碳/碳复合材料T型悬臂梁弯曲失效分析

Bending failure analysis of carbon/carbon composite T cantilever beam

首次对碳/碳复合材料T型结构件进行了悬臂梁弯曲试验。通过化学气相沉积工艺制备了宽度为40mm的T40试件和宽度为50mm的T50试件,分别对两种试件的损伤失效模式和弯曲应力进行了研究;根据结构破坏区域的应变随载荷增加的变化规律,得到了结构在弯曲过程中的损伤失效进程。结果发现,在悬臂梁弯曲载荷作用下,结构处于正应力和剪应力耦合状态,耦合应力会使宽厚比较小的结构件容易在腹板根部出现局部失稳现象。应用横力弯曲理论对结构破坏截面上腹板边缘的正应力和面内剪切应力进行了简单计算。结果表明:屈曲失效的T50试件比剪切型破坏的T40试件的最大弯曲正应力小22.93%,说明屈曲失效会使结构的弯曲强度大幅下降;而T50试件的最大剪切应力比T40试件的高31.46%,说明屈曲失效主要由材料的剪切性能控制。最后通过有限元方法对T50试件在发生剪切型破坏时的最大弯曲正应力进行了计算,计算结果与试验中发生压缩剪切破坏的T40试件相比仅相差3%,可以较好地表征T50试件的弯曲强度。

For the first time to carry out the bending test of the T structure of carbon/carbon composite material cantilever beam, the specimens are prepared by the chemical vapor deposition process, and are divided into T40(with 40 mm width) and T50(with 50 mm width) specimens by width, separately. The failure mode and bending strength of the structure are studied by the test and the failure process of the specimens is obtained by the law of the strain changing with the load on the breaking region. Results obtained show that the structure is in coupling state of normal stress and shear stress under the cantilever bending load, the coupling stress would cause local buckling phenomena in the thinner structure. Using the transverse bending theory in mechanics of materials to calculate the normal stress located at the edge of web plate and in-plane shearing stress on the damage cross-section, bending strength under the two different failure modes can be got. Analysis results show that the maximum bending normal stress of T50 which with buckling failure mode is 126.4MPa, and T40 which with shear-type failure is 164 MPa, this proves buckling failure made the bending strength of structure decreases dramatically. Finally, finite element calculation is used to analyze bending normal stress of the structure and the calculation results can well characterize the bending strength of T50 structure.