Study on Enhancement of Mechanical Strength by Knotted Shape Memory Alloy Fiber in TiNi Fiber Composites

2008 ◽  
Vol 385-387 ◽  
pp. 421-424
Author(s):  
Yong Li Zhao ◽  
Jie Li ◽  
Ming Jin
Keyword(s):  
Shape Memory Alloy ◽  
Mechanical Strength ◽  
Shape Memory ◽  
Fiber Composite ◽  
Stress Transfer ◽  
Fiber Composites ◽  
Tension Test ◽  
Fiber Tension ◽  
The Matrix ◽  
Straight Fiber

In this paper, the experimental investigation into the enhancement of mechanical strength in shape memory alloy (SMA) fiber composites is made by using knotted fiber at the two ends instead of straight fiber. TiNi SMA fiber with both ends knotted is used for purpose of better ensuring stress transfer from the matrix to the fiber than straight fiber. Tension test is carried out above the austenitic finish temperature in air. Specimens are heated by means of electrical resistive lamplight heating. The results indicate that the mechanical strength is larger in the knotted fiber composite than in the straight fiber composite. Knotted fiber exerts the superiority of TiNi SMA fiber composite.

An Experimental Investigation of Mechanical Strength of Knotted NiTi SMA Fiber Composite

2011 ◽  
Vol 675-677 ◽  
pp. 1147-1150
Author(s):  
Yong Li Zhao
Keyword(s):  
Mechanical Strength ◽  
Fiber Composite ◽  
Stress Transfer ◽  
Unidirectional Composite ◽  
Matrix Crack ◽  
Design Concept ◽  
Niti Sma ◽  
The Matrix ◽  
Unidirectional Composite Material ◽  
Straight Fiber

The paper presents a new design concept for evaluating the mechanical strength of unidirectional composite material with shape memory alloy (SMA) fiber in the presence of matrix crack. NiTi SMA fiber with both ends knotted is used to actively control the composite strength instead of straight fiber for purpose of better ensuring stress transfer from the matrix to the fiber. Experiment is conducted to verify the effectiveness of this new design concept.

Variational Estimates for the Effective Response of Shape Memory Alloy Actuated Fiber Composites

2002 ◽  
Vol 69 (4) ◽  
pp. 470-480 ◽  
Author(s):  
J. P. Briggs ◽  
P. Ponte Castaneda
Keyword(s):  
Composite Materials ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Thermal Activation ◽  
Fiber Composites ◽  
Homogenization Procedure ◽  
Effective Response ◽  
Linear Elastic ◽  
The Matrix ◽  
Active Composite

The homogenization procedure of Ponte Castan˜eda is used to estimate the effective behavior of active composite materials consisting of aligned shape memory alloy (SMA) fibers embedded in a linear elastic matrix. Results are presented for thermal activation of the SMA with various applied tractions on the composite. While increasing stiffness of the matrix phase inhibits the contraction of the SMA, the simulations indicate that the use of a prestress in the manufacturing of the composite may provide an increase in the response time of the system without reducing performance.

Micro and Macromechanical Study of Stress-Induced Martensitic Transformation in a Cu-Al-Be Polycrystalline Shape Memory Alloy

2006 ◽  
Vol 509 ◽  
pp. 87-92 ◽  
Author(s):  
F.M. Sánchez ◽  
G. Pulos
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Vector Fields ◽  
Displacement Vector ◽  
Optical Microscope ◽  
Image Sequences ◽  
Tension Test ◽  
Loading Device ◽  
Stress States

An experimental investigation of the micro and macromechanical stress-induced martensitic transformation in a Cu-Al-Be polycrystalline shape memory alloy is undertaken using a uniaxial tension test. Digital images are acquired at different stress states. The image sequences are analyzed to estimate the optical flow to get displacement vector fields. The experiments are carried out on a miniature hydraulic loading device mounted under an optical microscope. The stress-strain curves and associated images show stress-induced martensitic transformation in specific grains. Displacement vector fields for the polycrystalline shape memory alloy are obtained. They are inhomogeneous due to the martensitic transformation and inter-granular interactions.

Micromechanics of stress transfer in shape memory alloy reinforced three-phase composites

2018 ◽  
Vol 29 (15) ◽  
pp. 3151-3164 ◽  
Author(s):  
Fathollah Taheri-Behrooz ◽  
Mohammad Javad Mahdavizade ◽  
Alireza Ostadrahimi
Keyword(s):  
Finite Element ◽  
Stress Distribution ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Thermal Loading ◽  
Hybrid Composites ◽  
Stress Transfer ◽  
Shape Memory Alloy Wire ◽  
Alloy Wire ◽  
Pull Out

Due to the weak interface in shape memory alloy wire–reinforced composites, the influence of interphase on the mechanical properties and stress distribution of hybrid composites is of considerable importance. In this article, a three-cylinder axisymmetric model using a pull-out test is developed to predict stress transfer and interfacial behavior between shape memory alloy wire, interphase, and matrix. In this article, only superelasticity behavior of the shape memory alloy wire is considered. Based on the stress function method and the principle of minimum complementary energy, stress distribution is derived for three different cases in terms of loading and boundary conditions (thermal loading model, intact model, and partially debonded model). Inhomogeneous interphase and different radial and hoop stress components in each phase are considered to achieve deeper physical understanding. Finite element analysis also performed to simulate stress transfer from the wire to the matrix through the interphase. To evaluate the accuracy of this model, the results of the work are compared with the results of the two-cylinder model proposed by Wang et al. and finite element results.

Shear Load Transfer in Shape Memory Alloy Fiber Reinforced Composites During Elastic Axisymmetric Deformations

2000 ◽  
Author(s):  
Hungyu Tsai ◽  
Xinjian Fan
Keyword(s):  
Phase Transformation ◽  
Stress Concentration ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Transition Layer ◽  
Load Transfer ◽  
Fiber Reinforced Composites ◽  
Shear Load ◽  
Reinforced Composites ◽  
The Matrix

Abstract The axisymmetric elastic deformations in shape memory alloy (SMA) fiber reinforced composites are studied. We analyze the stress concentration near the interface between the fiber and the matrix as a result of a pre-described phase transformation in the active fiber. A typical model involving a single infinite fiber embedded in an infinite elastic matrix is studied. A portion of the fiber is allowed to undergo phase transformation along the axial direction so that its length is changed by the corresponding transformation strain (typically a few percentages), while the matrix is assumed to be linearly elastic and isotropic. Under certain bonding conditions, the deformation of fiber forces the matrix to deform in the elastic regime in order to accommodate the transformation strains. The problem is formulated as axisymmetric deformations coupled with a finite transformation region in the fiber. In order to avoid infinite stresses found under perfect bonding conditions, we adopt a “spring” model which accounts for the elasticity of a transition layer at the interface. This model allows for relative displacements between the fiber and the matrix. A linear relation between this relative displacement and the shear stress is used. The exact elasticity solution (in integral form) to this problem is found using Love’s stress function and Fourier transform. Numerical integration is performed to produce the stress distributions. In particular, the shear load transfer profiles along the interface are calculated for various spring stiffness. It is found that the singularity is eliminated and the stress concentration factor depends on the stiffness of the transition layer.

Active Stiffening of Composite Materials by Embedded Shape-Memory-Alloy Fibres

1996 ◽  
Vol 459 ◽  
Author(s):  
J.-E. Bidaux ◽  
J.-A. E. Månson ◽  
R. Gotthardt
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Vibration Frequency ◽  
Composite Beam ◽  
Natural Vibration ◽  
Transformation Strain ◽  
Natural Vibration Frequency ◽  
The Matrix ◽  
Clamping Device ◽  
Composite Response

ABSTRACTThe use of shape-memory-alloy (SMA) fibres to actively changethe stiffness of a composite beam is investigated on a model system composed of an epoxy matrix with a series of embedded pre-strained NiTi fibres. Stiffness changes are detected through shifts in the natural vibration frequency of the beam. When electrically heated, the pre-strained NiTi fibres undergo a phase transformation. Since the shape recovery associated with the transformation is restrained by the constraints of both the matrix and the clamping device, a force is generated. This force leads to an increase in the natural vibration frequency of the composite beam. Depending on the degree of fibre pre-strain, either ordinary martensite, R-phase or a mixture of the two can be stress-induced. It is found that the R-phase gives rise to the largest change in vibration frequency for a given temperature increase and the most reversible behaviour. Its low transformation strain is also more favourable for fibre-matrix adhesion. The effect of stress relaxation in the polymer matrix on the composite response is discussed.

Mechanics of NiTi Reinforced Self-Healing Materials Producing Crack Closing Loads

2017 ◽  
Author(s):  
Nathan Salowitz ◽  
Ameralys Correa ◽  
Afsaneh Moghadam
Keyword(s):  
Shape Memory ◽  
Paradigm Shift ◽  
Fiber Composite ◽  
Self Healing ◽  
New Approach ◽  
The Matrix ◽  
Composite Form ◽  
External Loads ◽  
Shape Memory Fibers ◽  
Structural Matrix

Self-healing material structures with the inherent capability to mend damage will lead to a paradigm shift in design as fracture may no longer constitute a failure. Generally, there are two techniques of self-healing that operate at different scales, require different approaches and often are dealt with separately; geometric restoration and crack filling/bonding. Geometric restoration uses shape memory materials that can mechanically close fractures after they occur. Crack filling and bonding fills and chemically bonds fractured parts in place. Materials capable of recovering from complete fractures, that have propagated across the entire component, have typically taken a sparse fiber composite form with a structural matrix encapsulating shape memory fibers. This form of self-healing material has demonstrated the ability recover original bulk geometry. However, lacking bonding, the healed structures have not had the ability to resist subsequent externally applied loads without re-opening the crack. A new approach of pre-straining the shape memory fibers before curing them in a matrix in the pre-strained state is presented in this paper with basic theory and experimental results. Pre-straining the shape memory fibers before casting them in the matrix causes them to undergo constrained recovery upon activation. Thus, the samples create closing loads across the crack which are capable of withstanding external loads without re-opening.

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