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Study on fatigue test method of titanium alloy for biological use

While the academic research on fatigue or corrosion fatigue of biological metal materials in the living environment is deepening, the complexity of fracture process is also increasing, and there are still many unsolved research areas. In the present biological environment, fatigue test methods are carried out in the laboratory alone. This topic discusses the comprehensive properties of biological titanium alloy including fatigue corrosion, wear resistance and cell influence. In particular, the test material shape, repeat speed, loading method, simulated body fluid, pH and dissolved oxygen concentration and other influencing factors, and verify whether the test method is appropriate.

1. The experimental method

The sample is Ti-6Al-4VELi alloy (ASTM F136) made of datong special steel. The shape of fatigue sample is quasi-sand glass round bar with standard spacing of 12mm and diameter of 6mm. Fatigue test conditions: a frequency of 10Hz under uniaxial tensile load, under sine wave. The test temperature was carried out in the atmosphere of the laboratory where the indoor temperature was adjusted to 22℃ by air conditioning. The number of repetitions of the fatigue load is 107.

Fatigue test parameters of biological titanium alloys include: surface properties of samples, stress ratio, the presence or absence of notch, repetition rate, loading method, type of simulated body fluids and PH, and the selection of dissolved oxygen concentration, all of which are influencing factors. Only the effect of surface properties on fatigue characteristics is reported. The surface properties of machined sample surface and mirror polishing materials were discussed.

2. The results of

Compared with machined materials, the surface roughness of the mirror polished samples is reduced to less than half. The tensile strength test results (stress-deformation curve) of samples with such surface roughness are as follows: no matter what the surface roughness is, the results of maximum tensile strength and elongation are the same, indicating that different surface properties have no influence on tensile properties.

On the one hand, the fatigue test results show that the number of repetitions of the mirror polished specimens at various stress levels is higher than that of machined specimens. That is, the effect of surface properties on fatigue life. As the number of repetitions increases, the starting point of the crack shifts from the surface to the interior, where the initial position of the internal crack appears on the outside (near the surface) of the machined material compared to the mirror-polished material. This is due to the large surface roughness of the material, near the surface of the high stress state, more sensitive to crack. That is, the degree of concave and convex accompanied by surface roughness promotes the generation of cracks, and the crack texture is larger. Therefore, with the increase of the number of samples, the relationship between crack origin and stress distribution was analyzed in detail, so as to understand one of the topics: the influence of surface properties on fatigue characteristics.

3. conclusion

This study focuses on various fatigue related conditions of biological titanium alloys and discusses the comprehensive fatigue test methods and characteristics. In particular, the surface properties of specimens are reported, that is, the influence of surface roughness on fatigue characteristics is made clear.