Single fiber compression test

Microcomposite tests have been used successfully to compare composites containing fibers with different prior surface treatment and to distinguish the interface-related failure mechanisms. However, all of these tests can hardly be regarded as providing absolute values for these interface properties even after more than 30 years of development of these testing techniques. This is in part supported by the incredibly large data scatter that is discussed in Section 3.2.6. 

The single fiber compression test has not been as popular as other microcomposite tests because of the problems associated with specimen preparation and visual detection of the onset of interfacial debonding. To be able to obtain accurate reproducible results, the fibers have to be accurately aligned. With time, this test method became obsolete, but it has provided a sound basis for further development of other testing techniques using similar single fiber microcomposite geometry. 

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Fig. 3.1. Single fiber compressive tests with (a) parallel-sided and (b) curved-neck specimen.

Fig. 3.14. Schematic drawings of slice compression test on a single fiber composite (a) before loading (b) peak loading with a maximum fiber protrusion length, (c) after unloading with a residual fiber protrusion length, After Hsueh (1993),...

Carman et al. [ 18] developed a test called the meso-indentation test which used a hard spherical ball indenter to apply a compressive force to a surface of the composite perpendicular to the fiber axis. The indenter was much larger than the diameter of a single fiber therefore, when the ball was forced into the end of the composite, it made a permanent depression in the material. From the size of the depression and the force-deflection curve, they calculated a mean hardness pressure as a function of strain in the coupon. Qualitative differences have been reported in tests conducted on carbon fiber-epoxy composites where the fiber-matrix adhesion had been varied systematically. 

Several methods have been used to determine the compression strength of carbon fiber and its composites—The Loop Test [90] Single Filament in a Beam [91] Critical Length under Compression [92] Micro-compression [93,94] Fiber Recoil [95-97] Piezo Method [98,99] Raman Spectroscopy [100-102] Composite [103,104] and Mini-composite [105]. 

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