Advanced Materials Research Vols. 197-198

Abstract: A new method of fracture toughness K_1C prediction of non power law hardening material by using cleavage fracture local approach is proposed in this paper. The fracture toughness of A508-Ⅲ 16MnR at different cleavage fracture probability are predicted by using the method. To most of pressure vessel carbon-manganese steels, cleavage fracture is likely to occur at the load corresponding to 62% cleavage fracture probability. Hence, the fracture toughness corresponding to the load is the most possible fracture toughness of the steels. The values of fracture toughness corresponding to 62% cleavage fracture probability is close to that of testing fracture toughness. The work of this paper expends the application of Beremin cleavage fracture model in predicting fracture toughness.

Abstract: The paper reports on an investigation of the fracture mechanism of both tensile and impact fracture in three types of casing-drilling steels. The results show that the tensile fracture surface of N80 steel includes fibrous zone, radiation area and shear lip zone, and those of both K55 and P110 steels include two zones; all the tensile fracture surfaces of three types of casing drilling steels show the ductile fracture mode, the ductile fracture mode indicated with dimples is observed on all zones; the impact fracture surface of the N80 steel possesses a combined quasi-cleavage and ductile fracture modes, a single fracture mode is observed on the fracture surface of both K55 and P110 steels, the K55 steel impact sample is fractured in a cleavage brittle manner, whereas the P110 steel impact sample is fractured in a dimpled ductile manner.

Abstract: Fatigue tests are carried out for 16MnR welded joint under constant strain control. Test results reveal that 16MnR weld metal exhibits characteristic of cyclic softening and non-masing obviously. The strain–life curve can be best described by the three-parameter equation. It shows the fatigue endurance limit in the heat-affecting zone (HAZ) of welded joint is lower than that in the weld metal.

Abstract: The deformation resistance of composite tapes was measured through compression tests. At room temperature, composite tapes were compressed and shaped at different deformation rates to different extents, and the real stress-strain curve of the composite superconducting tapes was obtained. Regression analysis was carried out on the curve using the Nonlinear Least Square Fitting (NLSF) method to acquire the parameters and coefficients regarding the curve, and a mathematical model for the deformation resistance of the composite superconducting tapes was built.

Abstract: With the aircraft structure design criterion from traditional static strength design to damage tolerance design and with the independent research and development of new-type civil turbofan regional aircraft and the implement of the plan to develop the country's own large passenger jets in China, it is essential to do some researches on casting TC4 alloys for the lack of the data of fatigue properties. The detail fatigue rating cut-off (DFR_cutoff) values of casting TC4 alloys are measured and calculated by double dots method, the thresholds in fatigue crack propagation and the fatigue crack growth rates at different stress ratios are studied and the fatigue fracture at different stress ratios are observed by scanning electron microscopy. The results show that DFR_cutoff value by double-dot method is 375.83 Mpa. The thresholds of fatigue crack propagation decrease with the increase of the stress ratio, whereas the fatigue crack growth rates increase with the increment of the stress ratio and the relationship curves between fatigue crack propagation rates and the stress intensity factor range have been obtained. Moreover, SEM observations indicate that the fatigue trips become wide with the increasing of the stress ratio.

Abstract: Cold recycling technology has been widely used in road maintenance projects. Many roads which have been reconstructed with cold recycling technology have emerged some diseases after a long-term used. In this condition, these roads can be rebuilt by secondary recycling technology. The microstructure characteristics of secondary recycled road materials after cement stabilizing were observed by SEM; then, material properties after being long-term used and secondary recycled were analyzed. CBR value and aggregate crush value are put forward for the evaluation indexes of secondary recycling. The unconfined compressive strength, splitting strength and modulus of cement stabilized secondary recycling materials are determined by laboratory tests. The results indicate that the existence of asphalt components lead the strength lower than ordinary base materials stabilized by cement. And temperature exerts an obviously influence on the compressive strength. Frost resistance, water stability and anti-erosion resistance are also determined by laboratory tests. The results indicate that the strength and pavement performance of cement secondary recycling materials can meet the requirements for base and sub base in asphalt pavement.

Abstract: In order to realize the dynamic mechanical property of a steel, the quasic-static and dynamic compressive and tensile mechanical tests of a steel are carried out. Based on the stress-strain curves of the steel, the constitutive relation is presented and it can be used to describe compressive and tensile mechanical property correspondently. The stress-strain curves at different strain rate and the obtained dynamic constitutive relationship show that the flow stress of the steel is increased with strain rate increased. The dynamic tension experimental results show that failure strain and stress of the steel are increased small with strain rate increased, and the fracture of tension sample is ductile fracture.

Abstract: The Bauschinger effect (BE) of X80 Pipeline Steel was tested through axial tension and compression loading. Forward and reverse axial loading schemes were performed to investigate the influence of deformation history on the mechanical character. The curves of forward and reverse stress-strain were both recorded. The results show that the yield strength decreases as the pre-plastic strain increases. On the basis of the experimental data, an empirical formula was derived regarding the decrement of the yield strength as a function of the pre-plastic strain. Additionally, further investigations on the BE of X80 steel were conducted by bending tests. The bending moment-strain curves were all recorded for both first and reverse loading. It shows that the yield moment also decreases as the pre-plastic strain increases. Based on the theory of elastic-plastic mechanics, the formula of yield moment decrement as the pre-plastic strain increase was obtained. The results show that the experimental tests are in good agreement with the formula prediction.

Abstract: Concrete cover cracking induced by reinforcement corrosion is an important problem in reinforced concrete structures. Several existing analytical models for cracking time are discussed, and it is found that the penetration of corrosion products into corrosion cracks is neglected in these models. Based on our study, a theoretical model that takes the ingress of rust into cracks into account is proposed to predict the cracking time. In order to analyze the amount of corrosion products deposited in cracks, an accelerated corrosion test was performed. Based on the experimental results, the parameter k, which deal with the ingress of corrosion products into cracks, is calibrated to be 0.1~0.3 for accelerated corrosion test. By comparing the predictions with the test results, it is found that the proposed model has high accuracy in analyzing the cracking time and that the mean absolute error between predictions and observations is about 9.4%.

Abstract: A few experiments are conducted to investigate the effects of different solidification process on the physical hardness and compressive strength of the home-made bone cement. 24 bone cement samples under different mixing conditions are prepared. The compressive strength, hardness and phase composition of bone cement samples are measured with electronic universal machine, Shore hardness tester and X-ray diffraction(XRD) respectively. The results show that the maximum compressive strength of 24 samples is 96.27MPa, and obviously superior to that of the clinical application of bone cement. The hardness of bone cement of group C( powder 20g and fluid 10ml, 80.43HD) and group D(powder 20g and fluid 12ml, 86.60HD) is higher than 80HD which is the clinical requirement.It is found by X-ray diffraction that the higher crystallinity could produce finer grain, which results in higher compressive strength and hardness with better ductility and toughness. Giving consideration to compressive strength and physical hardness and crystallinity of D3(20g:12ml, with stirring speed as 30 times/min and stirring time as 90 seconds), the solidification condition is best.