An experimental investigation of the relationship between fatigue and dynamic modulus of two polymers, using wave propagation techniques, has shown that the determination of dynamie modulus during constant-rate elongation of partially fatigued samples yields Information about the extent of fatigue, which is unobtainable from measurements of modulus during fatigue or from a conventional stress-strain test of the fatigued samples. It is possible to differentiate between normal and fatigued samples by comparing values of dynamic modulus at an arbitrary elongation subsequent to fatiguing. For polyethylene samples, a "fatigue severity index," based on frequency and stroke of axial cycling, is defined. The dynamic modulus measured subsequent to fatiguing is dependent on this index. The creep behavior of the two polymers tested. as reflected in measurement of dynamic modulus, is essentially different from the fatigue behavior disclosed by the same type of measurements. The dynamic modulus, measured subsequent to creep testing and during constant-rate elongation, provides information not obtainable by measurements during creep or from the stress-strain test by itself.The results support the theory that fatigue failure is due to fracture caused by the' formation and growth of micro-flaws under the conditions of frequency, strain, and temperature employed in the experiments. '
The following report, which covers the possibility of increasing the production of cotton cards, should be of particular value to the managements of cotton mills at this time when the capacity of the equipment is overtaxed because of war requirements. It would also seem reasonable that the principles set forth may be applicable to the carding of staple rayon. This is the first complete report on studies conducted under the direction of the Applied Research A progress report has been recently issued covering some of the material included in this article. However, in the course of finishing the study it has been possible to draw several important conclusions affecting the overall picture which were not justified at the time the progress report was issued. Additional results have now been summarized and, of course, the data provided are much more complete.The cotton carding capacity of the country, although in balance with other yarn manufacturing equipment for peacetime requirements, is inadequate for the manufacture of heavy volumes of military . fabrics. The greater predominance of the coarser yarns needed in wartime requires an increase in carding capacity in proportion to spinning equipment. Therefore any increase in the productivity of existing carding equipment should be reflected in direct increase in the country's yan1 production, as long as the production increase is not accompanied by significant lowering of the quality of the types of yarns used in military products.
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