Tensile stress influence

In many practical situations involving the flow of polymer melts through dies and along channels, the cross-sections are tapered. In these circumstances, tensile stresses will be set up in the fluid and their effects superimposed on the effects due to shear stresses as analysed above. Cogswell has analysed this problem for the flow of a power law fluid along coni-cylindrical and wedge channels. The flow in these sections is influenced by three factors ... 

Failure of copper alloys may occur by cracking due to the combined influence of tensile stress and exposure to a corrosive environment. When the stresses are produced in components during manufacture the trouble is usually known as season cracking and failures of brass components due to this form of stress corrosion have been known for many years ... 

Fig. 2-53 Example of the influence of tensile stress-strain curves subjected to an environment that influences the ductility of a specific plastic.

When sensitive metals are exposed to certain environmental factors or tensile stress, corrosion can occur. Exposure to only a few parts per million of a corrosive agent can initiate stress corrosion in some metals. High concentrations are often not necessary. Also, temperature and pH can be influencing factors. 

There are a number of subtle effects that have to be considered when making thin film stress measurements on silicon wafers First of all, the crystal orientation of the wafer Influences the resulting stress. The same thermal CVD silicon dioxide film thickness on the same substrate indicates larger tensile stresses on (100)-oriented wafers as compared with (111 (-oriented wafers. 

Stress—Strain Curves. The tensile stress-strain behavior of the blends in which PC is the continuous phase (blends with 5, 10, 20, and 25 wt% PST) also has been investigated. Some preliminary results regarding the influence of composition, strain rate, and temperature on the yield and fracture behavior of these blends will be reported. 

Fig. 6 Influence of the concentration of fibres and state of fibre/matrix interface on the uniaxial tensile stress-strain curves of fibre-reinforced nylon composites (a) type A interface (b) type B interface.

The differences in thermal expansion coefficients of the individual phases and also their anisotropies result in non-uniform shrinkage on cooling. Tf this non-uniform shrinkage cannot be met by deformation, stresses arise restricted to short distances (microstresse.s). This phenomenon is characteristic for ceramics and influences their mechanical properties. High tensile stresses may even result in the formation of ciacks visible under the microscope, for example iji fireclay or porcelain. These cracks arc usually situated at phase boundaries. 

For this comparison, a melt-spinning process was chosen. Each special thermoplastic process influences the structure and thus the properties of the obtained polymer samples differently. This is particularly pronounced for fibers, since especially melt spinning is a process which makes extremely high demands on the deformation ability of the polymer melts at high deformation speeds. Particularly the tensile stress within the fiber formation zone is a very important factor to reach a high orientation of the macromolecules along the fiber axis and a stress-induced crystallization. This crystallization should be discussed in relation to PLA and PHB multifilaments, and at the same time the general property spectrum of these polymers should be represented. 

Next, in two layers system consisting of diamond- dispersed layer and only matrix, effect of thickness of the diamond layer on the residual stresses was evaluated. In radial stress, the maximum compressive and tensile stresses in the diamond layer and in the interface of the layers became smaller in the thinner layer. In three layers system consisting of diamond- high, low dispersed layers (40 and 70 vol%) and matrix, influence of insertion of middle layer on the maximum stresses was compared with the two layers system. The residual stresses in each layer seems to become reduced by the insertion of middle layer. 

Most recently, the influence of the application of macroscopic tensile stress to the PPTA fiber on the microscopic dynamic structure has been studied with deuterium NMR [29]. 

Of the layers mentioned above, the thin films showing the widest range of stress are the PECVD oxides. The stress state of the oxide layers becomes important when such films are used as part of a membrane or as a passivation layer. Membranes that are under considerable compressive stress tend to buckle, severely changing their mechanical properties. In contrast, considerable tensile stress in membranes can lead to crack formation and fracture. The passivation properties of PECVD oxide layers, for example, towards humidity, depend sensitively on their composition, which, in turn, has a great influence on the stress. 

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