**1. Introduction**

The principle of critical energy (PCE) is the fourth principle of Energonics [1–3], a field of science that stands for energy in action. It was discovered and formulated in 1984 [4].

The principle of critical energy has allowed so far the finding of solutions to many prob‐ lems of superposition and/or cumulation of actions or their effects on engineering struc‐ tures [1–17], or on living organisms that find themselves under stress, abused and/or medically treated [2, 13].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The criterion of truth in scientific research is the experiment. For this reason, down below there have been presented the predictions resulting from the application of the principle of critical energy in comparison to experimental results. In this way, the critical energy principle has been validated by the experimental data reported in the literature by various authors.

The principle of critical energy has been used, for example, to solve the problems of superpo‐ sition and/or cumulation of the effects of actions definitory for such disciplines/chapters of engineering sciences as mechanical engineering, electrical and electromagnetic engineering, chemical engineering, etc. The question is whether we are dealing in this case with an inter‐ disciplinary or a transdisciplinary issue?

Interdisciplinarity means bringing together elements of two or more academic disciplines in order to solve a specific theoretical or practical problem. The result would not be possible without the 'cooperation' of different academic disciplines, out of which use is made of elements that have been time proven. Creation, in this case, refers to the combination of knowledge already extant in the academic fields under scrutiny.

Transdisciplinarity essentially means concerns that go beyond any discipline ('trans' = beyond) or away from a particular discipline, concerns based on the existing academic disciplines and finally capable of generating new areas of knowledge. The new concepts in the field can be retrieved and applied to other areas or academic disciplines.

Consequently, the PCE features transdisciplinarity but in conjunction with just one more academic discipline it becomes interdisciplinary.
