Evaluation of Mechanical Properties and Fracture Mechanism of Single Crystal Bulk High Tc Superconductors

用小试样测试了Sm基高温氧化物超导体的力学性能，阐明了断裂机制：1.用三点弯曲和拉伸试验测试了Sm基高温氧化物超导体的断裂韧性，断裂韧性为1.0- 1.3MPam ^（1/2）。由于a-b平面上的微裂纹的存在，c轴缺口试样的三点弯曲强度和杨氏模量高于垂直于c轴缺口试样的三点弯曲强度和杨氏模量，并且随着温度的降低，三点弯曲强度和杨氏模量从室温降低到77 K。在77 K下5 × 10^4次循环的弯曲疲劳极限为70 MPa，为弯曲强度的80%。3.压缩应力-应变曲线在垂直于c轴的载荷下为线性，在c轴载荷下为非线性。由于微裂纹的张开和闭合行为，压缩弹性常数和强度表现出各向异性。它们在77 K时更高，并且也高于拉伸试验中的那些。随着试样长度的增加，接头强度增加，但当试样长度为4倍厚度时，由于沿沿着解理面分层和屈曲，接头强度降低。4.在Y块体{110}面加入Er或Ag的Y123接头的抗拉强度分别为14 MPa和27 MPa。Y块体的压力低于46 MPa。前者在接头区中部观察到一些固溶体区域，后者在Y体内观察到一些固溶体区域，这些区域是断裂的起源。排除这些区域对应于退化的磁通量捕获区域应导致接头强度的提高。

By using small specimens of bulk high T_c oxide superconductor, the mechanical properties were evaluated and the mechanisms of fracture were clarified.1.The fracture toughness of Sm based bulk evaluated by 3-point bending and tensile tests were 1.0-1.3 MPam^<1/2>. Due to the pre-existing micro-cracks in a-b plane, values for specimens with notch in c-axis, were higher than those perpendicular to it. They increased as the temperature decrease from RT to 77K.2.The 3-point bending strength and Young's modulus of Y based bulk at 77K was higher than those at RT. These were slightly higher in the top region of bulk. The bending fatigue endurance limit for 5x10^4 cycles at 77K was 70 MPa, which is 80% of bending strength.3.Compressive stress-strain curves are linear for loading perpendicular to c-axis and non-linear for c-axis loading. The compressive elastic constants and strength showed anisotropy, due to the opening and closing behavior of the micro-cracks. They were higher at 77K and also higher than those in the tensile tests. Although the strength increased with increase in the length of specimen, it decreased when the length became 4 times of the thickness due to delamination along cleavage plane and buckling.4.The tensile strength of bulk joints, where the Y bulks were joined in {110} planes with Er or Ag added Y123, were 14 MPa or 27 MPa. They were lower than 46 MPa for Y bulk. Some solidified solution areas were observed in the middle of joint region in the former and within the Y bulk in the latter were found to be the origin of fracture. The exclusion of these regions which correspond to the degraded magnetic flux trapping areas should leads to the improvement of strength of joints.