灰铸铁抗拉强度测量方法比较

Comparison of Testing Methods for Tensile Strength of Gray Cast Iron

采用灰铸铁材料进行圆环劈裂试验、扭转试验、四点弯曲试验和直接拉伸试验,得到上述4种抗拉强度测量方法的结果比值约为2.87∶1.33∶1.17∶1。四点弯曲试验的测量结果与直接拉伸试验结果接近。结合文献中的试验数据,发现铸铁、岩石、混凝土等不同脆性材料的间接拉伸试验结果与直接拉伸试验结果比值相近,于是可给出带修正系数的通用间接测量抗拉强度公式。有限元分析表明,间接拉伸试验中试件断裂面上不是均匀应力,当断裂面的小部分单元达到应力极限时只产生微观裂纹,并没有发生整体破坏,当断裂面上大部分单元都达到应力极限时才会丧失承载能力,发生宏观破坏,这可能是导致不同测量方法结果不一致的原因。

Splitting test of circular ring, torsion test, four-point bending test, direct tensile test with grey cast iron were carried out.The ratios of tensile strength from the four measurements are about 2.87∶ 1.33∶ 1.17∶ 1.The results of four-point bending test is close to that of direct tensile test.Combined with the experimental data in literatures, it is found that the ratios of tensile strength from indirect tensile test to that from direct tensile test for different brittle materials such as cast iron, rock, concrete and so on are similar. Therefore, the universal formulae for indirect tensile strength with correction coefficient can be given.The finite element analysis indicates that there is not uniform stress on the fracture surface in indirect tensile test.When the minority of elements on the fracture surface reach the stress limit, specimen produces micro cracks but no whole damage occurs.When the majority of elements on the fracture surface reach the stress limit, specimen loses bear capacity and produces macro damage.That may be the reason for the inconsistency among the results of different testing methods.