Strain cycles, composites with

A series of six stress-strain cycles with a crosshead rate of 600 mm/min was applied to specimens having a parallel length of 25 mm and a cross-section of 1 x 4 mm2 on a tensile testing machine. The samples were continuously stretched in six hysteresis cycles up to 60% of their elongation at break values, as shown in Fig. 47. This procedure is an established one and widely practiced for elastomeric composites reinforced with fillers such as carbon black and silica, which tend to build a strong filler-filler network [83]. 

Figure 13. The composites were reinforced with 20 wt % filler and prepared by freeze-drying method (a) SSF composite (b) CB composite. Only T and o strain cycles are shown. R indicates the recovery curve after the samples were conditioned at 140 for 24 hours. Measured at 1 Hz and 140 C. (Reproducedfrom reference 28.)...

The close relation between the composition and the mechanical properties of these polymers is reflected in the stress-strain diagrams measured at 300 K and 348 K (Figs. 47 and 48). Hence, at ambient temperature for the spedfied experimental conditions a distinct increase of initial modulus (11. 45 and 1 MNm ), stress-hysteresis (ratio of area bounded by a strain cycle to the total area underneath the elongation curve 60,80 and 90 %) and extension set (30,65 and 100 %) can be obsened with increasing hard segment content of polyester urethane (a) to (c). 

To solve the decrepitation problem, several electrode morphologies and architectures have been explored to accommodate the strain and allow the volume changes to occur without subsequent pulverization. Electrodes composed of micron- and nano-sized particles,thin films,submicrometer pillars, " 3-D porous structures, and various composite anodes have all been explored. It was soon realized that thin films of silicon could accommodate the volume change and be cycled reversibly with little capacity fade, for example, 50 nm thick Si displayed capacities of 3600 mAh/g for 200 cycles. However, these structures fail when the film thickness increases, and also do not have enough active material for a viable battery. These thin film electrodes also critically rely on roughened substrates upon which the vacuum deposited Si can form a quasi-three-dimensional film with columnar-like structures, which can more easily accommodate the lithiation-induced strain and allow the volume expansion compared with a truly planar film. 

Fig. 47 Typical stress-strain curves of PTFE-based chloroprene composites. The first six hysteresis cycles are shown with solid lines. The seventh curve (dotted line) was investigated using an optical method...

Figure 14. Strain-to-failure versus number of cycles for two types of MEAs one with a reinforced composite membrane (Gore-5510) and the other with regular PFSA membrane (N- 111). The samples are cycled from 30 to 80% RH and from 80 to 120% RH.37...

FIGURE 12.11 Improvements of the mechanical properties of three-dimensional reinforced CMCs by hybrid infiltration routes (a) R.T. flexural stress-strain plots for a three-dimensional carbon fiber reinforced composite before and after cycles of infiltration (comparison between eight cycles with zirconium propoxide and fonr cycles pins a last infiltration with aluminum-silicon ester (b) plot of the mechanical strength as a fnnction of the final open porosity for composites and matrix of equivalent porosity, before and after infiltration (Reprinted from Colomban, R and Wey, M., Sol-gel control of the matrix net-shape sintering in 3D reinforced ceramic matrix composites, J. Eur. Ceram. Soc., 17, 1475, 1997. With permission from Elsevier) (c) R.T. tensile behavior (d) comparison of the R.T. mechanical strength after thermal treatments at various temperatures. (Reprinted from Colomban, R, Tailoring of the nano/microstructure of heterogeneous ceramics by sol-gel routes, Ceram. Trans., 95, 243, 1998. With permission from The American Ceramic Society.)... 

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