Bearing Stresses

In addition to the standard types of V belts (see Figure 3-19), many manufacturers make V belts that arc specifically designed to have a higher horsepower capacity. 4 hese V belts are shown and compared to standard V-belt cross-sections. These superpower V belts allow shorter center distances and narrow er sheaves without imposing any extra total bearing stresses. Such belts are able to reduce the drive by 30-. )0% and less for horsepow er capacity. In addition, speeds can be increased up to 6000 ft/ min without dynamic balancing of the sheaves because the sheaves arc smaller. 

Assume this is resisted by the 3.5 ft square footing. Area = 12.25 ft2 (11,381 cm2) bearing stress,... 

Bdval TK, ID Heliums, RT Solis The kinetics of platelet aggregation induced by fluid-bearing stress. MicrovascRes 1984 28 279-288. 

As could be expected, the mechanical properties of a crazed polymer differ from those of the bulk polymer. A craze containing even 50% microcavities can still withstand loads because fibrils, which are oriented in the direction of the load, can bear stress. Some experiments with crazed polymers such as polycarbonate were carried out to get the stress-strain curves of the craze matter. To achieve this aim, the polymer samples were previously exposed to ethanol. The results are shown in Figure 14.24 where the cyclic stress-strain behavior of bulk polycarbonate is also illustrated (32). It can be seen that the modulus of the crazed polymer is similar to that of the bulk polymer, but yielding of the craze occurs at a relatively low stress and is followed by strain hardening. From the loading and unloading curves, larger hysteresis loops are obtained for the crazed polymer than for the bulk polymer. 

These predictions need to be modified because real networks have defects. As shown in Fig. 7.7, some of the network strands are only attached to the network at one end. These dangling ends cannot bear stress and hence do not contribute to the modulus. Similarly, other structures in the network (such as dangling loops) are also not elastically effective. The phantom network prediction can be recast in terms of the number density of elastically effective strands v and the number density of elastically effective crosslinks ii. For a perfect network without defects, the phantom network modulus is proportional to the difference of the number densities of network strands v and crosslinks // = since there are fjl network strands per crosslink ... 

The bearing stresses (where the steel tower rests on the concrete pedestal) seldom cause any difficulty, but should be checked as a safety precaution. The bearing stresses consist of wind pressure stress plus the dead load stress. 

The bearing stress equation gives the bearing stress in pounds per linekl foot of shell circumference. These stresses are spread over the area of the base ring. Therefore, for practical purposes, the unit bearing stress can be determined as follows ... 

Table 3-35) bp = bearing stress, psi C = compressive load on concrete, lb d = diameter of bolt circle, in. db = diameter of hole in base plate of compression plate or ring, in. 

This procedure assumes that the pin diameter is no less than in. less than the hole diameter. If the pin diameter is greater than Xe in. smaller than the hole diameter, then the bearing stresses in the lug at the contact point are increased dramatically due to the stress concentration effect. 

Figure 3. The simulated distribution diagram of coal bearing stress and permeability in front of a mining...

Should a failure occur in the support structure, it would most probably occur in the post tip or seat. This has been observed in failure tests, where failure has resulted in graphite fragmentation around the post tip/seat, where high local bearing stresses occur. 

As discussed in Section 4.4.5.1.1.2, a core support seat could fail as a result of localized high bearing stresses in the post tip/seat. Also, failure of the seat could occur due to bending loads from locally non-uniform contact with the supporting structure beneath. 

Elastic modulus of the radial direction considered Elastic modulus in the x-direction Elastic modulus in the y-direction Elastic modulus in the tangential direction considered Direct force in the fastener Eoad on joint in the x-direction Eoad on joint in the y-direction Shear modulus in the shear-out plane (s—n) considered Shear modulus in the x—y plane Average bearing stress on the fasteners given by... 

Figure 5.13 Stress distribution around bolt holes for basic load case 1. Stress normalised by nominal bearing stress S b = F/dt. ...

Composites are particularly susceptible to creep and relaxation effects in the throughthickness direction for the normal range of planar reinforcements. For loads normal to the plane of the composite, creep will occur, and in many bolted clamped joints the need to design the joint to allow for relaxation of the bearing stress is well recognised. 

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