81 research outputs found
Shear Piezoelectricity in Poly(vinylidenefluoride-co-trifluoroethylene): Full Piezotensor Coefficients by Molecular Modeling, Biaxial Transverse Response, and Use in Suspended Energy-Harvesting Nanostructures
No full textNon-contact actuated snap-through buckling of a pre-buckled bistable hard-magnetic elastica
No full textSnap-through buckling of bistable structures is a classic topic in mechanics which has been widely studied and applied in various fields such as mechanical meta-materials and soft robotics. Obstacles that hinder broader applications of conventional bistable structures include the requirement of contact actuation to trigger instability and difficulty to control post-buckling configurations. In contrast, hard magnetic elastica (HME), a composite made of hard ferromagnetic particles and soft elastomer that deforms in response to an externally applied magnetic field, exhibits great potential to bring major advances in this field by allowing non-contact actuation and programmable control of snap-through buckling via magnetization distribution (M−distribution). Here, we develop a theoretical framework to trace the instability and post-buckling evolution process of snap-through buckling of a bistable HME. In contrast to the conventional snapping through end-end shortening, the design space for bistable HME includes two key parameters: the remanent magnetization density after pre-magnetization and the external magnetic field. We focus on two simple yet practical cases: a fixed amplitude of magnetization density along the HME with direction reversed at the magnetization interface (M−interface), and a uniform magnetic field with varied direction. We identify an optimal position for the single M−interface and direction for the uniform actuation field for pre-buckled beams with two-ends fixed, which can reduce the required actuation field for snapping to nearly half in comparison with the symmetric cases. Experiments and finite element analysis are performed to validate the model predictions. Our work may stimulate further studies on utilizing snap-through buckling in applications where fast and large shape transitions from one stable state to another can be actuated in a low-energy, non-contact mode through a remotely applied stimulus field.Agency for Science, Technology and Research (A*STAR)Nanyang Technological UniversityNational Research Foundation (NRF)This work is supported by the Cyber Physiochemical Interfaces (CPI) project #A18A1b0045 and the Singapore National Research Fellowship (NRF-NRFF11-2019-0004). H. Gao acknowledges a start-up grant (002479-00001) from Nanyang Technological University and Agency for Science, Technology and Research (A*STAR)
Experimental investigation of interface curing stresses between PMMA and composite using digital speckle correlation method
No full textAbstractThis paper studies the interface curing stresses between polymethyl methacrylate (PMMA) and composite by means of digital speckle correlation method (DSCM). A new method by combining DSCM with the marker points is developed to measure the interface curing stresses, and the measurement principle is introduced. The interface curing stresses between PMMA and composite with different curing bonding conditions are measured and analyzed, this indicates that the residual stress for furnace heating and furnace cooling is the smallest. Finally, the measurement error is discussed by means of finite element method, the influences of glass microsphere between adhesive and PMMA can be ignored
Oxidation mechanism of ZrB2/SiC ceramics based on phase-field model
No full textIn this paper, the phase-field oxidation mechanism of ultra-high temperature ZrB2/SiC ceramics is investigated theoretically. Firstly, a phase-field model is developed to analyze the oxidation behaviors of multiphase materials. Secondly, the evolutions of the porosity and the oxidation stress for the oxidized ZrB2/SiC ceramics with different temperatures and different oxygen partial pressures are predicted, and the influences of the mechanical factors on the oxidation behaviors of ZrB2/SiC ceramics are discussed. Finally, two-dimensional oxidation behaviors of ZrB2/SiC ceramics are simulated and analyzed. (C) 2012 Elsevier Ltd. All rights reserved.Materials Science, CompositesSCI(E)EI0ARTICLE101196-12027
Experimental characterization of contact angle and surface energy on aramid fibers
No full textIn this paper, both contact angles and surface energy of aramid fibers are investigated using the liquid droplet method. First, the contact angles between matrix resin and aramid fibers are measured at different degrees of cure, which indicate that the contact angles increased initially and then decreased after the consolidation. Second, surface energy components of aramid fibers are determined from the contact angle using the geometric-mean equations. Finally, the influences of various surface treatments on the surface energy of aramid fibers are analyzed. These results play an important role for designing and evaluating the fiber/matrix interfacial strength of aramid fiber-reinforced composites.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000317821800006&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, ChemicalMaterials Science, MultidisciplinaryMechanicsSCI(E)EI2ARTICLE91012-10222
Mechanics Design for Buckling of Thin Ribbons on an Elastomeric Substrate Without Material Failure
No full textThe ribbons selectively bonded to a prestrained elastomeric substrate may buckle into three-dimensional (3D) microstructures after the prestrain release, leading to three possible deformation modes, global, local, and no buckling, depending on the adhesion between the ribbons and substrate. This note establishes analytically the critical length-to-thickness ratio of ribbons, above which the global buckling mode (preferred for mechanically guided 3D deterministic assembly) occurs without material failure.</jats:p
Evaluation on the Seal Performance of SMP-Based Packers in Oil Wells
No full textPackers based on shape memory polymers (SMPs) are an emerging technology that have the advantages of compact structure, easy manufacture, and adaptability to complex wells. This paper proposes a finite element model to simulate the setting process and mechanical response of an SMP packer. The investigated material is an epoxy-based thermal responsive SMP, whose relaxation modulus and thermal expansion coefficient were measured at different temperatures. Based on the experimental data, the model describes the viscoelastic behavior of the SMP using the generalized Maxwell model. The results show that the SMP packer could provide sufficient contact stress under downhole conditions, even after the stress was relaxed. A further parametric study revealed that the most significant factor in sealing effects is the wellbore pressure, followed by the interference between the packer and the annular, the seal length, the pre-compression, and the setting temperature. High downhole pressures require more significant contact stress and increase the risk of slip between the packer and casing wall by promoting shear stress. Increasing the seal length and interference enhances the contact stress and mitigates the shear stress to improve the seal performance. Pre-compression and setting temperatures are minor factors that have little influence on sealability
Material innovation and mechanics design for substrates and encapsulation of flexible electronics: a review
No full text- …
