Advanced Materials Research Vols. 941-944

Abstract: With the development of numerical calculation and precision forming, constitutive equations are required to possess high accuracy and good reliability, rather than simplicity of mathematical form. Due to simple algorithm and constant parameters, the conventional constitutive models can not be suited to describing superplastic flow behavior which represents complex responses with a large strain. In this study, through surface fitting on experimental data from tension tests performed over a wide range of strain rates, tensile velocities and loads, an empirical approach was proposed to establish constitutive equation for complex superplastic behavior of Zn-5%Al alloy at 340 °C. The empirical constitutive equation not only represents the strain dependence and the strain rate dependence of stress, but also reflects the coupling effects of strain and strain rate on stress, which can not be achieved by traditional models. A comparison between the predicted flow stresses and the experimental data verified that the empirical constitutive equation has high accuracy and good reliability on modeling superplastic flow behavior of Zn-5%Al alloy at 340 °C in a wide range of strains 0~2.5 and strain rates 7.0×10^-5~8.0×10^-2 s^-1.

Abstract: In conventional analysis of instability, a rough prediction of uniform deformation was obtained due to taking material parameters as constants. In this study, the constitutive equation with varying parameters for Zn-5%Al alloy at 340 °C is employed to predict the critical values of uniform strain in tension based on Considere criterion and Hart criterion, respectively. It should address the factor of strain rate in the characterization of the capability of uniform deformation on superplastic alloys, or for that matter, on any rate-dependent material. Comparison and analysis indicated that the results on Hart criterion have the better predictability of uniform deformation than Considere criterion. The Considere criterion is dependent on strain path, while Hart crtierion is merely dependent on the values of strain and strain rate in tension, and is independent on the strain path or the deformation condition or the deformation history. Therefore, the uniform strain vs. strain rate relation can be taken as a quantitative reference for designing a reasonable strain path during superplastic forming with increase of formability and reduction of forming time.

Abstract: In this article, firstly, the strain hardening index and the strain rate sensitivity index were deducted from the general state equation and the mechanical meaning of the two indexes were correspondingly depicted, and then constitutive equations, where both/either of the two indexes appear as constants, were theoretically deducted from the same state equation. Secondly, constitutive equations where both/either of the two indexes present as variables were put forward by numerical simulation. Next, constitutive equations were built, where mechanical variables are replaced by test data obtained on an electronic universal tensile tester with the capacity to carry out a true constant strain rate path. Finally, based on the test data of Zn-5%Al during superplastic tension, it is proved that the theoretical results in this article are valid.

Abstract: Study of grain size and lamellar spacing on fatigue crack propagation resistance in TiAl alloy has been done. The effects have been analyzed specifically. Meanwhile, the influence has been verified with some fatigue crack propagation experimental results and Paris formula. The experimental results confirmed that the grain size and lamellar spacing have significant effect on fatigue crack growth resistance. According to the Paris formula, the specific values of the constants in the formula were calculated.

Abstract: Study on the Ti-43Al-9V-0.3Y alloys forged microstructure, which added a large amount of β phase stable element. The influence on the mechanical properties and synusia cluster refinement about β phase is analyzed. The test of material static tensile at 700 °C and room temperature is conducted. The results show that the V elements urges the grain size α₂ and β phase formation, β phase can inhibit α grain growth effectively. At the same time, its deformation ability can increase the high temperature plastic of the material. Experiments show that the main form of alloy tensile fracture at room temperature was intergranular fracture. Hole proliferation and communicated with each other through layers of crack is the main characteristics of high temperature tensile fracture of the alloy.

Abstract: The main objective of this work is to compare the different fracture behavior of carbon fiber-reinforced composite T300/epoxy with cross-play composite laminate. Tension-tension and three points bending fatigue are adopted, with optical microscopic and scanning electron microscopic observation of the specimen fracture surfaces. The specific objectives are: a) for tension-tension fatigue loading, the onset and multiplication of transverse matrix cracks continuously improve the delamination. Consequently, fibers rupture occurs in this locally region with high density of cracks. b) The density of intralaminar cracks increases with number of fatigue cycles. c) During the shear stress distribution under three points bending fatigue, delamination which is the main characteristic of T300/epoxy, initiates from the central and propagates alone the neutral axis of the sample. And a small quantity of fiber breakage occurs in the maximal compress region.

Abstract: In order to find out the relation between viscosity and adhesiveness (tack value), different rate printing varnish was respectively added to a lemon yellow ink for manufacturing several ink samples, and then their viscosity were tested. In addition, plastic viscosities of the 13 picking liquids were measured, and their tack values under 9 separation velocities were also tested. The study result showed that the picking liquid having high viscosity may be have low tack value, but printing varnish can decrease simultaneously plastic viscosity and tack value of one picking liquid.

Abstract: Experimental investigation on rolling texture evolution in commercially pure copper thinned from 5.8mm to 20μm by symmetrical rolling and asymmetrical rolling without annealing were carried out via orientation distribution functions and orientation line analysis. The results show that the rolling texture for the sample with initial rotate cube texture {100}<011>mainly consist of C and B, most crystallites aggregate along the α and β orientations lines. The texture density growth rate increased significantly in rolling process. That may relate to size effect of ultra-thin strip. The rate of dislocation reduction was more than dislocation multiplication due to disappear at grain size, when the thickness of ultra-thin strip decreased to an extremely value.

Abstract: Main purpose of research is establishing correlation of decreasing strength limit at the time of concretes thermo cycling. Research is based on invented in 2008 Method for definition of concretes frost resistance. This method is concerning to estimation of concrete's deformation after saturating of concrete sample by water, its freezing to standard temperature and defrosting. It has small labor input and high operability. During research, the theoretical analysis of results of experiment by the offered Method was carried out. Correlation between decreasing strength limit and unit strain of concrete samples was establish.

Abstract: Solid phase method was adopted to prepare the graphite fluoride solid lubricant. The friction and wear properties of graphite fluoride were tested with MMW-1 vertical universal friction and wear testing machine. The phase of graphite fluoride was analyzed with infrared spectrometer. The morphology of friction surface was analyzed with the scanning electron microscope. The results show that graphite fluoride has an excellent antifriction wear-resisting property, to compare with molybdenum sulfide, the anti-friction property increased by 35%, wear resistance increased by 49%. The main wear mechanism of the test specimens are fatigue wear and adhesive wear. The solid lubrication film for graphite fluoride was formed in the friction surface.