# An Extended Functional Design Approach Based on Working Principle and Property and Its Application
## 3 Working Principle and Property
### Property (P)  
To answer the question, \"What concepts shall be used to reason about the synthesis and structure of mechanical products?\", [PERSON] (2011) [32] proposed that the system's attributes in four domains (i.e., activity system, function system, organ system, and part system) should be distinguished as separate structural characteristics, which define or specify the system and behavioral properties. [PERSON] (2005) [33] introduced this terminology into the CPM/PDD theory, which is based mainly on the distinction between the characteristics and properties of a product. The characteristics describe the structure and the shape of a product. The properties describe the product's behavior; they are composed of the eigen property, relational property, and allocated property. These characteristics are very similar to those called \"internal properties\" by [PERSON] and [PERSON] and those called \"design parameters\" by [PERSON], i.e., the structure, geometry, material, and surface characteristics of a product. The properties are related to those called \"external properties\" by [PERSON] and [PERSON] and those called \"functional requirements\" by [PERSON] (e.g., weight, safety, reliability, and aesthetic properties), as well as properties such as \"manufacturability\", \"assembleability\", \"testability\", \"environmental friendliness\" and the cost of a product [34]. Based on the above understanding of properties, it is difficult to identify a reasonable category of properties by which to establish the mapping relationship between the working principle and structure. Therefore, a new understanding of properties is discussed in this work. Properties include the inherent property (IP) and designed property (DP) of the entity object, and environmental property (EP), as given by the environment. The general property composition of a designed object is shown in Figure 1. \begin{table}
\begin{tabular}{c c} \hline \hline  & **Technical Principle–XXX** \\ \hline
**ID** & TP-XXX \\ \hline
**Function** & normalized description of the target function(s) to be realized \\ \hline
**Description** & basic description of this TP \\ \hline
**Functional Character** & characters that interact with other structural objects to achieve the target function \\ \hline
**Assembly Character** & characters that have assembly relationships with other structural objects \\ \hline
**Key Parameter** & key parameters \\ \hline
**Formula** & mathematical description of this TP \\ \hline
**Graph** & schematic diagram/geometry model diagram \\ \hline
**Application** & application scenarios \\ \hline
**Annotation** & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The representation template of technical principles. Inherent properties refer to the physical and chemical properties of the designed object's base material, including its physical properties (such as thermal expansion, conductivity, magnetism, density, etc.) and chemical properties (such as oxidation, reduction, etc.). The inherent properties determine the potential use of the base material or the feasibility of the design from the root. In the design process, designers will usually only select pre-developed materials instead of designing base materials with the appropriate inherent properties from existing resources, according to the design requirements. For example, for thermal conductivity (TC), under the same conditions, TCcopper > TCiron > TCaluminum. When designing heat-dissipation structures, copper is usually selected as the base material and is processed into copper tubes or multilayer copper sheet arrays to realize the heat dissipation function. For example, a gear's base material is selected according to the load of the gear, mainly considering the strength and hardness of the tooth surface, as well as the toughness of the tooth core. The outer dimensions of the gear and the strength of the material will together determine the load that the gear can withstand.