Flexural loading

For convenience so far we have referred generally to creep curves in the above examples. It has been assumed that one will be using the conect curves for the particular loading configuration. In practice, creep curves obtained under tensile and flexural loading conditions are quite widely available. Obviously it is important to use the creep curves which are appropriate to the particular loading situation. Occasionally it is possible to obtain creep curves for compressive or shear loading but these are less common. 

The previous section has considered the in-plane deformations of a single ply. In practice, real engineering components are likely to be subjected to this type of loading plus (or as an alternative) bending deformations. It is convenient at this stage to consider the flexural loading of a single ply because this will develop the method of solution for multi-ply laminates. 

HDT heat deflection temperature under flexural load (1820 kPa) Heat distortion test (HDT) ASTM D-648-72 CEAST 6005... 

We perform flexural testing on polymer rods or beams in the same basic apparatus that we use for tensile or compressive testing. Figure 8.6 illustrates two of the most common flexural testing configurations. In two-point bending, shown in Fig. 8,6 a), we clamp the sample by one end and apply a flexural load to the other. In three-point bending, shown in Fig. 8.6 b), we place the sample across two parallel supports and apply a flexural load to its center. 

Birger, S., Moshonov, A. and Kenig, S. (1989). Failure mechanisms of graphite fabric epoxy composites subjected to flexural loading. Composites 20, 136-144. 

A good applications-oriented measure of the use temperature for a ma-teral is the heat distortion or heat deflection test (HDT). The HDT is described by ASTM-D648 as the temperature at which a sample of defined dimensions (5 X Vi X Vs (or Va) in.) deflects under a flexural load of 66 or 264 psi placed at its center. In case of a largely amorphous polymer, the HDT temperature is typically slightly (10 to 20 °C) lower than the Tg as determined by DSC or DTA, whereas with more-crystalline polymers, it more closely correlates with the Tm. The HDT temperature is a useful indicator of the temperature limits for structural (load-supporting) applications. A loaded cantilever beam is used in another heat deflection test called the Martens method. 

Three basic problems may cause a total joint replacement to fail or to have a limited service life. The first problem, arises, because the elastic modulus of the stem greatly exceeds that of the bone. Flexural loading caused by walking creates local cyclic stress concentrations due to the non-compliance of the stem. These stresses can be intense and even severe enough to cause death of local bone cells. If this... 

ASTM D648, Deflection Temperature of Plastics Under Flexural Load, Vol. 8.01, A SIM, Philadelphia, Pa., 1982 (reapproved 1988). 

Deflection temperature under flexural load (2641b-in-2), °C 124... 

---