Fiber orientation effects in supported adhesives

Abstract

The use of fabric supports (carriers) in structural film adhesives has been established for some time. Such carriers are commonly glass, nylon, or polyester in woven, mat, or knitted form. Supported adhesives may be regarded as fiber-reinforced composites of low fiber volume fraction. In the case of a woven glass carrier, where the fiber is of much higher modulus than the matrix and the fibers are aligned in two directions, anisotropy of properties is a possibility, and some evidence of this in the dynamic mechanical properties of an adhesive has been observed.' Although the effect of carriers on such properties as fatigue strength and durability of bonded joints has been examined to some extent,u the effect of fiber orientation in adhesives containing relatively high modulus carriers does not appear to have been reported. Some observations on this topic are presented here. EXPERIMENTALTwo adhesive systems were used: (1) a commercially available, 177°C curing, glass-fibersupported, epoxy adhesive for aerospace applications (overall composition shown in Table I) and (2) cast films of the Shell epoxy resin Epikote 828 and methylene dianiline (MDA) in the proportion 100:29, containing either (a) the same glass carrier as in (1) obtained by extraction from the uncured adhesive, (b) a polyester mat, or (c) no carrier.The glass fabric, approximately 32.8 g/m2, of an open, plain weave, constituted about 5% by volume in the commercial adhesive, as determined by a~h i n g .~ The polyester mat was approximately 8.0 g/m2; four layers of this were incorporated in the cast films. The construction of the two fabrics is shown in Figure 1.Dynamic mechanical properties were measured with a Rheovibron Model DDV-11