High torsion

The relative efficiency of the two stiffeners is compared principally on the basis of the torsional resistance. The reason for the lower efficiency rating of the sandwich-blade stiffener is its low torsional resistance (and the bending stiffness is not high) and for the high efficiency of the hat stiffener is its high torsional resistance because of the basic open-versus closed-section stiffener issue. Stiffener torsional resistance affects the buckling load of a stiffened panel or shell as shown by Card and Jones [7-3]. 

Considering first Table 5, it can be seen that Tg values for the reported poly(organophosphazenes) spanned from very low (-105 °C in the case of poly[bis(n-butoxy)phosphazene]) up to very high (-1-220 °C for poly[tris(2,2 -dioxy-l,T-binaphthyl)phosphazene]), covering almost all the intermediate temperatures between these two limits. Low TgS are indicative of very high torsional freedom of the polyphosphazene chain, which is manifested clearly when flexible substituents of reduced bulkiness are used in the substitution... 

The energetical description of rotations around bonds with high torsional barriers (e.g. the C=C double bond) demands the evaluation of the influence of higher cosine terms. Rotations around single bonds with sixfold symmetric torsional potentials have very low barriers (18) they occur in alkylsubstituted aromatic compounds (e.g. toluene), in nitro-alkanes and in radicals, for example. 

Fig. 13. The structure of 9-methyltriptycene derivatives with high torsional barriers for the methyl group re-orientation. The symbol X denotes halogen atoms, Y stands for either a halogen or hydrogen substituent, and Z denotes either H or CH3.

The controller is of the variable voltage, variable frequency type, thereby providing a complete speed range for the motor at constant torque. The system inherently provides soft start which is necessary to alleviate high torsional stresses within the motor-pump uniL that may otherwise damage the shaft and couplings. 

Section through a car bumper Three mouldings have been joined with electrofusion welds, to form a hollow beam, with high torsional and bending stiffness. 

Eton describes the contribution to the total energy due to hindered rotation around skeletal bonds. The formulas generally used for the torsional potentials are those of Brant and Flory [2,6-10] where the torsional barriers used can be of different values [2,6-10]. It is necessary to point out, however, the limiting condition that must be imposed on the rotational degrees of freedom. Rotations around bonds that have very high torsional barriers (C=C, C=0), and single bonds between them affected by their conjugation, as in the case of polypeptides, must not be considered [11]. 

The presence of the phosphorus-nitrogen backbone confers to these kind of polymers thermo-oxidative stability, fire resistance, very high torsional mobility (low barrier to skeletal bond twisting), high refractive index, and hydrophilicity. On the other hand, the side groups in polyphosphazenes control other properties such as solubility, secondary reaction chemistry, thermal decomposition, and resistance to hydrolysis. The possibility of tuning the properties of polyphosphazenes thanks to their synthetic flexibility has led to enormous interest in their applications in several areas of research. 

In the Figure 17 F stands for flexnral failnre and Y indicates yielding of the rebars. The pictnre clearly indicates that the high torsion of the first bent causes failure of the outmost external column. The base section at failnre is shown in Figure 18. There is... 

Poly(heterophosphazene)s whose backbones comprise phosphoms, nitrogen, and another element - carbon or sulfur -were also synthesized. " In poly(carbophosphazene)s (poly-114), every third phosphoms atom is replaced by carbon. Poly-114 obtained in the thermal polymerization of a cyclic carbophosphazene was further transformed into white, solid, hydrolytically stable poly((aryloxy)carbophosphazene) (stmcture 115 Af -lO ). The polymer backbone in stmcture 115 was less flexible than in classical polyphosphazenes. The reaction of poly-114 with alkylamines was also studied. Poly (carbophosphazene) s have higher glass transition temperatures than their classical polyphosphazene counterparts with the same side groups. The increased stiffness of the carbophosphazene backbone is attributed to the high torsional barrier of the organic C = N n-bonds compared to the low barrier of the P = N n-bonds. ... 

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