| In osteosynthesis materials fields, it's a new try to use three dimensional (3-D) braiding composites as internal fixation bone plates. As we know stainless steel and titanium alloy are stable and conventional materials for internal fixation, however a lot of disadvantages of those have been shown in the course of clinic using. One of the problems is the mechanical property matching between the human body and the internal fixation instruments. Other problems are about the biology comparability. 3-D braiding composites bone plates will possess excellent mechanical property design and structure design. The modulus of 3-D braiding composites bone plates can be designed by changing the parameters such as braiding angles, fiber volume fraction and fiber distributing. Better damage tolerance for impact loading, better fatigue properties and high specific strength and specific modulus are other advantages of 3-D braiding composites. Using 3-D braiding composites as bone plates can avoid the disadvantages of metal bone plates, such as the phenomena discussed above, and the disadvantages of degradative bone plates, such as a high price and not fixating the thighbone.In this paper the static and dynamic mechanical properties of 3-D braiding composites were deeply studied, which would provide references for their applications and developments in the fields of bone fracture fixation. Static mechanical properties were studied by changing the braiding angles and braiding structures parameters of specimens. The results showed that in 3-D four directions braiding structures the strength and modulus of tensile, compress and bending properties would decrease with the braiding angles increasing, and the values could change in a large range. The results also showed that braiding structures were important factors that could affect the mechanical properties. The strength and modulus of tensile, compress and bending properties of 3-D five directions structures were higher than that of 3-D four directions braiding composites, but the brittleness increased clearly. Comparing with the laminated structures, with the same fiber volume fraction the tensile and bending properties of 3-D braiding structure were better.The dynamic mechanical properties-fatigue properties were first studied in this paper. Tensile-tensile fatigue test were carried out at different maximum stress ratios .All tests were run at a stress ratio R(min/ max)=0.1. The fatigue frequency was 10 Hz. The fatigue properties were strongly determined by the braiding angles. The course of fatigue test could present different damnification and the hysteresis heat would occur more severely with the braiding angles increasing. The strain-stress curve of the specimens with large braiding angles would occur non-liner, and the later modulus is bigger than the initial modulus. This variational rule contrasted with the metal's rules. After one million times fatigue tests, the residual strength of the specimens are higher than the ultimate strength. This is due to fiber bundles being reoriented to a lower angle toward the tensile loading direction and the plasticity distortion.Comparing with laminated structures materials and metal materials, 3-D braiding composites possess strong superiority in mechanical properties design, and other ascendant mechanical properties, all of these provide possibility for 3-D braiding composites used as biomedical materials which are more suitable for bone plates. |
