Thermomechanical tensile tests

Cyclic, thermomechanical tensile tests were performed for the nanocomposites with POSS/polyol ratio = 2.63 (see Fig. 15b). The sample was firstly heated to 80°C (T > Tg) and deformed (1) by ramping to a load of 0.3N. The sample was cooled under this load (2) to 10°C, to fix the temporary, elongated shape. After unloading (3) the sample was heated (4) to 80°C to recover the permanent shape. The first cycle showed about 5% creep occurring between the elongation and fixing step over... 

The effect of magnetic nanoparticles on the cyclic, thermomechanical tensile tests of TFX nanocomposites is shown in Fig. 22. Here TE and a nanocomposite from TFX and 7.5 wt% magnetic particles were compared. In these tests, the samples were elongated at a temperature 71,igh, which was higher than Tsv, but lower than Tians of the hard domains. Strain was kept constant for a certain time interval to allow relaxation. The elongated samples were cooled to fix the temporary shape. This step was performed under stress-control, which resulted in an increase of strain as a consequence of entropy elasticity. The SME was initiated by reheating the composite to... 

Fig. 22 Results of cyclic, thermomechanical tensile tests under stress-free condition of TFX materials. Tiow = 0°C, Thigh = 80°C, and m = 50%. (a) TFX (b) composite from TFX and 7.5 wt% magnetic nanoparticles. Reprinted by permission from ref. [85]. Copyright 2006, National Academy of Sciences, U.S.A.

On the macroscopic level the extent to which a temporary deformation can be fixed and the recovery of the permanent shape or the recovery stress are the most important characteristics of the shape-memory effect (SME), which can be quantified in cyclic, thermomechanical tensile tests or bending tests. Such cycUc tests consist of a SMCP module that can be performed either under stress or strain control... 

Cyclic, Thermomechanical Tensile Tests of Dual-Shape Polymers. 118... 

Different test procedures have been described in the literature for quantification of an SME. One of the most powerful and widely used test procedures are cyclic, thermomechanical tensile tests. Quantification of the SME by cyclic, thermomechanical tensile tests follows tailored test procedures. These test procedures consist of a programming module, where the temporary shape is created, and a recovery module, where the permanent shape is recovered. The programming module can be performed under stress-controlled or strain-controlled conditions the recovery module can be carried out under stress-free conditions or under constant strain [4, 13]. The combination of certain programming and recovery modules results in different cycle types, which are presented in Table 2. Several thermomechanical... 

Table 2 Definition of cycle types in thermomechanical tensile tests for characterization of the...

Fig. 17 Cyclic, thermomechanical tensile test for quantification of triple-shape effect - two step programming, (a) Strain and temperature as a function of time taken from the fifth cycle for MACL(45) multiphase network composed of crystallizable PCL segments and amorphous poly(cyclohexyl methacrylate) segments with 45 wt% PCL content (rtrans,A = Tm.PCL = 50°C and Ftrans.B = = Fg pcHMA = 140°C). The solid line indicates strain the dashed line indicates tem-...

The microstructures of the consolidated and deformed samples were characterized by X-ray diffraction, optical and electron microscopy (SEM and TEM). The samples for mechanical testing have been prepared by spark erosion. The linear thermal expansion was determined by using a thermomechanical system (TMA). The temperature-dependent elastic moduli have been measured by the resonance frequency and the pulse-echo method. The bulk moduli were determined by synchrotron radiation diffraction using a high-pressure diamond-die cell at HASYLAB. The compression and creep tests were performed with computer-controlled tensile testing and creep machines. 

Fig. 5.37 Tensile test results for longitudinal microspecimens in friction stir welded 7349-T6. HAZ, heat-affected zone TMAZ, thermomechanically affected zone WN, weld nugget Source Ref 83...

Fig. 8.1 2 The mechanical properties for the stir zone in Fig 8.11, showing the distribution of (a) yield strength, (b) tensile strength, and (c) ductility for tensile test coupons aligned with the local longitudinal axis for the multipass raster pattern. Exceptional strength/ductility combinations are achieved near the plate surface, although low dii tTt apparent in the thermomechanically affected zone under the stir...

Figure 2. Thermomechanical analysis of tensile test on paper inmpregnated with different types of low molecular weight lignins displacement as a function temperature. Standard is the displacement obtained with non-impregnated paper used as a control.

Triple-shape polymers can change on demand from a first shape (A) to a second shape (B) and from there to a third shape (C), when stimulated by two subsequent temperature increases [10, 26, 27]. Specific cyclic, thermomechanical tensile experiments were developed to characterize the triple-shape effect (Chapter Shape-Memory Polymers and Shape-Changing Polymers [101] and Sect. 2.2) quantitatively. Analogous to the experiments for dual-shape materials, each cycle of these tests consisted of a programming and a recovery module. A cycle started with creating the two temporary shapes (B and A) by a two-step uniaxial deformation, followed by the recovery module, where shape (B) and finally shape (C) were recovered. 

Fig. 8 Effect of EN and EL loading, respectively, on stress-strain curves in strain-controUed cyclic thermomechanical experiments in air (a), shape-recovery curves upon heating in stress-controUed experiments (b), and stress-strain curves in tensile tests (c). Figures from [39], Copyright 2009, with permission from the Material Research Society...

First, the shape memory effect (SME) was quantified via the set of thermomechanical cychc tensile tests mentioned above. Figme 2.7 shows the SME of the segmented polyurethanes with varying HSC. It can be seen that the shape fixity decreases with an increase of HSC. When HSC < 35%, the shape fixity of the segment is over 94%, while when HSC > 40%, the shape fixity decreases abruptly. 

FIG. 14 Printed circuit board JR-01 used for thermomechanical fatigue testing utilizing the thermal cycling conditions from -40 to 125°C, with 30-min dwell times at the temperature extremes. Testing also included a shear test for chip components, and a tensile pull test for QFP leads. 

Dynamic properties are more relevant than the more usual quasi-static stress-strain tests for any application where the dynamic response is important. For example, the dynamic modulus at low strain may not undergo the same proportionate change as the quasi-static tensile modulus. Dynamic properties are not measured as frequently as they should be simply because of high apparatus costs. However, the introduction of dynamic thermomechanical analysis (DMTA) has greatly widened the availability of dynamic property measurement. 

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