Bending and Fiber Stiffness

ZONE OF EXTENSION NEUTRAL ZONE ZONE OF COMPRESSION 

Several methods have been described for measuring the bending modulus of hbers. The balanced hber method of Scott and Robbins [73,74] appears to be the easiest to handle experimentally (except for very curly hair) and provides less scatter than the other methods [74], The vibrating-reed method (oscillating hber cantilever) has also been used with human hair [10], The cantilever beam method [75], the loop deformation method [76], and the center load beam method [76] have been described for textile hbers. 

The distance d is an index of stiffness of the hber. The stiffness coefficient G (ratio of applied force to bending dehection) may be calculated from d using this expression  

The elastic modulus for bending Eb may also be calculated from d  

The bending modulus ( b) by this method at 62% RH and 75°F is approximately equal to Young s modulus for stretching ( 5) determined under similar experimental conditions by the load-extension method, Eb = 3.79 X 10 dynes/cm. These values have not been corrected for hber ellip-ticity. Such a correction may be considered academic, but it should make Eb higher than Es for human hair because elliptical hbers orient to bend over their minor axis in this method. 

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