XIII, A, 6 King: Philippine Coir and Coir Cordage 317 



The stress-deformation graphs of coir shown in fig. 3 are all 

 curved; that is, the value of E decreases rapidly after the first 

 millimeter of elongation. From this it may be seen that coir 

 belongs to the class of materials in which stress and deformation 

 while in tension are not directly proportional, and that even the 

 smallest stress permanently injures the fibers. Therefore, for 

 all practical purposes, coir is not distinguishably elastic, nor has 

 it a definite modulus of elasticity. Its lack of elasticity, together 

 with its comparatively low strength, condemn it for use in 

 cordage except of an inferior quality. These facts are entirely 

 at variance with the claims of "highly elastic properties" for 

 coir as discussed in preceding pages. 



The only coir filament that gave an elastic modulus within a 

 definitely measurable range is that of which a graph is shown 

 in fig. 2. Assuming that coir has a definite elastic modulus for 

 immeasurably small deformations, the maximum value that can 

 be assigned is 27,000 kilograms per square centimeter obtained 

 in test 2 of the machine-cleaned fiber, which in this maximum 

 case is only one-fifteenth of the maximum value for abaca. 



Resilience. — Elasticity is intimately connected with resilience, 

 or "jerk-resisting power," inasmuch as the latter depends largely 

 upon the former. Resilience is the springing back of a de- 

 formed body after being relieved of the deforming load, it being 

 always understood that the stress must be within the elastic 

 limit. It is usually measured in kilogram-meters or in foot- 

 pounds, though smaller units such as kilogram-centimeters or 

 inch-pounds are sometimes used. It should be borne in mind 

 that the energy expended in permanently deforming a body can- 

 not be given back as resilient work, but appears as heat, and 

 is used to break down the structure. 



Johnson ^* says : 



* * * the resilence, or energy, which can he absarbed, or stored, in 

 a body of a given material and form, up to a given fibre-stress, is no 

 function of the relative dimensions of the body, but only of its volume. 



The method of calculating resilience is very simple. If the 

 initial force of tension of coir is zero, and the final one at the 

 limit of elasticity is 308 kilograms per square centimeter as 

 obtained in my test for machine-cleaned filament No. 4, the 

 value of the average stress is 154 kilograms per square centi- 

 meter. The elongation of the test specimen at the limit of elas- 

 ticitj^ is 2 millimeters; then, since the average stress of 154 



"Johnson, J. B., Materials of Construction. John Wiley and Son, New- 

 York, 4th ed. (1912), 76. 



