Aug. i6, 1915 



Tensile Strength and Elasticity of Wool 



383 



Young's modulus a fabric manufactured from it will have high resistance 

 to deformation of shape. 



By what is known as Hook's law, the stress divided by the strain is 

 constant to a certain point and from that time on the ratio decreases. 

 This point is known as the elastic limit of the substance, and in deter- 

 mining Young's modulus we always take the observations before the 

 elastic limit is reached. WTien a force is applied that carries the deforma- 

 tion beyond the elastic limit, the wool will not come back to its original 

 shape. In fact, this force has begun to tear apart the molecules of the 

 fiber, and the wool has become permanently weakened. Thus, a record 

 of the elastic limit for the fibers is essential. 



Fig. 2. — Curve showing Young's modulus of elasticity of merino wool at different stresses. X = elastic 



limi t 



Figures i and 2 show the curves illustrating the elastic limit. The 

 former shows the stretch or strain as force is applied ; the latter shows the 

 modulus curve. 



Table III gives the variation in the elastic limits for various fibers, 

 as obtained from three sheep. 



Table III. — Variation in the elastic limits of wool fibers of three sheep 



