Papers by Keyword: Mechanical Property

Abstract: Ultra-high Strength Steel heat process mechanical property energy spectrometer Abstract: Microstructure and mechanical property variation vs. heat process was investigated by means of metallography and electron microscopy in Ultra-high Strength Steel with tensile strength 1000Mpa. The results show that microstructure variation in the steel with tempering temperature increasing is as follows:tempered martensite→main tempered sorbite and a small amount of M/A, at the meantime, growing in quantities and volume of second-phase, always decreasing in strength, firstly increasing and then decreasing in impact energy and elongation. Study on precipitated mechanism of second-phases, the crystal structure and volume of precipitation was characterized by TEM observation and energy spectrometer.

Abstract: The microstructure and mechanical properties of aged Mg-5.5Al-1.2Y magnesium alloy with Ca addition are investigated. The results show that with 1.0wt.% Ca addition, the phase of Al₂Y is refined obviously and the phase of Mg₁₇Al₁₂ has a dramatic decrease in number. And, high melting point intermetallic compounds Al₂Ca and Al₄Ca are formed. Meanwhile, the β-Mg₁₇Al₁₂ phase become more dispersed. After 1.0wt.% Ca addition, the mechanical properties of the alloy at room and elevated temperature are improved.

Abstract: The microstructure and mechanical properties of aged AZ81 magnesium alloy with Ca addition have been investigated. The results show that with proper content of Ca addition, the microstructure of AZ81 magnesium alloy is refined. Meanwhile, high melting point granular compounds Al4Ca are formed, and the quantity of β-Mg₁₇Al₁₂ phase is reduced significantly. And the mechanical properties of AZ81 magnesium alloy are enhanced at room temperature and 150°C.

Abstract: In the mechanical properties test, in order to ensure test results reflect the characteristics of the material itself reliably, the sample’s quality of processing is an essential prerequisite. Performance sample with different shapes were processed into different diameters, different shoulder of the transition area, and different width, to be conducted with tensile tests of mechanical properties. The results show that differences in sample processing on the mechanical test results are different, and we fine some disciplines by analyzing the reasons causing the differences.

Abstract: It is well-known that the Ti-Ni shape memory alloy (SMA) is applicable to the medical stent. The repeated heat-treatment under the constrained strain is necessary for the manufacturing process of the laser-cut SMA stent. In this research, the effect of heat-treatment under the constrained strain on mechanical properties of the Ti-Ni shape memory alloy wire was investigated. The applied strain at single heat-treatment (εap) was 4, 5 and 8%, and the heat-treatment is repeated so as to became total applied strain 40%. In the case of εap=4 and 5%, partial transformation occurs in the SMA wire, and so a necking appears in the SMA wire. Due to this necking, multi-step martensitic transformation, and decreasing of breaking strength / breaking strain are caused. The necking does not occur because the whole of the SMA wire is transformed for εap=8%. The mechanical properties are improved by increasing of εap. Nevertheless, the mechanical properties of each sample are inappropriate for the medical stent. However, the mechanical properties of the as-manufactured sample are improved greatly by training. In addition, it is desirable that the applied strain during training is slightly larger than the requested strain for application.

Abstract: A novel synthetic copolymer (PAA) for bone repair was prepared by melt condensation polymerization with 6-aminohexanoic acid (He) and 4R-hydroxy-L-proline (Hyp). The structure and thermal property were characterized by infrared spectrometer (IR), nuclear magnetic resonance (H1NMR) and differential scanning calorimeter (DSC). The results indicated that the PAA had amide linkages in their polymer chains. The Tg of PAA was 57.56°C and significantly higher than that of nylon6, 50.46°C. Meanwhile, the intrinsic viscosity and mechanical properties were investigated at different He/Hyp ratios. It revealed that appropriate introduction of Hyp group could control the degree of polycondensation and adjusted mechanical properties of PAA obviously close to natural bone. The prepared polymers had about 2.12~18.21 % weight loss after 8-week soaking in PBS, showed degradable properties which was essentials to new bone growth. The copolymer of He and Hyp with ratios of 90/10 had 6.57 % weight loss and maintained the yield compressive strengths with about 67.51 MPa after 8 weeks, which exhibited a compatible mechanical properties and degradation speed for bone repair.

Abstract: After heat treatment at 800°C for 15min, a Cu-Al alloy was cryogenic treated at -196°C for 30min, the micro-mechanical properties of the Cu-Al alloy before and after cryogenic treatment were measured by nanometer mechanical testing system and the microstructure of the Cu-Al alloy were also analyzed by optical microscope, SEM/EDS and XRD. On the basis of that, the effects of cryogenic treatment on micro-mechanical properties of the Cu-Al alloy were investigated. The results show that the cryogenic treatment can refine the grains, and increase the hardness, elastic modulus, elastic recovery rate and ratio of hardness to modulus of the Cu-Al alloy. As a result, cryogenic treatment can improve the ability to resist applied load and anti-indentation creep effectively.

Abstract: Since the mechanical properties of the skin and the core of corn stalk are different significantly. The basal fourth internode of the corn stalk was chosen to do the compression test. The Maximum Force, the Compressive Strength, and the Modulus of Elasticity of the stalk skin and the core were obtained respectively. Then, the modulus of elasticity parallel to the direction of stalk skin fiber was calculated based on the measured data. The fiber reinforcement effect of the corn stalk skin was analyzed, combined with the mechanics of composites. Furthermore, the finite element model of corn stalk, regarded as composites, was constructed by ANSYS to simulate the compression test. The results showed that the simulation of reinforcement effect was well consistent with the value calculated by the mechanics of composite.

Abstract: The fiber brakeage in compounding glass fiber-reinforced nylon-66 with different screw assemblies of the co-rotating twin screw extruder was studied, and comparative analysis of five different screw assemblies was made. The result shows that proper screw assembly could improve the residual fiber length and the mechanical property of the composite effectively

Abstract: Polybenzoxazine was one of the most widely employed matrix for advanced composites, due to their low viscosity, good dimensional stability, high glass transition temperature (Tg) and wide molecular design flexibility. To obtain high perfomance resin matrix, a fundamental understanding of the formation of crosslinking network structure and the relationship between structure and properties was essential. Therefore, the blends of benzoxazine precursor with different functionality were designed to achieve various network molecular architectures, and the effects of inhomogeneous structure of polybenzoxazine on mechanical and thermal properties were investigated. The bifunctional benzoxazine precursor (BA-a) based on bisphenol-A, formaldehyde and aniline, and the monofunctional benzoxazine monomer (Ph-a) based on phenol, formaldehyde and aniline were synthesized respectively. The blends of BA-a and Ph-a, in which the mole ratio was 1:0, 2:1, 1:1 and 1:2, repectively, were thermally cured through ring-opening reaction to obtain polybenzoxazines with various network structures. The fracture surface morphology of various polybenzoxazines was observed by atomic force microscopy (AFM). The hard phase with highly crosslinking density was dispersed in the soft phase with slightly crosslinking density, which led to the generation of inhomogeneous structure of polybenzoxazine. Dynamic mechanical thermal analysis (DMTA) of carbon fiber reinforced polybenzoxazine showed two glass transition temperatures (Tg), which corresponded to the soft phase and hard phase, respectively.With increasing the mole ratio of Ph-a, the increase of hard phase resulted in the enahncement of flexural modulus of polybenzoxazine, whereas the tensile and flexural strength of polybenzoxazine decreased due to the reduction of the crosslinking density of soft phase. Derivative thermogravimetric (DTG) analysis exhibited three major degradation steps, which characterized the decomposition, weight-loss and charring, respectively. Thermogravimetric analysis (TGA) showed that the onset degradation temperature and char yield at 850 oC increased with the increase of Ph-a mole ratio, indicating higher thermal stability and lower decomposition rate, which was attributed to the increase of hard phase with highly crosslinking density.