Triaxial geometry

An alternative geometrical set-up known as triaxial geometry (Bandhu et al. 2000) consists of an X-ray tube to fluoresce a selectable secondary target such as Ti, Ag, Ba and to reduce the backscattered radiation is as shown in Fig. 1.8. 

Fig. 1.8. The energy dispersive X-ray fluorescence set-up with triaxial geometry...

During service the impact behaviour of a plastic article will be influenced by the combined effects of the applied stress system and the geometry of the article. Although the applied stress system may appear simple (for example, uniaxial) it may become triaxial in local areas due to a geometrical discontinuity. Fig. 2.78... 

Mehldahl (65) depicts several failure surfaces by photographs of various three-dimensional models. Figure 23 illustrates three such surfaces taken from Ref. 110, which shows geometries which are symmetrical about the space diagonal, oi = triaxial compression octant should be open ( because hydrostatic compression cannot lead to failure in the ordinary sense ). 

Cloud shapes. While precollapse clouds often have a complicated appearance, attempts have been made to approximate their shapes with simple geometries. Triaxial spheroids seem to be required in general, though most lower-mass clouds appear to be more nearly oblate than prolate (Jones et al., 2001). On the larger scale, prolate shapes seem to give a better ht than oblate spheroids. 

The specimen geometry affects the dominant failure mechanism by causing the creation of different stress states in the specimen. For example, thick (bulk) specimens are more likely to fail in a brittle manner than thin films, because of the triaxial stresses created as a result of the substantial thickness of a bulk specimen. 

Figure 21.37 Structural geometry of triaxially woven fabric (basic weave). Source Reprinted with permission from Ko FK Buckley J, Edie DD eds., Carbon-Carbon Materials and Composites, Noyes Publications, Park Ridge, 71-104, 1993. Copyright 1993, William Andrew Publishing.

If plasticity is included in the adhesive characteristics, then an alternative failure criterion was proposed and implemented by Crocombe and Adams [9] using critical values of effective uniaxial plastic strain. The triaxial strain was expressed as an effective uniaxial strain, and then compared with the strain to failure of the bulk adhesive. Unfortunately, this too was seen to be dependent on the density of the finite element mesh, and in reality was a critical strain at a distance criterion. The choice of critical strain was also dependent on the adherends present as different plastic zone sizes will be given by different adherend combinations. The geometry considered in this paper was the peel joint. 

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