Mechanical metamaterials pave a way for designing and
optimizing
microstructure topology to achieve counterintuitive deformation including
negative Poisson’s ratio (NPR) and negative thermal expansion
(NTE). Previous studies were always limited to single anomalous mechanical
or thermal deformation, but current applications for high-precision
mechanical or optical equipment always require their combination and
customized and anisotropic deformation parameters. This work develops
programmable two-dimensional (2D) mechanical metamaterials based on
chiral and antichiral structures constructed with curved bimaterial
strips to produce tailorable NPR and arbitrary thermal deformation.
The coefficient of thermal expansion of the mechanical metamaterials
is tunable on a large scale across negative, near-zero, and positive
values depending on the bimaterial configurations and geometrical
parameters of curved strips, while the value of NPR is mainly determined
by the radian. Furthermore, it is programmable by coding the unit
cells to exhibit customized and anisotropic thermal deformation combining
homogeneous, gradient, and shear modes. The proposed mechanical metamaterials
are fabricated by multimaterial three-dimensional (3D) printing, and
the unusual deformation modes are verified experimentally, which is
well in agreement with the results of finite element analysis. This
work demonstrates a feasible approach to achieving customized mechanical
and thermal deformation through easy block building for specific engineering
applications including eliminating thermal stress, shape morphing,
and smart actuators.