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.

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.

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.

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