Material Properties Of Individual Layers Research Articles

Determination of Transverse Shear Stiffness of Sandwich Panels with a Corrugated Core by Numerical Homogenization.

Knowing the material properties of individual layers of the corrugated plate structures and the geometry of its cross-section, the effective material parameters of the equivalent plate can be calculated. This can be problematic, especially if the transverse shear stiffness is also necessary for the correct description of the equivalent plate performance. In this work, the method proposed by Biancolini is extended to include the possibility of determining, apart from the tensile and flexural stiffnesses, also the transverse shear stiffness of the homogenized corrugated board. The method is based on the strain energy equivalence between the full numerical 3D model of the corrugated board and its Reissner-Mindlin flat plate representation. Shell finite elements were used in this study to accurately reflect the geometry of the corrugated board. In the method presented here, the finite element method is only used to compose the initial global stiffness matrix, which is then condensed and directly used in the homogenization procedure. The stability of the proposed method was tested for different variants of the selected representative volume elements. The obtained results are consistent with other technique already presented in the literature.

Development of an equivalent shell finite element for modelling damped multi-layered composite structures

A new equivalent shell finite element (FE) for modelling damped multi-layered structures is presented in this study. The method used for developing the new FE for such structures is based on the idea that the strain energy of the equivalent single-layer FE must be equal to the sum of the strain energies of individual layers. The so-called energy coefficients are defined for this purpose for the extensional, bending and shear deformations of the composite structure. These coefficients are then determined and used as correction multipliers during stacking the elemental matrices of individual layers. Two approaches, based on second-order strain or stress distribution assumption through the composite thickness, are investigated for deriving the shear energy coefficients. The damping capability of the FE developed here originates from using complex Young’s modulus to define the material properties of individual layers. The resulting equivalent single-layer shell element with four nodes has six degrees-of-freedom per node. The accuracy, advantages and limitations of the composite FE developed in this work are investigated using experimental as well as theoretical results. In the light of the finding of these investigations, further enhancement in the formulation is made by also utilising a new shear correction factor for the individual layers in the equivalent shell element. Final results for free- and constrained-layered structures confirm that the equivalent shell FE developed here can be used effectively for the prediction of the modal properties of damped multi-layered structures.

Bending and free vibration analyses of antisymmetrically laminated carbon nanotube-reinforced functionally graded plates

In this paper, a simple four-variable first-order shear deformation theory is further applied to solve the bending and free vibration problems of antisymmetrically laminated functionally graded carbon nanotube (FG-CNT)-reinforced composite plates. The adopted four-variable theory contains only four unknowns in its displacement field which is less than the Reddy’s first-order theory. The equations of motion are derived from the Hamilton’s principle with the help of specific boundary conditions. Laminated FG-CNT-reinforced plates with different distribution types of carbon nanotube through the thickness are considered. The material properties of individual layer are estimated by using the extended rule of mixture. Analytical solutions of various simply supported antisymmetric cross-ply and angle-ply laminates are given for case study. The effects of carbon nanotube volume fraction, length to width ratio and thickness to width ratio on the non-dimensional fundamental frequency and the central deflection are investigated for antisymmetrically laminated FG-CNT-reinforced plates.

Homogenization and Stress Analysis of Multilayered Composite Offshore Production Risers

An approach for stress analysis of multilayered composite cylinders is proposed for the analysis of new composite risers used in deep-water oil production of offshore petroleum industries. Risers essentially comprise long cylindrical sections connected end-to-end. In the formulation, only stresses and strains that are continuous through the thickness of the multilayered composite risers are taken to be equal to reported solutions for homogenous orthotropic hollow cylinders using homogenized material properties. These stress and strain solutions are then used to calculate the remaining discontinuous stresses and strains from the material properties of individual layers of materials. The homogenized elastic constants of cylindrically orthotropic composite risers are derived from force-deformation equivalence, taking into account the stress and strain distributions in each layer. Four typical loading conditions are considered in the stress analysis, namely, internal and external pressures, axial loading, bending, and torsion. Examples of homogenized elastic constants and stress analyses of composite cylindrical structures with different layups and materials are presented to demonstrate the application of the proposed method. The results compared very favorably with those from other solutions. This method provides practical benefits for the design and analysis of composite risers. Because there is no requirement to explicitly enforce interfacial continuity in this method, stress analyses of composite cylinders with many layers of different fiber angles or materials can be carried out efficiently. The homogenized elastic constants can greatly expedite the analysis of entire composite riser systems by replacing complex models of riser sections with homogenized riser sections.

Analytical modelling of multilayer beams with compliant interfaces

Different mathematical models are proposed and their analytical solutions derived for the analysis of linear elastic Reissner's multilayer beams. The models take into account different combinations of contact plane conditions, different material properties of individual layers, different transverse shear deformations of each layer, and different boundary conditions of the layers. The analytical studies are carried out to evaluate the influence of different contact conditions on the static and kinematic quantities. A considerable difference of the results between the models is obtained.

Determination of the orthotropic material properties of individual layers of printed circuit boards

To improve the reliability of printed circuit boards (PCBs), occurring failure modes have to be studied and analysed. In order to reduce the expenses of experimental testing, finite element analysis (FEA) is used to describe the failure behaviour. Therefore, the availability of the proper material data is crucial. As the materials used in printed circuit boards, glass fibre reinforced epoxy resin and structured copper, show anisotropic material behaviour, it is necessary to determine the direction-dependent material properties. However, as only very thin layers were available of these materials, no experimental mechanical out of plane characterisation could be performed. Thus, a combination of experiments, mean-field calculations and FEA simulations was used to generate the material data for both, the insulating and the conducting layers of the PCB. The generated material models were tested in board level simulations and compared to the results of simulations based on isotropic material behaviour. Significant differences were observed, approving the importance of proper material data, especially when the local stress and deformation field are important.

Correlation of Asphalt Concrete Layer Moduli Determined from Laboratory and Nondestructive Field Tests

The falling weight deflectometer (FWD) is widely used for in situ nondestructive assessment of pavement layer moduli. For this purpose, FWD deflections are used with a number of back-calculation methodologies to come up with layer moduli. Back-calculating layer moduli from FWD deflections collected on thin asphalt concrete (AC) pavements is a challenge because the predicted deflection basin is not sensitive to the AC modulus. This study utilizes the portable seismic pavement analyzer (PSPA) to improve the reliability of back-calculated thin AC layer moduli. Compared with the FWD, the PSPA provides a direct measurement of seismic modulus at a higher load frequency level relative to the frequencies associated with typical truck traffic. Thus, the seismic modulus determined from PSPA tests needs to be corrected with the load frequencies typically used for pavement design. This paper compares AC moduli determined from laboratory dynamic modulus tests with corresponding values determined from FWD and PSPA measurements. The results exhibited favorable correlation between the AC moduli determined from laboratory and field tests at corresponding load frequencies and temperatures. The paper also proposes a methodology to obtain a composite modulus from mixture properties determined from laboratory tests of individual AC lifts for the purpose of comparing the composite modulus with corresponding values determined from field tests. The authors generated master curves of individual AC lifts on the basis of corresponding binder temperature–viscosity relationships and volumetric properties obtained from laboratory tests. A procedure was proposed for correcting PSPA AC seismic modulus at corresponding load frequencies and temperatures by using the master curves with Odemark’s assumption. This evaluation showed a promising correlation between the corrected PSPA modulus and FWD back-calculated AC modulus. From this, the authors provide a simple equation as an alternative method for correcting PSPA modulus when the material properties of individual layer are not readily available to employ the proposed methodology.

Measurement of material properties of individual layers for composite films by a pull-in method

There has been an increasing need for MEMS devices with composite films in recent years. This paper presents an improved model of pull-in voltage by finite-difference method (FDM) for a composite fixed-fixed beam, which takes influence of lateral residual stresses of each layer into account. Young's modulus and residual stresses of each layer for composite beam can then be extracted by these pull-in voltages. And fixed-fixed surface machined beams with multi-cup style anchor were fabricated to be suitable to the model of pull-in voltage. Validation and accuracy of the extracting method have been verified by FEM simulation and experiments.

Role of Material Properties in the Finite Element Solution for Three-Dimensional Composites—A Sensitivity Study

Three-dimensional material test data for orthotropic laminae are difficult to obtain. Consequently, various simplifications are made for the material properties of individual layers in a finite element analysis, ranging from the assumption of transversely isotropic layers to applying two-dimensional material data in a three-dimensional analysis. In order to investigate the impact and validity of such simplifications, the sensitivity of the stresses and deformations in a finite element analysis on the material properties was investigated.