Shape Memory Alloy Strips Research Articles

Effect of elevated temperature on the bond behaviour of adhesive shear joints between glass substrate and iron-based shape memory alloy strip

Glass has been increasingly used as structural elements, such as glass beams or fins. Previous feasibility studies have shown increased initial and post-fracture load-bearing capacity of laminated glass beams post-tensioned with adhesively bonded iron-based shape memory alloy (Fe-SMA) strips. However, the potential elevated service temperatures were not considered, which significantly degraded the material properties of the adhesive. This study experimentally investigated the mechanical behaviour of Fe-SMA-to-glass lap-shear joints with an epoxy adhesive at different temperatures of 23 °C, 50 °C, and 80 °C, representing room temperature and typical elevated service temperatures. The results showed that, compared with the one at room temperature, the load-carrying capacity remained nearly unchanged at 50 °C and decreased by approximately 20% at 80 °C. On the contrary, the effective bond length increased from approximately 116mm to 250-300mm. The failure modes, the tensile strain of the iron-based shape memory alloy, the bond-slip behaviour, and the fracture energy of the joints were also evaluated. The current study fills a significant research gap in the engineering application of strengthening glass structures by bonded pre-stressed Fe-SMA strips. Moreover, the results may also significantly contribute to the future application of the selected adhesive at elevated temperatures.

Shear strengthening and damage control effects of CFRP and self-prestressing iron-based SMA for concrete columns

Although prestressed shape memory alloy (SMA) has shown a great performance in flexural retrofitting of slender RC columns, its shear strengthening effect for squat RC columns has been barely studied. This study explores the shear strengthening and damage control effects of iron-based SMA (Fe SMA) for squat RC columns. The heat-activated prestressing of Fe SMA was evaluated first at material level, then applied to component level structural testing of RC columns. The four circular RC columns with different retrofitting schemes were tested under quasi-static lateral cyclic loading. The specimens strengthened with carbon fiber-reinforced polymer (CFRP) sheet and Fe SMA strip exhibited satisfactory global responses without showing significant shear failure. From the visual inspection and non-destructive damage assessment, the prestressed Fe SMA was found to be superior in delaying damage accumulation in concrete compared to CFRP.

Shear strengthening of damaged reinforced concrete beams with iron-based shape memory alloy (Fe-SMA) strips: numerical and parametric analysis

Shape memory alloys (SMAs) are metallic materials that are characterized by their ability to restore their original shape after large deformation when activated by heating. This unique property renders SMAs appealing for various civil engineering applications. Iron-based SMAs (Fe-SMAs), including alloys like Fe–Mn–Si, stand out due to their cost-effectiveness and high strength. The primary focus of this research lies in the computational modeling of Fe-SMA strips utilized to reinforce damaged concrete structures. To achieve this, details from an experimental test are leveraged for the computational simulation of real-scale reinforced concrete beams that were first loaded to some level of damage, then released and strengthened, and subsequently retested. The strengthening approach involves the application of external Fe-SMA strips wrapping around the beams. This paper presents an original computational modeling setup that incorporates a switch option for the Fe-SMA material. This feature enables one to use a single simulation platform for the whole process. The significance of this method originates from its capacity to ensure a robust analysis that includes all simulation steps-testing unstrengthened beams, installing and heating Fe-SMA strips, and testing both damaged and strengthened beams—in a single, multi-step analysis. The computational simulation results were compared with the outcomes of the experimental test, revealing an acceptable level of agreement. The findings indicate a substantial increase in both shear strength and ductility as a result of the application of Fe-SMA strips. Additionally, parametric and mesh sensitivity studies were conducted. These aimed to investigate the mesh dependency of the model and to identify the optimal mesh size. Furthermore, variations in the details of the Fe-SMA strips, including thickness, width, quantity, and effect of applied temperature were explored to compare the outcomes of different applications of these strips.

Experimental investigation on anchoring and bonding properties between Fe-SMA strip and concrete

In the technical system of the previous investigations, the prevalent method for external prestressed strengthening of concrete structures with iron-based shape memory alloy (Fe-SMA) strips is mechanical anchoring (without bonding). However, there is currently a lack of research on the adhesively bonded situation. In order to enhance the comprehension of the mechanical behavior of Fe-SMA/concrete joints, a total of 18 lap-shear test specimens were meticulously prepared, encompassing three distinct anchorage methods (single anchor-bolt anchorage, single-adhesive anchorage, and hybrid anchorage). The test series encompasses three varying bond lengths (300 mm, 350 mm, and 400 mm), three different activation temperatures (non-activated state, 200 ℃, and 300 ℃), as well as three diverse numbers of anchor bolts (1 bolt, 2 bolts, and 3 bolts). The bond-slip relationship before and after thermal activation was analyzed based on the data obtained from digital image correlation (DIC) tests. The results indicated that two or more anchors ensured strip rupture, exerting 40 % of its tensile strength. Single-adhesive bonding results highlighted the necessity for preventing debonding. The hybrid-anchorage method with anchor bolts and adhesive exerted 47 % strip strength and higher bond-slip stiffness. At 200 ℃ activation temperature, the interface rupture energy of the single-adhesive bonded specimen increased by approximately 30 %, but decreased by 22 % at 300 ℃. This paper provided an important reference for external prestressed strengthening of concrete structures with Fe-SMA strips under different situations.

Fully bonded iron-based shape memory alloy for retrofitting large-scale bridge girders: Thermal and mechanical behavior

This study presents a prestressed retrofitting solution for addressing fatigue issues in large-scale steel girders, employing iron-based shape memory alloy (Fe-SMA) strips and adhesive bonding. A comprehensive study encompassing design, experimental tests, and numerical analysis is conducted to develop and validate the proposed solution. A 4200×100×1.5 mm Fe-SMA strip is fully bonded along its entire surface using a two-component epoxy adhesive to a 5300 mm span steel girder. An activation strategy to prestress the Fe-SMA strip is formulated based on a series of finite element (FE) analyses, entailing successive block-by-block heating using a gas torch. Experimental and numerical studies illuminate the full-range thermal and mechanical behavior of the retrofitted girder throughout the activation process. A FE heat transfer analysis with experimental validation reveals the temperature developments and distributions during activation, highlighting a 160 ℃/mm temperature gradient along the adhesive thickness and longitudinal distributions with localized high temperatures. The mechanical behavior during activation, encompassing the effects of thermal expansion, Fe-SMA prestress, and adhesive softening and re-hardening, is interpreted based on experimental and numerical results, showing the evolutions and distributions of deflections, strains, and Fe-SMA prestresses. Static tests and a high-cycle fatigue test up to 3 million load cycles demonstrate the effectiveness and structural integrity of the proposed retrofitting solution.

Axial compression test on strengthening concrete cylinders by Fe-SMA/FRP-HDPE tube and rubber concrete cladding layer

This paper proposed a new method to strengthen and repair concrete columns, which combined active and passive confinement. The method involved the use of iron-based shape memory alloy (Fe-SMA) strips to quickly exert active confinement to these columns, followed by the use of fiber-reinforced polymer (FRP) and high-density polyethylene (HDPE) tubes as external passive confinement to improve the load-bearing capacity, durability, and ductility of concrete columns. Rubber concrete that performs high energy consumption and certain strength was used as the cladding layer to improve the impact resistance of the concrete column. This paper explored the effect of this method on the bearing capacity performance of concrete columns through axial compression tests and set three test variables, including different net-spacing of Fe-SMA, different FRP wrapping forms, and different FRP layers. The test outcomes showed that all three test variables obviously improved the load-bearing capacity and ductility of concrete columns, peculiarly when applying active confinement. Eventually, this paper proposed a theoretical model to predict the peak compressive strength of the specimen, which can provide a reference for designing this active-passive confinement strengthening method.

Shape memory alloys effects on the multi-story structures under extreme loading conditions

The use of intelligent materials with particular behavioral traits has grown significantly in recent years. The most common materials that may revert to their original shape after deformation due to stress or heat change are shape memory alloys (SMAs). Shape memory alloy (SMA) differs from conventional materials due to its shape memory property and hyperplastic nature. This research aims to explore the use of SMAs as a reinforcement to improve the performance of multi-story steel plate shear walls (SPSW) under explosive loading. The finite element (FE) software "ABAQUS" is utilized to simulate the models, and the results of the numerical modeling are validated against experimental research from the literature. The study investigates the impact of different parameters related to the explosion on the behavior of the reinforced multi story SPSW, including the amount of explosive material and the location of the explosion. The findings reveal that the minimum amount of explosive material required to cause rupture in a four-story SPSW reinforced by SMA, positioned at a distance of 1 m from the structure, is equivalent to 40 kg of TNT. Additionally, the minimum distance required for element rupture in the four-story SPSW, reinforced by SMA strips, is found to be 0.5 m. As the explosion height increases, the amount of out-of-plane base shear decreases. Furthermore, an interesting observation is that as the explosion height increases, the displacement of the infill plate also increases, leading to beam failure and, ultimately, infill plate failure. Niti SMA exhibited superior blast resistance compared to Iron-based SMA, showcasing its potential for enhancing structural resilience.

Flexural improvement of reinforced concrete beams strengthened with self-prestressing shape memory alloys

The study reported here aims to investigate the application of shape memory alloys (SMAs) in the form of strips for strengthening cracked reinforced concrete (RC) beams. The study proposes an innovative technique for prestressing RC beams by utilizing the shape recovery property of the alloy. Nine full-scale RC beams with a length of 3.75 m and a cross-section of 200 mm × 300 mm were categorized into three groups based on the steel reinforcement ratio, and tested under static loading. Three RC beams were used as control specimens and the other six were retrofitted with either one layer or two layers of SMA strips. The beams to be strengthened were exposed to an initial applied load before the installation of the SMA strip to simulate the deterioration scenario. SMA strips were retrofitted on the soffits of the deteriorated beams and activated by applying temperature from an external heat source while the temperature-deflection-strain measurements were monitored. Specimens were tested again up to failure to evaluate the strength improvement of the retrofitted specimens. Beams retrofitted with one layer of SMA experienced a deflection recovery up to 2.3 mm upon activation and an additional service load of up to 62%, whereas beams retrofitted with two layers experienced a deflection recovery up to 2.8 mm and an additional service load of up to 95%. In general, the deflection recovery was proportional to the ratio of the total reinforcement ratio after strengthening to the initial reinforcement ratio before strengthening. Therefore, tested specimens with two SMA layers experienced less improvement than specimens with one SMA layer. Finally, the experimental results were evaluated with two analytical methods: ACI method and the non-linear sectional analysis proposed by Oukaili.

Seismic performance of glulam frame with friction damper and column shoe: Experimental investigation and simplified numerical model

Resilient timber structure is a new branch of structure design. To reduce seismic damage of timber structures, an innovative resilient glulam frame (IRF) with friction dampers and column shoes was proposed in this paper. The IRF was connected by use of beam-to-column joints with friction dampers and column-base joints with column shoes. An IRF specimen and a conventional glulam frame (CF) specimen, with a scale ratio of 1:2, were tested under reversed cyclic load. The failure modes, hysteretic curves, stiffness degradation, and energy dissipation capacity of the specimens were obtained. Results indicated that the IRF was low-damage except replaceable Shape Memory Alloy (SMA) strips tensile failure. The load-carrying capacity of IRF did not significantly change compared to the CF specimen, but the energy dissipation capacity was enhanced by approximately 100%. A simplified numerical model of timber frames was developed and validated, and then the time-history analysis of multi-story IRF structure was performed. It was further demonstrated that the adoption of IRF significantly reduced the maximum story drift and residual drift of structures, especially during severe earthquakes.

Feasibility of iron-based shape memory alloy strips for shear strengthening of damaged RC beams promoting the formation of plastic hinges

This research focuses on the proof of concept of the feasibility of iron-based shape memory alloys strips (Fe-SMA) to strengthen damaged structures by promoting the yielding of longitudinal reinforcement. For this purpose, an experimental campaign on real-scale reinforced concrete beams previously damaged on shear and retested after being strengthened was carried out. The strengthening technique consists of external Fe-SMA strips wrapping the beams. The results show a very significant increase in both shear strength and ductility. In addition, shear predictions were calculated and compared by several design models. This study highlights the potentialities of Fe-SMA as a strengthening technique for damaged beams on shear.

Hybrid Simulation for Evaluation of Seismic Performance of Highway Bridge with Pier Retrofitted Using Fe-SMA Strips

The present research investigates the use of Fe-based shape memory alloy (SMA) strips for seismic retrofitting of rehabilitated RC bridge pier models. Four severely damaged bridge pier models were first rehabilitated by RC jacketing to retrieve at least their lost strength. Three configurations of Fe-SMA strips namely hoop (H), end-anchored (EA), and a combination of previous two approaches (EAH) were adopted. Prestrained Fe-SMA hoops, placed in the plastic hinge region of the bridge pier model, aims at utilizing the recovery stress developed upon thermal activation for application of active confinement pressure on the test specimen. The EA Fe-SMA strips utilize precompression developed in the concrete in the plastic hinge region of the test specimen. The EAH reinforcement scheme was studied for both precompression and active confinement. To compare the seismic performance of the various Fe-SMA retrofitted test specimens with respect to the control specimen, hybrid simulation (pseudodynamic) of an existing highway bridge located in Tripura, India was carried out with the scaled bridge pier test models as experimental elements. Earthquake excitations of different intensity levels were applied in a sequential manner to analyze the behavior of the structure over a damage spectrum ranging from minor cracking to major damage. To determine the ultimate capacity of the test specimens, cyclic tests were carried out after completion of a hybrid simulation. Bridge pier specimens with Fe-SMA in the form of EA reinforcement exhibited enhanced load-carrying capacity but marginal improvement in ultimate displacement while Fe-SMA hoops improved the ultimate displacement of the test specimen with marginal improvement in the peak lateral load. A combination of EA and hoop Fe-SMA reinforcement was found to be more efficient in improving all the seismic performance parameters such as lesser damage and higher load-carrying capacity, stiffness, and energy-dissipation capacity.

Shear capacity investigation of RC concrete beams using self-prestressing Fe-based shape memory alloys strips

Shear failure is a sudden and brittle failure, which causes human and economic losses. Hence, enhancement of shear capacity is critical for shear-deficient members of existing structures. In this study, the effectiveness of using Shape Memory Alloy ‘SMA’ strips on the shear capacity of reinforced concrete (RC) beams was investigated in a series of experiments. The experimental work included the study of six RC beams with a 200 × 300 mm cross-section considering shear parameters such as transverse shear reinforcement and the effect of prestressing. Beams were strengthened in U configuration using Fe-SMA strips 30 mm wide and anchored by one expansion anchor (M10-Hilti). The testing was performed in a simply supported condition where each beam was tested twice. The purpose of testing specimens twice was to confirm the results. The activation of the strips was achieved by heating the strips using a custom-made heater up to 200°. The method was proven effective, with an increase in shear capacity of up to 32–45% and 24–25% for specimens strengthened with passive strengthening (non-activated strips) and specimens strengthened by activated SMA strips, respectively. However, the active strengthening improved serviceability conditions by delaying the appearance of cracks and reducing the crack width. The occurrence of the main crack was delayed by 12.5–19.2%, the width of the crack was reduced by more than 65% compared to the reference beam, and the angle of the main crack increased compared to the reference beam as a result of activation. Beams containing internal transverse reinforcement performed better than the beams without shear reinforcement.

Two-Way Shape Memory Effect of a Shape Memory Composite Strip

In this work, a NiTi shape memory alloy (SMA) wire was embedded into a rubber/shape memory polymer (SMP) soft matrix to form a composite strip with a two-way reversible bending behavior. First, the elastic moduli of SMA wire were characterized as increasing about 3 times (18.6 GPa at martensite phase and 50.1 GPa at austenite phase) from 25 °C to 90 °C. Then, an SMA composite strip using SMP to replace the rubber matrix was fabricated to significantly improve the load-bearing ability (16-fold) at 28 °C. After that, the good two-way bending behaviors of the rubber/SMP-based SMA strip with high shape deploying ratio above 80% were demonstrated. Finally, the application of rubber/SMP-based composite strips in a space-deployable antenna model with two-way reversible bending behavior was developed and demonstrated through a heating and cooling temperature cycle.

Seismic Performance of Reinforced Concrete Columns Actively Confined with Iron-based Shape Memory Alloy Strips

Seismic Performance of Reinforced Concrete Columns Actively Confined with Iron-based Shape Memory Alloy Strips

On the characterization of the compressive response of shape memory alloys using bending

Determination of material parameters of metals/polymers under compressive loadings has been sometimes an onerous issue especially for thin sheets and wires. In the present paper, an approach is presented to determine the compressive material constants of the shape memory alloy (SMA) sheets by employing four-point bending tests. A three-dimensional (3D) asymmetric model is presented and implemented in COMSOL software. An SMA strip showing pseudoelasticity at the ambient temperature is trained under tensile loading, and the experimental results are used together with the model to determine the tensile material parameters of the specimen. On the other hand, a sample is subjected to four-point bending, and, after training, the strain distribution at the lateral surface of the sample is captured by using digital image correlation method. The empirical results for bending are utilized along with 3D simulations to determine the compressive material parameters of the specimens. The approach is finally validated by experimental data, and it appears to provide a reliable procedure for the compressive characterization of SMAs. The present research enables users to avoid performing susceptible compression tests and also empowers them to study the compressive mechanical response of a material during training cycles under quasi-static/adiabatic conditions.

Shape memory alloys enabled smart heat exchangers

Modern heat exchangers encounter the paradox between the high performance and low flow resistance while most of the tasks feature in wide operating conditions where great functional flexibility is required. In this paper, we propose to tackle the dilemma by integrating shape memory alloys into the design of heat exchangers, utilizing a two-way shape memory alloy (SMA) strip as the self-adjusting vortex generator (VG) for heat transfer enhancement. The SMA based vortex generators are trained with predetermined deformation according to the temperature of the working media. To be specific, at low temperature, the SMA strip is flat to reduce the flow resistance. While the temperature is high, the SMA strip is curved to form a rectangular wing vortex generator to enhance the heat transfer. This concept was firstly verified via the experimental study followed by detailed numerical investigation focusing on the mechanism explorations. The deformation characteristic was verified by water bath. With the increase of the temperature of fluid, the heat transfer is increased by 110 ∼ 125 %. On the other hand, the Darcy friction factor can be reduced by 74 ∼ 90 %, when the heat transfer demand decreases based on the concept proposed. The details of flow and heat transfer are given and analyzed by using numerical simulation. And the numerical results are in good agreement with the experimental ones with the relative error of 11 % ∼ 3 % (on heat transfer, Re=8004400) and the warping height ΔZ=4/5 hydraulic diameter (Dh)). The ratio of heat transfer and flow resistance are positively related to the warping height (ΔZ) of VG. Under six calculated Reynolds numbers (Re), the maximum heat transfer enhancement coefficient can be reached at Re = 400 and 800, respectively, with the values ranging from 1.18 ∼ 2.68 for different ΔZ. In the case that ΔZ equals to 4 / 5 hydraulic diameter (Dh), the best performance can be achieved with Re≤1600. If Re≤800, the design can always maintain better performance than the original flat channel, and the maximum performance evaluation criteria (PEC) achieved is 1.32. Based on our research, the smart heat exchanger is expected to satisfy the heat transfer requirements of specific variable working conditions in the future.

Design, experimental demonstration, and validation of a composite morphing space radiator

Future manned space missions will require thermal control systems that can adapt to larger fluctuations in temperature and heat flux exceeding the capabilities of current state-of-the-art technologies. Specifically, these missions will demand novel space radiators that can vary the system heat rejection rate to maintain the crew cabin at habitable temperatures throughout the entire mission. While current systems can provide a turndown ratio (defined as the ratio of maximum to minimum heat rejection rates) of 3:1 under adverse conditions, future missions are projected to demand thermal control systems that can provide a turndown ratio of more than 6:1. A novel morphing radiator concept autonomously varies the system heat rejection rate by altering the shape of the panel exposed to space, where composite materials can provide an ideal compromise between thermal conductivity, restorative stiffness and deformation capability. Shape change is accomplished through the use of shape memory alloys, a class of active materials that exhibit thermomechanically driven phase transformations and can be used as simultaneous sensors and actuators in thermal control applications. This work details progress towards testing and modeling a spaceflight-quality, high turndown ratio morphing radiator prototype in a relevant thermal environment. A prototype composite morphing radiator with shape memory alloy strip actuators and high performance thermal coatings achieved a turndown ratio of 7.2:1, while an associated multi-physical model thereof has been shown to capture all major effects and will enable future design improvements.

A space deployable antenna model based on shape memory alloy composite with folding‐deploying two‐way behavior

AbstractIn this study, a flexible space deployable antenna model with good self‐folding and deploying two‐way shape memory effect is proposed and prepared based on shape memory alloy composite strips and polyimide thin film. The thickness and cyclic properties of the shape memory alloy strip were considered for the two‐way shape memory effect. Good self‐folding at 110°C and self‐deploying at 20°C for 10 min were demonstrated. Moreover, the Joule heating method was applied to improve the folding speed within 90 s. The two‐way shape memory effect with reversible self‐folding and deploying behavior of the space deployable antennas is aimed at improving avoidance of space debris in future applications.

Enabling a Ductile Failure of Laminated Glass Beams with Iron‐Based Shape Memory Alloy (Fe‐SMA) Strips

AbstractLaminated glass beams are used as structural elements to support transparent roofs or to transfer wind loads acting on transparent facades. However, in case of breakage, laminated glass beams only exhibit a low residual load‐carrying capacity provided by the interlayers. A more efficient solution is to add a filigree ductile reinforcement on the tension side of the laminated glass beams, for instance by adhesive bonding. By these means, the post‐cracking behaviour of the beams and their redundancy can be improved and a ductile failure behaviour can be achieved. Moreover, an additional pre‐stressing of this reinforcement allows increasing the initial glass cracking resistance. Despite their obvious potential, an application of pre‐stressed laminated glass beams in real projects is prevented by the rather complicated necessary procedures for pre‐stressing. This contribution discusses first experimental results on a novel concept for pre‐stressed laminated glass beams with adhesively bonded strips made of an iron‐based shape memory alloy (Fe‐SMA). The pre‐stress can be applied in this case by heating up the Fe‐SMA. The feasibility of the concept is analysed based on results from four‐point‐bending tests on medium‐scale simple, reinforced and pre‐stressed laminated glass beams.

A Wirelessly Controlled Shape‐Memory Alloy‐Based Bistable Metal Swimming Device

Shape memory Nitinol has long been used for actuation. However, utilizing Nitinol to fabricate novel devices for various applications is a challenge, but has shown incredible promise and impacts. Bistable metal strips are widely adopted for shape morphing purposes (primarily in kid's toys, e.g., snap bracelets) due to their easy and robust transformation between two states. Herein, Nitinol shape memory alloy and bistable metal strip are combined to fabricate a swimming actuator with both slow moving and fast snapping capability, akin to an octopus swimming slowly in water, but quickly moving upon encountering a threat. The actuator developed here can also swim in multiple directions, all controlled by a wireless module. Furthermore, it is demonstrated that an onboard sensor can be incorporated for potential environmental monitoring applications. The fact that the device developed here has no mechanical parts, makes this an interesting potential alternative to more expensive, and energy consuming boats. A preprint version of the article can be found at: https://www.authorea.com/doi/full/10.22541/au.164199106.60208565.