Loading, static

Creep. The creep characteristic of plastic foams must be considered when they are used in stmctural appHcations. Creep is the change in dimensions of a material when it is maintained under a constant stress. Data on the deformation of polystyrene foam under various static loads have been compiled (158). There are two types of creep in this material short-term and long-term. Short-term creep exists in foams at all stress levels however, a threshold stress level exists below which there is no detectable long-term creep. The minimum load required to cause long-term creep in molded polystyrene foam varies with density ranging from 50 kPa (7.3 psi) for foam density 16 kg/m (1 lb /ft ) to 455 kPa (66 psi) at foam density 160 kg/m (10... 

Eracture mechanics concepts can also be appHed to fatigue crack growth under a constant static load, but in this case the material behavior is nonlinear and time-dependent (29,30). Slow, stable crack growth data can be presented in terms of the crack growth rate per unit of time against the appHed R or J, if the nonlinearity is not too great. Eor extensive nonlinearity a viscoelastic analysis can become very complex (11) and a number of schemes based on the time rate of change of/have been proposed (31,32). 

The hand-held comparative Brinell tester is the most portable device. With this device a hammer blow is substituted for the static load which is transmitted first through a standard bar of known hardness and then through the indenter into the workpiece. The indentations in both the standard bar and the workpiece are measured and from the ratio of the diameters the HBN is derived. The loss in accuracy is made up for by the exceUent portabUity. 

Another measure of refractoriaess is the hot-compressive strength or hot-load test for refractory bricks or formed specialties. The specimen carries a static load from 69 kPa (10 psi) to 172 kPa (25 psi). It is heated at a specific rate to a specific temperature which is then held for 1.5 h, or it is heated at a specific rate until it fads. The percent deformation or the temperature of fadure is measured. The procedure is described ia ASTM C16. 

The vertical vibratoiy mill has good wear values and a low-noise output. It has an unfavorable residence-time distribution, since in continuous operation it behaves like a well-stirred vessel. Tube mills are better for continuous operation. The mill volume of the vertical mill cannot be arbitrarily scaled up because the static load of the upper media, especially with steel beads, prevents thorough energy introduction into the lower layers. Larger throughputs can therefore only be obtained by using more mill troughs, as in tube mills. 

The values of these factors are provided by the bearing manufacturers in their catalogues, based on the ratios F /Cg and F IFy, where C is the static load rating in kg or N (based on a contact stress of 4200 MPg for ball bearings and 4000 MPj, for roller bearings, also provided in these catalogues. MPg is the unit of stress in Mega-Pascals. 

K = actual stress concentration factor for static loading... 

Figure 4.22 Transient loads may be many times the static load in operation (Nicholson et al., 1993)...

Maximum static loading stress, lmax> with variable strength... 

Variable static loading stress with a defined duty cycle of n load applications with variable strength using approaches by Bury (1974), Carter (1997) and Freudenthal et al. (1966)... 

Fracture Mechanics tests on a grade of ABS indicate Aat its K value is 2 MN and Aat under static loading its growA rate is described by the equation. 

Dynamic loading The loading imposed upon a structure as a result of motion as opposed to static loading. 

API Standard 4A (superseded by Standard 4F) provides rating of derrick capacities in terms of maximum safe load. This is simply the load capacity of a single leg multiplied by four. It does not account for pipe setback, wind loads, the number of lines between the crown block and the traveling block, the location of the dead line, or vibratory and impact loads. Thus, it is recommended that the maximum safe static load of derricks designed under Standard 4A exceed the derrick load as follows ... 

Maximum rated static load on rotary table beams. 

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