum trapped-field of prepared Y-Ba-Cu-O superconductor bulk at 15K is 4.916 tesla by extropolation of linear fit of measurements at higher temperatutre. We observed the Y-Ba-Cu-O bulk without resin impregnaiton broke at 7.22 MPa which originated from electromagnetic stress. In the sample with resin and carbon fiber impregnation, internal crack can be observed via 2D trapped-field mapping at 13MPa of electromagnetic stress. So the strength of Y-Ba-Cu-O bulk with resin impregnaiton is about twice of one without resin. We calculated the length of internal crack existed in our Y-Ba-Cu-O bulk is 1.75 mm. SEM image revealed that the cracks exists on Y-Ba-Cu-O (001) internal plane, and the range of length is 1-3mm.
The CO2 Laser is used to ablate cracks with three kind of length, which are 1mm, 7mm and 12mm respectively. It is articipated that with these known crack length and electromagnetic stress, the fracture toughness can be calculated. And these fracture toughness can then be compared with those data obtained via micro-hardness test. However, the trapped-field at 77K of Y-Ba-Cu-O superconductor was weakened after low velocity (2.286mm/sec) CO2 Laser ablation due to local heating. The trapped-field at 77K will be remained the same by high velocity (571.5mm/sec) CO2 Laser ablation, the “flux jump” phenomenon would occurr during trapped-field measurment. This flux jump phenomenon may be caused by the reduction of the heat conductivity of Y-Ba-Cu-O superconductor by Laser heating. So, the electromagnetic stress is insufficient to cause damage to Y-Ba-Cu-O bulk, which make the calculation of the fracture toughness is not possible.

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