# An Extended Functional Design Approach Based on Working Principle and Property and Its Application
## 3 Working Principle and Property
### Property (P)
Designed properties refer to the designed characteristics of the base material of the designed object, also known as its geometric features, including functional features and assembly features, as shown in Figure 2. A functional feature refers to a feature by which the designed object directly interacts with the acting object, such as the cutting-edge feature of the drill bit, the gear tooth feature, etc. ; the assembly feature refers to the actual feature by which the designed object associates with other objects in the system, such as hole features, thread features, groove features, etc. These assembly features include three characteristic relationships, namely, contact relationships, constraint relationships, and mating relationships. Specifically, contact relationships include both low-pair contact relationships and high-pair contact relationships. Constraint relationships include alignment relationships, coplanar relationships, coaxial relationships, parallel relationships, distance relationships, etc. Matching relationships include clearance-fit relationships, interference fit relationships, and transition fit relationships. The designed properties are the main design objects in the design process. The designer needs to create a suitable geometric shape for the selected base material, according to the relevant technical principles. For example, it is possible to determine the main tooth-profile characteristic parameters of a gear according to the gear design principle (such as the number of teeth, modulus, tooth width, standard pitch diameter, etc.). Figure 1: The general property composition of a design object. Environmental properties refer to the properties that are naturally given by the environment when the designed object is in the corresponding external environment, such as ambient temperature, humidity, air pressure, and gravity. Some of the inherent properties or designed properties of the designed object may interact with the environmental properties. Since the designed object ultimately has a specific application environment, environmental properties can be regarded as elements of the working conditions that the designed object needs to face. This presents a good supplement to considering environmental properties in the conceptual design process. Some inherent properties of the designed object may not be stable and will be more susceptible to environmental properties. For instance, the temperature of the environment may affect the ductility of the metal and the solubility of salt in water. Therefore, the inherent properties that can produce changes under the action of environmental properties are called influential properties. Influential properties are often the key objects by which the designed object can play a role. Therefore, the influential properties that are used to achieve the expected purpose are referred to as functional properties. For example, the thermal expansion of metal sheets will change with the ambient temperature. As the temperature increases, the expected deformation of the metal sheet will be generated as a corresponding displacement in the specified direction, acting to control the switch of the circuit. This thermal expansion is the physical property of the metal sheet, and it can be affected by the environmental property. The property (temperature) produces a certain change, and this change is used to achieve the desired purpose. Therefore, thermal expansion is regarded as a functional property of the metal sheet. The mapping model between the working principle and the property is shown in Figure 3, and several specific mapping examples are presented in Figure 4.  
Figure 2: The characteristics and the characteristic relationship model of designed properties.