Creep reference information

No more than a brief outline of the mechanical properties can be given here, for detailed information Reference 9 should be consulted. It should be noted that while steels used for creep resisting purposes may conform to the standard specifications, sometimes specially limited composition ranges within these specifications are used in the interests of strength, structural stability or resistance to embrittlement. 

MuUite is another important crystalline ceramic that is an oxide It is a solid solution of alumina and silica in the compositional range 71-75 wt% alumina. Mullite is represented by the formula, 3 Al203.2Si02. It has excellent strength and creep resistance as well as low thermal expansion and conductivity. For more detailed information on the structure and properties of mullite the reader is referred to Schneider et al. (1994). Table 6.2 provides a summary of the properties of mullite. 

Always consult the original references every time a paper is abstracted or condensed, some information is lost along the fine, or some misinterpretation may creep in. 

Yet another variation of this test, which is also used to obtain creep information, is to simply attach a load to a specimen and measure its time to failure. The results are then plotted in a format identical to the one shown in Fig. 12.1 la for cyclic fatigue, and are referred to as static fatigue or stress/life curves. 

Unlike the flows considered in Chapter 3 which were essentially imidirectional, the fluid flows in particulate systems are either two- or three-dimensional and hence are inherently more difficult to analyse theoretically, even in the creeping (small Reynolds number) flow regime. Secondly, the results are often dependent on the rheological model appropriate to the fluid and a more generalised treatment is not possible. For instance, there is no standard non-Newtonian drag curve for spheres, and the relevant dimensionless groups depend on the fluid model which is used. Most of the information in this chapter relates to time-independent fluids, with occasional reference to visco-elastic fluids. 

The situation is further complicated because the data here is for shortterm loading and do not provide information on a Joint s creep behaviour. Both members (references 11,12) and the connections (reference 10) are known to creep, such that in time there will be increased beam deflection and therefore an increase in the required rotation capacity of the connection. Rigorous procedures to account for creep in the design process are not available. Designers are advised to use creep moduli (i.e. reduced values from short term values) when determining deflections of beam members in a braced frame (reference 1). It may be assumed that the a web cleat connection does not adversely affect this design approach. 

We have already referred to various kinds of data on mechanical behavior of polymers. We are now going to consider methods of acquisition of such information. The most fi equently used are the so-called quasistatic methods which involve relatively slow loading. Tension, compression, and flexure belong here. The quasistatic methods have to be distinguished from so-called transient tests which include stress relaxation and creep. There are also impact tests and dynamic mechanical procedures which will be defined later. 

Macroscopic properties, alternatively referred to as bulk properties or simply performance , are of the utmost importance in material selection. For any application it is essential that the material provides the properties desired, under the conditions of use. In addition, it is wise to characterise the material more fully in order to understand what the effect might be, for example, of changing the temperature. Consideration should also be given to time-related phenomena, such as creep or stress relaxation. What are the consequences of dimensional instability Techniques that can provide this type of information directly include mechanical testing, rheology and thermal analysis. In cases where knowledge of the relationship between structure and properties is desirable, then obviously the techniques described here must be used in combination with those which follow. 

Unsteady simple shear flow would occur when the stresses involved are time dependent. Small-amplitude oscillatory flow, stress growlh, stress relaxation, creep, and constrained recoil are some examples of such types of flow [4]. In the following, small-amplitude oscillatory flow is treated in sufficient detail, whereas others are described briefly readers are encouraged to refer to Ref. 4 for more information. 

There appears to be no information on the uniaxial creep of polymers used as structural adhesives such as is available referring to the creep of adhesive joints in lap-shear or torsion. The latter is reserved for Chapter 7 where the few data that are available are given. An apparent exception is the careful study of a nylon-epoxy adhesive (FM 1000) by Shen and Rutherford (1972). These authors achieved something approaching uniaxial stress using a cylindrical butt joint in direct tension. However, what they called creep was simply the delayed elastic response. They likened the adhesive to a metal in its behaviour and used the classical but inappropriate concept of separating the creep behaviour into three stages as was done many years ago for metals. 

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