Elasticity types

The characteristic properties of the gels are dependent on the nature of the fibrils, the more coarse the fibrils the more moist and elastic the gel, the finer the fibril the drier and more rigid the resultant gel silica gel may be taken as representative of a dry rigid fine fibril gel and gelatine as that of the relatively coarse elastic type. 

A total of 19 different types of tourniquets were used in these studies (see Figs. 5.5-5.23). The tourniquet types ranged from the simple elastic type tourniquets to a pneumatic operated tourniquet. The tourniquet types included elastic, windlass, mechanical advantage cam, block and tackle, ratchet, and pneumatic. The tourniquets tested in these studies included ... 

Let s start by looking at a simple polymer, polyethylene, that has a lot going on in its stress/strain plots (Figure 13-38). Flexible, semi-crystalline polymers such as this (where the T of the amorphous domains is below room temperature) usually display a considerable amount of yielding or cold-drawing, as long as they are not stretched too quickly. For small deformations, Hookean elastic-type behavior (more or less) is observed, but beyond what is called the yield point irreversible deformation occurs. 

Cling films are usually elastic-type materials which will undergo stretch. The originally used cling films were based on plasticised PVC and PVdC (Saran) films. More recently, LLDPE and LDPE, particularly as mixtures with other plastics, are being widely employed. 

The liquid polymer state is characterized by a viscosity which strongly increases with the molecular mass. On the other hand, the response of the polymer liquid to a mechanical constraint, at the beginning is of the elastic type, the viscous flow appearing only after a time delay which increases with the molecular mass. The behaviour of such a material is called viscoelastic. 

When the amplitude of joint movement is likely to be 20% or more of the joint width, it is essential to use one of the elasto-plastic or elastic types of elastomeric sealant. 

The (two-dimensional) model for a relatively stiff molecule subjected to a simple shear flow, on the one hand, shows many features observed in NEMD simulations of finitely extendible nonlinear elastic (FENE) chain molecules. On the other hand, the dynamics found for the simple model is intriguingly complex and it deserved a careful study on its own. It seems appropriate also to analyse the system at higher temperatures. Furthermore, the model provides a convenient test bed for various thermostats other and additional thermostats, e.g. based on deterministic scattering [22] should be tested. Obvious extensions of the present model may involve other potential functions of nonlinear elastic type such as = (1/2) -I- (1/4) or = (1/4) (1 — r ) as well as... 

Most fluid pressure transducers are of the elastic type, in which the fluid is confined in a chamber with at least one elastic wall, and the deflection of the elastic wall is taken as an indication of the pressure. The Bourdon tube and the bellows are examples of elastic pressure transducers, which are used in laboratory-grade transducers and in some industrial process control applications. The fluid pressure transducer depicted in Fig. 18.7, which uses an elastic diaphragm to separate two chambers, is the type most frequentlyencountered in industrial process control. Diaphragms are constructed from one of a variety of elastic materials ranging from thin metal to polymerized fabric. 

Static fracture of the composite materials with thermoplastic matrix and unidirectional reinforced with short fibres H.L. Cox firstly treated, a case of fibre/matrix interaction, of elastic/elastic type, without taking in consideration the fibre ends. He found the fracture s determinant component is that characterised by the smallest/weakest deformation [1276]. This approximate... 

As with other physico-chemical properties of colloidal microgels the rheological behaviour of dispersions distinctly changes in response to environmental stimuli. At low temperatures the viscoelastic properties of poly(NIPAM) microgels change dramatically with temperature [89, 90]. At low temperatures poly(NIPAM) dispersions display elastic-type behaviour as... 

Adipic acid is used in elastic types because of the aliphatic chain length between the functional groups,... 

The methods discussed earlier are applied to the seat-occupant-restraint system of an aircraft. A description of a computer-aided analysis environment, including a multibody model of the occupant and a nonlinear finite element model of the seat, is provided, which can be used to re-construct variety of crash scenarios. These detailed models are useful in studies of the potential human injuries in a crash environment, injuries to the head, the upper spinal column, and the lumbar area, and also structural behavior of the seat. The problem of reducing head injuries to an occupant in case of a head contact with the surroundings (bulkhead, interior walls, or instrument panels), is then considered. The head impact scenario is re-constructed using a nonlinear visco-elastic type contact force model. A measure of the optimal values for the bulkhead compliance and displacement requirements is obtained in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panels, or interior walls of an aircraft. The developed analysis tool also allows aircraft designers/engineers to simulate a variety of crash events in order to obtain information on mechanisms of crash protection, designs of seats and safety features, and biodynamic responses of the occupants as related to possible injuries. 

A.2. (the constitutive equation of elastic type). For all x the Cauchy stress T is expressed through the elastic constitutive equation T = f(E/3t,Z K ). 

A distinctive feature of the mechanical behaviour of polymers is the way in which their response to an applied stress or strain depends upon the rate or time period of loading. This dependence upon rate and time is in marked contrast to the behaviour of elastic solids such as metals and ceramics which, at least at low strains, obey Hooke s law and the stress is proportional to the strain and independent of loading rate. On the other hand the mechanical behaviour of viscous liquids is time dependent. It is possible to represent their behaviour at low rates of strain by Newton s law whereby the stress is proportional to the strain-rate and independent of the strain. The behaviour of most polymers can be thought of as being somewhere between that of elastic solids and liquids. At low temperatures and high rates of strain they display elastic behaviour whereas at high temperatures and low rates of strain they behave in a viscous manner, flowing like a liquid. Polymers are therefore termed viscoelastic as they display aspects of both viscous and elastic types of behaviour. 

It may be useful to the reader to consider as an example the work by Adams et al (1978c) and some of their hitherto unpublished results. They used finite-element methods to examine the stresses in high-performance composites in symmetrical lap joints with parallel, bevelled, scarfed and stepped adherends. The composite adherends were assumed to be linearly elastic type II carbon fibre reinforced epoxy composites with a 60% fibre volume fraction. The mechanical properties of this material are given in Table 3. 

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