Stiffness and vibration characteristics of SMA/ER3 composites with shape memory alloy short fibers

Shape memory alloys (SMAs) possess both sensing and actuating functions due to their shape memory effect, pseudo-elasticity, high damping capability and other remarkable characteristics. Combining the unique properties of SMAs with other materials can create intelligent or smart composites. In this paper, epoxy resin composites filled with Ni–Ti alloy short fibers were developed. Microstructure was observed using digital HF microscope. The dynamic mechanical properties were investigated by measuring the first vibration mode of clamped cantilever beams and by dynamic mechanical analysis (DMA). Moreover, the natural frequency of SMA composites was predicted theoretically. As a result, the temperature dependency of vibration property and DMA characteristics is affected largely due to the addition of SMA short fibers. The vibrational characteristics of SMA composites can be improved by the addition of small amounts of SMA short fibers. The addition of 3.5 wt.% of SMA short fiber content to epoxy resin resulted in the maximum increment in both natural frequency and storage modulus. This suggested that there exists an optimum SMA fiber content for vibration characteristics.     

Vibration characteristics of SMA composite beams with different boundary conditions

Recently, the development of shape memory alloy (SMA) actuators, in the forms of wire, thin film and stent have been found increasingly in the fields of materials science and smart structures and engineering. The increase in attraction for using these materials is due to their many unique materials, mechanical, thermal and thermal-mechanical properties, which in turn, evolve their subsequent shape memory, pseudo-elasticity and super-elasticity properties. In this paper, a common type of SMA actuator, Nitinol wires, were embedded into advanced composite structures to modulate the structural dynamic responses, in terms of natural frequency and damping ratio by using its shape memory and pseudo-elastic properties. A simple theoretical model is introduced to estimate the natural frequency of the structures before and after actuating the embedded SMA wires. The damping ratios of different SMA composite beams were measured through experimental approaches. The natural frequencies changed slightly at a temperature above the austenite finish temperature of composite beams with embedded non-prestrained SMA wires. However, the increase of the natural frequencies of the beams with embedded prestrained SMA wires were found in both the theoretical prediction and experimental measurements. The damping ratios of SMA composite beams increased with increasing the temperature of the embedded wires with and without being pre-strained. Compressive and local failures of the beams with high wire content are a possible explanation.     

Finite element simulation of low velocity impact on shape memory alloy composite plates

Delamination of composite materials due to low velocity impacts is one of the major failure types of aerospace composite structures. The low velocity impact may not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures can decrease dramatically.

Shape memory alloy (SMA) materials possess unique mechanical and thermal properties compared with conventional materials. Many studies have shown that shape memory alloy wires can absorb a lot of the energy during the impact due to their superelastic and hysteretic behaviour. The superelastic effect is due to reversible stress induced transformation from austenite to martensite. If a stress is applied to the alloy in the austenitic state, large deformation strains can be obtained and stress induced martensite is formed. Upon removal of the stress, the martensite reverts to its austenitic parent phase and the SMA undergoes a large hysteresis loop and a large recoverable strain is obtained. This large strain energy absorption capability can be used to improve the impact tolerance of composites. By embedding superelastic shape memory alloys into a composite structure, impact damage can be reduced quite significantly.

This article investigates the impact damage behaviour of carbon fiber/epoxy composite plates embedded with superelastic shape memory alloys wires. The results show that for low velocity impact, embedding SMA wires into composites increase the damage resistance of the composites when compared to conventional composites structures.     

热载荷作用下嵌入SMA丝复合材料梁的横向自由振动

基于形状记忆合金Brinson一维热力学本构方程,采用复合材料细观力学分析方法,建立了热载荷作用下嵌入SMA丝复合材料梁的一维热弹性本构关系。其次利用Euler-Bernoulli梁的轴线可伸长几何非线性理论和自由振动理论,建立了嵌入SMA丝复合材料梁在均匀升温场内自由振动的动力学控制方程,导出了热过屈曲构形附近嵌入SMA丝复合材料梁微幅横向自由振动的模型。最后通过打靶法求解了两端固定约束条件下嵌入形状记忆合金丝复合材料梁在加热过程中的振动响应,获得了梁的前四阶固有频率在不同SMA相对体积含量时随温度变化的特征关系曲线。数值结果表明,SMA丝相变过程中的回复应力和弹性模量变化对梁在过屈曲前后的各阶固有频率均有影响,是实现梁自振频率主动控制的一种有效方法。     

Effect of superelastic shape memory alloy wires on the impact behavior of carbon fiber reinforced in situ polymerized poly(butylene terephthalate) composites

Low-velocity impact properties of shape memory alloy (SMA) wires and carbon fiber reinforced poly(butylene terephthalate) obtained by resin transfer molding were characterized. At the subcritical regime the dissipated energy is not affected by the presence of the wires. However SMA has a positive effect on the maximum absorbed energy, since the maximum allowable load is higher. The contribution of the SMA wires to the higher impact performance of the hybrid composite is suggested to be due to their energy absorbing capability, and also to the high reversible force that acts as a healing force.     

Stress distributions in single shape memory alloy fiber composites

Shape memory alloy (SMA) in the form of wires or short fibers can be embedded into host materials to form SMA composites that can satisfy a wide variety of engineering requirements. The recovery action of SMA inclusions induced by elevated temperature can change the modal properties and hence the mechanical responses of entire composite structures. Due to the weak interface strength between the SMA wire and the matrix, interface debonding often occurs when the SMA composites act through an external force or through actuation temperature or combination of the two. Thus the function of SMAs inside the matrix cannot be fully utilized. To improve the properties and hence the functionality of SMA composites it is therefore very important to understand the stress transfers between SMA fibers and matrix and the distributions of internal stresses in the SMA composite. In this paper, a theoretical model incorporating Brinson’s constitutive law of SMA for the prediction of internal stresses is successfully developed for SMA composites, based on the principle of minimum complementary energy. A typical two-cylinder model consisting of a single SMA fiber surrounded by epoxy matrix is employed to analyze the stress distributions in the SMA fiber, the matrix, and at the interface, with important contributions of the thermo-mechanical effect and the shape memory effect. Assumed stress functions that satisfy equilibrium equations in the fiber and matrix respectively are utilized, as well as the principle of minimum complementary energy, to analyze the internal stress distributions during fiber pull-out and the thermal loading process. The entire range of axisymmetric states of stresses in the SMA fiber and matrix are developed. The results indicate substantial variation in stress distribution profiles for different activation and loading scenarios.     

形状记忆合金混杂复合材料层板的有限元分析与强度研究

形状记忆合金(SMA)与复合材料层板结合后,构成可驱动材料。形状记忆合金的非线性及其与复合材料层板的结合界面的力学性能对整体材料的性能影响较大。通过对埋入形状记忆合金驱动器的复合材料层板进行有限元模拟分析与试验研究,用有限元模拟分析的方法可以比较准确地模拟埋入形状记忆合金后复合材料的应力分布情况,结果表明,形状记忆合金的埋入不会对材料的强度产生较大影响。     

Effect of phase on debond strength in shape memory alloy reinforced composites

Systematic single fiber pullout tests were performed on epoxy composites embedded with nickel titanium shape memory alloy (SMA) wires. The SMA wires were tested in the austenitic or martensitic states to study and decouple the elastic moduli from martensite transformation or reorientation stresses in the analysis of debond loads. The results reveal that the SMA wires that were in the austenite phase consistently produced higher debond loads as compared to that of those wires that started in the martensite phase, likely due to differences in the Poisson’s ratio. Additionally, there appears to be a relationship between the elastic modulus and debond load where reinforcements with a higher elastic modulus displayed lower debond loads. Lastly, for SMA reinforcements that underwent a martensitic phase transformation or reorientation, the debond load was equivalent to the martensite transformation or reorientation load. The results of this work illustrate the sensitivity of SMA reinforced composites on the mechanical behavior and phase transformation characteristics of the constituent materials.     

A three-dimensional model describing stress-temperature induced solid phase transformations: thermomechanical coupling and hybrid composite applications

Between composite materials, shape memory alloy (SMA) composites are having a more and more relevant role. Typically, SMA wires are embedded in a metallic or a polymeric matrix to obtain materials with native multi-functionality and adaptive properties. This work approaches the computational study of the mechanical response of a composite in which SMA wires, previously deformed, are activated by electrical current heating, and accordingly try to recover the original shape inducing a shape change or a prestress in the structure. In particular, since the SMA behaviour is strongly affected by the thermo-mechanical coupling, in the first part of this work we present a 3D phenomenological model able to take into account this aspect. The model time-discrete counterpart is used to develop a 3D solid finite element able to describe the thermo-electro-mechanical coupled problem due to shape memory alloy response and to Joule effect. Finally, in the second part of the paper, we employ the developed computational tool to simulate different feasible SMA composite applications. Copyright © 2004 John Wiley & Sons, Ltd.     

An investigation of shape memory alloys as actuating elements in aerospace morphing applications

Two innovative actuating concepts for aerospace morphing applications, based on shape memory alloys (SMAs), are proposed. The first concept investigates a composite plate incorporating embedded SMA wires. A nonlinear auto regressive with exogenous excitation model is proposed for controlling single-cycle/multi-cycle loading conditions of the SMA wires. The second actuating concept studies a novel rib configuration, which incorporates a compliant mechanism for enabling aerofoil's leading edge morphing. Different rib-compliant mechanism concepts are designed and analyzed. The most efficient rib concept is experimentally characterized. The experimental results from both actuating concepts showed good agreement with the respective numerical.     

SMA纤维混杂层合梁的振动分析

提出一类形状记忆合金(SMA)纤维混杂层合梁的数学模型。采用多胞模型、形状记忆合金一维本构关系分析方法,同时考虑铁木辛柯剪切和马氏体相变的影响。目的是为了更进一步了解层合梁的振动控制。SMA纤维用来作为驱动器,它能够改变弹性模量和回复力,以此改变梁的频率。分析了SMA纤维含量、铺设角度和横向剪切变形的影响。结果表明,通过激活形状记忆合金纤维及改变初始变形,对层合梁的自振频率有很强的控制和调节能力。     

形状记忆合金纤维混杂正交对称铺层板的固有频率

形状记忆合金（SMA）混杂复合材料板是将有预应变的SMA纤维与普通纤维混杂单层内构成的。基于主动应变能调节（ASET）的概念,可实现对板的固有频率的调整。本文采用Galerkin法导出形状记忆合金（SAM）纤维混杂对称正交智能复合材料铺层板自由振动的频率的分析表达式。数值结果表明,SMA纤维的相变激发温度、体积含量、分布方式及其预应变对固有频率均有的影响,尤其是温度、SAM含量及其分布的作用更为显著,是结构振动控制的重要设计参数。     

埋入形状记忆合金丝的复合材料圆柱壳壁板的热振动特性分析

采用有限元软件ABAQUS实现了埋入形状记忆合金（SMA）丝的复合材料圆柱壳壁板结构热振动特性分析．基于“ang-Rogers本构模型编写用户子程序（UMAT）模拟形状记忆合金材料的超弹性行为和形状记忆效应，并在不同温度和应力状态下验证了程序的正确性．基于此程序，计算了埋入SMA丝的复合材料圆柱壳壁板在温度和机械载荷作用下的一阶固有频率，分析了其热振动特性和屈曲特性．模拟结果表明：加热驱动SMA丝一般会提高结构的固有频率和屈曲临界，SMA丝的数量对结构的热振动和屈曲特性有显著影响。这些结论将对智能复合材料结构设计、抗热设计有一定的指导作用。     

A thermo-micro-mechanical modeling for smart shape memory alloy woven composite under in-plane biaxial deformation

This paper presents a theoretical study of the in-plane behavior of Smart Shape Memory Alloy Woven Composites (SSMAWC) under biaxial loading by developing an integrated micromechanical constitutive model. The model studied in this research is established on the geometric parameters of fibers, metal layers, unit cell, the material constants of composite constituents, and the orientation of fibers, in which the fibers in one direction are SMA ones. The Helmholtz free energy of a Shape Memory Alloy, in 3-Dimensional and 1-Dimensional applications is derived. Using mechanical energy of matrix and elastic yarns, the constitutive relations are developed with the use of strain energy approach and energy variation theorem. The kinetic relations of SMA depicted by Brinson is coupled with the final governing equation of the composite to predict the stress history in smart shape memory alloy woven composites. The deflection of the structure, subjected to uniform biaxial loading is studied numerically. It is found that the effect of Shape Memory Effect (SME) of the SMA wires on the behavior of plain woven flexible fabric composite is significant.     

Damping,tensile, and impact properties of superelastic shape memory alloy (SMA) fiber-reinforced polymer composites

The potential of superelastic shape memory alloy (SMA) fibers to enhance the damping capacity and toughness of a thermoset polymer matrix was evaluated. A single-fiber winder was designed and built to manufacture a pre-form consisting of 102 μm diameter SMA fibers aligned parallel to each other. This pre-form was loaded to varying amounts of pre-strain and impregnated with vinyl ester to manufacture SMA fiber composites with 20% fiber volume fraction. The composites were tested using a Differential Scanning Calorimeter (DSC) and a Dynamic Mechanical Analysis (DMA), to evaluate the improvement in damping capacity of the polymer matrix due to the SMA fibers. Tensile and instrumented impact testing were carried out to evaluate improvements in mechanical properties and toughness of the composites. Appreciable improvement was observed in damping, tensile, and impact properties of the polymer matrix due to reinforcement with superelastic SMA fibers, highlighting the advantages of their use in polymer composites.     

形状记忆合金混杂复合材料弯曲变形的设计

为了预报形状记忆合金混杂复合材料的物理性能与弯曲变形能力,提出了兼顾常规力学性能和主动变形能力的系统的设计方法.以形状记忆合金体积含量为主要设计变量,分析了丝状、带状及板状形状记忆合金埋入复合材料层合板后,这种混杂复合材料力学性能的变化.经过某种特殊加工的板状NiTi合金,不但增大了NiTi合金的体积含量,还增大了形状记忆合金电阻值,以此来提高NiTi合金的响应速度.采用有限元方法进行设计计算及分析,验证了该设计方法的正确性.     

Embedded shape memory alloys confer aerodynamic profile adaptivity

Within the framework of a European collaboration, a feasibility study has been carried out on adaptive composites and their potential applications. Two aerospace companies and three universities have shared their expertise to investigate different aspects of adaptive composites with embedded shape memory alloy (SMA) wires. This highly multidisciplinary project reached from basic research on the materials' constituents to their possible industrial use, resulting in an ‘adaptive’ aircraft winglet as a demonstrator device.     

记忆合金驱动的感温自动闭门器的研制

 为实现消防门在缺电状态下自动感应火场温度并关闭,达到隔烟阻燃的目的,研制了记忆合金驱动的感温自动闭门器,具有全机械传感和驱动的特点,无电耗,寿命长,灵活可靠.基于偏动式记忆合金驱动器原理,针对普通闭门器的连杆机构,通过几何解析和力学分析,提出了一种新型的自动锁闭、解锁装置.根据感应温度范围的要求和锁紧、解锁载荷的计算,选用窄滞环记忆合金并确定了偏动弹簧和记忆合金弹簧的设计参数.通过试验验证,所研制的闭门器达到了灵敏度高、可靠性好的要求.     

A simulation study on the thermal buckling behavior of laminated composite shells with embedded shape memory alloy (SMA) wires

In this paper, numerical simulation analyses of the thermal buckling behavior of laminated composite shells with embedded shape memory alloy (SMA) wires were performed to investigate the effect of embedded SMA wires on the characteristics of thermal buckling. In order to simulate the thermomechanical behavior of SMA wires, the constitutive equation of the SMA wires was formulated in the form of an ABAQUS user subroutine. The computational program was verified by showing the response of the pseudoelasticity and shape memory effect (SME) at various temperatures and stress levels. Modeling of the laminated composite shells with embedded SMA wires and thermal buckling analyses were performed with the use of the ABAQUS code linked with the subroutine of the formulated SMA constitutive equations. The thermal buckling analyses of the composite shells with embedded SMA wires show that the critical buckling temperature can be increased and the thermal buckling deformation can be decreased by using the activation force of embedded SMA wire actuators.     

Development and characterization of active nanocomposites with embedded shape memory alloy wires

Active nanocomposites of epoxy resin containing bentonite clay and shape memory alloy (SMA) were made to evaluate the thermomechanical behavior in the range of phase transformation of shape memory alloy during heating. The epoxy resin system studied was prepared using bifunctional diglycidyl ether of bisphenol A (DGEBA), crosslinking agent diaminodiphenylsulfone (DDS), purified bentonite organoclay (APOC) and thin Ni‐Ti shape memory alloy wires. The evaluated ratio DGEBA/DDS was 100:40, for the epoxy resin/clay system was 100:1 and the shape memory alloy volumetric fraction of Ni‐Ti wires were 1.55%; 2.56%; 3.57% and 4.54%. The formation of nanocomposite was confirmed by X‐ray diffraction analysis. Phase transformation of the shape memory alloy wires were determined by differential scanning calorimetry (DSC). Specimens of the active nanocomposites were characterized mainly by dynamic mechanical analysis (DMA). According to the DMA results was evidenced a significant increase in glass transition temperature and storage modulus when 1 parts per hundred resin of clay is added to epoxy resin. A recover of storage modulus was observed in the active nanocomposite during heating in the range of the phase transformation of Ni‐Ti shape memory alloy wires when the volumetric fraction is above 3.5%.