Stimulus-responsive shape memory materials: A review

This study evaluates the properties of superelastic Ni.Ti shape memory alloys under cyclic loading to assess their potential for applications in seismic resistant design and retrofit. Shape memory alloy wire and bars are tested to evaluate the effect of bar size and loading history on the strength, equivalent damping, and recentering properties of the shape memory alloys in superelastic form. The bars are tested under both quasistatic and dynamic loading. The results show that nearly ideal superelastic properties can be obtained in both wire and bar form of the superelastic Ni.Ti shape memory alloys. However, the wire form of the shape memory alloys show higher strength and damping properties compared with the bars. The recentering capabilities (based on residual strains) are not affected by section size. Overall, the damping potential of shape memory alloys in superelastic form is low for both wire and bars, typically less than 7% equivalent viscous damping. Cyclical strains greater than 6% lead to degradation in the damping and recentering properties of the shape memory alloys. Strain rate effects are evaluated by subjecting the shape memory alloys to loading rates representative of typical seismic loading. The results show that increased loading rates lead to decreases in the equivalent damping, but have negligible effects on the recentering properties of the shape memory alloys.

Cyclic properties of superelastic shape memory alloy wires and bars

It is 100 years since the well-know Mohr-Coulomb strength theory was established in 1900. A considerable amount of theoretical and experimental research on strength theory of materials under complex stress state was done in the 20th Century. This review article presents a survey of the advances in strength theory (yield criteria, failure criterion, etc) of materials (including matellic materials, rock, soil, concrete, ice, iron, polymers, energetic material, etc) under complex stress, discusses the relationship among various criteria, and gives a method of choosing a reasonable failure criterion for applications in research and engineering. Three series of strength theories, the unified yield criterion, the unified strength theory, and others are summarized. This review article contains 1163 references regarding the strength theories. This review also includes a biref discussion of the computational implementation of the strength theories and multi-axial fatigue.

Advances in strength theories for materials under complex stress state in the 20th Century

Electrochemical studies on the stability and corrosion resistance of titanium-based implant materials.

Ratchetting under tension–torsion loadings: experiments and modelling

Uniaxial tensile tests on Ti−Ni alloy wire under cyclic loading and unloading were carried out. The influences of maximum strain, test temperature, and shape memory processing temperature upon the cyclic characteristics of pseudoelasticity were examined

Cyclic characteristics of pseudoelasticity of Ti-Ni alloys (effect of maximum strain, test temperature and shape memory processing temperature)

Particle to liquid mass transfer in a rotating catalyst basket reactor

Cyclic Characteristics of the Shape Memory Effect in Ti-Ni Alloy Wires and Helical Springs

S ome characteristics of strain-induced anisotropy and effects of strain-rate on them are experimentally investigated under non-proportional loadings at elevated temperature By applying combined loadings of axial force and internal pressure to thin-walled tubes of an aluminium alloy at 200°C, inelastic stress-responses are observed at several constant strain-rates along bilinear strain trajectories It is found that a softening of material and a non-coaxiality between stress and inelastic strain-increment deviators occur after the corner of bilinear strain trajectory These phenomena appear more markedly and then decay more gradually with the increase of corner angle and/or strain-rate Experimental results are qualitatively discussed in terms of the activation of piled-up dislocations as well as the so-called back stress and drag stress

Inelastic stress-responses of an aluminium alloy in non-proportional deformations at elevated temperature

The hypothesis of local determinability proposed by V.S. Lensky was experimentally confirmed to hold with high accuracy on a curved part of strain path. That is, a rate dθ/ds (θ is a difference between directions of stress and strain increment vectors, and s is a length of strain path) depends only on the current values of θ(s) and curvature K(s) of strain path. Experiments were performed along some strain paths with two circular parts in a two-dimensional space of strain, by applying combined loads of axial force and torque to thin-walled tubular specimens of initially isotropic brass. A simple stress-strain relation which reflects the curvature effect was formulated by using the hypothesis for a practically important set of strain paths with intermediate curvature.

Yoshio Ohashi

Papers

Cyclic characteristics of pseudoelasticity of Ti-Ni alloys (effect of maximum strain, test temperature and shape memory processing temperature)

Particle to liquid mass transfer in a rotating catalyst basket reactor

Cyclic Characteristics of the Shape Memory Effect in Ti-Ni Alloy Wires and Helical Springs

Inelastic stress-responses of an aluminium alloy in non-proportional deformations at elevated temperature

On the Hypothesis of Local Determinability and a Concise Stress-Strain Relation for Curved Strain Path