Elastic adjustment

Manually adjusted screw or ratchet take-ups that adjust the position of the tail pulley to control belt tension can be used on relatively short, light duty conveyors. Automatic take-ups are used on conveyors over about 25 to 30 m long. The most common is the weighted automatic gravity take-up (see Fig. la). Other types of automatic take-ups have hydrauHc or pneumatic powered devices to adjust a snub pulley position and maintain a constant belt tension. The requited take-up movement varies according to the characteristics of the belt constmction and the belt length. Typically, take-up movements for pHed belts are 2% to 3% of the center distance between head and tail pulley, and about 0.5% for steel cable belts. The take-up movements requited for soHd woven belts are usually shorter because of the lower elastic stretch. Take-up requirements for a particular situation should be confirmed by the belt manufacturer. 

Dynamic explosion detectors use a piezoresistive pressure sensor installed behind the large-area, gas-tight, welded membrane. To ensure optimum pressure transference from the membrane to the active sensor element, the space between the membrane and the sensor is filled with a special, highly elastic oil. The construc tion is such that the dynamic explosion detec tor can withstand overpressures of 10 bar without any damage or effect on its setup characteristic. The operational range is adjustable between 0 and 5 bar abs. Dynamic explo-... 

Romanchenko and Stepanov (1981) recognized that the impulse imparted at the spall plane to material downstream, because of the elastic-plastic nature of this material, led to an attenuating tensile stress pulse propagating toward the sample-window interface as is illustrated in Fig. 8.9. Thus, the maximum tension inferred from the measured spall signal should be adjusted for this attenuation in estimating a material spall strength at the spall plane. 

It is instructive to describe elastic-plastic responses in terms of idealized behaviors. Generally, elastic-deformation models describe the solid as either linearly or nonlinearly elastic. The plastic deformation material models describe rate-independent behaviors in terms of either ideal plasticity, strainhardening plasticity, strain-softening plasticity, or as stress-history dependent, e.g. the Bauschinger effect [64J01, 91S01]. Rate-dependent descriptions are more physically realistic and are the basis for viscoplastic models. The degree of flexibility afforded elastic-plastic model development has typically led to descriptions of materials response that contain more adjustable parameters than can be independently verified. 

There are two well-accepted models for stress transfer. In the Cox model [94] the composite is considered as a pair of concentric cylinders (Fig. 19). The central cylinder represents the fiber and the outer region as the matrix. The ratio of diameters r/R) is adjusted to the required Vf. Both fiber and matrix are assumed to be elastic and the cylindrical bond between them is considered to be perfect. It is also assumed that there is no stress transfer across the ends of the fiber. If the fiber is much stiffer than the matrix, an axial load applied to the system will tend to induce more strain in the matrix than in the fiber and leads to the development of shear stresses along the cylindrical interface. Cox used the following expression for the tensile stress in the fiber (cT/ ) and shear stress at the interface (t) ... 

Some wild species have larger capacities for osmotic adjustment, a trait which may improve yield during drought (Table 3, Turner, 1986). Interesting examples of this are Dubautia species from Hawaii which differ in osmotic adjustment mainly as a result of differences in cell wall elasticity. Interspecific hybrids can be made which have intermediate properties (Robichaux, Holsinger Morse, 1986). Material such as this could make a basis for the molecular study of differences in cell wall elasticity. 

Gerk showed that Equation (2.1) is followed not only for metals, but also for ionic and covalent crystals if two adjustments are made. For covalent crystals, the temperature must be raised to a level where dislocations glide readily, but below the level where they climb readily. For ionic crystals, G (an average shear modulus) must be adjusted for elastic anisotropy. Thus it becomes ... 

Early in the history of crystal dislocations, the lack of resistance to motion in pure metal-like crystals was provided by the Bragg bubble model, although it was not taken seriously. By adjusting the size of the bubbles in a raft, it was found that the elastic behavior of the raft could be made comparable with that of a selected metal such as copper (Bragg and Lomer, 1949). In such a raft, it was further found that, as expected, the force needed to form a dislocation is large. However, the force needed to move a bubble is too small to measure. 

The first (exponential) term represents repulsion between electron orbitals on the atoms. The second term can be seen to be opposite in sign to the first and so represents an attraction—the weak van der Waals interaction between the electron orbitals on approaching atoms. The adjustable parameters can sometimes be calculated using quantum mechanics, but in other systems they are derived empirically by comparing the measured physical properties of a crystal, relative permittivity, elastic constants, and so on, with those calculated with varying parameters until the best fit is obtained. Some parameters obtained in this way, relevant to the calculation of the stability of phases in the system SrO-SrTiC>3, are given in Table 2.3. 

Contrary to the model with fixed prices and infinitely elastic supply factor, the CGE model proves considerably less sensitive to assumptions about international competitiveness. If the international production structure for hydrogen cars deviates from that of conventional cars, prices and production structures are adjusted. The consequences for aggregate variables, like real consumption and GDP, are small. 

Calculations of the elastic properties, the main tensions and tensile strength of natural rubber carried out without using the empirical adjusting parameters are in good agreement with the experimental data. 

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