Mechanics Research Communications 110 (2020) 103624 Contents lists available at ScienceDirect Mechanics Research Communications journal homepage: www.elsevier.com/locate/mechrescom Programmable assembly of bi-walled nonuniform beams: Concept, modeling and performance Talal Salem c , Pengcheng Jiao a,b,∗ , Hamed Bolandi c , Hassene Hasni c , Nizar Lajnef c a Institute of Port, Coastal and Offshore Engineering, Ocean College, Zhejiang University, Zhoushan 316021, Zhejiang, China b Engineering Research Center of Oceanic Sensing Technology and Equipment, Zhejiang University, Ministry of Education, China c Department of Civil and Environmental Engineering, Michigan State University, East Lansing, MI 48824, USA a r t i c l e i n f o Article history: Received 4 August 2020 Revised 28 October 2020 Accepted 2 November 2020 Available online 5 November 2020 Keywords: Postbuckling Nonuniform beams Assembly Theoretical modelling Numerical simulation a b s t r a c t Postbuckling structural instabilities has been shown to have useful mechanical characteristics such as well deformation resistance and recovery. However, the difficulties in control and programmability, due to the complex interconnected sensitivities to geometric and material properties, severely hinder the phe- nomenon use in multifunctional structural applications. In this paper, we propose a concept of nonuni- form beam assembly to increase the the controllability of the postbuckling response. Bilaterally con- strained, nonuniform beams are theoretically investigated to obtain the buckling instability, and the pre- dictions are compared with the experimental and numerical results with satisfactory agreements. Para- metric studies are carried out to demonstrate the tunability of the reported beam assembly with respect to the geometric properties and material parameters (i.e., Young’s modulus) of the nonuniform beams. Fi- nally, the use of the proposed beam assembly method is investigated for novel applications as mechanical triggers and deformation detectors. This study demonstrates an exciting approach to tune the mechani- cal characteristics of engineered assembly structures for novel applications, such as material embedded mechanical sensing. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Buckling has been usually considered as a limit state to avoid in typical structural design [1–3]. However, in recent years sig- nificant interest has been raised toward the potential positive us- ages of the buckling and postbuckling states in smart materials and structures [4]. For instance, instability of slender elements (i.e., buckling) has been designed in advanced structures to obtain pre- dominant mechanical response such as negative Poisson’s ratio [5], enhancement of deformation resistance [6], or deformation recov- ery caused by geometric nonlinearity [7]. Buckling-enabled monos- table, bistable, and multistable systems have been reported in mul- tifunctional devices [8]. Moreover, the instability behavior of a stiff thin film device integrated on a cylindrical substrate was inves- tigated for potential uses in smart wearable devices (e.g., smart- watch, wristband, etc.) [9]. The buckling behavior of mechanical metamaterials was also studied to develop energy absorption de- vices by maximizing its snap-through response [10]. In oreder to maximize the generated electrical energy, the control and opti- ∗ Corresponding author. E-mail address: pjiao@zju.edu.cn (P. Jiao). mization of the postbuckled beams (generators) mechanical char- acteristics, is required beams. Four control approaches have been reported for the tuning of the postbuckling response: (i) Mate- rial altering, specifically the switching of isotropic and orthotropic properties [11–13]; (ii) Geometric approach absed on investigat- ing non-uniform and non-prismatic geometries [14,15]; (iii) Con- straint changing strategies, from regular confinements to irregu- larly distributed constraints [16,17]; and (iv) our investigated as- sembly strategies based combining multiple easy to build and de- sign uniform beams to form a system with multi-variable control possibilities Theoretical, numerical and experimental studies were con- ducted to investigate the influence of material and geometric prop- erties on the beams. It was shown that the material variables are less influential when compared with the effects of geometry changes. More importantly, modifying a single beam element is in- suffient for effective optimization of the overall postbuckling mode transitions. Therefore, the constraint strategy was used to change the rigid and fixed walls into movable and spring-constrained walls [18,19]. In addition, Borchani at al. [20] used the assembly strategy to investigate a multi-beam system that stacks the elasticas in a parallel configuration, thus tailoring the postbuckling response of https://doi.org/10.1016/j.mechrescom.2020.103624 0093-6413/© 2020 Elsevier Ltd. All rights reserved.