Shape Memory Alloy Reinforcement Research Articles

Experimental study on improving the compressive property of damaged RC columns with prestressed SMA spirals

Shape memory alloy (SMA) reinforcement is an emerging approach to efficiently strengthen structures. However, the effect of SMA on repairing the damaged structures is not clear. This study aimed to explore the availability of SMA on strengthening damaged reinforcement concrete (RC) columns through compression tests. The damaged specimens were strengthened with NiTiNb-SMA spirals, and the effect of pitch spacing was also considered. In addition, a theoretical framework was proposed to predict the ultimate bearing capacity of the strengthened damaged RC columns. Experimental results revealed that SMA strengthening can achieve a significant improvement in the compressive properties of damaged specimens, particularly in terms of strength (increase by 22%) and ductility (increase by 286%) which surpassed those of the intact ones. The strengthening effect of SMA was significantly influenced by the pitch spacing, with the lowest pitch spacing yielding the most favorable strengthening effect. Finally, the theoretical results agreed with the experimental results well (error < 6%), indicating the accuracy of the proposed theoretical framework. This study validated the effectiveness of the pre-stressed SMA spirals in strengthening the damaged RC columns.

Towards a self-healing aluminum metal matrix composite: Design, fabrication, and demonstration

This paper presents a novel approach to designing and synthesizing a self-healing aluminum-based metal matrix composite (MMC) at the macro-scale. The composite comprises an Al 5083 matrix embedded with low melting point particles (LMPPs) that act as healing agents. A two-step electroless micro-encapsulation process is developed to create LMMPs with a diffusion and thermal barrier designed to protect the Zn-8Al core with a Co-P shell. The MMC is fabricated using spark plasma sintering. Following controlled total fracture under tension, external compressive force is applied during heat treatment to heal the fracture effectively. The evolution of phases and interfaces is characterized using electron microscopy, and transient liquid phase bonding (TLPB) is identified as the fracture-healing mechanism, facilitated in areas with sufficiently high Zn concentration to fill the crack. The design can be expanded to incorporate other matrix and LMMP materials, mechanical crack volume reduction by integrating shape memory alloy (SMA) reinforcement during MMC synthesis, and processing of the self-healing MMC using Directed Energy Deposition additive manufacturing.

Large Deformation Dynamic Characteristics of Cracked Laminated Panel and Improvement of Stiffness Using Shape Memory Alloy Fiber

Abstract This study explores the investigation of the nonlinear dynamic responses or time-dependent deflection analysis of a laminated composite shell panel integrated with a shape memory alloy (SMA), considering both undamaged and damaged set-ups. The primary focus of this research is to examine the impact of SMA incorporation on the structural behavior of the parent configuration, aimed at enhancing its structural stiffness. To ensure the validity of the proposed model, sensitivity analyses and numerical validations are presented. The mathematical framework employed in this study employs the higher-order shear deformation theory (HSDT), which offers enhanced accuracy in capturing the intricate behaviors of these shell panels. The dynamic responses are obtained using the Newmark average acceleration method. Numerical simulations are carried out using a dedicated MATLAB code developed in-house, allowing amplified correctness in outcomes and widespread analysis. The study thoroughly assesses a range of geometric parameters and those relevant to SMA for both intact and impaired shell panels. The outcomes of the investigation reveal affirmative findings, underscoring notable improvements in structural strength and enhanced nonlinear dynamic responses through the introduction of SMA reinforcement into the composite shell panel.

Seismic performance of Fe-SMA prestressed segmental bridge columns with 3D printed permanent concrete formwork

The integration of digital fabrication technology with prestressed segmental column construction offers significant potential for accelerated bridge construction with material-efficient design. This study aims to explore this potential by developing a novel prestressed segmental column system that utilizes permanent 3D printed concrete (3DPC) formwork for column segment fabrication. Prestressing is achieved in the proposed system by using partially bonded iron-based shape memory alloy (Fe-SMA) reinforcement. Large-scale experiments were conducted on two columns under combined gravity and lateral loading to evaluate the seismic performance and feasibility of the proposed system. The ratio of steel to Fe-SMA reinforcement in the column design was the variable considered in this study. The experimental results showed that the columns could withstand lateral drifts of up to 5% without collapse and the permanent 3DPC formwork showed no premature failure or delamination. Furthermore, the columns exhibited self-centering characteristics, maintaining a residual drift of 1% up to a target drift of 4% when the reinforcement ratio of steel to Fe-SMA rebars was 0.3. The results highlight the potential of the proposed prefabrication concept in designing material-efficient and seismically resilient bridge columns with low damage characteristics.

Strengthening Cracked Steel Plates with Shape Memory Alloy Patches: Numerical and Experimental Investigations

To investigate the retarding effect of bonding the shape memory alloy (SMA) patches on crack propagation in steel plates, both numerical and experimental analyses were conducted in the present study. A compact tension (CT) model was developed to clarify the feasibility of bonding the SMA patch to the reinforcement of the mode Ⅰ, mode Ⅱ, and mode Ⅲ cracks. On this basis, parametric analysis was conducted to investigate the strengthening parameters, i.e., the bonding area, the thickness, and the strengthening angle of the SMA patch. Subsequently, fatigue tests on the unreinforced steel plate and cracked steel plate strengthened by the SMA patches were conducted. The monitored stress variation, crack propagation behavior, and fatigue fracture surfaces were analyzed. Findings are meaningful to the application of the SMA reinforcement method in practical engineering.

Analysis of Shape-Memory-Alloy Fiber Interface Strength for Optimization of Self-Healing Composites

Self-healing materials, possessing an innate ability to mend damage and restore structural strength, have tremendous potential to improve safety and reliability, especially in space applications where recovery or manual performance of repairs may be prohibitive, dangerous, or impossible. Self-healing metallic materials developed with Nickel Titanium (NiTi) Shape Memory Alloy (SMA) reinforcement showed a promising prospect for recovering from larger scale damage. However, NiTi is known to form an inert oxide (TiO2) surface layer that is extremely hard to attach to. In this research, to promote better strength between the fiber and matrix, TiO2 surface layer has been removed by etching the NiTi wires in an inert environment and a pull test has been performed to evaluate the resulting change in adhesion strength between the fiber and metallic matrix. The experimental investigation of these interface fracture scenarios will enable the efficient design of composite materials.

Self-centering technique for existing concrete bridge columns using prestressed iron-based shape memory alloy reinforcement

Reinforced concrete (RC) bridge columns are expected to undergo large inelastic displacements during major earthquake events, which in turn can result in residual displacements that can potentially affect the functionality of the bridge. While post-tensioning has been used to develop self-centering column systems for new bridge construction, the self-centering of existing bridge columns remains a challenge, mainly due to the limitations associated with the application of conventional post-tensioning techniques to existing structures. This study aims to address this important research gap by developing a robust self-centering technique to mitigate the residual displacements of the existing bridge columns. The proposed self-centering technique exploits the unique self-prestressing characteristics of iron-based shape memory alloy (Fe-SMA) bars to prestress existing bridge columns. The effectiveness of the proposed technique was evaluated through the large-scale experimental investigation of four columns. The variables of the study included the ratio of steel to Fe-SMA reinforcement, the total longitudinal reinforcement, and the initial prestress. The experimental results showed that the proposed technique could significantly reduce the residual drifts of existing bridge columns. The residual drift of the columns was found to be less than 1% up to a target drift of 4% when the ratio of steel to Fe-SMA reinforcement was ≤ 0.3. The paper concludes with a discussion of the self-centering mechanism of columns reinforced with prestressed Fe-SMA bars, where it is shown that, unlike post-tensioning tendons which do not contribute much to the energy dissipation of columns, prestressed Fe-SMA bars begin to contribute to the energy dissipation after the initial prestressing is lost at high drifts, resulting in an enhanced seismic resilience of the columns.

Finite element modeling of reinforced concrete beams posttensioned with supplemental unbonded near surface mounted nickel‐titanium‐niobium shape memory alloy wire reinforcement

AbstractA novel posttensioning technique using nickel‐titanium‐niobium (NiTiNb) shape memory alloy (SMA) wires for the repair of reinforced concrete beams was evaluated numerically. A finite element model of a reinforced concrete beam was developed within a damage mechanics framework to simulate concrete cracking and subsequent posttensioning. The predicted yield and ultimate moment capacities of the simulated posttensioned beams were up to 14% less than the corresponding experimental results. Cumulative discrepancies in the assumed material models led to the conservative model results. The effects of concrete tensile damage, SMA reinforcement ratio, SMA‐concrete interaction (bonded vs. unbonded), and the effective prestress on the service and ultimate behavior of the posttensioned beam were evaluated. Partial loss of prestress in the SMA due to elastic shortening of the concrete was insignificant (&lt;3%) because of the relatively low elastic modulus of the SMA. Increasing the SMA reinforcement ratio by three times increased the yield moment of the posttensioned beam by 99%. Reducing the effective SMA prestress to 80% of the initial prestress to account for the possible losses resulted in a decrease in the yield moment by up to 7.8%.

Design Recommendations for Columns Made of Ultra-High-Performance Concrete and NiTi SMA Bars

The use of new materials in construction endows structures with better mechanical characteristics. The combination of ultra-high-performance concrete (UHPC) and nickel and titanium (NiTi) shape memory alloy (SMA) improves the behavior of building structures by increasing both their ductility and dissipation energy due to the low-damage and self-centering properties of NiTi SMA. Since UHPC and NiTi SMA are expensive materials and still scarce in distribution channels, this article tries to offer design recommendations to reduce the length of the column-beam connection in which these new materials should be introduced, leaving the rest of the column with conventional materials. To achieve this, a nonlinear static pushover analysis of columns using finite element software, SeismoStruct, was performed. This model was calibrated using experimental results. Next, a parametric analysis was carried out to propose the design recommendations. Results indicated that an adequate design for the column–beam connection, considering both economy and performance, should include a main zone with UHPC and SMA reinforcements, a transition zone with UHPC and steel reinforcements, and another zone with conventional reinforced concrete. The transition zone improved the hybrid column’s performance without excessively raising the cost. The main zone length, the transition zone length, and the strength of the concrete in the rest of the column must be determined to ensure that the critical section of the column was in the main zone to develop the maximum strength and ductility. The length of the main zone depended on the compressive strength of the conventional concrete, the relative axial load of the column, and the required ductility.

Shape memory alloy reinforcement for strengthening of RCC structures—A critical review

Significant performance and safety issues can arise from the deterioration of reinforced concrete (RC) structural components brought on by ageing processes and high stress occurrences. Shape memory alloys (SMAs), one of the options for restoring such components, have special qualities including recovering inelastic strain when unloaded (super elasticity) or heated (shape memory effect, SME). To lessen permanent deformations into RC constructions, super elasticity and SME of SMA bars can be used. The stiffness and strength of RC structures can also be improved by the addition of SMAs, allowing them to withstand loads of high intensities with minimal damage. Despite the wide range of studies done on the applications of SMAs in structures, a comprehensive analysis of the present state, key results, potential drawbacks, and future contemplation of SMA bars for the reinforcement of RC structures lacking in the literature. Additionally, detailed instructions for choosing the types and traits of SMAs best suited for a certain strengthening application are lacking. We conducted an extensive examination of the applications of SMA bars in RC beams, in order to fill the basic and practical gaps that were observed. The implementations were investigated from the viewpoints of crack recovery, strength augmentation, confinement, and shear strengthening of new and existing RC structures. The benefits and drawbacks of strengthening with SMAs are then discussed critically, particularly in light of other strengthening techniques and materials. The end of this review highlights the challenges of using SMAs as well as potential future opportunities that might arise from their effective use of RCC.

Experimental Study on Flexural Behavior of Seawater Sea-Sand Concrete Beams Reinforced with Superelastic Shape Memory Alloy Bars

In order to research the flexural behavior of shape memory alloy (SMA)-reinforced seawater sea-sand concrete (SWSSC) beams and improve their self-healing ability, three SMA SWSSC beams and one anti-corrosive steel bar SWSSC beam were designed. The influence of the reinforcement ratio, strength grade of SWSSC and type of reinforcement on the flexural performance of the beam were considered. The failure process, maximum crack width, mid-span deflection, displacement ductility and stiffness degradation of beams were studied by cyclic loading tests. The test results showed that the number of cracks in SMA-reinforced beams were significantly smaller than that in anti-corrosive-reinforced beams, and the crack width and mid-span deflection recovery effect were better after unloading. However, the effect of increasing the SMA reinforcement ratio on crack recovery was not obvious. The increase in SMA reinforcement ratio and the strength grade of SWSSC can significantly improve the bearing capacity of the beam and the stiffness, but the stiffness degradation rate decreased. Moreover, the ductility of concrete beams with SMA bars was significantly increased.

Numerical modeling of iron-based SMA confined concrete columns under axial compressive loading

This paper presents the results of a Finite Element (FE) model developed to simulate the behavior of confined concrete columns with iron-based shape memory alloys (Fe-SMA) under compressive loading. The performed simulations aimed to accurately demonstrate the combined effect of external shape memory alloy (SMA) reinforcement and internal transverse steel reinforcement under different loading conditions and presented a simplified approach to model external confinement as discrete elements near the surface of the concrete element.The primary objective of this study was to develop a FE model that can be used to predict and replicate the response of actively confined columns using Fe-SMA. The FE model was developed using the results of an experimental study conducted on circular Fe-SMA confined columns under concentric loading. The experimental study evaluated the influence of: 1) the presence of internal reinforcement, and 2) the ratio of external SMA confinement used. The simplifications and approximations considered in the numerical approach to predict the capacity and deformation responses showed to be adequate, and the results obtained were in good agreement with the compressive behavior of the actively SMA confined columns obtained from the experimental work.In addition to the concentric case, eccentric loading simulations are presented in this study to evaluate the combined confinement mechanism in terms of the structural element response to a different loading configuration. The predictions obtained in terms of load-carrying capacity and deformations can be used to expand the research work done using the SMA as a form of active confinement.

Behavior of Smart Reinforced Concrete Beam Column Joints by Using Shape Memory Alloy Reinforcement Under Repeated Loading

Using the super elastic materials in structures design is becoming very important in the research field because of their rare ability in sensing the around effect and reacting against the mechanical and thermal react. The major intent in this research is designing smart concrete beam column joints reinforced by Shape Memory Alloy (SMA) bars. The suggested systems use the (super elastic) Pseudo Elastic (PE) react of the SMA as reinforcement after being subjected under monotonic and repeated load. The behaviors of systems were explored experimentally and by using finite element simulation. In order to estimate load-displacement relationships of these specimens in this study, Analytical models were developed. A comparison of the reinforced specimens by SMA was carried out and it contained that the variation in percentage of the SMA in flexural reinforcement (25%, 50%, 75%) of the total flexural reinforcement by using this substitution get a clear effect on the failure load and the ultimate displacement of the specimens with these different ratios. The Finite Element models were developed by using the software ABAQUS. The models have been checked with the experimental results in the load-displacement terms in the top reinforcement. The models showed reasonable response. Where the ultimate load decreased by using SMA bars in (25%, 50%, 75% ) percentage of total flexural reinforcement about (50.51%, 28.32%, 38.15%) respectively, in case of static loading and (20.7%, 10.7%, 9.3%) respectively in case of repeated loading, and the deflection is increasing by using SMA in (25%, 50%, 75% ) percentage of total flexural reinforcement about (1.2%, 8.4%, 0.36%) respectively, in case of static loading and (9.6%, 5.28%, 10.9%) respectively in case of repeated loading

Estimating the plastic hinge length of rectangular concrete columns reinforced with NiTi superelastic shape memory alloys

Earthquake-induced damage in a reinforced concrete (RC) column is often concentrated in a region where the largest moment and deformation are expected. The length of this region is widely known as plastic hinge length. To help minimize the operational and repair costs of damaged plastic hinge region in concrete columns under earthquake loading, this study focuses on deriving an analytical expression for the plastic hinge length of rectangular concrete columns reinforced with nickel-titanium shape memory alloy (SMA) bars based on the results from well-calibrated nonlinear finite element models. A parametric study was conducted to investigate the effect of various parameters on the plastic hinge length, such as the axial load ratio, section information, and material properties of concrete and SMA. A multiple stepwise regression analysis was performed to derive an expression to estimate the plastic hinge length of SMA-RC columns, which can help designers determine the optimal length for SMA reinforcement. Two SMA-RC building frames with their plastic lengths determined using the proposed and existing plastic hinge length expressions were analyzed to compare their nonlinear response under earthquake loading. When the proposed plastic hinge expression is used, the SMA usage can be nearly halved, while the maximum and residual story drift remained similar to the result obtained using the existing expression.

Cyclic response of precast column-to-foundation connection using UHPC and Ni[sbnd]Ti SMA reinforcements in columns

Earthquakes are catastrophic natural events with a special impact on reinforced concrete structures due to the horizontal loads that they introduce into structures. To adequately resist an earthquake, a precast structure must have a high deformation capacity, dissipate energy in each earthquake cycle, undergo less damage and fewer residual deformations. To achieve all this, the behaviour of precast columns made with UPHC was herein experimentally analysed. Steel rebars were replaced with NiTi shape memory alloy (SMA) bars with superelasticity (SE) in the critical zone of the column-to-foundation connection. The NiTi SMA bars crossed the interface between the column and foundation. Two types of connection with the foundation were studied: smooth pocket type and protruding bar type. Columns were subjected to constant compression and a cyclic lateral load. Rocking behaviour was observed at the connection critical section. The use of advanced materials allowed a moment-rotation behaviour of the connection to be developed without any significant damage. Low residual deformations were observed while testing because of both the damage in UHPC was low and the superelasticity of the NiTi SMA bars.

Influence of shape memory alloy on seismic behaviour of hollow-section concrete columns

The influence of shape memory alloy (SMA) reinforcement on the non-linear static and dynamic responses of hollow-section concrete columns to earthquakes was investigated. The seismic performance of concrete columns reinforced with steel and with a mix of SMA and steel was compared by assessing their ductility ratios, dissipated energies, strain recovery capacities and collapse drifts. The influence of near- and far-field ground motions on the static and dynamic responses of the test columns was also investigated. To verify the results, the columns were subjected to a near-field ground motion related to an existing earthquake and the relative displacement response history was compared with experimental results. Compared with the steel-reinforced column, it was found that the use of the hybrid SMA–steel reinforcement was more effective at recovering strains and reduced the residual deflections. On the other hand, the steel-reinforced column had a greater ductility ratio and energy dissipation capacity. It is therefore important to find an optimal combination length for the two types of reinforcement in a concrete column. The results indicated that the optimum reinforcement configuration involves replacing steel with SMA at 15–20% of column height, which includes the probable plastic hinge length.

Modelling of mid-rise concrete shear walls reinforced with superelastic shape memory alloys: Nonlinear analysis

The response of hybrid Shape Memory Alloy (SMA)-steel reinforced concrete shear walls containing Nickel-Titanium superelastic SMA as alternative reinforcement in the plastic hinge region was investigated using nonlinear finite element modelling. The hybrid wall system promotes self-centering and significant reduction of permanent deformations. Two types of conventional steel-reinforced concrete shear walls were designed for a prototype 10-storey office building according to the current Canadian concrete design standard, assuming two distinct seismic design scenarios. A moderately ductile shear wall was designed for a moderate seismic zone in eastern Canada, whereas a ductile shear wall was designed for a high seismic zone in western Canada. Equivalent, hybrid SMA-steel reinforced concrete shear walls were defined following the design of the two conventional shear walls, in terms of geometry and reinforcement layout. Full-scale, two-dimensional finite element models were developed to assess the pushover and hysteretic responses of the walls. Similarities in wall cross-section and yield force capacity of the steel and SMA reinforcement permitted a comparison between the walls, including strength, stiffness, self-centering, and energy dissipation capacities. The results indicate similar lateral strength and displacement capacities, and superior restoring capacity of the SMA-reinforced walls in comparison to the steel-reinforced walls. Furthermore, a preliminary study was conducted to investigate the effect of the SMA-bar length in the ductile wall due to concentration of damage near the base of the wall. Lengths corresponding to approximately 50% and 20% of the original SMA length were considered. Based on the analyses, a satisfactory response could be achieved with shorter SMA reinforcing bars, which reduces the quantity of SMA reinforcement without significant loss in self-centering capacity.

RESEARCH ON ASEISMIC BEHAVIOR OF STRAIGHT TENON JOINTS REINFORCED BY SMA STRINGS IN ANCIENT TIMBER BUILDINGS

The semi-rigid mortise-tenon joints in the wooden structures of ancient buildings are often destroyed before beams and columns under major earthquakes, which are the important positions for reinforcement and protection. A new type of shape memory alloy (SMA) preventive reinforcement device is designed, and low-cyclic loading tests are carried out on five reinforced joints and one unreinforced joint. The failure modes, moment-rotation relationship, strength degradation, stiffness degradation, energy dissipation, self–centering ability and deformation capacity of the joints reinforced by SMA strings with different numbers and different pretension strains are studied. A calculation method for bending capacity of straight tenon joints reinforced by SMA strings is established. The results show that the bending capacity of the joints after SMA reinforcement is improved. The maximum bending capacity of the reinforced joint is 1.49 times that of the unreinforced joint. Compared with the unreinforced joint, the strength degradation of the reinforced joints is not serious, which indicates that the SMA strings can still continue to provide the bending capacity for the joints when the rotation is large. The maximum rotational stiffness of the reinforced joint is 2.24 times that of the unreinforced joint. With the increase of the rotation of joints, the energy dissipation of unreinforced joint gradually decreases, however the energy dissipation of reinforced joints increases first and then decreases. At the same rotation, the relative residual deformation decreases with the increase of numbers and of pretension strains of SMA strings, and the self-centering ability is enhanced. The results of research can provide a reference for the preventive conservation of the mortise-tenon joints in ancient timber structures.

쉬트와 와이어 형태를 가진 형상기억합금 강화 케블라 고분자 복합체와 일반 케블라 고분자 복합체의 비교 연구

The main objective of this work is to investigate the effect of shape memory alloy reinforcement in Kevlar polymer composites on mechanical and low-velocity impact properties. The sheet and wire forms of shape memory alloy (SMA-nickel-titanium alloy) are used as potential reinforcements in Kevlar-reinforced polymer composite. The developed composites were analyzed for tensile and flexural behavior. The effective bonding area, referred to as core density, contributes to incremental flexural strength in the SMA sheet reinforced composites. The developed composites exhibited better impact resistance during low-velocity impact tests at different velocities, 2.80, 3.96, and 4.85 m/sec, and simulated using a CEAST drop hammer testing machine. The impact surface of the specimen was studied on a micro-level using SEM analysis and macro-level using Image J software. The impact force, the energy absorbed, and the deformation of the specimen during impact were recorded and analyzed. The experimental results reveal that the SMA sheet reinforced Kevlar composites exhibited appreciable impact resistance with maximum energy absorbing capacity comparatively with plain Kevlar and SMA wire reinforced composites.

Strengthening and prestressing of bridge decks with ribbed iron-based shape memory alloy bars

Given the increasing age of our built environment, including concrete structures, stakeholders in the construction industry require innovative and effective strengthening methods. In several studies and onsite applications, iron-based shape memory alloy (Fe-SMA) reinforcements have proven to be competitive alternatives to well-established materials. The objective of this investigation was to study the effectiveness of two different prestressed strengthening methods for concrete members in flexure using recently available ribbed Fe-SMA (“memory-steel”) bars. Reinforced concrete slabs similar to the cantilever extension of box-girder cross-sections were strengthened using only cementitious anchorages and subjected to quasi-static loading. The first strengthening method comprised the removal of the concrete cover and the installation of memory-steel bars with an additional mortar layer. The second strengthening method comprised the cutting of grooves in the concrete cover, followed by the installation of memory-steel bars with mortar (near-surface-mounted). The prestress was obtained via resistive heating of the memory-steel bars. The strengthened specimens exhibited highly improved cracking, yielding, and maintained ductility until ultimate concrete compression failure. Observations utilizing a digital image correlation system indicated a damage-free prestressing process and no premature failure of the strengthening reinforcement. Different analytical approaches were used to estimate the prestress.