STP972: Mechanical Behavior of Braided Composite Materials

    Simonds, RA
    Instructor, professor, and professor, Virginia Polytechnic Institute and State University, Blacksburg, VA

    Stinchcomb, W
    Instructor, professor, and professor, Virginia Polytechnic Institute and State University, Blacksburg, VA

    Jones, RM
    Instructor, professor, and professor, Virginia Polytechnic Institute and State University, Blacksburg, VA

    Pages: 16    Published: Jan 1988


    Abstract

    Graphite/epoxy composite material specimens manufactured with AS-4 fiber and 3501 matrix in a 3-D braiding process were subjected to tension, compression, impact, and cyclic loading. The type of braiding utilized for the specimens results in a material that is not subject to delamination as experienced by laminated composites. Further, braiding has potential for the direct creation of structural shapes such as I-beams or stiffened panels which can be manufactured as one piece rather than being assembled from several laminated elements. The specimens employed in this study, however, were more familiar straight-sided coupon shapes. Tension test results indicate a tensile strength of 1280 MN/m2 (186 ksi) and a tensile Young's modulus of 106 GN/m2 (15.3 Msi). The compression strength is 447 MN/m2 (64.8 ksi) and the compressive Young's modulus is similar to that for tension. A series of impact tests was performed on the material to determine the threshold of detectable impact damage. An energy of 5.4 J (4 ft·lb) was found to produce damage that was detectable by both radiography and by ultrasonic C-scanning. Fatigue tests were run on the material at a stress ratio of −1 to determine the fatigue life of the braided composite. Specimens fatigued at 290 MN/m2 (±42 ksi) had nominal lives of 20 000 cycles. Reducing the fatigue stress to ±(40 ksi) 276 MN/m2 extended the life to 80 000 cycles. Lower stresses produced longer lives. In addition, compression, and fatigue tests were run on specimens that had been subjected to the 5.4-J (4-ft·lbs) impact test. There was virtually no change in compressive strength and fatigue life compared to specimens without the prior impact loading. Thus, impact loading has little, if any, effect on the mechanical behavior of the braided composites included in this study. In conclusion, braided composites have potential to solve many of the shortcomings of more conventional laminated composite materials.

    Keywords:

    composite materials, mechanical properties, braid, woven


    Paper ID: STP26151S

    Committee/Subcommittee: D30.02

    DOI: 10.1520/STP26151S


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