Absence Of Bending Research Articles

Spontaneous change of symmetry in a magnetoactive elastomer beam at its critical bending induced by a magnetic field

The features of the critical bending deformation and magnetization of a magnetoactive elastomer (MAE) beam with a fixed end in a transverse uniform magnetic field have been studied. After the beam reaches a critical bending, the symmetry of the beam shape and the symmetry of the MAE magnetic state change spontaneously. At the critical point, a continuous transition from the highly symmetric magnetic state in the unbent MAE beam to the low symmetric magnetic state in the bent MAE beam (this is the angular state with the effective magnetization inclined to the field) takes place. The beam bending occurs due to the gain in the magnetic energy of the beam. The formation of an angular magnetic state in it has a magnetoelastic origin and is characterized by the critical behavior of the mutually related bending and longitudinal effective magnetization of the MAE, but it is the magnetization that plays the role of order parameter. Furthermore, there is no longitudinal magnetization in the absence of bending and, vice versa, there is no bending in the absence of longitudinal magnetization. The influence of a low remanent magnetization, which eliminates the uncertainty in the bending direction, on the critical bending has been analyzed. The role of the magnetorheological effect, which affects the critical field magnitude and leads to the appearance of field-induced bending hysteresis near the critical point, has also been elucidated.

Energy Minimizing Configurations for Single-Director Cosserat Shells

We consider a class of single-director Cosserat shell models accounting for both curvature and finite mid-plane strains. We assume a polyconvexity condition for the stored-energy function that reduces to a physically correct membrane model in the absence of bending. With appropriate growth conditions, we establish the existence of energy minimizers. The local orientation of a minimizing configuration is maintained via the blowup of the stored energy as a version of the local volume ratio approaches zero. Finally, we specialize our results to three constrained versions of the theory commonly employed in the subject.

VDNA: The virtual DNA plug-in for VMD

Summary: The DNA inter base pair step parameters (Tilt, Roll, Twist, Shift, Slide, Rise) are a standard internal coordinate representation of DNA. In the absence of bend and shear, it is relatively easy to mentally visualize how Twist and Rise generate the familiar double helix. More complex structures do not readily yield to such intuition. For this reason, we developed a plug-in for VMD that accepts a set of mathematical expressions as input and generates a coarse-grained model of DNA as output. This feature of VDNA appears to provide a unique approach to DNA modeling. Predefined expressions include: linear, sheared, bent and circular DNA, and models of the nucleosome superhelix, chromatin, thermal motion and nucleosome unwrapping.Availability: VDNA is pre-installed in VMD, http://www.ks.uiuc.edu/Research/vmd. Updates are at http://dna.ccs.tulane.edu.Contact: bishop@tulane.edu

High-Fidelity Micromechanical Modeling of Continuously Reinforced Elastic Multiphase Materials Undergoing Finite Deformations

The purpose of this communication is twofold. First, we demonstrate the predictive capability of a recently extended micromechanics model known as the high-fidelity generalized method of cells, originally developed for unidirectionally reinforced periodic multiphase materials characterized by elastic or elasto-plastic phases undergoing infinitesimal deformation. The recent extension incorporates finite-deformation capabilities to enable modeling of heterogeneous materials such as fiber-reinforced rubbers or certain types of biological tissues characterized by potential-based, nonlinear elastic phases. The model's capability to accurately estimate both the homogenized nonlinear elastic response and the local stress fields in the individual phases is demonstrated by comparison with an exact elasticity solution for a porous composite with four different types of the matrix material under axisyrmnetric loading, and a finite-element analysis of a repeating unit cell representative of a unidirectionally reinforced periodic composite subjected to transverse loading. Second, we demonstrate the micromechanics model's utility as a subroutine in a structural analysis setting by implementing it into a specialized lamination theory framework in the absence of bending. Examples of the nonlinear response of families of [±θ]s lay-ups under biaxial inplane loading are provided, demonstrating how the developed model can be used either to validate or to construct macroscopic constitutive laws for materials, such as certain biological tissues, characterized by multi-directional reinforcement.

Fiber fragmentation during processing of metallic matrix composites

Fiber fragmentation is a problem frequently encountered during the processing of metallic matrix composites. In this study, we examine the fragmentation of continuous fibers during a common composite consolidation process based on hot pressing in an open-ended channel die with fibers aligned parallel to the die walls. During the latter stages of consolidation, flow of the matrix along the die cavity may occur such that the resulting load transfer to the fibers can cause their fracture even in the absence of bending. This study analyzes the combination of conditions necessary for both matrix flow along the die cavity and the shear-lag loading of the fibers to a level that causes fragmentation. In order to validate the analysis, we model the fragmentation of fibers during elevated temperature hot pressing of Ni-base composites by the room-temperature consolidation of degraded sapphire fibers in a tin matrix. The observed fiber fragmentation behavior is in good agreement with theoretical predictions. The analysis also indicates that this mode of fiber fragmentation is confined either to low volume-fraction fiber composites or to the ends of panels of high volume-fraction fiber composites.

Fiber fracture in the absence of bending during MMC processing

Fiber fragmentation during hot pressing of metal matrix composites has been examined for the case where the matrix flows along the die cavity. In this case, fiber fracture occurs due to load transfer from the deforming matrix onto the fibers. Fiber bending is not a necessary condition. A shear lag model is developed to predict fragmented fiber lengths, which are comparable to observed lengths of fragmented sapphire fibers hot pressed in a niobium matrix.