Ashby principle

Ross Ashby, W. (1947) Principles of the self-organizing dynamic system. J, Gen, Psych, 37, 125-128. 

Assuming that structural data are available, and that a property has been correctly measured, the next problem is to establish a relationship. Fundamental models are preferred by engineers because tlrey are based on basic principles of physics and the physical chemistry of the described phenomenon. Once it is realized that foods are essentially composite hierarchical structures, we can borrow models and theories developed for nonfood systems and apply them. A good example is the adaptation of mechanical principles for the description of cellular solids, (Gibson and Ashby 1988) to the properties of solid food foams (Attenburrow et al. 1989 Warburton et al. 1990). Examples are provided in Chapter 10. 

Ashby, W. R. 1962. Principles of the self-organizing system. In Principles of Self-Organization, ed. H. 

As underlined by Ingegnoli (2002), scientists have to avoid two representations of nature which tend to a world of alienation (1) the deterministic one, with no possibility of novelty and creation, (2) the stochastic one, which leads to an absurd world with no causality principle and without any ability to forecast. Possibly, the major incentive toward a new conception of nature comes from scientists like W. Ashby (1962), Von Bertalanffy (1968), Weiss (1969), Lorenz (1978, 1980), Popper (1982, 1996) and Piigogine (1977, 19%), who observed how nature creates its most fine, sensitive and complex structures through non-reversible processes which are time oriented (time arrow). No doubt that thermodynamics becomes the most important physical discipline when complex adaptive systems exchanging energy, matter and information are involved with life processes. 

Note that this exponential model results in a zero relative tensile modulus only in the limiting case of 100 % porosity. Without doubt, porosities close to 100 % can in principle be achieved, eg. in some aerogels [Gibson Ashby 1997]. However, the usual case encoimtered in practice will be a complete structural breakdown (loss of integrity) at significantly lower porosity levels. In order to allow for the possibility oi E =0 at porosities lower than 100 % (i.e. < 1), it is necessary to include a critical volume fraction (f)/ in the modulus-porosity relation, which is able to take the possible occurrence of a... 

I say "in principle" deliberately, with caution. Ashby, in order to explain the basic concepts simply but thoroughly, used toy examples for the most part... 

Ashby et al. [LI 87] have developed the approach of HIP maps , where, for a material under given conditions, the areas in two-dimensional space (relative density depending on the pressure), in which the predominant phenomenon that controls the densification has been identified, are traced (in particular the grain size and temperature). These maps make the pendant of the creep maps and deformation maps also credited to Ashby et al. (see Figure 7.2 in Chapter 7). The principle of these maps is certainly attractive, but their applicability requires three conditions i) having a sufficient number of experimental data, ii) estabhshing, for each of these data, the nature of the predominant mechanism, and lastly iii) verifying the... 

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