Microdebonding

The single filament pull out test, sometimes called the microdebond test, has received attention for some years as a way to assess the adhesion between fibers and matrices in fiber composite [90,91]. It provides a direct measure of interfacial adhesion and can be used with both brittle and ductile matrix resins. 

It has been noted in a round robin test of microcomposites that there arc large variations in test results for an apparently identical fiber and matrix system between 13 different laboratories and testing methods (Pitkethly et al., 1993). Table 3.1 and Fig 3.15 summarize the IFSS values of Courtaulds XA (untreated and standard surface treated) carbon fibers embedded in an MY 750 epoxy resin. It is noted that the difference in the average ISS values between testing methods, inclusive of the fiber fragmentation test, fiber pull-out test, microdebond test and microindentation test, are as high as a factor of 2.7. The most significant variation in ISS is obtained in the fiber pull-out /microdebond tests for the fibers with prior surface treatments, and the microindentation test shows the least variation. 

Fig. 3.15. Interface shear strength. Xb, of (a) untreated and (b) treated LXA500 carbon fiber-epoxy matrix system measured at 10 different laboratories and using different testing methods. (O) fiber pull-out test ( ) microdebond lest ( ) fiber push-out lest (A) fiber fragmentation test. After Pitkelhly el al. (1993).

Testing method Pull-out Microdebond Fragmentation Push-out ... 

Chen, E.J.H. and Croman R.B. (1993). Microdebonding investigation on the effects of thermal residual stress on the bond strength of a graphite/polyimide composites. Composites Sci. Technol. 48, 173-179. 

Mandell, J.F., Chen, J.H. and McGarry, F.J. (1980). A microdebonding test for in situ assessment of fiber/matrix bond strength in composite materials. Int. J. Adhesion Adhesives 1, 40-44. 

Miller, B., Gaur, U- and Hirt, D.E. (1991). Measurement of mechanical aspects of the microdebond pullout technique for obtaining fiber/resin interfacial shear strength. Composites Sci. Technol. 42,207-219. 

Other methods to evaluate the IFSS have been proposed mainly for synthetic fibers. Among these, the microdebond, also known as the microindentation test, first proposed by MandeU et al. [54], has been theoretically investigated [34, 35] and applied to synthetic and metallic fibers. To the knowledge of the authors of this chapter, the microindentation test has not yet been used to measure the IFSS of lignocellulosic fibers embedded in polymeric resins. In spite of advantages listed by Herrera-Franco and Drzal [34], they also emphasized the following drawbacks for this test ... 

The microdebonding indentation system was developed by the Dow Chemical Company [109], and overcomes some deficiencies of the method described by Mandell and co-workers. This fully automated instrument is designed for use outside the research environment. It is based on a Zeiss optical microscope. A... 

McAlea, K.P. and Besio, G.J., Adhesion between polybutylene terephthalate and E-glass measured with a microdebond technique. Polym. Compos., 9, 285—290(1988). 

Grande, D.H., Microdebonding Test for Measuring Shear Strength of the Fiber/Matrix Interface in Composite Materials. M.S. Thesis, Massachusetts Institute of Technology. Cambridge, MA, June 1983. 

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