Pull-out rate

Another approach to high loading rate fibre pull-out tests has been developed [82], in which an air gun is linked to the bottom of the specimen to create a high speed pull-out rate the upper half of the specimen is suspended from a dynamic load cell. Pull-out rates of greater than 2 m/s can be achieved. The apparatus is shown in Figure 6.27 [83]. 

The zero-rate fracture energy Go is therefore larger than the thermodynamic work of adhesion W. This result is nontrivial since one would expect the pull-out contribution to the fracture energy to vanish when the crack propagation rate goes to zero. In fact, as explained in section III, there is a minimum force f (eqn (3.4)) required for a fibril to exist, even at zero pull-out rate. As the force on a chain that is being pulled-out remains... 

Pull-out or breakdown torque (maximum torque) Rated torque... 

The nearest standard rating to this is 7.5 kW, and a motor of this rating will suit the duty cycle. To ensure that it can also meet the torque requirement of 10.5 kW, it should have a minimum pull-out torque of 10.5/7.5 or 140% with the slip at this point as low as possible so that when operating at 140%... 

The minimum value of pull-out torque at the rated voltage should be 150% of the rated torque according to IS 9283. 

The motor should be mounted with a suitable loading arrangement and the rotor fully locked. The rated voltage at the rated frequency will then be applied to the motor terminals in the locked rotor condition. The loading on the motor will then be reduced slowly so that the motor can start and pick up speed. The value of pull-up torque at which the rotor picks up speed and attains speed corresponding to pull-out torque condition must be noted. 

The motor should be mounted with a suitable loading arrangement. The rated voltage, at the rated frequency, is then applied to the motor terminals at the no-load condition. The load on the motor may then be gradually increased, and the maximum load at which the motor stalls noted. The torque determined at this point is the pull-out torque. 

Pull-out torque -10% of the guaranteed torque, except that after allowing for this tolerance, the torque will not be less than 1.6 or 1. .5 times the rated... 

The larger hp ratings provide increased pull-out torque, starting torque, and pull-up torque. 

The above-mentioned models differ in the relation that is derived between the rate of pull-out of the individual chain and the crack velocity. These models also differ in their interpretation of the threshold stress and the threshold toughness (Go). Also, V is expected to be dependent on the configuration of the connector chain at the interface. The value of v when connector chain crosses the interface just once is higher than the value when the chain forms multiple stitches, even though Go is not altered. When the chain forms multiple stitches, the block and tackle effect ensures that the viscous processes dominate even at lower velocities, and V is reduced by a factor of N from the value obtained from the single crossing case. These models are discussed by Brown and coworkers [45,46]. 

Viscoelastic polymers essentially dominate the multi-billion dollar adhesives market, therefore an understanding of their adhesion behavior is very important. Adhesion of these materials involves quite a few chemical and physical phenomena. As with elastic materials, the chemical interactions and affinities in the interface provide the fundamental link for transmission of stress between the contacting bodies. This intrinsic resistance to detachment is usually augmented several folds by dissipation processes available to the viscoelastic media. The dissipation processes can have either a thermodynamic origin such as recoiling of the stretched polymeric chains upon detachment, or a dynamic and rate-sensitive nature as in chain pull-out, chain disentanglement and deformation-related rheological losses in the bulk of materials and in the vicinity of interface. 

Micro-mechanical processes that control the adhesion and fracture of elastomeric polymers occur at two different size scales. On the size scale of the chain the failure is by breakage of Van der Waals attraction, chain pull-out or by chain scission. The viscoelastic deformation in which most of the energy is dissipated occurs at a larger size scale but is controlled by the processes that occur on the scale of a chain. The situation is, in principle, very similar to that of glassy polymers except that crack growth rate and temperature dependence of the micromechanical processes are very important. 

Pull-out torque For a synchronous motor, this is the maximum sustained torque that the motor will develop at synchronous speed for one minute with rated voltage applied at rated frequency and with normal excitation. 

The process of a solute dissolved in one solvent being pulled out, or extracted into a new solvent actually involves an equilibrium process. At the time of initial contact, the solute will move from the original solvent to the extracting solvent at a particular rate, but, after a time, it will begin to move back to the original solvent at a particular rate. When the two rates are equal, we have equilibrium. We can thus... 

Because the normal area. Ax = dy dz, of our box does not change with x it can be pulled out of the partial with respect to x. This is done in the second part of equation (2.10a). The same can be done with the y- and z-components of convective flux rate... 

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