Bending stress

Tension leg platforms (TLP) are used mainly in deep water where rigid platforms would be both vulnerable to bending stresses and very expensive to construct. A TLP is rather like a semi-submersible rig tethered to the sea bed by jointed legs kept in tension. Tension is maintained by pulling the floating platform down into the sea below its normal displacement level. The legs are secured to a template or anchor points installed on the seabed. 

Rotating Beam Fatigue Test for Steel Cords. The purpose of this test method is to evaluate steel cord for pure bending fatigue (121). The test sample consists of a 3-mm diameter mbber embedded with steel cord. Different bending stress levels are appHed and the time to failure is recorded. The test stops at 1.44 million cycles. The fatigue limit is calculated from S—N (stress—number of cycles) curve. 

Fig. 3. Bending stress versus bending strain for typical carbon, glass, and aramid fibers. To convert MPa to psi, multiply by 145.

S tandard Practicefor Making and Using U-Bend Stress—Corrosion Test Specimens, ASTM G 30-84, American Society for Testing and Materials, Philadelphia, Pa., 1992. 

Plain-end pipe used for socket-weld joints (Fig. 10-126) is available in all sizes, but fittings and valves with socket-weld ends are limited to sizes 3 in and smaller, for which the extra cost of the socket is outweighed by much easier alignment and less skill needed in welding. The joint is not so resistant to bending stress as the butt-welded joint but is otherwise equal, except that for some fluids the crevice between the pipe and the socket may promote corrosion. ANSI B16.il—1973,... 

The code provides no guidance for analysis but requires that external and internal attachments be designed to avoid flattening of the pipe, excessive locahzed bending stresses, or harmful therm gradients, with further emphasis on minimizing stress concentrations in cyclic service. 

The resiiltant bending stresses S, to be used in Eq. (10-100) for elbows and miter bends shall be calculated in accordance with Eq. (10-101), with moments as shown in Fig. (10-167) ... 

Unstayed flat heads and covers can be designed by very specific rules and formulas given in this subsection. The stresses caused by pressure on these members are bending stresses, and the formulas include an allowance for additional edge moments induced when the head, cover, or blind flange is attached By bolts. Rules are provided for quick-opening closures because of the risk of incomplete attachment or opening while the vessel is pressurized. Rules for braced and stayed surfaces are also provided. 

Most coils are firmly clamped (but not welded) to supports. Supports should allow expansion but be rigid enough to prevent uncontrolled motion (see Fig. ll-29b). Nuts and bolts should be securely fastened. Reinforcement of the inlet and outlet connections through the tank wall is recommended, since bending stresses due to thermal expansion are usually high at such points. 

The confinement of the cracks to a specific area of the cooler suggests that condensate from atmospheric moisture initially formed in this area and dissolved a corrodent from the atmosphere such as ammonia, sulfur dioxide, or oxides of nitrogen. Since the previous cooler had been in service for 20 years, it is conjectured that the rapid failure of this exchanger was due principally to very high bending stresses, which may have been induced during construction of the cooler. 

The cyclic stresses responsible for this failure were apparently bending stresses associated with cyclic thermal expansion and contraction. 

The orientation of the cracks reveals that cyclic bending stresses or cyclic axial stresses were active. The intensification of these stresses at pits and intergranular corrosion sites produced the cracks observed. 

But when other configurations are adopted as shown in Figure 28.34, this concept may not hold true. In other configurations, however, the sectional modulus will only rise and reduce the bending stress on the busbars. 

The minimum shearing strength of aluminium is 1650 kg/cm (Table 30.1) which is much larger than the actual force to which the busbars will be subject, in the event of a fault. They are thus more than adequate in cross-section and numbers. Other than bending stress, there is no significant tensile or shearing force acting on the busbars. 

SMC supports alone must be used with a modified design, to withstand a higher bending stress or the design of the bus system itself be modified as mentioned below under note 3. 

We have seen that welds can be very weak in a fatigue situation, and we would be wise to check that the modified weld in Fig. 28.7 is adequate for the job. Although it is difficult to spot immediately, the weld is in fact subjected to large bending stresses (Fig. 28.8). These can be calculated as follows. 

We need this speeial algebra to operate on the engineering equations as part of probabilistie design, for example the bending stress equation, beeause the parameters are random variables of a distributional nature rather than unique values. When these random variables are mathematieally manipulated, the result of the operation is another random variable. The algebra has been almost entirely developed with the applieation of the Normal distribution, beeause numerous funetions of random variables are normally distributed or are approximately normally distributed in engineering (Haugen, 1980). 

Serviee faetors and material index number tabulation are provided for various typieal applieations, allowing the determination of the K faetor. Gear tooth size and geometry are seleeted so that bending stresses do not exeeed eertain limits. The bending stress number is given by... 

---