The concept of 4D printing involves the formation of complex three-dimensional structures having the ability to adopt different shapes and forms when subjected to different environmental stimuli. Some researchers simply view this technique as an extension of 3D printing or additive manufacturing with the added constraint of time. However, the unique shape change mechanism exhibited in this process is due to a combination of shape programming and the usage of smart active materials mostly polymers. This review article highlights the various smart materials, activation mechanisms and the shape-changing techniques employed in the 4D printing process. The potential of these shape-changing structures and their current applications in various biomedical and engineering fields is also explored. The article aims to emphasize the potential and viability of 4D printing and is directed towards providing an in-depth insight into the 4D printing process.

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A mechanical assembly is a composition of interrelated parts. Assembly data base stores the geometric models of indi-vidual parts, the spatial positions and orientations of the parts in the assembly, and the relationships between parts. An assembly of parts can be represented by its liaison which has a description of its relationships between the various parts in the assembly. The problem is to not only make the information available but also use the relevant information for making decisions, especially determination of the assembly sequence plan. The method described in this paper ex-tracts the feature based assembly information from CAD models of products and build up liaisons to facilitate assembly planning applications. The system works on the assumption that the designer explicitly defines joints and mating condi-tions. Further, a computer representation of mechanical assemblies in the form of liaisons is necessary in order to automate the generation of assembly plans. A novel method of extracting the assembly information and representing them in the form of liaisons is presented in this paper

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In the present work, the nonlinear free flexural vibration of thick curvilinear fiber composite laminates is investigated using a higher-order shear flexible eight-noded quadrilateral element developed considering the variation of in-plane and transverse displacement through the thickness. The formulation includes both the geometric nonlinearity and inertia effects. The governing equations, derived based on Lagrange’s equations of motion, are solved iteratively through an eigenvalue approach. The formulation is tested against various problems for which the solutions are available in the literature. A detailed analysis is made to assess the influence of fiber angles, lamination schemes, boundary conditions, thickness, and aspect ratios on the nonlinear frequency ratio at large amplitude vibrations of the laminates. A comparative study is also done along with the first-order and simple higher-order theory deduced from the present model by neglecting the thickness stretching effects. The present analysis shows the degree of hardening behavior getting affected noticeably compared to those of the traditional straight fibers, thus exhibiting the occurrence of drop off in frequency ratio and redistribution of mode shapes at certain amplitudes of vibration.