Upper yield strength

They are almost completely elastic until the upper yield strength Ren (UYS) is reached. At this stress, plastic deformation sets in rather suddenly, which is localised in so-called Liiders bands or flow lines. While the stress oscillates, these lines extend until they cover the whole specimen. The lowest stress occurring during this process is called lower yield strength i eL (lys). Why this localised plastic deformation occurs, will be explained in section 6.4.3. After the specimen has plastified completely, it behaves identical to a metal without apparent yield point. 

For stainless steel, the stress-strain curve (see Fig. 26-37) has no sharp yield point at the upper stress limit of elastic deformation. Yield strength is generally defined as the stress at 2 percent elongation. 

In a material exhibiting a distinct yield point, the stress corresponding to the yield point may be taken as the yield strength. When both upper and lower yield points occur, generally the stress corresponding to the lower yield point is taken to be the yield strength. 

Beyond point E, the material begins to plasticly deform, and at point Y the yield point is achieved. The stress at the yield point corresponds to the yield strength, Oy [see Eq. (5.20)]. Technically, point Y is called the upper yield point, and it corresponds to the stress necessary to free dislocations. The point at which the dislocations actually begin to move is point L, which is called the lower yield point. After point L, the material enters the ductile region, and in polycrystalline materials such as that of Eigure 5.26, strain hardening occurs. There is a corresponding increase in the stress... 

In detail, however, the growth of the domes appears more complicated in many instances. First of all, the rheological behaviour of the crust is considerably more complicated than that of a newtonian viscous fluid. Particularly, the cool upper crust will have a finite yield strength that any buoyant instability will have to overcome before it can rise significantly and break through to the surface. Any structure or deformation event that weakens the upper crust may... 

Figure 1 (a) is a schematic diagram of the MSP equipment employed, and Fig. 1 (b) is the model used for calculating strength, a and b in Fig. 1 (b) represent the radii of the supporting die s hole and of the upper punch, respectively, t is the thickness of the specimens. Yield strength, a nux> can be calculated from the following formula ... 

Fig. 1. Specific yield strength (0.2 % proof stress in compression per unit weight density at 10 4s 1 strain rate in compression) as a function of temperature for the D022 phase Al3Nb [112, 113], the Heusler-type phase Co2TiAl [67], the Laves phasesTiCr15Si05 andTaFcAl [67,114], the two-phase alloy NbNiAl-NiAl with 15 vol.% NiAl in the Laves phase NbNiAl [67,114], and the hexagonal D8g phase Ti5Si3 [100] in comparison to the superalloy MA 6000 (in tension) [115] and the hot-pressed silicon nitride HPSN (upper limit of flexural strength) [116],...

The hydrostatic test pressure is 1.25 times the design pressure corrected for temperature, rather than the usual 1.5. Division 2 establishes upper limits for the test pressure relative to the yield strength at test temperature. The pneumatic test pressure is 1.15 times the design pressure corrected for temperature rather than 1.25 required by Division 1. Division 2 has no provision for proof tests to establish the maximum allowable working pressure. But Appendix 6, Experimental Stress Analysis, provides for the determination of the critical or governing stresses for unusual geometries for which theoretical stress analysis is inadequate. 

SSC SSC is an important cracking phenomenon in hydrogen sulfide medium and a special case of HIC. Natural aqueous environments contaminated with hydrogen sulfide are very corrosive. The hydrogen sulfide present in salt water in sour oil wells places an upper limit of 620 MPa on the yield strength of steel that can be tolerated. 

The allowable buckling stress is the critical buckling stre.ss multiplied by some factor of safety. The safety factor for buckling ranges from 1.5 1 to. 3 1. In addition, certain upper boundaries are specified, such as one-half the yield strength. 

Figure 12.9. Effect of volume fraction of glass beads on yield strength of poly(phenylene oxide). (O) Untreated ( ) A-llOO treated. The term A-1100 refers to the silane coupling agent used to enhance adhesion (Wambach et al., 1968). Note that the upper curve corresponds to ultimate strength, for fracture occurred prior to yielding.

The effect of neutron fluence on radiation embrittlement has been reported to be signiflcant at fluences above 10 n/cm ( > IMeV). An increase in neutron fluence results in an increase in RTndt, yield strength and hardness, and a decrease in upper-shelf toughness. 

The graph depicted in Fig. 8.3 illustrates this phenomenon. The upper curve indicates that the value at O F is 14,000 Ib/in. At 72°F, it has dropped to around 12,000 Ih/in. By the time it reaches 140°F, the tensile yield strength is approximately 7000 Ih/in. This data is for nylon, a polymer particularly affected by moisture. The lower curve illustrates the effect of 2.5% moisture. In the range of temperatures between 30 and 100°F, the tensile yield strength appears to be about 20% lower for the moist material. Note that the curves begin to nm together beyond 150° F as most of the water has been driven off by that point. 

---