Advanced Materials Research Vols. 197-198

Abstract: Single crystal nickel base superalloys, such as Chinese material DD6 have been used in gas turbine blade in China more and more widely. In order to make better use of single crystal superalloys with many excellencies, constitutive models have been developed. In this paper, general method of crystallographic constitutive modeling was summarizes and a new constitutive model, based on crystallographic theory was proposed with phenomenological models' advantages. Based on crystallographic slip system principle, the basic slip-based viscoplasticity theory equations were set up on 12 octahedral slip systems and 6 cubic slip systems, total 18 slip systems. In micro-level slip system, the general unified constitutive formulations were used as the flow equations and hardening law. In the model, scalar forms were applied for constitutive equations on slip systems and the number and types of active slip systems were used to describe the material anisotropy, which was satisfied automatically by slip systems not anisotropic tensors and. The experimental and calculation results of two kind single crystal superalloys PWA1480 and DD6 were compared. The model had the capability to predict many mechanical response and analyze structure of single crystal superalloys. The modeling procedures and results showed that this crystallographic model had more clear physical meaning and was exact.

Abstract: When the operating process of delay coking is cyclically changing from 25°C to 500°C, it would usually induce the effect of heat treatment on the shell of coke drum. After a special model of the kinetic medium climbing along the inside-wall of the coke drum at a steady rate set up, the resulting two-dimensional kinetic temperature field of shell in radial and axial directions has been calculated and analyzed by FEM. The relation between the material physical property of the shell and its temperature has been considered. The results show that the radial temperature difference or the axial temperature difference caused by the cooling water is more than that caused by the hot oil. The maximum temperature difference between the inside-wall and the outside-wall is 40°C below the medium level, 30mm by the hot oil and 60 °C or 25 mm by the cooling water. The circumferential uneven temperature field, location and concave/convex or incline/bend of body have been surveyed and analyzed. The lat-circle deformation of transverse section has been discussed.

Abstract: Fatigue tests were carried out at different stress levels on cruciform welded joints made from mastensitic stainless steel. The purpose of the present paper was to verify the validity of the thermographic method and to extend its capability on welded structural evaluation, considering the real operating situations. Due to limitations of the traditional fatigue test, the infrared thermographic technique was developed to predict and assess the fatigue limit and the entire S-N (Stress-Life) curve of cruciform welded joints. Through the comparison, the predictions of the fatigue behavior by the thermographic method (TM) manifested good agreement with the traditional method. The present research paper concludes that the TM as a promising method enables us to rapidly obtain reliable fatigue characteristics of welded structural components.

Abstract: 35CrMo and 42CrMo are the two main structural alloy steels in China, and are widely used in making important structural components subjected to heavy loads. In order to search after their fatigue properties under cyclic loads, 33 specimens were tested, under different stress level and different stress ratio from each other, to observe their crack initiation lives and the failure lives, together with the growing short crack lengths at various cycles. All tests were conducted using the MTS 810-22 material testing system. Based on the results from the tests, the relationships between the maximum stress range at crack tip and the number of cycles prior to crack initiation were determined, and in the meanwhile, the small crack propagation laws and the threshold stresses for fatigue crack initiation were obtained. In the end, the fatigue life prediction method for the two structural alloy steels was carried out.

Abstract: The second development of ABAQUS is implemented to simulate the initiation, propagation processes of flaws in brittle materials under compressive loading (in the paper ‘flaw’ means ‘the initial crack’, and ‘crack’ means ‘the branch crack’), by which the propagation paths and the corresponding stress intensity factors of the branch crack can be calculated. Further more the experiment is carried out to verify the validity of the above numerical method. By the numerical method, the propagation processes of open flaws and close flaws are simulated, and the comparative analysis of propagation characteristics between the open flaw and the close flaw is carried out. The results show the obvious difference in the propagation characteristics between open flaws and close flaws with the same initial flaw length and angle. Firstly, compared with the close flaw, the branch crack of the open flaw grows along a more obviously curvilinear path, and the propagation path gradually approaches to a line, which passes through the middle point of the open flaw and parallel to the maximum principal stress. Secondly in the early stage of the crack propagation, the stress intensity factors of the branch crack of the open flaw are greater than of the close flaw, but with the further propagation of the branch cracks, the stress intensity factors of the branch crack of the open flaw will be less than of the close flaw. Additionally, according to the close flaw, with the decrease of the friction coefficients, the curve characteristics of the crack propagation paths become more obvious. Therefore, it is noteworthy that the wing crack of the close flaw can be regard as the straight line if the friction coefficient of the flaw surface is very small. The above differences of the propagation characteristics between the open flaws and the close flaw show that the two flaws should be distinguished strictly in the fracture analysis.

Abstract: This paper takes decorticator's core part (Illustration of roller and shutter equipment) as the object of study, through analyzing the principle of the gingko decorticator for peeling off the shell, and choosing the roller's material and its superficial shape, we calculate the action of gingko’s entrance to the gap between roller and shutter, and elaborate the two influences on the effect of peeling off the shell, the gap between roller and shutter and the speed of peeling. The decorticator which makes through this research may achieve good results that the husking yield is bigger than 85%, percentages of damage is smaller than 10%, the broken kernel rate is smaller than 7%. And it provides the theory basis for the improvement design and use of the next generation installment for peeling the shell.

Abstract: The fracture of the Cr12MoV guide pillar in a progressive die during punching was investigated by SEM observation, metallographic examination, chemical composition analysis, hardness testing. It is showed that the failure of the guide pillar was caused by fatigue. The fatigue crack initiated from the circumferential groove by repeated punching, and propagated throughout about 1/3 of fracture surface, then, instantaneous fracture eventually took place. Besides, there are some bigger eutectic carbides and inclusions in the pillar that made the material worse.

Abstract: The process of stress-induced fracturing around underground excavations is associated with dilatancy-bulking behavior of the fractured rock. Due to the importance in earth science and engineering design, this paper presents an experimental investigation of rock dilatancy-bulking behavior based on triaxial loading and unloading tests carried out on weak sandstone samples from the Gubei colliery. Through experimental and theoretical analyses, it is found that the volume increase of stress-fractured rock can be divided into two groups: (1) pre-peak dilatancy due to crack opening and propagation, (2) post-peak bulking by the sliding, rotate or detachment of rock blocks. And the post-peak bulking deformation is the main cause of the rock volume expansion. Moreover, the evolution of characteristic stresses and dilation angle show strong pressure dependence, which means that confining pressure strongly inhibits dilatancy-bulking behavior. It also indicates that the rock response under loading and unloading conditions is substantially different.

Abstract: This paper systematically analysis the stress-strain behaviour of mud stone under different confining pressure. The relationship between the mechanical behaviour of mud stone and confining pressure is established, and the curves of stress-strain relationship of mud stone are fitted. The results indicate that the failure pressure and the elastic modulus increase with the increasing of confining pressure conforming to the linear function. The stress- strain of mud stone is divided into four different stages which are fracture closing, elastic strain, fracture expanding and plastic strain stage. The stress-strain behaviour in different stage has different function law, the stage of fracture closing can be fitted by polynomial function, the stage of fracture expanding can be fitted by hyperbola function, the fitting result is ideal.

Abstract: The marble acoustic emission characteristics under different temperature tested and analyzed under uniaxial compression, and the contrast analysis that passes to acoustic emission the signal and the mechanics parameters to the marble can get,The characteristic curve of acoustic emission is distinguishing with the variety of temperature and stress level, the acoustic emission characteristic and stress-strain curve of fracture rock exists corelation characteristic. At the same stress-level, along with the temperature raising up, the relevant dimension has the trend of the aggrandizement, and the related coefficient will change randomly. The marble then expresses a mechanics characteristics of soft rock at over 1000oC, and the strength-limit descending sharply. The process parameters of AE count in the time domain has a better self-similar characteristics.