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Cleavage fracture in an Al-Li alloy 8090 总被引:1,自引:0,他引:1
Jiang Daming Wang Yinong Hong Bande Lei Tingquan Sun Fenglian 《Journal of Materials Science Letters》1996,15(18):1597-1600
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本文研究了δ-Ni_3Nb相的尺寸及分布对Inconel718合金在650℃,恒应变控制循环应变作用下断裂行为的影响。结果表明,由高温固溶及中间时效造成的δ相沿晶界的锯齿状分布,可以提高材料对裂纹沿晶扩展的抗力,使低周疲劳断口由标准工艺处理后的沿晶型转变为穿晶。但是,与形成锯齿晶界的工艺相伴随的,δ相在晶内沿孪晶界面及贯穿晶粒的粗大片状析出,降低材料对循环应变的适应能力,常常过早地在δ相与基体界面处形成微孔甚至界面分离,使材料疲劳寿命降低。 相似文献
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R Tumbarello G Cardu A Bande RM Bini PA Abbruzzese V Martelli A Sanna 《Canadian Metallurgical Quarterly》1994,24(5):491-502
AIM OF THE STUDY: To verify changes of pulmonary venous flow pattern before and after surgical or percutaneous correction of valvular heart disease. METHODS: The pulmonary venous flow pattern was studied by transesophageal echocardiography in 27 patients affected with heart valve disease (11 mitral insufficiency, 10 mitral stenosis, 2 aortic stenosis and 4 pulmonary stenosis), before and after surgical or percutaneous correction. Pulmonary venous flow velocity variables measured included peak systolic and diastolic flow velocities (VmaxS and VmaxD), systolic and diastolic velocity time integrals (IS and ID) and their respective ratios (VmaxS/VmaxD and IS/ID). Paired Student's t-test was used for analysis of data; a p value < 0.05 was considered statistically significant. RESULTS: In mitral stenosis and insufficiency, as well as in pulmonary stenosis, the VmaxS/VmaxD and IS/ID ratios were constantly < 1. Aortic stenosis, on the contrary, showed a normal preoperative pattern of pulmonary venous flow, which did not change after correction. All other successful corrections (17 surgeries, 4 angioplasties) were characterised by an increase of VmaxS/VmaxD and IS/ID ratios. (Mitral stenosis: VmaxS/VmaxD 0.80 +/- 0.31 vs 1.4 +/- 0.5, p = 0.006; IS/ID 0.86 +/- 0.77 vs 1.62 +/- 0.62, p = 0.016. Severe mitral insufficiency: VmaxS/VmaxD -0.71 +/- 0.32 vs 1.19 +/- 0.32, p < 0.0001; IS/ID 0.41 +/- 0.19 vs 1.04 +/- 0.31, p = 0.006. Moderate mitral insufficiency: VmaxS/Vmax D 0.38 +/- 0.04 vs 0.95 +/- 0.06, p = 0.001; IS/ID 0.32 +/- 0.05 vs 0.95 +/- 0.07, p = 0.02. Pulmonary stenosis: VmaxS/VmaxD 0.43 +/- 0.23 vs 1.09 +/- 0.35, n.s. e IS/ID 0.49 +/- 0.34 vs 0.92 +/- 0.65, n.s.). Failure to return to a normal pulmonary venous pattern was observed in the 2 cases of partially successful mitral valvuloplasty (one of which was subsequently transformed into a mitral valve replacement with immediate normalisation of the pattern) and in the 2 cases of incomplete relief of a pulmonary stenosis after pulmonary valvuloplasty. CONCLUSIONS: Though preliminary, these observations suggest a high sensitivity of this method and, therefore, a possible role of pulmonary venous pattern studies in the assessment of the efficacy of treatment in mitral and pulmonary valve disease. 相似文献
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本文把Brown的Φ(ρz)表达式用于Russ的直接无标样定量计算中,代替了常规的Z、A校正模型(即Ducomb—Reed的原子序数校正模型和Philibert的吸收校正模型。在一些二元合金特别是轻金属二元合金的测试中,取得了较好的效果,而且对其分析精度及Z、A校正因子与加速电压的关系进行了探讨。 相似文献
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