Brittle-elastic

Creep of polymers is a major design problem. The glass temperature Tq, for a polymer, is a criterion of creep-resistance, in much the way that is for a metal or a ceramic. For most polymers, is close to room temperature. Well below Tq, the polymer is a glass (often containing crystalline regions - Chapter 5) and is a brittle, elastic solid -rubber, cooled in liquid nitrogen, is an example. Above Tq the Van der Waals bonds within the polymer melt, and it becomes a rubber (if the polymer chains are cross-linked) or a viscous liquid (if they are not). Thermoplastics, which can be moulded when hot, are a simple example well below Tq they are elastic well above, they are viscous liquids, and flow like treacle. 

The constant value of 0.25 for Poisson s ratio versus depth reflects the geology and the rock mechanics of the mature sedimentary basin in the West Texas region. Since mature basins are well cemented, the rock columns of West Texas will act as compressible, brittle, elastic materials. 

Griffith s law was derived for the surface energy for a perfectly brittle, elastic material undergoing no plastic work. However, for many materials, plastic work is not negligible and when included, 2es = G, where G can include both plastic and surface work. 

A.3. Material characteristics (chemistry, density, porosity, plasticity, brittleness, elasticity, wettability, abrasivity)... 

Gravity studies, based on tracking spacecraft orbits, have revealed that the density of the outer 100-150 km is about 1 gm/cm3 (Anderson et al. 1997). Evidently, the H2O extends from the surface down to that depth. The outermost portion of this thick layer of water is a lithosphere , meaning that it is cold, brittle, elastic ice. The lithosphere is probably M km thick, although that value is somewhat uncertain, and also depends on the timescale for deformation the transition depth from elastic to viscous ice depends on the rate of strain as well as on the temperature. The viscous portion of the ice crust lies below the lithosphere, and extends to a depth of several km below the surface. A belief that the ice crust is 20 km thick or greater has been widely promoted, but the evidence cited for that model (Pappalardo et al., 1998) has not survived quantitative study (Greenberg et al. 2003b). If the ice were that thick, the ocean would be isolated from the surface. 

Material characteristics, such as chemistry, particle density or porosity, brittleness, elasticity, plasticity, wettability, and abrasivity, etc., play important roles in the choice of an agglomeration method. A particular chemistry may be necessary to bring about... 

For FE simulations of experimental joints with UHM-CFRP, failure can be either adhesive-related (i.e. as in the previous point) or fibre-related (i.e. pure UHM-CF rupture at the central gap between both steel plates, as in Fig. 10.5(e)) therefore both cases should be assessed to find out the critical one (i.e. the case that satisfies its failure criterion at a smaller time increment). For the pure UHM-CF rupture, the FE maximum principal stress of the fibres is plotted with time increments for a selected integration point within the vicinity of the central gap and since the fibre material is modelled as brittle elastic, its assumed mpture (i.e. failure) onset is predicted at the time increment when the fibre s experimental tensile strength is slightly exceeded in the aforementioned curve. The above method for ultimate stress, joint capacity and failure pattern predictions has been successfully validated in Al-Shawaf (2010). 

Stresses Caused by the Support System. After dropping below the transformation temperature, the glass is in a visco-elastic or a brittle-elastic condition. It must then be observed that the 8 m blank has a limited stiffness because of its low thickness. This means that, because of the deformation of the 8 m blank under its own weight, tensile stresses of > 5 N/mm occur at the surface with a maximum deformation of 0.8 mm with a static three-point support. In particular, blanks with damaged surfaces can break due to tensile stresses of this magnitude. 

Besides the brittle elastic behavior, when a gel is subjected to a tensile load, under a compressive load the porous network can be irreversibly transformed. This plasticity effect depends strongly on the volume fraction of pores, but is also clearly affected by macropores and by the OH content. In fact, either under tension or compression, the gel material is not stable and its structure and mechanical features evolve. 

The theory of LEFM applies to brittle elastic materials, whereas gels are viscoelastic, so the theory would be expected to apply only when the strain rate is too fast for significant relaxation to occur. It can be shown [73] that there is an elastic region near the tip of a moving crack whose dimension, d, is given by... 

Fig. 21 is a plot that depicts the relative strengths of several features of a solder joint. In a properly fabricated joint, the intermetallic compounds are very strong and deform elastically, but should never fracture. In a tensile test, a properly formed high Pb/Sn solder joint always fails within the bulk solder which implies that the strengths of the interfaces depicted in Fig. 25 are greater than the strength of the solder. Note that the stress-strain behavior of only one interface is shown in Fig. 26. Although each interface shown in Fig. 25 exhibits a different stress-strain behavior, each must possess a tensile strength greater than the solder. If an interface in the structure is weaker than the solder, it will result in a brittle, planar failure in a tensile pull test. A change in fracture mode from plastic solder fracture to brittle elastic interface fracture is usually an indication that a terminal is defective. Lead-rich solders are usually weaker and more ductile than tin-based solders (Fig. 26).

For constant fracture resistance R (Griffith theory for a brittle elastic material),... 

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