Stress transverse/longitudinal

Poisson s ratio is a measure of the reduction in the cross section accompanying stretching and is the ratio of the transverse strain (a contraction for tensile stress) to longitudinal strain (elongation). Poisson s ratio for many of the more brittle plastics such as polystyrene, the acrylics, and the thermoset materials is about 0.3 for the more flexible plasticized materials, such as cellulose acetate, the value is somewhat higher, about 0.45. Poisson s ratio for rubber is 0.5 (characteristic of a liquid) it decrease to 0.4 for vulcanized rubber and to about 0.3 for ebonite. Poisson s ratio varies not only with the nature of the material but also with the magnitude of the strain for a given material. All values cited here are for zero strain. 

A slight change of the transverse, longitudinal or vertical loading imposes a stronger impact on tensile stress than that on compressive stress. 

SCC has been defined as failure by cracking under the combined action of corrosion and stress (Fig. 9.1). The stress and corrosion components interact S3mergistically to produce cracks, which initiate on the surface exposed to the corrodent and propagate in response to the stress state. They may run in any direction but are always perpendicular to the principal stress. Longitudinal or transverse crack orientations in tubes are common (Figs. 9.2 and 9.3). Occasionally, both longitudinal and transverse cracks are present on the same tube (Fig. 9.4). Less frequently, SCC is a secondary result of another primary corrosion mode. In such cases, the cracking, rather than the primary corrosion, may be the actual cause of failure (Fig. 9.5). 

Figure 9.4 Both longitudinal and transverse stress-corrosion cracks on a brass heat exchanger tube that had been exposed to ammonia. Note the branching of the cracks.

While the transverse voltage stresses the main wall insulation, the longitudinal voltage stresses the interturn insulation. The bulk of the components of both... 

The properties of a unidirectional fibre will not be nearly so good in the transverse direction compared with the longitudinal direction. As a material in service is likely to be subjected to stresses and strains in all directions it is important to be aware of the properties in all directions. The transverse direction will, of course, be the weakest direction and so it is necessary to pay particular attention to this. 

In the [ 45]j tensile test (ASTM D 3518,1991) shown in Fig 3.22, a uniaxial tension is applied to a ( 45°) laminate symmetric about the mid-plane to measure the strains in the longitudinal and transverse directions, and Ey. This can be accomplished by instrumenting the specimen with longitudinal and transverse element strain gauges. Therefore, the shear stress-strain relationships can be calculated from the tabulated values of and Ey, corresponding to particular values of longitudinal load, (or stress relations derived from laminated plate theory (Petit, 1969 Rosen, 1972) ... 

The [10°] off axis tension specimen shown in Fig 3.23 is another simple specimen similar in geometry to that of the [ 45 ]s tensile test. This test uses a unidirectional laminate with fibers oriented at 10° to the loading direction and the biaxial stress state (i.e. longitudinal, transverse and in-plane shear stresses on the 10° plane) occurs when it is subjected to a uniaxial tension. When this specimen fails under tension, the in-plane shear stress, which is almost uniform through the thickness, is near its critical value and gives the shear strength of the unidirectional fiber composites based on a procedure (Chamis and Sinclair, 1977) similar to the [ 45°]s tensile test. 

Ki = a y/a is the stress intensity factor, and F, the material constant, both of which depend on the degree of anisotropy of the composite controlled by the composite elastic moduli in the longitudinal and transverse directions, El and Ej, in-plane Poisson ratio, vlt, and Glj. For a perfectly isotropic material, jr/8(l + Vlt) 0.3. Also, the material parameters, i and < 2 are given by ... 

---