Light induced bending of photochromic liquid crystal polymer (LCP) thin films sandwiched with some transparent
polymer substrates is studied. Kirchhoff plate model is analyzed. We found that under the irradiation of light with
suitable wavelength, an effective bending moment of the composite film will be produced and has two contributions, the
opto moment and the bi-film moment. The opto moment is due to the inhomogeneous distribution of the light induced
contraction resulted from the light absorption decay. It acts as a bending moment for single layered LCP film as well and
has been studied by many authors. The bi-film moment, on the hand, is resulted from the homogeneous contraction
induced by light and will act only to the composite similar to the well-known bi-metal bending. By utilizing the two
contributions, the magnitude of the total effective moment and the bending curvature can be enhanced largely. Moreover,
the bending direction can be well controlled by suitable design of the multilayered structures. The variational
formulation of the bending equation is derived, according to which any commercial finite element code can be used to
simulate the light induced bending behavior under various boundary conditions. Some interesting bending patterns of the
film composites are shown to be possibly produced by patterned layer structures.
The technique of introducing graded interlayers has been used extensively to mitigate residual thermal stresses in joining
dissimilar materials. The case-to-case numerical methods have often been used to discuss the effectiveness of the graded
interlayers, because it is always a mathematical difficulty in analytical analysis. In this work, thermal stress reduction of
bilayered systems with linearly graded interlayer is considered with analytical approaches. It has been found that the
maximal stress in the system will always be lowered with a thick enough interlayer. However, if the interlayer thickness
is restricted, a critical range of the elastic modulus and layer thicknesses of the original bilayered system can be
identified only in which the maximal stress can be reduced. An even smaller range is found within which the maximal
stress always decreases with the increase of the interlayer thickness.
Shape memory alloys (SMAs) show strong hysteresis in stress-strain-temperature relations. The hysteretic behavior is
mainly caused by the thermodynamic irreversibility during the thermoelastic martensitic transformation. The various
types of stress-strain hysteresis observed for SMAs at different temperatures have been attributed to the martensitic
reorientation (MR) and the stress-induced martensitic transformation (SIMT) processes occurred under loading. Based
on such observations, a model is proposed to consist of two types of elements: MR elements and SIMT elements. The
MR elements show only martensitic reorientation and the SIMT elements can behavior only according to the stressinduced
martensitic transformation. A SMA sample is a proper combination, determined by two temperature dependent
distribution functions, of these two types of elements in series, i.e. the stresses on the elements are identical and the
strains sum up. Experiments are designed to determine the distribution functions and numerical simulations are
performed to show the capability of the model in reproducing the stress-strain hysteresis of SMAs in the whole
temperature range of applications
Light-induce bending of photochromic LCEs is a newly found phenomenon, with potential applications such as artificial
muscles, nano actuators and remote-controllable implements. To simulate this, light-induced bending models of straight
and curved beams can be derived from the simple beam theory. The effect of the light is substituted as an effective
bending moment. Several examples, with different approximations, boundary conditions, under uniform or nonuniform
illuminations, are demonstrated to calculate the curvature, the restraining force or the deflection. Especially, under weak
light intensities and low temperature, the analytical expression of the curvature is obtained. A simplified remote
controllable grip hand is simulated by the curved beam bending model. We calculate the grip force of the hand to hold a
body, controlled by light and heat. The simulation shows that the largest value of grip stress can be about 1Mpa. In
order to optimize the light-induced bending, the effects on the effective moment of the parameters, such as the light
intensity, the thickness of the beam and the decay distance of the material are further analyzed. It is found that the
effective moment is not a monotonic function of these parameters. Therefore, proper light intensity, material and
thickness must be chosen to get the largest bending.
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