The ablation properties of C/C composites with four different needled preforms prepared by isothermal chemical vapor infiltration （ICVI）, which are super-thin mat lay-up, 0°/90° weftless fabric lay-up, 0&#...The ablation properties of C/C composites with four different needled preforms prepared by isothermal chemical vapor infiltration （ICVI）, which are super-thin mat lay-up, 0°/90° weftless fabric lay-up, 0°/45° weftless fabric lay-up and 0°/45° twill fabric lay-up, were quantitatively evaluated by performing the ablation tests with an engine torch. And their ablation discrepancies were analyzed according to the surface characteristic, porosity and thermal diffusivity. The results show that the 0°/45° weftless composite has a fiat eroded surface with no obvious macroscopic pits. Its thickness and mass erosion rates are decreased by about 46.8% and 34.8%, 25.0% and 27.5%, and 17.5% and 19.4% compared with those of the mat, the 0°/90° weftless and the 0°/45° twill composites, respectively. The ablation properties are mainly controlled by the thermo-chemical effect （oxidation）, and a little by the thermo-mechanical effect （mechanical denudation）. The needling fiber bundles play an important role in accelerating the ablation process and resulting in the heterogeneous ablation.展开更多
An indirect method, Angstroms method was adopted and an instrument was designed to determine the thermal conductivity of magnesium metal and alloys. Angstroms method is an axial periodic heat flow technique by which t...An indirect method, Angstroms method was adopted and an instrument was designed to determine the thermal conductivity of magnesium metal and alloys. Angstroms method is an axial periodic heat flow technique by which the thermal diffusivity can be measured directly. Then thermal conductivity can be obtained with relation to thermal diffusivity. Compared with the recommended data from the literature the fitted values of the thermal diffiusivity correspond with 3%, and the credible probability of the thermal conductivity in the range of 0 450 ℃ is about 95%. The method is applicable in the given temperature range.展开更多
基金Project(200202AA305207) supported by the National High Technology Research and Development Program of China
文摘The ablation properties of C/C composites with four different needled preforms prepared by isothermal chemical vapor infiltration （ICVI）, which are super-thin mat lay-up, 0°/90° weftless fabric lay-up, 0°/45° weftless fabric lay-up and 0°/45° twill fabric lay-up, were quantitatively evaluated by performing the ablation tests with an engine torch. And their ablation discrepancies were analyzed according to the surface characteristic, porosity and thermal diffusivity. The results show that the 0°/45° weftless composite has a fiat eroded surface with no obvious macroscopic pits. Its thickness and mass erosion rates are decreased by about 46.8% and 34.8%, 25.0% and 27.5%, and 17.5% and 19.4% compared with those of the mat, the 0°/90° weftless and the 0°/45° twill composites, respectively. The ablation properties are mainly controlled by the thermo-chemical effect （oxidation）, and a little by the thermo-mechanical effect （mechanical denudation）. The needling fiber bundles play an important role in accelerating the ablation process and resulting in the heterogeneous ablation.
文摘An indirect method, Angstroms method was adopted and an instrument was designed to determine the thermal conductivity of magnesium metal and alloys. Angstroms method is an axial periodic heat flow technique by which the thermal diffusivity can be measured directly. Then thermal conductivity can be obtained with relation to thermal diffusivity. Compared with the recommended data from the literature the fitted values of the thermal diffiusivity correspond with 3%, and the credible probability of the thermal conductivity in the range of 0 450 ℃ is about 95%. The method is applicable in the given temperature range.
