Transverse stresses

In a similar way the Griffith length, Lq, due to the strain energy caused by the stress transverse to the chain direction can be derived... 

Laminated Composite, Residual stress, transverse cracking, fracture mechanics... 

Fig. 3.18. Average values of the normalized principal stress transverse to the oxide line orientation

Fig. 4.25 Moisture content (average of two to four specimens) vs. i/i in unidirectionally reinforced AS4/3502 composite coupons during absorption. Coupons subjected to various levels of stress transversely to fiber direction T = 40°C, RH = 97% (Henson and Weitsman 1986)...

However, it is possible that the constant rate of AE activity is interrupted by local peaks of high rate of AE. This is due to the formation of local (internal) delaminations because of interlaminar stresses arising due to the presence of transverse cracks. This is more accentuated in less severe loading conditions. Under severe loading conditions = 80% CTu, R = 0.1) the rate of damage development (delamination growth) is so fast that leads to an overall high rate of AE emission. 

We consider the limiting case corresponding to (5 = 0 in (2.185). A restriction obtained in this manner corresponds to the condition of mutual nonpenetration of the crack faces without including the thickness of the shell. We note that in taking full account of the thickness one must bear in mind that the stresses aij, the moments m w) and the transverse forces t w) depend on 5. Thus 5 = 0 in (2.185) carries the implication that the thickness of the shell is taken to be fixed, and the nonpenetration conditions on the crack faces are described approximately. At this point we mention other problems of a passage to limit (Attouch, Picard, 1983 Schuss, 1976 Roubicek, 1997 Oleinik et ah, 1992 Moet, 1982 Telega, Lewinski, 1994). 

The strength of laminates is usually predicted from a combination of laminated plate theory and a failure criterion for the individual larnina. A general treatment of composite failure criteria is beyond the scope of the present discussion. Broadly, however, composite failure criteria are of two types noninteractive, such as maximum stress or maximum strain, in which the lamina is taken to fail when a critical value of stress or strain is reached parallel or transverse to the fibers in tension, compression, or shear or interactive, such as the Tsai-Hill or Tsai-Wu (1,7) type, in which failure is taken to be when some combination of stresses occurs. Generally, the ply materials do not have the same strengths in tension and compression, so that five-ply strengths must be deterrnined ... 

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 9.3 Transverse stress-corrosion cracks in a condenser tube the presence of the cracks along just one side indicates that a bending moment provided the stress.

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.

The transverse orientation of the cracks along just one side of the tube reveals that bending provided the stresses for cracking. The tube sheet acted as a constraint to the bending, intensifying stresses in the tube wall adjacent to the sheet. 

The transverse orientation of the cracks, coupled with their predominance along one side, reveals that bending of the tube induced the responsible stresses. The rapidity of crack propagation and the high crack density indicate that the stress level was high. 

The transverse (circumferential) crack path reveals that the stresses responsible for SCC were axially oriented that is, the tube was pulled at its ends. Residual tube-forming stresses may also have contributed in this case. The specific cracking agent was caustic, which was apparently concentrated by evaporation when water flashed to steam in these locations. 

Microstructural examinations revealed that branched cracks originated at shallow pit sites on the external surface. The pits, which may have formed during idle periods from differential oxygen concentration cells formed beneath deposits, acted as stress concentrators. The transverse (circumferential) crack orientation and the localization of cracks along just one side of the tube revealed that bending of the tube was responsible for the stresses involved. 

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

The manufacturers stress ease of processing as a particular feature of the material. Recommended melt temperatures are in the range 320-340°C and mould temperatures are 135-165°C. Mould shrinkage of glass-filled grades is usually of the order of 0.2-0.4% in the flow direction and up to twice this value in the transverse direction. The materials are notable for their ability to withstand vapour phase and infrared soldering processes. 

The melt-spinning process used to convert mesophase pitch into fiber form is similar to that employed for many thermoplastic polymers. Normally, an extruder melts the pitch and pumps it into the spin pack. Typically, the molten pitch is filtered before being extruded through a multi-holed spinnerette. The pitch is subjected to high extensional and shear stresses as it approaches and flows through the spinnerette capillaries. The associated torques tend to orient the liquid crystalline pitch in a regular transverse pattern. Upon emerging from the... 

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