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[en] Deficiencies in practical applications for magnetic shape memory actuators motivated the authors to start experimental and theoretical research in the field of multifunctional materials. The authors present the concept of using magnetic shape memory actuators for controlling, altering and tuning the forced vibration of a rotor. The main goal of their experimental research is to show how the activation of magnetic shape memory actuators can influence the forced vibration responses of a rotor in terms of altering and tuning selected rotor natural frequencies and modes of vibrations. Experimental results show that magnetic shape memory actuators can be successfully applied for vibration reduction and vibration control in the case of rotor systems
[en] We report two approaches to realize the triple-shape memory effect (SME), i.e., returning to the original shape from the temporary shape through one intermediate shape in a gradual/step-by-step heating induced recovery, in NiTi shape memory alloys (SMAs). In the programming process (which is to fix the temporary shape) in both approaches, the deformation is uniform throughout the whole length of the SMA samples without introducing any permanent change in the material properties. The requirements/conditions for this phenomenon and the underlying mechanisms are presented, together with experimental verifications. As revealed, with this technique, we are now able to achieve ‘the material is the machine’ for well controlled multi-positional maneuvers in SMAs. (paper)
[en] Shape memory polymers (SMPs) have attracted significant research efforts due to their ease in manufacturing and highly tailorable thermomechanical properties. SMPs can be temporarily programmed and fixed in a nonequilibrium shape and are capable of recovering the original undeformed shape upon exposure to a stimulus, the most common being temperature. Most SMPs exhibit a one-way shape memory (1W-SM) effect since one programming step can only yield one shape memory cycle; an additional shape memory cycle requires an extra programming step. Recently, a novel SMP that demonstrates both 1W-SM and two-way shape memory (2W-SM) effects was demonstrated by one of the authors (Mather). However, to achieve two-way actuation this SMP relies on a constant externally applied load. In this paper, an SMP composite where a pre-stretched 2W-SMP is embedded in an elastomeric matrix is developed. This composite demonstrates 2W-SM effects in response to changes in temperature without the requirement of a constant external load. A transversal actuation of ∼ 10% of actuator length is achieved. Cyclic tests show that the transversal actuation stabilizes after an initial training cycle and shows no significant decreases after four cycles. A simple analytic model considering the programming stress and actuator dimensions is presented and shown to agree well with the transverse displacement of the actuator. The model also predicts that larger actuation can be achieved when larger pre-stretch of 2W-SMP is used. The scheme used for this polymer composite can promote the design of new shape memory composites at micro- and nano-length scales to meet different application requirements
[en] We consider a model of shape memory materials in which hierarchical twinning near the habit plane (austenite-martensite interface) is a new and crucial ingredient. The model includes (1) a triple-well potential (φ6 model) in local shear strain, (2) strain gradient terms up to second order in strain and fourth order in gradient, and (3) all symmetry allowed compositional fluctuation-induced strain gradient terms. The last term favors hierarchy which enables communication between macroscopic (cm) and microscopic (A) regions essential for shape memory. Hierarchy also stabilizes tweed formation (criss-cross patterns of twins). External stress or pressure modulates (''patterns'') the spacing of domain walls. Therefore the ''pattern'' is encoded in the modulated hierarchical variation of the depth and width of the twins. This hierarchy of length scales provides a related hierarchy of time scales and thus the possibility of non-exponential decay. The four processes of the complete shape memory cycle-write, record, erase and recall-are explained within this model. Preliminary results based on 2D molecular dynamics are shown for tweed and hierarchy formation. (orig.)
[en] Amorphous melt spun ribbons of Ti50Ni25Cu25 and Ti40.7Hf9.5Ni44.8Cu5 alloys were partially crystallized to different volume fractions of the crystalline phase from 0 to 100%. The mechanical and functional properties of amorphous–crystalline thin ribbons were studied. It was shown that the fully amorphous sample of Ti50Ni25Cu25 alloy was deformed elastically up to 2.2% and then it was deformed plastically up to breaking. The fully amorphous sample of Ti40.7Hf9.5Ni44.8Cu5 alloy was deformed elastically up to failure and plastic deformation was not observed. It was found that amorphous–crystalline samples demonstrated the shape memory effect on heating. The maximum recovered strain was 3.3% in fully crystallized Ti50Ni25Cu25 alloy and it attained 5% in Ti40.7Hf9.5Ni44.8Cu5 alloy. The Ti40.7Hf9.5Ni44.8Cu5 alloy demonstrated the two-way shape memory effect if the amorphous and crystalline phases co-existed in the sample. (fast track communication)
[en] This paper concerns 3D phenomenological modeling of shape memory alloys using microplane theory. In the proposed approach, transformation is assumed to be the only source of inelastic strain in 1D constitutive laws considered for any generic plane passing through a material point. 3D constitutive equations are derived by generalizing the 1D equations using a homogenization technique. In the developed model, inelastic strain is explicitly stated in terms of the martensite volume fraction. To compare this approach with incremental constitutive models, such an available model is applied in its 1D integral form to the microplane formulation, and it is shown that both the approaches produce similar results for different uniaxial loadings. A nonproportional loading is then studied, and the results are compared with those obtained from an available model in which the inelastic strain is divided into two separate portions for transformation and reorientation. A good agreement is seen between the results of the two approaches, indicating the capability of the proposed microplane formulation in predicting reorientation phenomena in shape memory alloys. The results of the model are compared with available experimental results for a nonproportional loading path, and a good agreement is seen between the findings. (paper)
[en] Carbon-fiber-reinforced (CFR) and shape-memory polymer (SMP) composites have been manufactured by molding commercial prepregs used for aeronautical structures. These prepregs typically do not show any shape memory behavior as they consist of CF fabrics impregnated with high performance epoxy resins. In the current study, shape memory (SM) properties have been added by using uncured SMP interlayers during the prepreg lamination, and following co-curing of the laminate layers. A new test has been adopted to quantify SM properties of final CFR-SMP laminates. A full thermo-mechanical cycle is applied to the composite samples during bending and shape fixity, shape recovery and frozen stresses data are extracted. By means of this test, the effect of the number of plies on the SM behavior of composite laminates has been studied. Furthermore, dynamic mechanical analysis and dimensional observations have been carried out to understand the physical phenomena at the basis of the laminate behavior. Results show that manufacturing of CFR-SMP composites is feasible also by using available commercial products, and final laminates are able to combine strength and stiffness of traditional aeronautical composites with the functionality of SMP materials. (paper)
[en] Highlights: • Available elastic polymeric shape memory polymers at present are revealed. • Potential applications in comfort fitting are demonstrated. • We may utilize the shape memory effect to realize one size-for-all in a cost effective manner. In this paper, we briefly review the recent progress in comfort fitting using elastic polymeric shape memory materials (SMMs). First, the required features on elastic SMMs for comfort fitting are discussed. A few types of polymeric SMMs (including some commercially available ones), which have these features, are presented. A number of prototypes made of these SMMs are used to demonstrate the feasibility to achieve the concept of comfort fitting in a one-for-all manner, i.e., one sized product to comfort fit any individuals.
[en] The review concerns the state-of-the-art in the field of investigations of the shape memory effect in various polymeric materials, namely, homopolymers, copolymers, polymer blends, filled polymer composites and polymer gels. New theoretical approaches to the description and practical applications of the shape memory effect are discussed.