El theory

In all materials (plastics, metals, wood, etc.) elementary mechanical theory demonstrates that some shapes resist deformation from external loads. This phenomenon stems from the basic physical fact that deformation in beam or sheet sections depends upon the mathematical product of the modulus of elasticity (E) and the moment of inertia (I), commonly expressed as El (Chapter 3, Stress-strain behavior). It is applied to all types of constructions such as solids, foams, and sandwich structures. In many applications plastics can lend themselves in the form of a sophisticated lightweight stiff structure and the requirements are such that the structure must be of plastics. In other instances, the economics of fabrication and erection of a plastics lightweight structure and the intrinsic appearance and other desirable properties make it preferable to other materials. 

This theory has been applied to many different constructions including many plastic products. In each case displacing material from the neutral plane makes the improvement in flexural stiffness. Use of this engineering principle that has been used for many centuries relates to the basic 

The El principle applies to the basic beam structures as well as hollow channel, Tshape, T-shape, etc. where it imparts increased stiffness in one direction much more than in the other. Result is more efficient strength-to-weight products and so forth. While this construction may not be as efficient as the sandwich panel, it does have the advantage that it can be easily fabricated (molded, extruded, etc.) direcdy in the required configuration at a low cost and the relative proportions be designed to meet the load requirements. 

It would be more acceptable for the design analysis to be based on methods developed specifically for the materials, but this action will require the designer of metals to accept new ideas. Obviously, this acceptance becomes easier to the degree that the newer methods are presented as far as possible in the form of limitations or modifications to the existing methods discussed in this book. 

Property Aluminum Mild steel Polypropylene (PP) Glass-fiber reinforced plastics (GRP) 

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In summary, the concept of fransformation leadership and the El theory allow one to see how the behavior of fhe leader affects the behavior of the follower. Valuing the human aspect of fhe follower, that is, identifying with and appreciating the emotional and professional needs of the follower, is a key aspecf of an effective leader. The transformational theory of leadership espouses a moral and efhical balance to leadership, whereas the El theory supports the recognition of the emotional connection between the follower... 

Glesston S., Leidler K., Eiring El. Theory of Absolute Reactions Rates, Scientific Literature Edition , Moscow (1948) (in Russian). 

El theory See design, El theory, ejector See mold ejector. 

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