Normal tensile stress

Elongation flow fields are likely to be present whenever streamlines cease to be parallel and in particular converging flow typical of that at the entrance of, for example, a capillary flow device is known to develop strong stretching flow The strength of elongational flow at the entrance of a capillary can be determined by one of several equations [106]. In the case of capillary flow, an estimate of the normal (tensile) stress at the entrance can be obtained from ... 

Consider a grain boundary containing a uniform distribution of small pores (as shown in Fig. 16.13) that is subjected to a normal tensile stress a n at a large distance from the boundary. 

In thermomechanical analysis (TMA) the deformation of the sample under stress is monitored against time or temperature while the temperature increases or decreases proportionally to time. Changes are detected by mechanical, optical, or electrical transducers. The stress may be a compression, penetration, tension, flexure, or torsion. Generally the instruments are also able to measure the sample dimensions, a technique called thermodilatometry. The stress F/A) expressed in N/m or Pa may be a normal tensile stress cr, a tangential shearing stress x, or a pressure change Ap the force applied is F and A is the area. 

FIGURE 1.17, Deformation-mechanism map of pure tungsten with grain size of 10 pm (p = 4 x 10 cm ) normalized tensile stress refers to the shear modulus (p) is the melting point [1.65]. 

Under the action of tangential stresses t and normal tensile stresses... 

Upon re-heating, regions of tensile stress may develop in the TGO. With an increase in the number of thermal cycles, the shear stresses induced in the bond coat upon cooling exceed the bond coat yield strength, so that it flows plastically from valleys to peaks at the undulation sites, allowing the undulation amplitude to increase (Fig. 11). As a result, the normal tensile stresses increase and ultimately lead to separation of the TGO [69]. 

The primary desired method of load transfer through an adhesive bonded joint is by shear. This means that the design mnst avoid peel, cleavage, and normal tensile stresses. One practical apphcation of a method avoiding other than shear stresses is the nse of a rivet bonded construction (Fig. 4.35). The direction of the fibers in the onter ply of the composite (against the adhesive) should not be 90° to the expected load path. 

The equilibrium vacancy concentration in a plane can be inereased by a normal tensile stress [172], but Galvele applied the relevant equation to the crack tip where this stress is zero. Lacking diis effect, one must appeal to small, second-order effects. 

---