Papers by Author: Ying Xia Yu

Abstract: Porous ceramics composite was prepared with mixed powders (Al, TiO₂ and B₂O₃) by SHS (Self-propagating High-temperature Synthesis) method. The effects of the particle size of aluminum power, the additives of SiC and the compacting pressure on the product properties and the pore size, as well as the combustion process in the Al₂O₃-TiB₂ system were researched. The effects of all factors on properties of the product were tested in this paper. The microstructure and mechanical properties (density and compressive resistance strength) were reported. It is learnt from the study that the relation between the open porosity and the pore size does not exist, the former depends on the green density, and the latter depends on the particle size of the aluminum powder. The porous ceramic composite with porosity is ranged from 45% to 68%, pore size is ranged from 1um to 400um, and the compressive strength is about 9.5 MPa. SEM observations of fracture surface suggest that the fracture mode is brittle fracture, and the microstructures of the porous of ceramic composite is very homogenous.

Abstract: In this paper, the reliability of welded pressure pipe with circumferential surface crack was calculated by using three dimensional stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on three dimensional elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as fracture toughness, bending moment and the depth of the circumferential surface crack on the structure reliability were also discussed. The calculation results indicate that the crack depth has great effect on the reliability of the welded pipe. When the mean value of the crack depth is changed from 3mm to 7mm, the failure probability of the welded pipe will change from 10-8 to 10-2. The bending moment also has great effect on the reliability of the welded pipe. When the mean value of moment is changed from10000 N.m to 15000 N.m, the failure probability of the welded pipe increases dramatically for the same circumferential crack depth. Irrespective of the changing of moment, the pipe has higher reliability if the crack depth is less than 5mm(a/t<0.5, t is the thickness of the pipe). The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.

Abstract: The reliability of welded pressure pipe with circumferential surface crack was calculated by using 3-D stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on 3-D elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as bending moment, the inner pressure on the structure reliability were discussed. The calculation results indicate that the bending moment has great effect on the reliability of the welded pipe, and the inner pressure has little effect on the reliability of the welded pipe if the inner pressure is less than 10MPa. If the mean value of the inner pressure changed from 0.5MPa to 30MPa, the failure probability will changes from 10-6 to 10-2. The bending moment also has great effect on the reliability. When the mean value of moment is changed from10000 Nm to 15000 Nm, the failure probability of the welded pipe increases dramatically for the same inner pressure. Irrespective of the changing of moment, the pipe has higher reliability if the inner pressure is less than 6 MPa. The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.

Abstract: The effect of undissolved ferrite amount on impact fatigue properties and failure mechanism were studied by using 42CrMo steel with subcritical quenching process The amount of undissolved ferrite were 0%, 10% and 15%, respectively. The experimental results show that the existence of undissolved ferrite can not only change the microstructure, but also increase the impact fatigue life The impact fatigue life elongates with increasing of amounts of undissolved ferrite The grain can be fined by using subcritical quenching process and the area of phase boundaries can also be greatly increased because of undissolved spheroidal carbide. The martensite and carbide form can also be changed by using subcritical quenching process The stress relaxation due to the moving of dislocations inside the ferrite and the promotion of strength due to occurring of plastic deformation and the enwinded dislocations are main reasons of improving the impact fatigue life. The impact fatigue life elongates with the increase of amounts of undissolved ferrite before the amount of undissolved ferrite reaches 10%. Under the experiment conditions, when the amount of undissolved ferrite is 10%, the impact fatigue life will be the longest.

Abstract: The effect of undissolved ferrite amount on bending fatigue properties and failure mechanism were studied by using 42CrMo steel with subcritical quenching process The amount of undissolved ferrite were 0%, 10% and 15%, respectively. The hardness of the specimen was treated to medium hardness. The experimental results show that the existence of undissolved ferrite can not only change the microstructure, but also increase the bending fatigue life. The bending fatigue life elongates with increasing of amounts of undissolved ferrite. The grains can be fined by using subcritical quenching process and the area of phase boundaries can also be greatly increased because of undissolved spheroidal carbide. The martensite and carbide can also be changed using subcritical quenching process. Stress relaxation due to the move of dislocations inside the ferrite and the promotion of strength due to occurring of plastic deformation and enwinded dislocations are main reasons of improving the bending fatigue life. The bending fatigue life elongates with the increase of amounts of undissolved ferrite before the amount of undissolved ferrite reaches 10%. Under the experiment conditions, when the amount of undissolved ferrite is 10%, the bending fatigue life will be the longest.