Design of bond strength testing method of concrete layers for creating a material model

On the modeling and design of composite multilayered structures using solid-shell finite element model

We present in this paper an efficient and accurate low-order solid-shell element formulation for analyses of large deformable multilayer shell structures with non-linear materials. The element has only displacement degrees of freedom (dofs), and an optimal number of enhancing assumed strain (EAS) parameters to pass the patch tests (both membrane and out-of-plane bending) and to remedy volumetric locking. Based on the mixed Fraeijs de Veubeke-Hu-Washizu (FHW) variational principle, the in-plane and out-of-plane bending behaviours are improved and the locking associated with (nearly) incompressible materials is avoided via a new efficient enhancement of strain tensor. Shear locking and curvature thickness locking are resolved effectively by using the assumed natural strain (ANS) method. Two non-linear 3-D constitutive models (Mooney–Rivlin material and hyperelastoplastic material at finite strain) are applied directly without requiring the enforcement of the plane-stress assumption. In particular, we give a simple derivation for the hyperelastoplastic model using spectral representations. In addition, the present element has a well-defined lumped mass matrix, and provides double-side contact surfaces for shell contact problems. With the dynamics referred to a fixed inertial frame, the present element can be used to analyse multilayer shell structures undergoing large overall motion. Numerical examples involving static analyses and implicit/explicit dynamic analyses of multilayer shell structures with both material and geometric non-linearities are presented, and compared with existing results obtained from other shell elements and from a meshless method. It is shown that elements that did not pass the out-of-plane bending patch test could not provide accurate results, as compared to the present element formulation, which passed the out-of-plane bending patch test. The present element proves to be versatile and efficient in the modelling and analyses of general non-linear composite multilayer shell structures. Copyright © 2005 John Wiley & Sons, Ltd.

In this paper a general methodology for the modeling of material composite multilayered shell structures is proposed using a Hex-shell finite element modeling. The first part of the paper is devoted to the general FE formulation of the present composite 8-node Hex-shell element called SCH8, based only on displacement degrees of freedom. A particular attention is given to alleviate shear, trapezoidal and thickness locking, without resorting to the classical plane-stress assumption. The anisotropic material behavior of layered shells is modeled using a fully three dimensional elastic orthotropic material law in each layer, including the thickness stress component. Applications to laminate thick shell structures are studied to validate the methodology, and good results have been obtained in comparison with ABAQUS© commercial code.

The paper provides a brief overview of domestic and foreign guidelines (manuals) for the design of composite steel and concrete structures: steel-concrete slabs on profiled flooring, combined beams, and columns with rigid reinforcement. The necessity of creation of the actual manual corresponding to the modernlevel of development of construction science, normative documents and design practiceslinked to the new formulary SP 266.1325800.2016 is proved. It will facilitate the design, reduce labor expenditures and improve the reliability of composite steel and concrete structures. The new guidance provides general recommendations for the design of composite steel and concrete structures and the basic regulations for the calculations. The new guidance describes recommendations for modeling of composite steel and concrete structures and elements in the calculated complexes, the recommendations for calculation of combined beams fully concreting rectangular and T-section, partially concreting along with support slab on the lower flange of the beam, columns with rigid reinforcement, shear a connection of composite beams. Recommendations on the registration of creep, shrinkage and crack formation in the appointment of the modulus of elasticity are given. Recommendations on the use of diagrams of the state of concrete, reinforcement, and steel in the calculation of steel-concrete elements on a nonlinear deformation model are given. Recommendations on the use of the range of sheet flooring for steel-reinforced concrete slabs, as well as metal profiles as steel beams and rigid reinforcement in the cross sections of columns and combined beams, are presented. Recommendations on a design of units and details of composite steel and concrete structures are given, refined recommendations on buffer are presented. The examples of connection of steel beams with columns with rigid reinforcement are given. The examples of calculation of composite steel and concrete structures taking subject to the recommendations given in the Manual are presented.

Advanced composite structures have been used for many years in the aerospace industry. When designing multilayered structures special attention must be paid to the bonding techniques since the interface conditions have a direct effect on the mechanical coupling between the individual layers. Previous studies have shown the overall acoustical performance such as transmission loss and surface absorption to be sensitive to this structural path mainly in the lower frequency range. The state of the art shows that a comprehensive model is still lacking in the framework of the transfer matrix Method. The present paper proposes a new analytical modeling approach to tackle systems with stiffeners in the low-frequency range. This technique is based on the so-called Series-Parallel network of the transmission line theory in the framework of the classical electro-acoustical analogies. The simulations show that in the typical case of a double plate with stiffeners, with regards to transmission loss the design change due to the mechanical path is captured and the increase of the overall stiffness of the system shifts the resonance to the higher frequencies. The other important acoustical properties of multilayered systems will be highlighted during the presentation with regards to optimizing the overall acoustical performance.

The high corrosion resistance of fiber-reinforced polymers (FRPs) and related concrete structures means that they are suitable for application in the marine environment. Therefore, the replacement of steel bars with fiber-reinforced polymer (FRP) bars enhances corrosion resistance in seawater sea-sand concrete (SSC) structures. Geometric parameters significantly influence the performance of the bond between ribbed FRP bars and SSC, thereby affecting the mechanical properties of the concrete structures. In this study, the performance of the bond between ribbed (i.e., with fiber wrapping) basalt-fiber-reinforced polymer (BFRP) bars and SSC was investigated through pull-out tests that considered rib geometry and SSC strength. The results demonstrated that an increase in rib and dent widths reduced the bond stiffness, while an increase in rib height and SSC strength gradually increased the bond stiffness and strength. Additionally, the bond stiffness and bond strength were relatively low because the surface fiber bundles buffered the mechanical interlocking force between the BFRP ribs and the concrete, resulting in plastic bond failure during the loading process. Furthermore, the adhesion of the fiber bundles to the surface of the BFRP bars also influenced bond performance, with higher adhesion leading to greater bond stiffness and strength.

Lengths and strengths of hydrogen bonds are exquisitely sensitive to temperature and pressure. Temperature and pressure sensitivity is the result of the fact that hydrogen bonds are so weak that the internal energy of the bond is important to bond strength, and the equilibrium bond distance is controlled by a combination of thermodynamics and quantum mechanics, rather than quantum mechanics alone. The importance of thermodynamics in the bond length, and strength, of hydrogen bonds is the result of a breakdown in the Born-Oppenheimer approximation that occurs when the energy of the first vibrational excitation of a bond is of the order of kT. Variation of water–water hydrogen bond length and strength with temperature and pressure is discussed in light of the data for the specific volume of ice Ih, the enthalpy of vaporization of liquid water, and the internal energy of the liquid. In most chemical contexts, correction of covalent bond strength for internal energy is not necessary. For hydrogen bonds this is not the case. In hydrogen bonded systems, like liquid water, the internal energy associated with hydrogen bonding is a significant fraction of the internal energy of the system. The variation of hydrogen bond length with temperature is approximately quadratic. Bond strength should also be quadratic with temperature because bond strength depends linearly on bond distance in second order. The internal energy correction is empirically quadratic in temperature. The net result is a linear dependence of apparent hydrogen bond strength on temperature. This can be seen directly in the variation of ΔHvaporization0/T for water with the reciprocal of temperature. The known variations in hydrogen bond equilibria with temperature in liquid formamide are discussed. Variation of the density of ice Ih with pressure, at constant temperature, demonstrates the nonlinear pressure dependence of hydrogen bond length. Because hydrogen bond strengths depend upon temperature and pressure, equilibria that involve hydrogen bonds explicitly depend upon temperature and pressure in addition to the universally appreciated dependence of the equilibrium constant on temperature. The temperature and pressure dependence of hydrogen bond length needs to be explicitly considered when one is modeling the properties of hydrogen bonded networks such as liquid water. Temperature dependence can be easily introduced by utilization of the hydrogen bond length, temperature relationship that is known for ice Ih and using a perturbation molecular orbital (PMO) treatment for bond formation. Our PMO treatment of hydrogen bonding involves second order perturbations between the donor and acceptor molecules. A random structural network model for liquid water based on this approach should be relatively easy to construct. The PMO model gives the relationship between hydrogen bond strength and hydrogen bond length as linear. This quantum mechanical result is quite distinct from the bond strength–bond length relationships obtained in classical models.

Over the last three decades, composite materials have been increasingly used in different engineering field due to their high stiffness-to-weight and strength-to-weight ratios. Nowadays, relatively thick laminated composite and sandwich materials with one hundred or more layers find their applications in primary load-bearing structural components of the modern aircraft. To ensure a reliable design and failure prediction, accurate evaluation of the strain/stress state is mandatory. A high-fidelity analysis of multilayered composite and sandwich structures can be achieved by adopting detailed 3D finite element models that turn into a cumbersome modeling at high computational cost. Thus, most of the researchers efforts are devoted to the development of approximated models wherein assumptions on the distribution of displacements and/or stresses are made. In the ‘80s, thanks to the original works by Prof. Di Sciuva, a new modeling strategy of multilayered composite and sandwich structures arose: the so-called Zigzag theories, wherein accuracy comparable with that proper of the Layer-wise models is achieved but saving the computational cost. For accuracy, computational cost and efficient finite element implementation, the most remarkable Zigzag model, inspired by the Prof. Di Sciuva's work, is the Refined Zigzag Theory. From its first appearance, the Refined Zigzag Theory has experienced several developments in terms of beam and plate finite element implementations and has been extensively assessed on static problems. The present research activity supports the great accuracy of the Refined Zigzag Theory and for this reason deals with some overlooked aspects, as the application to the functionally graded materials (Chapter 2), the mixed-field formulation (Chapter 3), the implementation of a beam finite element employing exact static shape functions (Chapter 5) and the correlation with experimental results (Chapter 8). By enriching the Refined Zigzag Theory and using the Reissner Mixed Variational Theorem, a novel higher-order mixed zigzag model is developed (Chapter 4). The higher-order zigzag model constitutes the underlying theory for a beam finite element, suitable for a thermo-mechanical analysis, and a plate element, formulated taking into account only mechanical loads. The results presented (Chapters 6-8), along with those already published in the open literature by other authors, still encourage the use of the Refined Zigzag Theory in the analysis of relatively thick multilayered composite and sandwich structures. Moreover, when the transverse normal stress and the transverse normal deformability effects are not negligible, the novel higher-order mixed zigzag model appears proficient to solve these cases in virtue also of its efficient finite element implementations. The author's auspice is that the models belonging to the Refined Zigzag Theory class becomes to attract attention of the companies involved in the design and analysis of multilayered composite and sandwich structures and of the finite element commercial codes that still implemented models not suitable for the analysis of composite and sandwich structures, as extensively demonstrated

Classical ply-by-ply analysis of multi-layered thick-section composite structures with tens of layers through the cross-section is often impractical, especially when material nonlinearity and time-dependent effects are included. This study introduces an integrated micromechanical-sublaminate modeling approach for the nonlinear viscoelastic analysis of thick-section and multi-layered composite structures. The sublaminate model is used to generate three-dimensional (3D) effective nonlinear responses at through-thickness material integration points with given spatial variations of strains determined from the trial strain increments of the standard displacement-based finite-element (FE). The number of material integration points is determined by the resolution of the FE discretization of the composite structure. The sublaminate model at a selected material point represents the effective nonlinear continuum behavior in its neighborhood using the 3D lamination theory with uniform in-plane strain and out-of-plane stress patterns through the representative layers. Therefore, the sublaminate has first-order stress and strain paths and cannot recognize the local sequence of the layers. While this approach is very effective approximation especially in the case of a very large number of repeating layers using relatively few elements (integration points) through the thickness, it cannot be used to represent the interlaminar stresses or bending/extension/twisting coupling effects within a sublaminate. A previously developed micromechanical model by the authors for a nonlinear viscoelastic unidirectional lamina is used for each layer in the sublaminate. The proposed modeling approach is first calibrated and verified against creep tests on off-axis glass/epoxy performed by Lou and Schapery (J. Compos. Mater. 5:208–271, 1971). Analyses for different thick-section laminated structures are presented using the integrated sublaminate with both shell and 3D continuum elements. The proposed 3D nonlinear time-dependent sublaminate model is computationally efficient and robust in analyzing multi-layered composite structures having large number of plies.

This paper deals with the magneto-electric effect observed in multilayer composite structures. A numerical modelling, based on the association of magneto-elastic and piezoelectric constitutive laws, is compared to an analytical solution. Various configurations of composite structures are studied.

Numerical investigation of the mechanical behavior of segmental tunnel linings reinforced by a steel plate – Concrete composite structure

SUMMARY Concerning composites plate theories and FEM (Finite Element Method) applications this paper presents some multilayered plate elements which meet computational requirements and include both the zig-zag distribution along the thickness co-ordinate of the in-plane displacements and the interlaminar continuity (equilibrium) for the transverse shear stresses. This is viewed as the extension to multilayered structures of well-known Co Reissner-Mindlin finite plate elements. Two different fields along the plate thickness co-ordinate are assumed for the transverse shear stresses and for the displacements, respectively. In order to eliminate stress unknowns, reference is made to a Reissner mixed variational theorem. Sample tests have shown that the proposed elements, named RMZC, numerically work as the standard Reissner-Mindlin ones. Furthermore, comparisons with other results related to available higher-order shear deformation theories and to three-dimensional solutions have demonstrated the good performance of the RMZC elements. Major portions of aerospace structures, as well as automotive and ship vehicles consist of flat and curved panels that are used as primary load-carrying components. Due to their obvious advantages, such as critical strength/stiffness-to-weight ratios, an increasing number of these panels are made of laminated composite material. This has led to extensive research activities in the mechanical properties, loading behaviour, structural modelling, and failure assessment of multilayered composite structures. Due to the geometry of laminated structural components, two-dimensional approaches have been extensively used to trace their response. The classical Kirchhoff's plate theory (CLT, Classical Lamination Theory) has revealed its limits when applied to thick panels with high orthotropic ratio.' - The shear deformation theories of Reissner-Mindlin-type (FSDT, First Shear Deformation Theories), even though, they are quite acceptable to study global response of high shear deformable thick composite structures, are not adequate for forecasting local stress-strain characteristics. In fact, some representative problems, exact three-dimensional have shown the failure of FSDT both to fulfill the interlaminar transverse shear stresses continuity at each interface and to describe the so-called zig-zag form' of the

The wear and failure mechanism for multilayered nanostructured coatings has a number of significant differences from the one typical for monolithic single-layered coatings. In particular, while the strength of adhesion bonds at the “substrate-coating” boundary is important for monolithic coatings, then for multilayered nanostructured coatings, the strength of adhesion and cohesion bonds at interlayer boundaries and boundaries of separate nano-sublayers becomes of significant significance. Meanwhile, the delamination arising in the structure of multilayered nanostructured coatings can have both negative (leading to loss of coating uniformity and subsequent failure of coating) and positive influences (due to decrease of internal stresses and inhibition of transverse cracking). Various mechanisms of formation of longitudinal cracks and delaminations in coatings on rake tool faces, which vary based on the compositions and architectures of the coatings, are studied. In addition, the influence of internal defects, including embedded microdrops and pores, on the formation of cracks and delaminations and the failure of coatings is discussed. The importance of ensuring a balance of the basic properties of coatings to achieve high wear resistance and maximum tool life of coated metal-cutting tools is shown. The properties of coatings and the natures of their failures, as investigated during scratch testing and dry turning of steel C45, are provided.

Electrically controlled liquid crystal nonlinear optical devices prepared by multi-layer composite structures

Structural concrete is a widely used building material due to its versatile characteristics including higher compressive strength and longevity. However, when exposed to fire, concrete experiences faster degradation in its mechanical properties and is also susceptible to spalling. To overcome this problem, the possibility of lightweight plaster application on High Strength Concrete (HSC) is explored in the presented investigation. Insulation plasters, namely Sand Plaster (SP), Gypsum Perlite Plaster (GPP), and Gypsum Mineral Wool Plaster (GMP) were developed. This investigation evaluates the compressive strength, bond strength, and shear strength of concrete which is exposed to the standard fire temperature. Varying cooling conditions which involved air and water were adopted to cool the concrete specimens after the elevated temperature test. Further, the damaged concrete and the plaster were examined to analyse the physical changes. Analysis of the study reveals that more number of denser surface cracks and higher mass loss was observed for reference and SP specimens. Temperature penetration at the core of cube, bond, and shear specimens is less for the GPP and GMP specimens when compared with the SP specimens. At higher temperatures (986 °C), the reference and SP specimens show a lower bond and shear strength with higher slip values. Specimens insulated with GPP and GMP exhibited a low-temperature penetration at the core portion. Also, the results of the study reported the higher residual compressive, bond, and shear strength compared to other specimens.