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Dynamic Mechanical Analysis part 10

Tham khảo tài liệu 'dynamic mechanical analysis part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | as shown for the polyurethane in Figure 7.2. Due to the hard and soft segments of this polyurethane the polymer has very different behavior under creep and DMA conditions. One can also use the results of free resonance studies to obtain higher fiequencies using either a free-resonance instrument28 cm by performing a recovery experment in a stress-controlled rheometer.4 This was discussed in Chapter 4. There data can also be added to the frequency scan as shown. These approaches are relatively under-used compared to the concept of time-temperature superposition. Time-temperature superposition was described by I Cii y as a method of reduced variables. 29 Shifting a series of multiplexed frequency scans relative to a reference curve performs the superposition. This is shown in Figure 7.17a. After shifting the curves the resultant master curve Figure 7.17b covers a range much greater than that of the original data. .Sts mentioned above materials were studied by various techniques to obtain a heSes of curves often referred to as a multiplex. This is normally done to develop Semaster curve which is a collection of data that have been treated so they are displayed as one curve against an axis of shifted values. This has traditionally been done using a frequency seale for the x hxis and temperature as the variable to create Sr multiplex of curves. Using the idea of time-temperature equivalence discussed cSove we can assume that the changes seen by altering the temperature are similar tfthose caused by frequency changes. Therefore the data can then be superposi-iioned to generate one curve. Unfortunately current use of this technique seems to be limited to mainly time-temperatrne superposition. As shown by Ferry29 rnd Goldman 30 this approach srn be used for a wide range of variables including humidity degree of cure strain hie. Goldman s tour de force27 gives many examples of the application of this idshnique to many properties of polymers. We will limit our discussion to