Prestressing Effect of Shape Memory Alloy Reinforcements Under Serviceability Tensile Loads

Repairing and strengthening of existing aged steel-reinforced concrete structures is a major challenge. Today, much of the repair work completed is insufficient and brittle. A promising new solution for repair and strengthening tasks is the use of iron-based shape memory alloy (Fe-SMA). The pre-strained Fe-SMA components enable the pre-stressing of existing building components due to the heat-triggered contraction of the steel. Thus, deflections can be reduced or even recovered. In addition, the cracking process can be adapted, and an improvement in the load, under which the first crack appears, is possible. In this paper, the effects of pre-stress generated by activated Fe-SMA rebars, which were centrally embedded inside of a concrete specimen, are shown. The objective of the study is to quantify the improvement in the loads of the first crack and show the influences of the pre-stressing on the load-bearing behavior and the cracking process. For this purpose, axial tensile tests were performed on concrete bars with height, width, and length of 50 mm, 70 mm, and 900 mm, respectively. These were compared to usual construction steel rebars, pre-strained but nonactivated Fe-SMA rebars, and activated Fe-SMA steel rebars. The evaluation of crack patterns and openings was done using digital image correlation (DIC). The pre-stressing of the concrete causes an increase in the first crack loads of more than 150%, which indicates a clear improvement in the state of serviceability limit.

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Effect of Crystallographic Orientation and Grain Boundaries on Martensitic Transformation and Superelastic Response of Oligocrystalline Fe–Mn–Al–Ni Shape Memory Alloys

Shape Memory and Superelasticity ◽

10.1007/s40830-021-00340-3 ◽

2021 ◽

Author(s):

A. Bauer ◽

M. Vollmer ◽

T. Niendorf

Keyword(s):

Martensitic Transformation ◽

Grain Boundary ◽

Shape Memory Alloys ◽

Shape Memory ◽

Grain Boundaries ◽

Tensile Tests ◽

Image Correlation ◽

Stress Concentrations ◽

Grain Orientations ◽

High Degree

AbstractIn situ tensile tests employing digital image correlation were conducted to study the martensitic transformation of oligocrystalline Fe–Mn–Al–Ni shape memory alloys in depth. The influence of different grain orientations, i.e., near-〈001〉 and near-〈101〉, as well as the influence of different grain boundary misorientations are in focus of the present work. The results reveal that the reversibility of the martensite strongly depends on the type of martensitic evolving, i.e., twinned or detwinned. Furthermore, it is shown that grain boundaries lead to stress concentrations and, thus, to formation of unfavored martensite variants. Moreover, some martensite plates seem to penetrate the grain boundaries resulting in a high degree of irreversibility in this area. However, after a stable microstructural configuration is established in direct vicinity of the grain boundary, the transformation begins inside the neighboring grains eventually leading to a sequential transformation of all grains involved.

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Deformation Behavior of a Shape Memory Alloy: Nitinol

Volume 1: Advanced Energy Systems; Advanced and Digital Manufacturing; Advanced Materials; Aerospace ◽

10.1115/esda2008-59187 ◽

2008 ◽

Author(s):

Samantha Daly ◽

Kaushik Bhattacharya ◽

Guruswami Ravichandran

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Rolling Texture ◽

Image Correlation ◽

Space Applications ◽

Deformation And Failure ◽

Full Field ◽

New Information ◽

Macro Scale ◽

First Time

Nickel-Titanium, commonly referred to as Nitinol, is a shape-memory alloy with numerous applications due to its superelastic nature and its ability to revert to a previously defined shape when deformed and then heated past a set transformation temperature. While the crystallography and the overall phenomenology are reasonably well understood, much remains unknown about the deformation and failure mechanisms of these materials. These latter issues are becoming critically important as Nitinol is being increasingly used in medical devices and space applications. The talk will describe the investigation of the deformation and failure of Nitinol using an in-situ optical technique called Digital Image Correlation (DIC). With this technique, full-field quantitative maps of strain localization are obtained for the first time in thin sheets of Nitinol under tension. These experiments provide new information connecting previous observations on the micro- and macro-scale. They show that martensitic transformation initiates before the formation of localized bands, and that the strain inside the bands does not saturate when the bands nucleate. The effect of rolling texture, the validity of the widely used resolved stress transformation criterion, and the role of geometric defects are examined.

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Effect of Aging on Mechanical Properties of Ti-Mo-Al Biomedical Shape Memory Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.654-656.2150 ◽

2010 ◽

Vol 654-656 ◽

pp. 2150-2153 ◽

Cited By ~ 6

Author(s):

Hideki Hosoda ◽

Makoto Taniguchi ◽

Tomonari Inamura ◽

Hiroyasu Kanetaka ◽

Shuichi Miyazaki

Keyword(s):

Mechanical Properties ◽

Shape Memory Alloy ◽

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

Shape Recovery ◽

Tensile Tests ◽

Single Step ◽

Two Phase ◽

Solution Treated

Effects of single- and multi-step aging on mechanical properties and shape memory properties of Ti-6Mo-8Al (mol%) biomedical shape memory alloy were studied using tensile tests at room temperature (RT). The solution-treated alloy at RT was two phase of bcc β and martensite α". Tensile tests revealed that the solution-treated alloy exhibited good shape memory effect. As for the single-step aging, (1) pseudoelastic shape recovery by unloading was observed after aging at 623K, (2) the alloy became brittle after aging at 773K due to ω embrittlement, and (3) strength was improved with small shape memory effect by aging at 1023K. On the other hand, after a multistep aging at 773K-1023K-1123K, the alloy was strengthened and showed perfect shape recovery. The improvement must be achieved by the formation of fine and uniform hcp α precipitates.

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Thermomechanical effects on phase transformations in single-crystal Cu–Al–Ni shape-memory alloy

Journal of Materials Research ◽

10.1557/jmr.2007.0116 ◽

2007 ◽

Vol 22 (4) ◽

pp. 994-1003 ◽

Cited By ~ 8

Author(s):

H.-S. Zhang ◽

K. Komvopoulos

Keyword(s):

Phase Transformation ◽

Shape Memory Alloy ◽

Single Crystal ◽

Shape Memory ◽

Elevated Temperatures ◽

Czochralski Method ◽

Tensile Tests ◽

Transformation Temperatures ◽

Experimental Findings ◽

Cyclic Straining

Single-crystal rods of Cu–Al–Ni shape-memory alloy fabricated from a molten pool of 82 wt% Cu, 14 wt% Al, and 4 wt% Ni by the Czochralski method were first heated to ∼870 °C and then quenched to obtain austenitic microstructures. Various microanalysis techniques were used to determine the chemical composition, microstructure, and phase-transformation temperatures of the produced alloy. Cyclic tensile tests with in situ temperature control demonstrated the occurrence of pseudoelastic deformation at elevated and close to phase-transformation temperatures and provided insight into the temperature dependence of the phase-transformation stress, damping characteristics, and cyclic straining of single-crystal Cu–Al–Ni alloy. The stress hysteresis observed in the pseudoelastic deformation cycles decreased at elevated temperatures. The stress response at different temperatures is associated with the formation, growth, and coalescence of martensite variants. Stress-induced phase-transformation mechanisms, coalescence of twin variants, and energy dissipation by pseudoelastic deformation are discussed in the context of experimental findings. The results illustrate the potential of single-crystal Cu–Al–Ni as a structural material for dynamic microsystems and temperature sensors.

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The low-velocity impact and compression after impact (CAI) behavior of foam core sandwich panels with shape memory alloy hybrid face-sheets

Science and Engineering of Composite Materials ◽

10.1515/secm-2019-0034 ◽

2019 ◽

Vol 26 (1) ◽

pp. 517-530 ◽

Cited By ~ 2

Author(s):

Ye Wu ◽

Yun Wan

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Sandwich Panels ◽

Image Correlation ◽

Low Velocity Impact ◽

Foam Core ◽

Low Velocity ◽

Velocity Impact ◽

Compression After Impact ◽

The Impact

AbstractDue to the properties of shape memory effect and super-elasticity, shape memory alloy (SMA) is added into glass fiber reinforced polymer (GFRP) face-sheets of foam core sandwich panels to improve the impact resistence performance by many researchers. This paper tries to discuss the failure mechanism of sandwich panels with GF/ epoxy face-sheets embedded with SMA wires and conventional 304 SS wire nets under low-velocity impact and compression after impact (CAI) tests. The histories of contact force, absorbed energy and deflection during the impact process are obtained by experiment. Besides, the failure modes of sandwich panels with different ply modes are compared by visual inspection and scanning electron microscopy (SEM). CAI tests are conducted with the help of digital image correlation (DIC) technology. Based on the results, the sandwich panels embedded with SMA wires can absorb more impact energy, and show relatively excellent CAI performance. This is because the SMA wires can absorb and transmit the energy to the outer region of GFRP face-sheet due to the super-elasticity-behavior. The failure process and mechanism of the CAI test is also discussed.

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Shape Memory Alloy Cables for Civil Infrastructure Systems

Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation and Control of Adaptive Systems; Structural Health Monitoring; Keynote Presentation ◽

10.1115/smasis2014-7562 ◽

2014 ◽

Cited By ~ 3

Author(s):

Sherif Daghash ◽

Osman E. Ozbulut ◽

Muhammad M. Sherif

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Mechanical Response ◽

Civil Engineering ◽

Large Diameter ◽

Small Diameter ◽

Image Correlation ◽

Temperature Fields ◽

Uniaxial Tensile ◽

Civil Infrastructure

Shape memory alloys (SMAs) have attracted a great deal of attention as a smart material that can be used in various civil engineering applications due to their favorable mechanical properties such as ability to undergo large deformations, high corrosion and fatigue resistance, good energy dissipating capacity, and excellent re-centering ability. In contrast to the use of SMAs in the biomedical, mechanical and aerospace applications, which requires mostly small diameter of material, the larger size bars are usually needed in a civil engineering application. It is well known that properties of large-section SMA bars are generally poorer than those of wires due to difficulties in material processing. Furthermore, large diameter SMA bars are more expensive than thin SMA wires. Shape memory alloy cables have been recently developed as an alternative and new structural element. They leverage the superior mechanical characteristics of small diameter SMAs into large-size structural tension elements and possess several advantages over SMA bars. This study explores the performance of NiTi SMA cables and their potential use in civil engineering. The SMA cable, which has a diameter of 8 mm, is composed of 7 strands and each strand has 7 wires with a diameter of 0.885 mm. The uniaxial tensile tests are conducted at various loading rates and strain amplitudes to characterize the superelastic properties of the SMA cable and study the rate-dependent mechanical response of the SMA cable under dynamic loads. An optical digital image correlation measurement system and an infrared thermal imaging camera are employed to obtain the full-field strain and temperature fields. Potential applications of SMA cables in civil infrastructure applications are discussed and illustrated.

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Study on Hysteretic Energy Dissipation of SMA Wires, Bars and Plates

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.5339 ◽

2011 ◽

Vol 243-249 ◽

pp. 5339-5342

Author(s):

Ji Gang Zhang ◽

Yan Mei Liu ◽

Jing Jing Zhang ◽

Ke Yong Gao

Keyword(s):

Energy Dissipation ◽

Cyclic Loading ◽

Shape Memory Alloy ◽

Shape Memory ◽

Engineering Application ◽

Tensile Tests ◽

The Other ◽

Test Results ◽

Hysteretic Energy ◽

Better Than

Through tensile tests of shape memory alloy(SMA)wires,bars and plates, this paper analyzes hysteretic energy-dissipating capacities of thesesmartSMA materials in cyclic loading conditions. According to the test results, this article demonstrates the influence on energy dissipating capacity of SMA wires,bars and plates by different strain amplitudes, loading frequencies, cyclic numbers and pre-strains, then obtains change rules of hysteretic energy-dissipation.The test results show that the SMA wires is better than the other two SMA bars and plates, the SMA wires, bars and plates had better to be trainingbefore civil engineering application.

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Bending of Superelastic Shape Memory Alloy Tubes

ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Volume 1 ◽

10.1115/smasis2011-4906 ◽

2011 ◽

Author(s):

Benjamin Reedlunn ◽

Christopher Churchill ◽

Emily Nelson ◽

Samantha Daly ◽

John Shaw

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Mechanical Response ◽

Surface Displacement ◽

Beam Theory ◽

Image Correlation ◽

Reasonable Assumption ◽

Significant Shift ◽

Localized Deformation ◽

Tension And Compression

Many shape memory alloy (SMA) applications exploit superelasticity in a bending mode, yet the large displacements and rotations associated with bending of slender structures make controlled experiments difficult. A custom pure bending fixture was built to perform experiments on superelastic NiTi tubes. To understand the bending results, the tubes were also characterized in uniaxial tension and compression, where a custom fixture was utilized to avoid buckling. In addition to measuring the global mechanical response, stereo digital image correlation (DIC) was used in all the experiments to capture the local surface displacement and strain fields. Consistent with the tension/compression data, our bending experiments showed a significant shift of the neutral axis towards the compression side. Also, the tube had strain localization on the tension side, but no such localization on the compression side. Detailed analysis of the strain distribution across the tube diameter revealed that the usual assumption of beam theory, that plane sections remain plane, did not hold along the tension side. Averaged over a few diameters of gage length, plane sections remain plane is a reasonable assumption and can be used to predict the global moment–curvature response. However, this assumption should be used with caution since it can under/over predict local strains by as much as 2× due to the localized deformation morphology.

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Sustainable mineral coating of alkali-resistant glass fibres in textile-reinforced mortar composites for structural purposes

Journal of Composite Materials ◽

10.1177/0021998319855765 ◽

2019 ◽

Vol 53 (28-30) ◽

pp. 4203-4213 ◽

Cited By ~ 6

Author(s):

Cesare Signorini ◽

Andrea Nobili ◽

Cristina Siligardi

Keyword(s):

Mechanical Performance ◽

Sol Gel ◽

Mineralogical Composition ◽

Tensile Tests ◽

Image Correlation ◽

Axial Tensile ◽

Nano Coating ◽

Bonding Properties ◽

Textile Reinforced Composite

The mechanical performance of a silica-based mineral nano-coating applied to alkali-resistant glass textile-reinforced composite materials aimed at structural strengthening is investigated experimentally. The silica nano-film is directly applied to the alkali-resistant glass fabric by sol–gel deposition. Two lime mortars are adopted as embedding matrix, which differ by the ultimate compressive strength and elongation. Uni-axial tensile tests of prismatic coupons are carried out according to the ICC AC434 guidelines. Remarkable strength and ductility enhancements could be observed in the silica-coated group, as compared to the uncoated group, for both mortar types. Digital image correlation, electron scanning and optical microscopy provide evidence of improved interphase strength. X-ray diffraction of the anhydrous mortars brings out the role of the mineralogical composition of the embedding media on the overall bonding properties of the composites. Consideration of design limits and energy dissipation capabilities reveals the crucial role of matrix ductility in bringing the contribution of interphase enhancement to full effect. We conclude that best performance requires optimizing the pairing between fabric-to-matrix adhesion and matrix ductility.

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