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Composite materials reinforced with braided, woven, knit, and stitched fibrous preforms are emerging as potential alternatives to unidirectional prepreg tape. A variety of these material forms are currently being evaluated by major airframe manufacturers.
These new forms of composite materials bring with them potential testing problems. The applicability of existing test methods to the 2-D and 3-D braided, woven, stitched, and knit materials being evaluated bears investigation. The overriding concern is that the values measured are accurate representations of the true material response.
This paper will provide a review of efforts to establish a set of strain gage selection guidelines for textile reinforced composite materials.
A variety of strain gages were evaluated in the study to determine the sensitivity of strain measurements to the size of the strain gage. The strain gages were chosen to provide a range of gage lengths and widths. The gage aspect ratio (the length-to-width ratio) was also varied.
The gages were tested on a diverse collection of textile composite laminates. Test specimens featured eleven different textile architectures: four 2-D triaxial braids, six 3-D weaves, and one stitched uniweave architecture. All specimens were loaded in uniaxial tension. The materials’ moduli were measured in both the longitudinal (parallel to the 0° yarns) and the transverse (perpendicular to the 0° yarns) directions. The results of these measurements were analyzed to establish the strain gage guidelines.
Staff engineer, Lockheed Martin Engineering and Science, Hampton, VA
Assistant professor, University of Florida, Gainesville, FL
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