Number Of Shape Memory Alloy Wires Research Articles

Design and Hysteretic Performance Analysis of a Novel Multi-Layer Self-Centering Damper with Shape Memory Alloy

This paper presented the development process of a novel multi-layer self-centering damper utilizing a NiTi shape memory alloy (SMA) with remarkable superelastic properties. The construction and operating principles of the novel damping device were introduced. A model for calculating the restoring force–displacement hysteretic curve of the novel damper was established, and based on this theoretical model, a parameter analysis of the damper’s hysteresis performance was conducted. The effect of SMA pre-strain, SMA diameter, number of layers in the damper, and number of SMA wires per layer on the damper’s stiffness, the unit cycle energy dissipation, and the equivalent viscous damping ratio were investigated, respectively. The results showed that the restoring force–displacement hysteretic curve of the novel SMA damper exhibits a full spindle shape, demonstrating the damper’s excellent energy dissipation capacity, self-centering capability, significant stroke, and unique variable stiffness characteristics (i.e., appropriate initial stiffness, minimal isolation stiffness, and significant limit stiffness). The results also indicated that the SMA pre-strain has a minor impact on the damper’s stiffness but a significant influence on unit cyclic energy dissipation and equivalent damping ratio. As the SMA pre-strain increased from 0.03 to 0.04, 0.05, and 0.06, the maximum stroke of the damper continuously decreases, while the unit cyclic energy dissipation initially increases and then decreases, with the optimal energy dissipation achieved at a pre-strain of 0.04. Increasing the SMA diameter results in a higher damper stiffness and energy dissipation capacity, with no significant change in maximum stroke and equivalent damping ratio. Increasing the number of damper layers leads to an increase in maximum stroke and unit-cycle energy dissipation, accompanied by a decrease in stiffness and almost constant equivalent damping ratio. As the number of SMA wires per layer increased from 8 to 16 and 32, the maximum stroke and equivalent damping ratio presented little variation, but the damper’s stiffness and unit cyclic energy dissipation continuously increased.

Numerical simulation of buckling behavior of thin walled composite shells with embedded shape memory alloy wires

In this research, the buckling behavior of thin walled composite shell with embedded shape memory alloy (SMA) wires is examined numerically. To model the SMA wire properties, constitutive equation of Brinson is used and a UMAT subroutine is developed to link with ABAQUS finite element (FE) model performed to simulate the buckling behavior of composite shells. To validate the FE modeling, some experimental specimens are fabricated by filament winding process and tested under axial compressive loading to analyze the buckling behavior of the structure. The results show that the numerical model has sufficient accuracy and the effect of tensile pre-strain and the number of embedded SMA wires on the buckling capacity of the cylindrical composite shell are investigated. As the results obtained, by embedding 4 SMA wires without pre-strain in composite shell, the critical buckling load increases about 35%. Also, by increasing the pre-strain and the number of SMA wires (more than 4), the stiffness of the structure and the magnitude of the critical buckling load are decreased.

Cyclical behavior of timber mortise-tenon joints strengthened with shape memory alloy: experiments and moment-rotation model

ABSTRACTThis article presents the results of a study on the cyclical behavior of mortise-tenon joints strengthened with shape memory alloy (SMA) wires. Four 1/3.52 scaled joint specimens reinforced with different number of SMA wires were subjected to low-cyclic reversed loading tests and the moment-rotation hysteretic curves were obtained. The cyclic behavior of joints strengthened with SMA were compared with that of joints strengthened with conventional reinforcement methods, such as cramp, carbon fiber, steel pins, U-shaped hoop, angle steel, curved plate, etc. Results indicated that the strength, stiffness, and energy dissipation capacity of the mortise-tenon joints strengthened with SMA were improved markedly. The residual deformation of the mortise-tenon joints strengthened with SMA is approx. 20% less than that strengthened with the conventional strengthening methods. A nonlinear model composed of one three-parameter power function and one straight line was presented for the moment-rotation of the mortise-tenon joints and good agreement between predictions and tests were observed.

Sensitivity analysis of a smart soft composite robotic finger design using geometrically nonlinear laminated composite finite beam elements

Soft robotics is an emerging research field that uses deformable materials to build compliant and adaptable systems, using simple integrated mechanisms, enabling biomimetic behavior. This paper presents a sensitivity analysis of a shape memory alloy (SMA)-driven smart soft composite (SSC) bending actuator that is used as an artificial finger in robots or prosthetics. This SSC structure is made of a flexible material, such as polydimethylsiloxane (PDMS), reinforced with some layers of glass fiber sheets, and actuated via SMA wires embedded in the flexible material. The SMA wires shrink when thermally activated, resulting in bending the three flexible hinges of the finger. Designing such smart soft structures involves optimizing large number of design parameters such as the flexible hinge length and thickness, the number of composite layers and their orientation, the number of SMA wires and their diameters. Hence an accurate and efficient computational tool is required to perform sensitivity analysis, and facilitate and accelerate the design process. The mathematical model should also account for geometric nonlinearity due to the large deformation and rotation of the structure in hand. A recently-developed accurate and efficient novel geometrically-nonlinear laminated composite beam finite element model is used in this work for analyzing the SSC robotic finger. The sensitivity analysis revealed that the effect of the flexible hinge thickness in the studied design is much more significant than the hinge length, and that the relationship between the fingertip rotation and the hinge thickness is nonlinear for the case of one glass fiber sheet and approaches linearity as the number of sheets increases to three.

Fatigue crack growth analysis of steel elements reinforced with shape memory alloy (SMA)/fiber reinforced polymer (FRP) composite patches

This paper describes a numerical framework to simulate the fatigue crack growth of single edge-notched steel elements patched with shape memory alloy (SMA)/fiber reinforced polymer (FRP) composite patches. The framework includes the small crack propagation. The small crack propagation stage was simulated using the analytical model based on the equivalent initial flaw size method. The bridging effects of the SMA/FRP composite patch were simulated by two consecutive finite element simulations considering the interfacial debonding during fatigue loading. Numerical predictions were validated by comparison with experimental results. A parametric study was conducted using the validated model. The considered parameters were the number of SMA wires used in the patch, the applied stress range, and the length of the crack in the steel substrate at the time of installing the patch. The numerical results indicated that the SMA wires increased the critical crack length at which fracture occurred and that the patch was more effective at lower stress ranges. Further, the SMA/FRP patch can substantially delay the failure of a member with very little remaining fatigue life. The results demonstrate the potential of this technique and highlight the importance of early intervention when repairing fatigue sensitive details.

Aeroelastic characteristics of cantilever wing with embedded shape memory alloys

In this paper, the effect of embedded shape memory alloy (SMA) wires on the natural frequency, flutter, limit cycle oscillation (LCO) amplitude and aeroelastic stability margin of a rectangular cantilever wing are investigated. Wings are modeled in accordance to classical plate theory (CPT) as well as first-order shear deformation plate theory (FSDT) and large deflection Von Karman plate theory. The effects of pre-strain, temperature and number of SMA wires on aeroelastic characteristics are considered. Significant improvements in aeroelastic behaviors due to the in-plane load of the SMA wires are obtained.

Shape memory alloy actuation for active tuning of composite beams

This paper presents an experimental - analytical study on the active tuning of composite beams using shape memory alloy (SMA) wires. Two graphite - epoxy composite beams with embedded fused silica tubes (also called sleeves) with `dummy' steel wires inserted in the sleeves were manufactured using an autoclave molding technique. After curing, the `dummy' wires were replaced by pre-strained SMA wires. During testing of such a beam, the beam and SMA wire are independently clamped at both ends and the SMA wires are activated using electrical resistive heating. A large tensile recovery force develops in the wires due to a phase transformation and the mechanical constraints provided by the clamps. The influence of this recovery force on the vibration behavior of the composite beams was determined by vibration testing. Analytically, these beams with SMA wires inserted in embedded sleeves were examined as beams on an elastic foundation; the spring constant of the elastic foundation depended on the axial recovery force of the SMA wire. Good correlation between analysis and experiment was achieved. A numerical parametric study of natural frequencies of composite beams with activated SMA wires was conducted. The parameters considered were the diameter and the number of SMA wires. The numerical study suggests that inserting 25 SMA wires of 20 mils diameter into a graphite - epoxy beam of 30 in length, 1 in width and 62 mils thickness increases its first frequency by 276%.