Thermo-mechanical Properties Of Alumina Fiber And Fabric

As a high temperature thermal protection material,continuous flexible alumina fiber has the advantages of lighter weight,high temperature resistance,corrosion resistance,high temperature oxidation resistance and high temperature creep resistance than traditional metal thermal protection structure,and can be widely used in aircraft engines,land-based turbines,rocket power generation systems,hypersonic missiles and aircraft and other thermal protection material fields.Therefore,the tensile properties at high temperature of continuous alumina fiber and the thermal insulation properties of its composites have become the research focus of scholars in related fields.The mechanical properties of continuous flexible fiber reinforced ceramic composites are closely related to the mechanical properties of the reinforced materials,so it is very important to investigate the mechanical properties of alumina fiber and its fabric as the reinforced phase of the composite.In this paper,the structural composition,chemical corrosion resistance,mechanical properties at room temperature and high temperature of three representative alumina fibers were studied.The crystal types of alumina fibers from the United States,Japan and China areγ-Al₂O₃,γ-Al₂O₃,δ-Al₂O₃,respectively.The three kinds of alumina fibers are acid-resistant and alkali-resistant.Among them,the diameter reduction rate,weight loss rate and strength loss rate of the Japanese alumina fibers are the smallest among the three kinds of alumina fibers.It is considered that the Japanese alumina fibers have better acid-resistant properties.The breaking force retention rates of American,Japanese and domestic alumina yarns treated at 950℃for 4 h are 64.2%,68.4%and 69.5%,respectively.The retention rates of breaking force of MG,RB,imitation fabric of MG and RB were 68.1%,67.6%,71.0%and 76.3%,respectively.The critical twist of alumina fiber of 65 tex,130 tex,195 tex and 260 tex is 80twist/m,60 twist/m,60 twist/m and 40 twist/m respectively,and the corresponding critical twist factors are 6.4498,6.8411,8.3785 and 6.4498,respectively.The smaller the radius of the simulated cylinder,the smaller the breaking force and strength of the alumina yarn,that is,the greater the bending degree of the alumina fiber,the greater the loss of its tensile strength from the wear of the cylinder.Then,the influence of weaving parameters on the tensile properties of alumina fiber is investigated.The strength of plain weave,twill,rearranged twill and satin weave increases successively.The strength of rearranged twill fabric is 35.98%higher than plain fabric.And the rearranged twill fabric has the best comprehensive performance and is suitable for the industrial production of alumina fabric.When the weft count is 5 or 6number/cm,the higher the linear density,the higher the strength of the fabric.When the weft count is 7number/cm,the fabric strength increases first and then decreases with the increase of linear density.When the linear density is constant,the fabric strength decreases gradually with the increase of weft count,and the decreasing rate increases with the increase of linear density.In the production process of alumina fabric,both linear density and weft count should be taken into account.When the weft count of the fabric is larger,the smallest linear density should be selected.When the linear density is larger,the weft count of the fabric should be reduced as far as possible.Finally,the effects of different thickened coatings on the thermal insulation and mechanical tensile properties of alumina fabric,the thermal insulation properties of different high temperature resistant materials and high temperature airflow erosion properties,and the high temperature tensile properties of coated alumina fabric were further investigated.The difference between the back temperature and the heating table temperature of alumina fabric with 0.2,0.4,0.6 and 0.8 mm coating thickness increases successively,which are 31.4,41.6,43.3 and 55.3℃,respectively.Adding a layer of aluminum foil or copper foil on the back of Mullite felt can increase the temperature difference between the back of Mullite felt and the heating table by 36.5%and 49.5%,respectively.With the increase of coating thickness,the strength of coated alumina fabric decreases gradually,and the tensile strength becomes stable when the coating thickness is 0.2-0.5mm.Under high temperature ablative environment,the breaking force of coated fabric has no obvious change,only decreased by 1.16%.When the high temperature air flow at 1000℃washed 120 s,the maximum heating temperatures of the back of the coated fabric,coated fabric+mullite felt,coated fabric+aluminum foil+Mullite felt,coated fabric+copper foil+Mullite felt were 346.3℃,109.6℃,81.7℃and 71.3℃,respectively.The designed combined heat insulation material has good heat insulation performance.Through the above three aspects of the research content,obtained basic mechanical properties of alumina fibers and the best weaving process of alumina fabric,as well as the best preparation process of high temperature resistant coating fabric,and gives the high temperature resistance excellent heat insulation material combination,provides a more systematic theoretical basis for the weaving of alumina fiber and the preparation of thermal protection insulation materials.