. The Bell System technical journal . ugh submarine insulation is not subjectedto tensile deformation in practice, tensile properties indicate to somedegree the relative mechanical suitability of a given material for thepurpose. Figure 5 shows the stress-strain characteristics of paraguttaand gutta percha submarine cable insulation. These results show 142 BELL SYSTEM TECHNICAL JOURNAL that paragutta has tensile properties equal to cable gutta perchaalthough its gutta content is substantially lower. Compression Properties: The insulated submarine cable conductorcommonly known as the core is fre
. The Bell System technical journal . ugh submarine insulation is not subjectedto tensile deformation in practice, tensile properties indicate to somedegree the relative mechanical suitability of a given material for thepurpose. Figure 5 shows the stress-strain characteristics of paraguttaand gutta percha submarine cable insulation. These results show 142 BELL SYSTEM TECHNICAL JOURNAL that paragutta has tensile properties equal to cable gutta perchaalthough its gutta content is substantially lower. Compression Properties: The insulated submarine cable conductorcommonly known as the core is frequently subjected to uneven com-pression stresses during manufacture, laying and repairing. Theinsulation must therefore be capable of withstanding these stresseswithout appreciable deformation. To determine the relative meritsof paragutta and gutta percha in this respect their comparative stress-strain characteristics under compression have been measured, using aspecial compression machine,^ and are shown in Fig. 6. In this test 125. 200 300 400 500 ELONGATION-PER CENT Fig. 5—Comparative tensile properties of paragutta and gutta percha at 25° C. a steel rod cm. in diameter was forced endwise into a sheet of thematerial .375 cm. in thickness at a rate of about 4 cm. per minutewhile simultaneously recording the deformation and load. Theseresults show that very little difference exists between these materialsin this test, and factory handling of cores confirms the general con-clusion. Flexibility: The flexibility of submarine cable insulation is importantbecause the core is subjected to considerable flexing during manu- 3 Hippensteel, Bell Laboratories Record, S, 153 (1928). PARAGUTTA, A NEW INSULATING MATERIAL 143 facture, laying and repairing and possibly at times during use, espe-cially where tidal currents may cause movement in the cable. Para-gutta and gutta percha cores have been subjected to slow and con-tinuous flexing at 0° and 25° C. for long periods and it was
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