Dynamic analysis of prestressed variable stiffness composite shell structures

An efficient D-vine copula-based coupling uncertainty analysis for variable-stiffness composites

For Variable Stiffness (VS) composites with steered curvilinear tow paths, the fiber orientation angle varies continuously throughout the laminate, and is not required to be straight, parallel and uniform within each ply as in conventional composite laminates. Hence, the thermal properties (conduction), as well as the structural stiffness and strength, vary as functions of location in the laminate, and the associated composite structure is often called a “variable stiffness” composite structure. The steered fibers lead not only to the alteration of mechanical load paths, but also to the alteration of thermal paths that may result in favorable temperature distributions within the laminate and improve the laminate performance. Evaluation of VS laminate performance under thermal loading is the focus of this chapter. Thermal performance evaluations require experimental and numerical analysis of VS laminates under different processing and loading conditions. One of the advantages of using composite materials in many applications is the tailoring capability of the laminate, not only during the design phase but also for manufacturing. Heat transfer through variable conduction and chemical reaction (degree of cure) occurring during manufacturing (curing) plays an important role in the final thermal and mechanical performance, and shape of composite structures. Three case studies are presented in this chapter to evaluate the thermal performance of VS laminates prior to and after manufacturing. The first case study is a numerical analysis that investigates the effect of variable conductivity within the VS laminate on the temperature and degree of cure distribution during its cure cycle. The second case study is a numerical analysis that investigates the transient thermal performance of a rectangular VS composite laminate. Variable thermal conductivity will affect the temperature profile and results are compared to a unidirectional composite. The effect of fiber steering on transient time and steady state solutions is compared to the effect of unidirectional fibers. The third case study is an experimental one that was conducted to evaluate the thermal performance of two variable stiffness panels fabricated using an Advanced Fiber Placement (AFP) Machine.

Design, manufacturing, and testing of a variable stiffness composite cylinder

In the present work, a geometrically nonlinear finite shell element is first presented to predict nonlinear dynamic behavior of piezolaminated functionally graded carbon nanotube-reinforced composite (FG-CNTRC) shell, to enrich the existing research results on FG-CNTRC structures. The governing equations are developed via an improved first-order shear deformation theory (FSDT), in which a parabolic distribution of the transverse shear strains across the shell thickness is assumed and a zero condition of the transverse shear stresses on the top and bottom surfaces is imposed. Using a micro-mechanical model on the foundation of the developed rule of mixture, the effective material properties of the FG-CNTRC structures, which are strengthened by single-walled carbon nanotubes (SWCNTs), are scrutinized. The effectiveness of the present method is demonstrated by validating the obtained results against those of other studies from literature considering shell structures. Furthermore, some novel numerical results, including the nonlinear transient deflection of smart FG-CNTRC spherical and cylindrical shells, will be presented and can be considered for future structure design.

A new first-order shear deformation theory (FSDT) has been developed and verified for laminated plates and sandwich plates. Based on the definition of Reissener–Mindlin’s plate theory, the average transverse shear strains, which are constant through the thickness, are improved to vary through the thickness. It is assumed that the displacement and in-plane strain fields of FSDT can approximate, in an average sense, those of three-dimensional theory. Relationship between FSDT and three-dimensional theory has been systematically established in the averaged least-square sense. This relationship provides the closed-form recovering relations for three-dimensional variables expressed in terms of FSDT variables as well as the improved transverse shear strains. This paper makes two main contributions. First an enhanced first-order shear deformation theory (EFSDT) has been developed using an available higher-order plate theory. Second, it is shown that the displacement fields of any higher-order plate theories can be recovered by EFSDT variables. The present approach is applied to an efficient higher-order plate theory. Comparisons of deflection and stresses of the laminated plates and sandwich plates using present theory are made with the original FSDT and three-dimensional exact solutions.

Failure analysis of variable stiffness composite plates using continuum damage mechanics models

Modeling and Cutting Path Optimization of Shallow Shell Considering its Varying Dynamics During Machining

In this article, lead-free piezoelectric ceramics are investigated for active vibration control of piezolaminated composite shell structure. The shell structure is in the form of layered composite shell. Finite element modeling is performed to obtain vibratory response of the piezolaminated shell structure. Modeling is based on first-order shear deformation theory and linear piezoelectric theory. Fuzzy logic controller is used as controlling technique to reduce the vibration amplitude of vibrating shell using piezoelectric ceramics (both lead-based and lead-free). The simulation results reveal that Pb0.83La0.17(Zr0.3Ti0.7)0.9575O3 (lead zirconate titanate sensor) and (K0.475Na0.475Li0.05)(Nb0.92Ta0.05Sb0.03)O3 (KNLNTS actuator) combination reduces the vibration amplitude of vibrating shell structure faster than lead zirconate titanate (sensor) and lead zirconate titanate (actuator) combination. Moreover, for complete replacement of lead-based piezoelectric ceramics, 0.885(Bi0.5Na0.5)TiO3–0.05(Bi0.5K0.5)TiO3–0.015(Bi0.5Li0.5)TiO3–0.05BaTiO3 (BNKLBT sensor) and KNLNTS (actuator) combination is a potential candidate for active vibration control application.

Soft robots have advantages such as low weight and compact size compared to rigid robots. Variable stiffness is one of the key methods of improving the performance of a soft robot. The soft gripper grasps objects of various shapes or sizes based on the variable stiffness. In a previous study, we validated the variable stiffness mechanism where flexible and rigid segments were connected alternately in series. This paper presents a soft variable stiffness gripper that can be used to control the stiffness by pulling tendons. The soft gripper has three variable stiffness structures acting as fingers and the stiffness can be controlled using two motors by winding tendons. To understand the tendency of the stiffness variation and determine the design parameters, a compliant mechanism was developed using a pseudo-rigid-body model (PRBM). The experimental results show that the difference between the lowest and highest stiffness values of the fabricated variable stiffness gripper was 5.6 times the original. Similarly, the difference in the gripping weight was 19 times. Using the experimental results, the variable stiffness gripper can be designed and manufactured based on the required stiffness and used to grip various types of objects.

Variable stiffness manipulators balance the trade-off between manipulation performance needing high stiffness and safe human-robot interaction desiring low stiffness. Variable stiffness compliant links provide a solution to enable this flexible manipulation function in human-robot co-working scenarios. In this paper, we propose a novel variable stiffness link based on discrete variable stiffness units (DSUs). A DSU is a parallel guided beam that can adjust stiffness discretely by changing the cross-sectional area properties of the hollow beam segments. The variable stiffness link (named Tri-DSU) consists of three tandem DSUs to achieve eight stiffness modes and a maximum stiffness change ratio of 31. To optimize the design, stiffness analysis of the DSU and Tri-DSU under various configurations and forces was performed by a derived theoretical model compared with finite element analysis (FEA). The analytical stiffness model is derived using the approach of serially connected beams and superposition combinations. It works not only for thin-walled flexure beams but also for general thick beam models. 3-D printed prototypes were built to verify the feature and performance of the Tri-DSU in comparison with the FEA and analytical model results. It’s demonstrated that our analytical model can accurately predict the stiffnesses of the DSU and Tri-DSU within a certain range of parameters. The developed variable stiffness link method and analytical model are extendable to multiple DSUs with different sizes and parameter configurations to achieve modularization and customization. The advantages of the stiffness change mechanism are rapid actuation, simple structure, and compact layout. These methods and results provide a new conceptual and theoretical basis for the development of new reconfigurable cobot manipulators, variable stiffness structures, and compliant mechanisms.

A soft gripper with variable stiffness inspired by pangolin scales, toothed pneumatic actuator and autonomous controller

Geometrically nonlinear transient analysis of laminated composite super-elliptic shell structures with generalized differential quadrature method

Winkler–Pasternak foundation effect on the static and dynamic analyses of laminated doubly-curved and degenerate shells and panels

Considering the instability of the shell structure in a thermal environment, this paper presents a generalized approach to deal withthermal-mechanical coupling vibration properties of rotating functionally graded porous-graphene nanoplatelet reinforced composite (FGP-GNPRC) bolt-connected conical–cylindrical shells. A discontinuous circular arc connection is constructed to describe the bolt connection by improving the full-circle continuous artificial spring method. Meanwhile, arbitrary boundary conditions of the shell are derived using the artificial spring technology. The effective material properties of the FGP-GNPRC are obtained by using the Halpin–Tsai micromechanical model and open-cell body theory. The intrinsic relationships of the shell are derived through the first-order shear deformation theory (FSDT). The thermal strain caused by temperature difference is introduced into the energy equation using the Rayleigh–Ritz method, and admissible displacement functions are developed by Chebyshev polynomials. Finally, the effectiveness of the proposed method is verified by comparing numerical examples with the results from existing literature and the finite element method (FEM). Meanwhile, the influence of various parameters on the traveling wave frequency of the FGP-GNPRC bolt-connected conical–cylindrical shell is analyzed, with a particular focus on thermal-mechanical coupling vibration behaviors. The results indicate that the proposed method can flexibly adjust geometric parameters, material properties, bolt parameters, rotation speed, temperature variations, and so on, which can efficiently guide the dynamic design of rotating composite shell structures in the thermal environment.

Variable stiffness composite structures take full advantages of composite’s design ability. An enlarged design space will make the structure’s performance more excellent. Through an optimal design of a variable stiffness cylinder, the buckling capacity of the cylinder will be increased as compared with its constant stiffness counterpart. In this paper, variable stiffness composite cylinders sustaining combined loadings are considered, and the optimization is conducted based on the multi-objective optimization method. The results indicate that variable stiffness cylinder’s loading capacity is increased significantly as compared with the constant stiffness, especially when an inhomogeneous loading is considered.