Research On Cast Iron Fracture Mechanism Under The Complex Stress By Test

The cast iron material applies in the project, which mechanics performance is very important factor influence under complex stress fracture, the study is not fully because of testing conditions. This paper, through the LZQT400-15 cast iron in tension, torsion, compression and the combined tension/torsion do the destructive test under the different stress condition to research the cast iron under the complex stress condition macroscopic fracture form and microscopic fracture mechanism. The paper, first, designs the experiment of the fracture test under the complex stress condition. Second, it uses the scanning electricity mirror (SEM) to observe the graphite and the interface microscopic fracture process under the different stress condition, to analyze crack extending under different stress condition. Third, it uses the stress tri-axicity to research mechanics performance energy, and studies the stress strain relations in the complex stress field. The last application stress condition parameter stress tri-axicity establish criterion on metal material fracture.The experiment and the analysis discussion draw conclusion: 1.The cast iron under the complex stress the breaking-down process take place the contact surface of between the graphite and the body at first. Micro-crack disseminate always along material structure plane of weakness. 2. Under the different stress condition, the cast iron has the different fracture mechanism, when tension is tensile break, torsion and compression are shear break with the hole influence and the plasticity shears the mechanism, tensile break and shear break with the hole influence are the coexistence in different the combined tension/torsion, only the occupy area the ratio is different. 3. The materials behavior differently with the stress condition change influence, in the material fracture process, the physical mechanism can appear the change; the component occur the different break form. 4. The metal material fracture mechanism divides into three kind of fracture mechanisms: tensile break, shear break with the hole influence, shear break without the hole influence; regarding the different physical mechanism break, thestress tri-axicity has the dividing line value, which relates to the materials behavior, and the different material stress tri-axicity dividing lines value is different.