Shape fixity rate

Shape fixity rate in air (Rf) and water (/ f,H2o) describes the capability of a sample to remain in its programmed shape. Programming was conducted with cooling rates of 10Kmin (air) and 2 K min (water)... 

Strained silicon wafers, in scaling to deep submicron dimensions, 22 256 Strainers, in refrigeration systems, 27 539 Strain fixity rate (R ), in testing shape-memory polymers, 22 361... 

Table 1 Shape fixity and shape recovery rates for thermally and magnetically-induced SME under stress-free condition for TXF and PDC nanocomposites with ditferent nanoparticle contents for the first cycle. Adapted with permission from ref. [85]. Copyright 2006, National Academy of Sciences, U.S.A. ...

The strain fixity rate R describes the ability of the switching segment to fix the mechanical deformation which has been applied during the programming process. It describes how exactly the sample can be fixed in the stretched shape after a deformation to m- The resulting temporary shape u(.N) always differs from the shape achieved by deformation. 

Nanofibres have been successfully electrospun from SMPU solutions by different people. The structures had ultrafine diameters in a range of 50 nm to 2 xm. Uniform nanofibres can be prepared by adjusting applied voltage, concentration and feeding rate. In particular, the concentration plays a key role in controlling its diameters. The cycUc tensile test proves that the resulting nanofibres have good SME 98% shape recovery and 80% shape fixity can be obtained after several cycles. ... 

Some holes appear on the surface of fibers that are treated at 80°C (Figs 11.20 to 11.24), and this distortion is one of the reasons for the reduction of shape fixity ratios in specimens after a high temperature treatment. When this is combined with the FT-IR results, it supports the argument that high temperature and humidity conditions will increase the decomposition rate of PB A-based fibers, and reduce shape fixity ratios. 

Tensile tests were performed (ASTM D 882) at room temperature and at 60°C using Instron 4204 machine equipped with a heating chamber. Shape memory properties were evaluated as follows Samples were stretched at 60°C and a strain rate of 50 mm/min to predefined stretching ratios of 30%, 60% and 100%. Upon completion of stretching, samples were cooled down quickly to room temperature with the aid of a fan. Shape fixity was calculated from the values of sample lengths before and after stretching. Shape recovery test was conducted using a smaller sample cut from the middle section of the stretched specimen. The recovery stress was obtained from the peak value of stress vs. time... 

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