Randomly-oriented dispersion type

Figure 6.1 Different types of compact 3D metal deposits according to Fischer [6.8]. (a) Field-oriented isolation type (FI) of an Ag deposit (b) field-oriented texture type (FT). Cross section of Cu deposit from acid CUSO4 solution with addition of /5-naphthaquinoline (c) base-oriented reproduction type (BR). Cross section of Cu deposit (d) randomly-oriented dispersion type (RD). Cross section of Cu deposit from acid CuSO solution with addition of naphthaquinoline.

The phenomenological classification of compact 3D Me deposits by Fischer (cf. Section 6.1) can be related to the nucleation and growth parameters discussed above. For example, the field-oriented isolation (FI) and texture (FT) types are caused by electric field-enhanced normal growth, the base-oriented reproduction (B t3 e corresponds to a relatively low nucleation rate and comparable normal and lateral growth rates, and the randomly-oriented dispersion (RD) type to an enhanced nucleation rate. 

In the model presented by Hammond, the HS, tied together by a polydiacetylene backbone, are oriented laterally in lameUar-like hard domains oriented in random directions before stress is applied, and possibly forming spherulitic type superstructures. The SS are randomly coiled macromolecules spaced between the hard domains. At low moderate strains, when the material is stretched, stress is transferred to the hard domains. The HS orient perpendicular to the stress direction. Upon removal of the stress, the SS relaxation allows the hard domains to return in a random orientation. This results in a small residual hard domain orientation. Therefore, the two-phase microstructure of the material is not highly interconnected. It consists of discontinuous hard domains dispersed throughout a continuous SS phase [364]. 

In the continuous form, the fibres can be aligned in a preferred orientation, which is controlled by the production process (orientation of winding, or lay-up direction of the mat) and the structure of the mat. This type of fibre reinforcement bears some resemblance to ferrocement applications it is less common in FRC composites which are usually reinforced by discrete, short fibres, but has recently been the focus of intense development efforts (see Chapter 13 for details). In the case of dispersed fibres the dispersion in the matrix is more uniform, and the short fibres tend to assume a more random orientation. Flowever, even in these systems the fibre distribution is rarely completely uniform, and their orientation is not... 

Based on this analysis it is evident that materials which are biaxially oriented will have good puncture resistance. Highly polar polymers would be resistant to puncture failure because of their tendency to increase in strength when stretched. The addition of randomly dispersed fibrous filler will also add resistance to puncture loads. From some examples such as oriented polyethylene glycol terephthalate (Mylar), vulcanized fiber, and oriented nylon, it is evident that these materials meet one or more of the conditions reviewed. Products and plastics that meet with puncture loading conditions in applications can be reinforced against this type of stress by use of a surface layer of plastic with good puncture resistance. Resistance of the surface layer to puncture will protect the product from puncture loads. An example of this type of application is the addition of an oriented PS layer to foam cups to improve their performance. 

Mechanical properties of PMC are strongly influenced by the filler (by its size, type, concentration and dispersion) and by the properties of the matrix, as well as the extent of interfacial interactions and adhesion between them and their micro-structural configurations. The interrelation of these variables is rather complex. In FRC, the system is anisotropic where fibres are usually oriented uniaxially or randomly in a plane during the fabrication of the composite, and properties are dependent on the direction of measurement. Generally, the rule of mixture equations are used to predict the elastic modulus of a composite with uniaxially oriented (continuous) fibres under iso-strain conditions for the upper bound longitudinal modulus in the orientation direction (Equation 6.10). 

---