Monitoring fiber stress during curing of single fiber glass- and graphite-epoxy composites

Technical Report · Tue Nov 01 04:00:00 EST 1994

OSTI ID:6661589

Madhukar, M S; Kosuri, R P; Bowles, K J

The difference in thermal expansion characteristics of epoxy matrices and graphite fibers can produce significant residual stresses in the fibers during curing of composite materials. Tests on single fiber glass-epoxy and graphite-epoxy composite specimens were conducted in which the glass and graphite fibers were preloaded in tension, and the epoxy matrix was cast around the fibers. The fiber tension was monitored while the matrix was placed around the fiber and subjected to the temperature-time curing cycle. Two mechanisms responsible for producing stress in embedded fibers were identified as matrix thermal expansion and contraction and matrix cure shrinkage. A simple analysis based on the change in fiber tension during the curing cycle was conducted to estimate the produced stresses. Experimental results on single fiber glass- and graphite-epoxy composites show that the fiber was subjected to significant tensile stresses when the temperature was raised from the first to the second dwell period. When initial fiber pretension is about 60 percent of the fiber failure load, these curing-induced stresses can cause tensile fracture of the embedded fiber.

• Research Organization: National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center
• OSTI ID: 6661589
• Report Number(s): N-95-13641; NASA-TM--4568; E--8522; NAS--1.15:4568; CNN: RTOP 505-63-12
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360601* -- Other Materials-- Preparation & Manufacture
360603 -- Materials-- Properties
CARBON FIBERS
CURING
EPOXIDES
EXPANSION
FIBERS
MATERIALS
MATRIX MATERIALS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
SHRINKAGE
STRESS ANALYSIS
THERMAL EXPANSION