Creep - recovery tests

DMA can be used to make creep, creep-recovery and sometimes stress-relaxation experiments. In some respects these tests defeat the purpose of a DMA, in that generally the dynamic data ( , tan 8) are more useful and give greater insight into the materials mechanical behaviour than these constant load tests. However, they can be useful where a component is used at a specific temperature and load, e.g. a fixing lug, and it 

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Figure 2 Creep-recovery tests of chemically treated woods. U, untreated wood Fs, vapor phase formalization F, liquid phase formalization A, acetylation PO, etherification with propylene oxide MG, treatment with maleic acid and glycerol PFl, impregnation with low molecular weight phenol-formaldehyde resin PEG-ICP, impregnation with polyethylene glycol (PEG-IOOO) WPC, formation of a wood- polymer composite (PMMA) WIC, formation of a wood-inorganic material composite.

The maximum deflection of 0.125" at 300-lb -concentrated load at midspan, plus adjustments for end use as stated in Section 5.4 of ASTM D 7032 (Creep-Recovery Test). 

Tensile modulus, effect on, 174 Tensile strength, effect on, 174 Water absorption, effect on, 174 Covalent bonds, 161, 162 With wood fiber, 161 Cox-Merz rule, 640 Crane Plastics Co., 79, 80, 84, 87-91 Creep, 56, 293, 225, 260, 290-302 Creep-Recovery Test, 260 Creosote, 416, 417, 436 Critical moisture content, 413 Critical shear rate, 644, 664, 669 Critical shear stress, 658 Cross equation, 622, 623 Cross Timbers, 56, 58, 597 Sales, 58... 

Figure 11 shows the geometry of the tensile dogbone specimen used to carry out the creep and creep recovery tests. This geometry is identical to the one used by Rochefort and Brin-... 

Fig. 3.13 Creep and creep recovery tests stress input (above) and qualitative material strain response (below).

The response of a four parameter fluid in a creep and creep recovery test is given in Fig. 3.26 and is recognized as the response of a thermoplastic type polymer as given earlier in Fig. 3.13. 

Sketch the response of a Maxwell fluid to a creep and a creep recovery tests. 

Example 1 Assume it is desirable to find the strain output in a creep and creep recovery test shown in Fig. 6.3(a). First note that the stress can be easily represented by two step inputs as illustrated schematically in Fig. 6.3(b) and given by... 

Schapery Equation for a Creep and Creep Recovery Test Schapery suggested using a creep and creep recovery test (as shown in Fig. 10.9) to determine the stress dependent parameters g, g, g, a . This condition is a special case of the two step loading of Eq. 10.32a in which stresses a = Oo and Ob = 0 and thus... 

Determining Materiai Parameters from a Creep and Creep Recovery Test... 

Both controlled-angular displacement (strain-controlled) and controlled-torque (stress-controlled) rotational rheometers are used, with the former giving superior performance at high frequencies and the latter better precision at low frequencies. There have also recently appeared on the market instruments said to be capable of operating in both modes. Controlled torque instruments can also be used to make creep and creep recovery tests, which are described in the next section. In order to obtain a linear viscoelastic characterization that includes the terminal zone, it is sometimes useful to combine data from oscillatory flow with those from a creep experiment, and this is also discussed in the following section. Rheometrical methods are described in some detail in several books [3,8,9]... 

Small amplitude oscillatory shear measurements, creep and creep recovery tests are examples of small perturbation tests carried out on hydrogels. The principle of small amplitude oscillatory shear measurements is shown in Fig. 2. 

After a sample is allowed to creep under load, the materiaTs elastic behavior can be obtained by abruptly relieving the imposed stress and measuring the extent the sample recovers. A creep/recovery test can be carried out as follows. 

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