Incompatible Modes Research Articles

Incompatible-mode geometrically non-linear finite element for micropolar elasticity

In this work a new three-dimensional geometrically non-linear hexahedral micropolar finite element enhanced with incompatible modes is presented. The analytical model is expressed in terms of Biot-like stress and couple-stress tensors and corresponding Biot-like strain and curvature tensors, with a linear, elastic and isotropic constitutive law. The numerical model is derived based on the principle of virtual work, and the residual derivation together with the linearisation and static condensation procedure is given in detail. The newly developed finite element is tested against the analytical solution of the geometrically non-linear micropolar pure bending problem and the element accuracy and robustness is compared against hexahedral Lagrangian finite elements of first and second order on several numerical examples. It is shown that the newly presented element is fast convergent, more robust and more accurate than the available Lagrangian elements. Moreover, the operator split and static condensation provide for a significantly lower computational cost than standard elements.

Magnesium nanoparticle modified cement-based composites: Performance and compatibility in repair applications

Applying ordinary repair mortars onto the surface of degraded concrete elements has been a common approach in restoration operations. Since the properties of cement-based composites depend on nano-structural features, proper addition of nanoparticles can enhance performance. In the present study, the physico-mechanical performance of concrete and mortar mixtures incorporating magnesium nanoparticles was investigated. The workability and flowability of the mixtures, along with compressive, tensile, and flexural strengths of specimens were evaluated. A total of 284 cylindrical, cubic, and prismatic beam specimens having different dosages of magnesium nanoparticles as partial replacement for cement were assessed to quantify the effects of adding magnesium nanoparticles. Furthermore, analysis of the compatibility between the repair mortar and the existing concrete substrate was examined using four-point bending tests on repaired beam elements to characterize the different modes of failure. Two approaches of substrate surface preparation featuring smooth and rough interfaces were adopted, and the effect of interface texture on the mechanical properties of the repaired beam specimens was evaluated. The results show that specimens incorporating magnesium nanoparticles achieved 37%, 37%, and 63% higher compressive, tensile, and flexural strengths, respectively, compared with that of the reference specimens. Moreover, the set of concrete beams with rough interface showed compatible failure modes, while those with smooth contact interface had incompatible modes of failure.

Three-dimensional Non-linear Finite Element Analysis of Impact Response and Damage in Laminated Composite Shells

The impact response and the impact-induced damage in curved composite laminates subjected to transverse impact by a metallic impactor are studied using three-dimensional non-linear transient dynamic finite element formulation. A layered version of isoparametric eight-noded hexahedral element with incompatible modes is developed which incorporates geometrical non-linearity based on total Langragian approach. The non-linearity of both strain displacement relation and contact loading are simultaneously solved using Newton-Raphson incrementaliterative method. Impact-induced damages (matrix cracking and delamination) are predicted using appropriate three-dimensional stress-based failure criteria. Some example problems of graphite/epoxy laminated cylindrical shells with variation of important parameters such as impactor velocity, shell curvature, laminate dimension and fibre orientation of plies are solved and the influence of geometrical non-linear effect on both impact response and resulting damages is demonstrated.

Geometrically exact beam theory with embedded strong discontinuities for the modeling of failure in structures. Part I: Formulation and finite element implementation

We introduce a three-dimensional geometrically nonlinear Reissner beam theory with embedded strong discontinuities for the modeling of failure in structures and discuss its finite element implementation. Existing embedded beam theories are geometrically linear or two-dimensional, motivating the need for the present work. We propose a geometrically nonlinear beam theory that accounts for cracks through displacement discontinuities in 3D. To represent the three modes of fracture inside an element, we enrich each displacement field with an incompatible mode parameter in the form of a jump, an additional degree of freedom. We then eliminate these nodeless degrees of freedom through static condensation and evaluate them within the framework of inelasticity by utilizing an operator split solution procedure. Seeing that the coupled strain-softening problem is non-convex, we present an alternating minimization (staggered) algorithm, thus retaining a positive definite stiffness matrix. Finally, the four-parameter representation by quaternions describes a three-dimensional finite rotation. We demonstrate a very satisfying and robust performance of these new finite elements in several numerical examples, including the fracture of random lattice structures with application to fibrous materials. We show that accounting for geometrical nonlinearity in the beam formulation is necessary for direct numerical simulations of fiber networks regardless of the density.

Two 8‐node quadrilateral unsymmetric elements with different incompatible modes immune to severe distortion

AbstractMost unsymmetric quadrilateral elements have demonstrated a high tolerance to mesh distortion in pure bending problems involving coarse meshes. However, they have difficulty achieving acceptable results in shearing‐dominated problems, and the element's performance is affected by the degree of mesh distortion. In this paper, two 8‐node quadrilateral elements are developed by introducing two different incompatible modes into the unsymmetric formulation. The unsymmetric framework with two different sets of interpolation functions for displacement fields provides the basis for the immunity property. The incompatible displacement mode and the enhanced assumed strain guarantee the completeness of the displacement field interpolation polynomials, and the satisfaction of ‐orthogonality condition ensures the accuracy of the simulations. The resulting elements, respectively, denoted as UQ10 and UQ10/E4, can provide exact solutions for both pure and linear bending problems and exhibit excellent insensitivity in shear‐dominated tests. Furthermore, they are invariant, rapidly converging, and free of various locking problems.

The moderating impact of product shadows on ad effectiveness perceptions for gestalt versus component product frames, product presentation color, and consumer visual processing modes

PurposeThis research aims to investigate the moderating impact of product shadows in gestalt versus component product frames on ad effectiveness perceptions. It offers insights on shadow-compatible and incompatible modes of product presentation color as well as consumer visual processing modes that offer optimal advertising effectiveness.Design/methodology/approachThis research begins with a content analysis of some popular print magazines and builds on qualitative findings from interviews conducted with two industry executives. It then undertakes four experiments to test the proposed hypotheses following a more deductive approach.FindingsResults reveal that incorporating product shadows increase ad effectiveness for gestalt products presented in black-and-white, but lower ad effectiveness for component products presented in color. Additionally, ad effectiveness for a gestalt (component) product presented in black-and-white (color) increases (decreases) in the presence of product shadow when consumers are currently processing in a compatible, gestalt (component) visual mode.Research limitations/implicationsIn addition to extending the limited marketing research on product shadows, this research contributes to the literature studying information communication theory (ICT) and advertising effectiveness, Construal-Level Theory (CLT), Heuristic–Systematic Model (HSM) of information processing and stylistic visual cues used in advertising.Practical implicationsThis research is focused on advertising effectiveness, providing a tangible outcome of interest to practitioners. An optimal use of this simple, inexpensive and stylistic ad element can help managers design effective communications without forgoing established brand equity.Originality/valueLimited marketing research on product shadows has only looked at their impact on product luxury implications (Sharma, 2016), experiential versus functional brand evaluations (Sharma, 2018) and product heaviness perceptions (Sharma and Romero, 2020). To the best of the authors’ knowledge, this work is the first to investigate specific gestalt versus component product contexts and the role of black-and-white and colored product presentations, along with specific consumer visual processing modes where shadows either increase or decrease the overall ad effectiveness.

Popularizing Moral Philosophy by Acting as a Moral Expert

Abstract This paper is concerned with the ethics of popularizing moral philosophy. In particular, it addresses the question of whether ethicists engaged in public debates should restrict themselves to acting as impartial informants or moderators rather than advocates of their own moral opinions. I dismiss the idea that being an impartial servant to moral debates is the default or even the only defensible way to publicly exercise ethical expertise and thus, to popularize moral philosophy. Using a case example from the public debate about the human use of nonhuman animals, I highlight the benefits and risks of endorsing an advocate’s and a teacher’s or moderator’s role, respectively. I argue for a general requirement of judgment transparency which entails that the publicly engaged philosopher ought to be clear and consistent about the type of role she takes on, her publicly advanced opinions generally ought to be her professional ones and that she ought to flag her private opinions. I finally show that, despite general concerns about conflicts of interest, exercising ethical expertise and engaging in advocacy, i.e., acting as if one were a moral expert, are not incompatible modes of public engagement for the moral philosopher.

Crack propagation simulation without crack tracking algorithm: Embedded discontinuity formulation with incompatible modes

We show that for the simulation of crack propagation in quasi-brittle, two-dimensional solids, very good results can be obtained with an embedded strong discontinuity quadrilateral finite element that has incompatible modes. Even more importantly, we demonstrate that these results can be obtained without using a crack tracking algorithm. Therefore, the simulation of crack patterns with several cracks, including branching, becomes possible. The avoidance of a tracking algorithm is mainly enabled by the application of a novel, local (Gauss-point based) criterion for crack nucleation, which determines the time of embedding the localisation line as well as its position and orientation. We treat the crack evolution in terms of a thermodynamical framework, with softening variables describing internal dissipative mechanisms of material degradation. As presented by numerical examples, many elements in the mesh may develop a crack, but only some of them actually open and/or slide, dissipate fracture energy, and eventually form the crack pattern. The novel approach has been implemented for statics and dynamics, and the results of computed difficult examples (including Kalthoff’s test) illustrate its very satisfying performance. It effectively overcomes unfavourable restrictions of the standard embedded strong discontinuity formulations, namely the simulation of the propagation of a single crack only. Moreover, it is computationally fast and straightforward to implement. Our numerical solutions match the results of experimental tests and previously reported numerical results in terms of crack pattern, dissipated fracture energy, and load–displacement curve.

Kenneth (Ken) Ronald Walter Brewer (1931–2021)

Kenneth (Ken) Ronald Walter Brewer (1931–2021)

Efficient flexible multibody dynamic analysis via improved C0 absolute nodal coordinate formulation-based element

Considering that the existing C1 absolute nodal coordinate formulation (ANCF) elements must satisfy C1 continuity, herein a four-node plane C0 ANCF element is proposed to overcome current limitations. The existing C1 ANCF elements, including differential degrees of freedom, cannot use various element types, and require considerable computation time. To overcome this limitation, a C0 derivation process for the ANCF element is proposed. Further, the incompatible mode is applied to improve the performance of the C0 ANCF elements. Moreover, the proper orthogonal decomposition method is applied to improve the calculational efficiency.

Finite element analysis of flexural behavior of precast segmental UHPC beams with prestressed bolted hybrid joints

To further enhance the joint mechanical performance in precast segmental ultra-high performance concrete (UHPC) beams, a new hybrid joint configuration combining prestressed strands and bolt connection (with or without epoxy resin at the joint surface) was proposed. The concept of the bolt connection stems from the design of steel structures. This new hybrid joint takes advantages of the high ductility of UHPC. This study developed a three dimensional finite element (FE) model to investigate the flexural behavior of precast segmental UHPC beams with the new prestressed bolted hybrid joints. All the structural components except for steel reinforcement bars were simulated through eight-node linear brick elements with incompatible modes. The interaction of the structural components and non-linear material properties were taken into account in the model. The prestressing force was applied on the beam by the equivalent temperature drop method and pre-tightening forces of high strength bolts were applied by the function of Bolt Load available in ABAQUS software. The FE results were compared with the previous experimental results in terms of load-deflection behaviors, characteristic loads, and failure modes for verification of the accuracy of the developed FE model. Based on the validated FE models, parametric studies were conducted to investigate effects of the friction coefficient of the steel plate, the amounts of prestressed steel strands, and the high strength bolt borehole diameter on the flexural behavior of precast segmental UHPC beams. This study might provide a reference for future use and design of precast segmental UHPC beams with prestressed bolted hybrid joints.

Interaction between a motorized walker and its user: effects of force level on within-stride speed and direction fluctuations

Motorized walkers are among assistive devices that are currently in development that aim to help older adults maintain their independence, which is of growing importance in today’s ageing world. However, motorized walkers attempt to combine two different modes of generating forward motion: the user’s bipedal gait and the motorized walker’s wheel-driven locomotion. In contrast to the uninterrupted propulsion and continuous motion of wheel-driven locomotion, bipedal gait is cyclical, whereas propulsion occurs mainly in the push-off phase and the velocity and position of its center of mass oscillate within each gait cycle. This study aimed to explore the consequence of combining these two incompatible modes by investigating the effects of different force magnitudes applied by the motorized walker on the within-stride fluctuations generated from interactions with its user. When a constant force is applied by a motorized walker, regardless of whether the force is assistive or resistive, the magnitudes of the within-stride speed and directional fluctuations during the steady-state use increase as the magnitude of the applied force increases. The increase in fluctuations may be attributed to the conflict between the cyclical nature of walking and the continuous force applied.

Estudo de deslocamentos em placas utilizando um elemento sólido de baixa ordem enriquecido com modos incompatíveis

The work proposes to study the displacement in plates, characteristics of geometry and diverse loads. The computational implementation of an 8-node hexahedral solid finite element is performed. After that, this element is enhanced through incompatible modes in order to improve the performance of the element in situations of multiaxial stresses, commonly present on plates. Then, we perform comparative analyzes with the purpose of studying the performance of the developed algorithm and compare its results with the final values of analyzes made by other authors, and with the results obtained by the modeling of the plates in commercial software. The analyzes take place in the static, linear and elastic range. It has been found that the enrichment of the low-order eight-node hexahedral solid element significantly improves its performance in plate analyzes, making it a viable alternative to the application.

A modified four-node rectangular element

The sensitized principle of virtual work is applied to modify the stiffness matrix of the ordinary four-node rectangular element by sensitizing terms. The sensitizing parameter values are determined by the single-element strain energy test. The reference solutions used are of bending mode types and their application removes the so-called parasitic shear behavior. A stiffness matrix of good quality is obtained corresponding exactly to an earlier formulation using incompatible modes.

A multifiber Timoshenko beam with embedded discontinuities

An enhanced high order multifiber Timoshenko beam is introduced to simulate structural behavior up to failure. The beam is displacement based and geometrically linear, its section can be of arbitrary shape and a local constitutive law is assigned to each fiber. The Strong Discontinuity Approach is adopted to enhance the displacement field of the fibers to describe crack openings. The material behaviour at the discontinuity is characterized by a linear cohesive law linking the axial stress and the displacement jump. The variational formulation is presented in the context of the incompatible modes method and details are given on the corresponding computational procedure and the numerical integration of the constitutive laws. The simulation of the non linear behavior of a cantilever beam structure and of a reinforced concrete frame are provided to illustrate the performance of the novel enhanced high order multifiber Timoshenko beam.

Comparison of advanced discretization techniques for image-based modelling of heterogeneous porous rocks

This contribution presents an assessment of computational techniques enabling automated simulations of complex porous rocks microstructures based on 3D imaging techniques. A subset of a CT-scanned sandstone sample is used to compare the results obtained by two advanced discretization frameworks. Raw scan results are processed by a level-set-based segmentation technique to produce smooth geometries prone to finite element discretizations. A recently developed technique is outlined for conforming mesh generation for complex porous geometries described implicitly by functions. This allows generating high-quality tetrahedral meshes with selective refinement. Next to this, a technique that uses a kinematic enrichment by incompatible modes to represent the heterogeneous geometry is explained. Both techniques use the same implicit geometry as main input for the simulations. Mechanical simulations are conducted on a subset of a scanned sample of a sandstone under triaxial loading conditions for isotropic compressive loading and for loading conditions involving a stress deviator. The results are compared and discussed based on local stress distributions and on a Mohr–Coulomb criterion with tensile cut-off. The results show that both discretization strategies yield complementary tools and allow envisioning automated simulations based on raw CT scan data for porous rocks exhibiting complex pore space morphologies.

Teacher Education in India, Issues and Challenges

Teacher education is a continuous process and its pre-service and inservice components are complimentary to each other. Education is instrumental in the preparation of teachers who can in their practice ensure transformative learning,where teacher and learner, learner and learner are co constructors of knowledge. The intent of the present paper is to enhance the teacher education quality in India by focusing on the emerging issues & related concerns. Various issues of teacher education namely, institutional inertia, brand inequity, quality crisis, overgrowing establishment, rare humane and professional teachers, poor integration of skills, alienated and incompatible modes of teacher education, little contribution to higher education, domain pedagogy mismatches, identity crisis, rare innovations, stake holders' non-alignment, inadequate technology infusion, little choice base, poor research scenario, vision and vision mismatches, non-scientific manpower planning, illusive laboratories, over activism of distance open universities, invalid recognition and accreditation and no teacher education policy have been dealt on in this paper. The paper concludes that teacher education system in India that calls for revolutionary change.

Numerical and experimental investigation on the deformation mechanism of micro single point incremental forming process

Single-point Incremental Sheet Forming (ISF) is a die-less forming process with advantages of high-flexibility, low-cost and short lead time. Recently, micro components have been employed in many applications, especially in medical industry using as implant components, surgical tool and tooth caring accessories etc. Therefore, the reduction of component size to micro-domain has becoming one of the key elements for the development of ISF technique, which will encounter many challenges, such as reduction of formability, tool wear, inaccuracies in tooling fabrication, etc. This work combined numerical and experimental approaches to study the deformation mechanisms in micro ISF process. Aluminum 1145 soft-temper foils with thickness of 38.1 μm and 50.8 μm were employed. A truncated pyramid with variable half-apex angle was employed here as the standard geometry for measuring the maximum forming angle that could be achieved in micro-ISF process. The result shows that forming angle has direct link with material formability. A full tool path micro-ISF finite element model has been developed using incompatible mode eight-node brick element C3D8I, which is capable to capture the shape and thickness distribution of the formed parts with most accuracy and least computational time. The thickness distribution of the workpiece was compared with the Sine Law to unveil the additional stretch region appearing at the top edge of the formed feature in the micro ISF as compared to macro ISF.

Inf-sup testing of some three-dimensional low-order finite elements for the analysis of solids

We assess some 8-node hexahedral three-dimensional (3D) solid elements using inf-sup tests focusing on locking behavior in volumetric, shear, membrane, and pinching actions. Inf-sup tests have been widely used to see whether a finite element discretization is effective. In this paper we use a rather simple approach to inf-sup testing for the coercivity of the discretization to obtain insight into the convergence behavior of the standard displacement-based element, the 8-node element with incompatible modes, and the 3D-MITC8 element, and include geometric nonlinear analysis. We see that the 3D-MITC8 element performs better than the incompatible modes element in plate bending problems and can also be used with a small modification in the solution of thick or moderately thick curved shell structures.

Numerical modelling of lockbolted lap connections for aluminium alloy plates

A numerical modelling method for lockbolted lap connections of aluminium alloy plates is studied based on experimental tests. The mechanical properties and constitutive models of aluminium alloy 6061-T6 and stainless steel 304HC were intensively determined by tensile tests. A tensile test of a single-lockbolted lap connection was conducted to obtain its elongation and strain responses. A basic numerical model that considers the lockbolt preload, interface contact and friction, and gaps between the lockbolt and bolt hole was established to simulate the tensile behaviours of this connection. This model was updated to minimize errors between the numerical and test results, and values for the friction coefficients of different contact surfaces were suggested. To improve the accuracy and efficiency of the numerical analysis, an incompatible mode solid element was adopted in the numerical model. It was determined to be better than refining the mesh or accepting a higher-precision element type. This numerical modelling method was investigated by two types of double-lockbolted connections, and its validity was verified by comparing the displacement and strain responses between the numerical and test models. The modelling method suggested in this paper is applicable for simulating the mechanical behaviours of complicated joints with lockbolted lap connections.