Shape Memory Materials from Rubbers

Smart materials are much discussed in the current research scenario. The shape memory effect is one of the most fascinating occurrences in smart materials, both in terms of the phenomenon and its applications. Many metal alloys and polymers exhibit the shape memory effect (SME). Shape memory properties of elastomers, such as rubbers, polyurethanes, and other elastomers, are discussed in depth in this paper. The theory, factors impacting, and key uses of SME elastomers are all covered in this article. SME has been observed in a variety of elastomers and composites. Shape fixity and recovery rate are normally analysed through thermomechanical cycle studies to understand the effectiveness of SMEs. Polymer properties such as chain length, and the inclusion of fillers, such as clays, nanoparticles, and second phase polymers, will have a direct influence on the shape memory effect. The article discusses these aspects in a simple and concise manner.

Особенности деформации монокристаллов Ni-Fе-Ga-Co, выращенных из расплава методом Степанова

The influence of thermomechanical cycles (compression along the [011] direction and recovery of the shape memory strain upon crystal heating) on the form and characteristics of the compression diagrams of Ni_49Fe_18Ga_27Co_6 alloy crystals not subjected to high-temperature annealing and quenching in water after the growth has been investigated. It is found that these characteristics change during the first nine cycles. Starting from the tenth thermomechanical cycle, they become stable and the deformation properties of the crystals become similar to those of quenched crystals of this alloy. This means that antiphase nanodomains are dispersed by dislocations during the thermomechanical cycling, as a result of which the disordered B _2 crystal structure is transformed into the ordered L 2_1 structure, which is characteristic of quenched crystals.

An Investigation on Thermomechanical Flexural Response of Shape-Memory-Polymer Beams

In this paper, the predictions of different beam theories for the behavior of a shape memory polymer (SMP) beam in different steps of a thermomechanical cycle are compared. Employing the equilibrium equations, the governing equations of the deflection of a SMP beam in the different steps of a thermomechanical cycle, for higher order beam theories (Timoshenko Beam Theory and von-Kármán Beam Theory), are developed. For the Timoshenko Beam Theory, a closed form analytical solution for various steps of the thermomechanical cycle is presented. The nonlinear governing equations in von-Kármán Beam theory are numerically solved. Results reveal that in the various beam length to beam thickness ratios, one of the beam theories provides the most accurate results. In other words, employing the Euler–Bernoulli Beam Theory for developing the governing equations, especially in the large and small beam length to beam thickness ratios, leads to erroneous results.

Interaction of V, Al, and N in Microalloyed Forging Steels after Hot Deformation

A medium-carbon V-microalloyed steel (38MnSiVS5) with three different Al levels (0.006, 0.020, and 0.031 wt pct) was used to examine the interaction of V, Al, and N after hot deformation. A complete thermomechanical cycle was simulated in the laboratory using a Gleeble® 1500. Specimens were heated to a soaking temperature that varied from 1100 to 1250 °C for 5 or 45 min and control cooled to 1000 °C in 6 min, where they were compressed to 40 pct reduction at a strain rate of 1.0 s-1. After compression, the specimens were control cooled to 500 °C at 0.25 °C·s-1 and die quenched to room temperature. Additional specimens were processed without the compression step for comparison. The thermal and thermomechanically processed specimens were characterized by quantitative metallography and microhardness testing. The thermomechanically processed specimens with 0.006 wt pct Al maintained their hardness while reducing pearlite fraction by approximately 10 pct. The thermomechanical processed specimens with 0.020 and 0.031 wt pct Al showed a significant drop in microhardness and pearlite fractions, as compared to the thermal only processed specimens. The decrease in microhardness and pearlite fraction for the two higher-Al–containing alloys in both the thermal and thermomechanically processed specimens appears to follow the same linear trend, suggesting that AlN precipitation reduces the amount of N in solid solution, lowers the temperature at which V(C,N) precipitation occurs, and effectively reduces such strain-induced precipitation.

Microstructure Evolution and Microstructure-Property Relationships in Friction Stir Processing of NiAl Bronze

Friction stir processing (FSP) has been employed for localized modification and control of microstructures in NiAl bronze materials, which are widely utilized for marine components. The thermomechanical cycle of FSP results in homogenization and refinement and the conversion of microstructures from a cast to a wrought condition within stir zones in the material. However, the direct measurement of stir zone temperatures, strains, strain rates and cooling rates is difficult due to steep gradients and transients in these quantities, and this is an impediment in the assessment of FSP-induced microstructures and properties. Quantitative microstructure analyses following FSP of cast NiAl bronze materials have been used to develop estimates of stir zone thermomechanical cycles. The estimation procedures will be reviewed and the microstructure-based estimates will be compared to results from computational models and embedded thermocouples measurements. Stir zone microstructures comprise a mixture of primary α grains and transformation products of the β that formed during processing. Recrystallization in the primary α occurred due to particle-stimulated nucleation in this low stacking fault energy material. Factors that influence the distribution of strength and ductility in the stir zone appear to include the mixture of microstructure constituents and gradients in microstructure due to gradients in processing conditions.

Enhancement of Ductility and Strength through Microstructural Refinement by FSP of Nickel Aluminum Bronze

Friction stir processing (FSP) is a severe plastic deformation (SPD) method that has been applied to as-cast NiAl bronze (NAB) materials, which are widely used for marine components. The thermomechanical cycle of FSP results in homogenization and refinement, and the selective conversion of microstructures from a cast to a wrought condition. The physical metallurgy of NAB is complex and interpretation of the effects of FSP on microstructure has required detailed analysis by optical and electron microscopy methods. Annealing and isothermal hot rolling have been employed to confirm microstructure-based estimates of stir-zone peak temperatures. The variation of mechanical properties was assessed by use of miniature tensile samples and correlated with microstructure for samples from stir zones of single and multi-pass FSP. Exceptional improvement in strength – ductility combinations may be achieved by FSP of NAB materials.

Anisotropy of Cu-Based Shape Memory Alloys In Tension/Compression Thermomechanical Loads

Tension/compression thermomechanical experiments were performed on oriented CuAlNi shape memory alloy single crystals and CuAlZnMn single and polycrystals. Response of the single crystals in thermomechanical loads was strongly anisotropic, dependent on the orientation of the load axis and sense of the load. Tension/compression stress-temperature diagrams were constructed from experimentally determined transformation stresses and temperatures. It was shown that the history dependent strain response of the single crystal in a complex tension/compression thermomechanical cycle could be predicted from the diagram. Thermomechanical behaviors of the CuAlZnMn polycrystal under tension/compression were reported and discussed on the basis of the knowledge of the single crystal anisotropy.