The plastic deformation of crystalline polymers, in a particular polyethylene, has been studied intensively from the viewpoint of changes in morphology. It is now evident that very drastic reorganization occurs at the morphological level, with the structure changing from a spherulitic to a fibrillar type as the degree of plastic deformation increases. The molecular reorientation processes are very far from being affine or pseudo-affine and can also involve mechanical twinning in the crystallites. It is surprising that some of the continuum ideas for mechanical anisotropy are nevertheless still relevent, although they must be appropriately modified.
(Ward I.M., Sweeney J., An introduction to the mechanical properties of solid polymers, second edition, pg.270)
New and better answer because this one is simple to understand with the examples.
Crystalline polymers have a ‘reasonably’ regular chain structure and a specific preferred chain conformation. The presence of chain defects, e.g. atactic sequences and/or chain branches at high concentrations, makes it impossible for the polymers to crystallize and on cooling they ultimately from a fully amorphous glass. There are exceptional cases of crystlline atactic polymers due to side-group crystallization or to the small size of the pendant group. The hydroxyl group in poly(vinyl alcohol) is, for example, sufficiently small and the atactic polymer is crystallizable. Polymers with a small proportion of chain defects crystallize to a lower overall crystallinity than that of the polymer containing no chain defects. The chain defects are normally confined to the amorphous component. Small groups may, however, be housed within the crystals.
( Gedde, U. W. (1995). Crystalline polymers. Polymer physics ( p.134 ). )
2-Elastomers ( Group : Material )
Elastomers are polymers capable of large elastic deformation when subjected to relatively low stresses. Some elastomers can withstand extensions of 500% or more and still return to their original shape. The more popular term for elastomer is, of course, rubber. We can divide rubbers into two categories: (1) natural rubber, derived from certain biological plants; and (2) synthetic elastomers, produced by polymerization processes similar to those used for thermoplastic and thermosetting polymers.
(Mikell P.Groover, Fundamentals of Modern Manufacturing , materials,processes, and systems third edition page 167)
Elastomers are long-chain polymers above their glass-transition temperature, Tg. The covalent bonds that link the units of the polymer chain remain intact, but theweaker Van derWaals and hydrogen bonds that, below Tg, bind the chains to each other, have melted. This gives elastomers unique property profiles: Young’s moduli as lowas 10_3GPa (105 time less than that typical ofmetals) that increase with temperature (all other solids show a decrease), and enormous elastic extension. Their properties differ so much from those of other solids that special tests have evolved to characterize them.This creates a problem: ifwewish to select materials by prescribing a desired attribute profile (as we do later in this book), then a prerequisite is a set of attributes common to allmaterials.Toovercomethis, we settle on a common set for use in the first stage of design, estimating approximate values for anomalies like elastomers. Specialized attributes, representative of one family only, are stored separately; they are for use in the later stages.
( ASHBY, M. F. (2005). The families of engineering materials. Material selection in mechanical design 3rd (p.30 ). )
3-Conceptual design (Group : Design)
After completing the task clarification phase, the conceptual design phase determines
the principle solution. This is achieved by abstracting the essential problems,
establishing function structures, searching for suitable working principles
and then combining those principles into a working structure. Conceptual design
results in the specification of a principle solution (concept).
(Engineering Design A Systematic Approach; G. Pahl, W. Beitz; Page: 131 )
New and better answer because this one is simple to understand with the graphic.
New and better answer because this one is simple to understand with the graphic.
Design generally begins with a need. This need may be met already by existing designs; in such cases the designer hopes he can meet the need beter (i.e. generally more cheaply). It ends with a set of drawings and other information to enable the thing designed to be made. Ideally the intervening stages should be of successively increasing precision, of gradual crystallisation or hardening. The early stages differ in character somewhat from the later ones, largely because of the greater fluidity of the situation. These early stages, when there are stil major decisions to be made, are called ‘conceptual design’.The products of the conceptual design stages will be called ‘schemes’.
It takes the statement of the problem and generates broad solutions to it in the form of schemes. It is the phase that makes the greatest demands on the designer, and where there is the most scope for striking improvements. It is the phase where engineering science, practical knowledge, production methods, and commercial aspects need to be brought together, and where the most important decisions are taken.
( French, M. J. (1999). Design: conceptual design: schemes. Conceptual design for engineers (pp. 1-3). )
4-Kaizen ( Group : Improvement)
Kaizen is a Japanese word for “continuous improvement and incremental change.” The philosophy of kaizen is about involving everyone in the organization to focus on overall organizational improvements. The cornerstone of lean manufacturing is removing waste to better respond to the needs of the customer in regard to on-time delivery, competitive cost, and better quality. More important, kaizen emphasizes developing a process-oriented culture that is driven to improve the way a company operates. Think of the number of processes that exist in a company. Changing company culture is an ongoing battle, and you want to address issues that may arise early on. So in essence, kaizen is about coaching and mentoring people to become better at what they do in all aspects of their work.
(Kaizen and Kaizen Event Implementation, Chris A. Ortiz, p.4)
New and better answer because this one is simple to understand.
Kaizen means, simply, continuous improvement. In Japanese kai means “to take part” and zen means “to make good.” Together these two words mean to take something apart in order to make it better. Kaizen is based on the fundamentals of scientific analysis in which you analyze ( or take apart ) the elements of a process or system to understand how it works, and then discover how to influence or improve it ( make it better). Lean production is founded on the idea of kaizen, or continuous improvement – the small, gradual, incremental changes applied over a long period that add up to a major impact of business results
( Productivity Press. Development Team (2002). What is kaizen?. Kaizen for the shopfloor ( p.2 ). )
5-Creep (Group: Material)
Creep Rupture Strength
Creep is that phenomenon associated with a material in which the material elongates with time under constant applied stress, usually at elevated temperatures. A material such as tar will creep on a hot day under its own weight. For steels, creep becomes evident at temperatures above 650F. The term creep was derived because, at the time it was first recognized, the deformation which occured at the design conditions occured at a relatively slow rate. Depending upon the stress load, time, and temperature, the extention of a metal associated with creep finally ends in failure.
Creep-rupture or stress-rupture are the terms used to indicate the stress level to produce failure in a material at a given temperature for a particular period of time. For example, the stress to produce rupture for carbon steel in 10,000 hours(1.4 years) at a temperature of 900F is substantially less than the ultimate tensile strength of the steel at the corresponding temperature. The tensile strength of carbon steel at 900F is 54,000 psi, whereas the stress to cause rupture in 10,000 hours only 11,500 psi.
(Rules of thumb for chemical engineers, Yazar: Carl Branan, page 288)
New and better answer because this one is simple to understand with the graphics and formulas.
At temperatures above 1/3 Tm (where Tm is the absolute melting point), materials creep when loaded. It is convenient to characterize the creep of a material by its behavior under a tensile stress 𝜎, at a temperature Tm. Under these conditions the steady-state tensile strain rate ἐss is often found to vary as a power of the stress and exponentially with temperature:
where Q is an activation energy, A is a kinetic constant, and R is the gas constant. At constant temperature this becomes
where ἐ0 (s-1), 𝜎0 (N/m2), and n are creep constants.
The behavior of creeping components is summarized on the facing page. The equations give the deflection rate of a beam, the displacement rate of an indenter and the change in relative density of cylindrical and spherical pressure vessels in terms of the tensile creep constants. Prolonged creep causes the accumulation of creep damage that ultimately leads, after a time tf, to fracture. To a useful approximation
where C is a constant characteristic of the material. Creep-ductile material have values of C between 0.1 and 0.5; creep-brittle materials have values of C as low as 0.01.
( ASHBY, M. F. (2005). Creep and creep fracture. Material selection in mechanical design 3rd (pp. 499,500 ). )
