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Journal of Applied Mechanics
Journal Prestige (SJR): 1.133
Citation Impact (citeScore): 2
Number of Followers: 178  
 
  Full-text available via subscription Subscription journal
ISSN (Print) 0021-8936 - ISSN (Online) 1528-9036
Published by ASME International Homepage  [25 journals]
  • Electromechanical Instability of Dielectric Elastomer Actuators With
           Active and Inactive Electric Regions
    • Authors: Sharma A; Kumar P, Singh AA, et al.
      Abstract: Electrically driven dielectric elastomers (DEs) suffer from an electromechanical instability (EMI) when the applied potential difference reaches a critical value. A majority of the past investigations address the mechanics of this operational instability by restricting the kinematics to homogeneous deformations. However, a DE membrane comprising both active and inactive electric regions undergoes inhomogeneous deformation, thus necessitating the solution of a complex boundary value problem. This paper reports the numerical and experimental investigation of such DE actuators with a particular emphasis on the EMI in quasistatic mode of actuation. The numerical simulations are performed using an in-house finite element framework developed based on the field theory of deformable dielectrics. Experiments are performed on the commercially available acrylic elastomer (VHB 4910) at varying levels of prestretch and proportions of the active to inactive areas. In particular, two salient features associated with the electromechanical response are addressed: the effect of the flexible boundary constraint and the locus of the dielectric breakdown point. To highlight the influence of the flexible boundary constraint, the estimates of the threshold value of potential difference on the onset of electromechanical instability are compared with the experimental observations and with those obtained using the lumped parameter models reported previously. Additionally, a locus of localized thinning, near the boundary of the active electric region, is identified using the numerical simulations and ascertained through the experimental observations. Finally, an approach based on the Airy stress function is suggested to justify the phenomenon of localized thinning leading to the dielectric breakdown.
      PubDate: Tue, 19 Mar 2019 00:00:00 GMT
       
  • Riccati Transfer Equations for Linear Multibody Systems with Indeterminate
           In-Span Conditions
    • Authors: Zhang J; Rui X, Gu J.
      Abstract: The transfer matrix method for linear multibody systems is capable of providing precise solutions for the dynamics of various mechanical systems, but it may also suffer from numerical instability in some cases, where serial chains with a large number of mechanical elements are involved or high-frequency harmonic responses are computed. Combining such a transfer strategy with the Riccati transformation yields the Riccati transfer matrix method (RTMM), which can help improve the numerical stability. According to the existing method, the conventional transfer matrices of all the mechanical elements should be obtained first; in other words, the existence of conventional transfer matrices is a prerequisite for the application of the RTMM. Thus, it seems that the RTMM is incapable of performing the dynamics analysis of linear multibody systems with indeterminate in-span conditions due to the nonexistence of the corresponding conventional transfer matrices. Observe that, for any state variables with indeterminate input–output relationships, the complementary state variables (the complementary state variable of a displacement is the corresponding internal force and vice versa) are identically equal to zero, and that the dimension of the Riccati transfer equation is only half of that of the conventional transfer equation. It reveals that the Riccati transfer equations for the connection points associated with indeterminate in-span conditions can be formulated directly, and that there is no need to rely on the conventional transfer equation. Two numerical examples are simulated and the computational results are compared with those obtained by the finite element method, which verifies the proposed method.
      PubDate: Tue, 19 Mar 2019 00:00:00 GMT
       
  • Tunable Contact of Epidermal Electronics With Skin Based on Ionic
           Polymer–Metal Composite Material
    • Authors: Chen W; Ren X, Wang Q, et al.
      Abstract: Epidermal electronics mounted on the body provides the robust and noninvasive interfaces to monitor the electrophysiological signals of human body. The contact characteristic of the epidermal electronics with the skin affects the accuracy of the measured signals. In this paper, ionic polymer–metal composite is used to regulate the interface force for the consistency of the contact performance. The patterns of the ionic polymer–metal composite are designed for the flexibility and the contact characteristic of the epidermal electronics with the skin. This study provides an approach for the adjustment of the contact characteristic, which is very valuable for the longtime accurate monitoring of the epidermal electronics attached on the skin.
      PubDate: Sat, 16 Mar 2019 00:00:00 GMT
       
  • Effect of Partition on the Mechanical Behaviors of Soft Adhesive Layers
    • Authors: Zhong D; Liu J, Xiang Y, et al.
      Abstract: A soft adhesive layer bonded between two rigid substrates, which are being pulled apart, may exhibit diverse instability phenomena before failure, such as cavitation, fingering, and fringe instability. In this study, by subdividing the soft layers into different numbers of disconnected smaller parts, we achieve desired instability modes and mechanical responses of the layer. The partition process not only retains the monotonicity on the tensile curve but also tunes the modulus and stretchability of the adhesive layer. Meanwhile, cavitation in layers of large aspect ratios is suppressed, and the hysteresis during cyclic loading is reduced. This study provides a guideline for the structural design of soft joints and adhesive layers.
      PubDate: Sat, 16 Mar 2019 00:00:00 GMT
       
  • An Innovative Approach of Using Continuous Impedance-Graded Metallic
           Composite System for Attenuation of Stress Waves
    • Authors: Fernando PN; Mohotti D, Remennikov A.
      Abstract: This paper presents an innovative approach of stress attenuation through a continuous impedance-graded material system for high strain-rate events. High energetic dynamic events such as blasts and impact could cause stress waves—in the form of elastic, plastic, and shock—to propagate in a solid material. An impedance-graded composite is created by arranging different metallic alloys in the reducing order of their impedance through the system. Impedance, which is the product of volumetric mass density and wave velocity, is chosen as the function as it plays a governing role in elastic, plastic, and shock waves. An analytical framework to quantify the stress wave propagation through an impedance-graded multimaterial system is developed based on the principles of shock and elastic wave theories. The numerical simulations carried out using nonlinear finite element code, LS-DYNA, were able to capture and quantify the elastic, plastic, and shock waves and their reflections at different interfaces. It was identified that the final transmitted stress wave, which could comprise elastic, plastic, and shock waves, as well as the reflected tensile elastic wave at each material interface, needs to be controlled in order to develop a robust multimaterial system.
      PubDate: Sat, 16 Mar 2019 00:00:00 GMT
       
  • Controllable Propagation of Bending Waves in Wrinkled Films
    • Authors: Ding X; Zhao Y, Yan D, et al.
      Abstract: Wrinkling is a common phenomenon in natural and engineering film structures. The wrinkles influence the geometry and dynamic response of these structures. In this work, we investigate the wrinkling of a stretched thin film containing engineered microstructures and its derived functionality on controlling the propagation of bending waves. The underlying mechanism is revealed and the effect of wrinkles on the bandgap of bending waves is systematically evaluated via numerical simulations based on the Bloch wave theory. We show that wrinkles with a customized wavelength can be triggered in the microstructured film due to the mismatched deformation in the film. The bandgap of the wrinkled film can be finely tuned via applied stretching, resulting in the controllable propagation of bending waves in thin films. Our work provides fundamental insights into wave propagation in wrinkled films and potential applications for dynamic control of the wave propagation in engineering film structures.
      PubDate: Sat, 16 Mar 2019 00:00:00 GMT
       
  • Nonlinear Buckling and Postbuckling of Shallow Arches With Vertical
           Elastic Supports
    • Authors: Zhou Y; Yi Z, Stanciulescu I.
      Abstract: This paper presents an analytical method to investigate the effects of symmetric and asymmetric elastic supports on the nonlinear equilibria and buckling responses of shallow arches. It is found that arches with symmetric elastic supports can bifurcate into secondary paths with high-order symmetric modes. When a small asymmetry exists in the elastic supports, the equilibria of the arch may abruptly split and lead to the occurrence of remote unconnected equilibria. Such unconnected equilibria can be obtained experimentally or numerically using typical path following controls only with prior knowledge of location of these paths. A small asymmetry in the elastic supports may also make a secondary branch shrink into points connecting surrounding equilibria, resulting in the appearance of more limit points. The analytical solutions are also derived to directly calculate critical loads. We find that the magnitude of the stiffness of symmetric elastic supports has no influence on limits loads and bifurcation loads at branching into secondary paths with symmetric configurations, but greatly affect the bifurcation loads of secondary paths with asymmetric configurations. All critical loads are very sensitive to the degree of asymmetry in the elastic supports. The asymmetry in the supports reduces the top values of all pairs of critical loads compared to the case of symmetric elastic supports. The results obtained from the analytical derivations are confirmed using finite element analysis (FEA).
      PubDate: Sat, 16 Mar 2019 00:00:00 GMT
       
 
 
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