Stiffness Of Filler Research Articles

Composites with Re-Entrant Lattice: Effect of Filler on Auxetic Behaviour.

This study is focused on the deformation behaviour of composites formed by auxetic lattice structures acting as a matrix based on the re-entrant unit-cell geometry with a soft filler, motivated by biomedical applications. Three-dimensional models of two types of the auxetic-lattice structures were manufactured using filament deposition modelling. Numerical finite-element models were developed for computational analysis of the effect of the filler with different mechanical properties on the effective Poisson's ratio and mechanical behaviour of such composites. Tensile tests of 3D-printed auxetic samples were performed with strain measurements using digital image correlation. The use of the filler phase with various elastic moduli resulted in positive, negative, and close-to-zero effective Poisson's ratios. Two approaches for numerical measurement of the Poisson's ratio were used. The failure probability of the two-phase composites with auxetic structure depending on the filler stiffness was investigated by assessing statistical distributions of stresses in the finite-elements models.

Multi-objective optimisation methodology for stiffness combination design of bridge-embankment transition zones in high-speed railways

Bridge-embankment transition zones, in which unexpected amplifications of vehicle-track interactions and infrastructure degradation are concentrated, are critical areas of high-speed railways. To mitigate the dynamic issues induced by uncertain filler stiffness, an available stiffness combination of transition zone components is required. Combining with robust designs, a multi-objective optimisation methodology is proposed to determine the compromise design of transition zones, which considers trade-offs among dynamic stress, dynamic displacement and system robustness. An optimal stiffness combination of subgrade bed surface layer (E1) and graded broken stone area (E2) in a typical bridge-embankment transition zone is presented by employing this methodology. The results indicate that the Pareto fronts visually show the dynamic response contradiction. Based on the conflicting evaluation criteria, i.e., minimizing the displacement and stress of the subgrade and maximizing the system robustness, the knee points objectively render the best compromise design with E1 and E2 values of 1200 and 1000 MPa, respectively. Not only the dynamic response of the vehicle-track-subgrade system but also the negative effect brought by filler uncertainties are well controlled. Such a methodology is available for configuration design of projects in which uncertainties exist and design criteria are hard to weigh.

Utilization study on red brick waste as novel reinforcing and economical filler for acrylonitrile butadiene rubber composite

Red brick waste (RBW) powder was used as a reinforcing filler for acrylonitrile butadiene rubber (NBR) for preparing eco-friendly composites. The main constituent of this waste is silica which is considered to be one of the traditional fillers used in the rubber industry. So it was worthwhile to get (RBW) in a suitable manner by using this waste as a filler for NBR. Physicomechanical properties were evaluated, including tensile strength, elongation at break, hardness shore A, and change in mechanical properties after thermal-oxidative aging for seven days at 90 °C. In addition, equilibrium swelling in toluene for prepared composites was also included. Moreover, cross-linking density was measured according to Flory Rehner's equation. From physicomechanical measurements, it is observed that the tensile strength and hardness (shore A) increased with increasing the waste filler content because of the red brick filler's stiffness. In contrast, the elongation at break and equilibrium swelling degree decreased with increasing the waste filler content. The morphology of the polymeric composites was monitored using a scanning electron microscope which reflects the uniform distribution of the filler inside the NBR matrix. The electrical and magnetic properties of NBR/RBW composites were evaluated. The electrical measurements revealed that the values of ε′ increase by increasing red brick waste while ε'' decreases by increasing filler content. The dc conductivity σdc values lie in the order of 10–11 S/cm. This finding recommends that such composites could be used for insulation and antistatic applications. In addition, the magnetic measurements show superparamagnetic behavior in NBR/RBW composites. Therefore, the obtained composites be used as electromagnetic composites based on electrical and magnetic measurements.Graphical

Elastoplastic buckling of a cylindrical shell with initial geometric imperfections and an elastic filler at external pressure

A technique has been developed for the numerical calculation of deformation and elastoplastic stability loss nonlinear problems rotating shells based on the Tymoshenko hypotheses for nonshallow shells taking into account geometric nonlinearities. Kinematic relations are formulated in velocities and constructed in the current status metric taking into account large deformations, displacements and rotation angles of shell elements. plastic flow theory with nonlinear isotropic hardening describes physical relations. The motion equations result from the virtual working power balance. Winkler foundation models the revolution shell and the elastic filler contact interaction. The numerical calculation is based on an explicit “cross” type mesh scheme. The dependence of the elastoplastic revolution shell stability loss form and the load critical value on the filler stiffness under various values of the initial imperfections amplitude was studied.

Stability and Initial Post-Buckling Behavior of Orthotropic Cylindrical Sandwich Shells with Unidirectional Elastic Filler

The problem of the stability and initial post-buckling behavior of sandwich shells with transversely elastic light-weight filler is solved. The governing system of nonlinear equations is derived with allowance for structural discreteness that allows independent deformation of load-bearing layers. The system is solved with the asymptotic Koiter–Budiansky method. Structures composed of two cylindrical carbon-fiber shells interacting through a spring-type filler are analyzed. It is shown that the critical load under axial compression with like forces falls between the critical loads for the inner and outer shells. In the post-buckling state, the bending modes may be different. It is rational to increase the filler stiffness to a certain level.

Finite element analysis of a sandwich pipe joint

Sandwich pipes in which the core material performs both thermal insulation and structural function are viewed as a lightweight alternative to conventional pipe-in-pipe systems in which insulation material carries no loading. Developing a suitable method that permits the joining of sandwich pipes in an efficient manner is essential for their successful application. In this paper, the mechanical response of a swaged field joint between sandwich pipes subjected to bending is investigated using a series of finite element models. In order to gain a thorough understanding of the response of the joint components to installation based loadings, parametric studies are carried out to establish the effect of the inner pipe thickness, cutback length, and stiffness of the field joint filler on the strain concentration at the joint, with particular focus on the swaged weld region and the girth weld region. The influence of interface adhesion properties and weld metal yield strength on the variation of strain intensity is also evaluated. Numerical studies show that increasing filler stiffness and maintaining a cutback length less than 2.5 times the radius of the inner pipe could produce lower strain intensity at the two regions of interest.

DO WE NEED VERY STIFF FILLERS?

ABSTRACT The influence of reinforcing fillers on the stretching of a rubber matrix is analyzed. It is shown that a filler stiffness higher than a critical stiffness does not further enhance the stiffness of the reinforced elastomer. The stiffer filler induces a higher stress–strain concentration and causes filler–rubber dissociation or chain scission at a lower macroscopic strain. Reducing filler stiffness can reduce the stress–strain concentration and therefore delay rubber chain scission or dissociation from the filler surface. Accordingly, the toughness of the reinforced elastomer could be improved. A simple material model is developed to predict the maximum macroscopic strain without bond scission in a reinforced elastomer. It is shown that reduced filler stiffness is beneficial for cases with (i) reduced bond strength, (ii) increased rubber matrix stiffness, and (iii) increased application strain of the reinforced elastomer. The model can be used to design the appropriate filler stiffness to balance trade-offs of stiffness and toughness of reinforced elastomers.

Evaluation of Progressive Failure of Composite T-Joint Using Mixed Mode Cohesive Zone Model

T shaped stiffeners are the most commonly used structures in aerospace components. De-lamination/de-bond initiation followed by its growth is one of the most common reasons for failure in a fiber reinforced composite structure. It is caused by the interlaminar normal and shear stresses between different structural constituents. In a typical structural T-joint, the failure mechanism and location may differ based on the structural design parameters like fillet radius, thickness, layup sequence, filler stiffness, etc. In this study, finite element analysis has been performed using cohesive zone model (CZM) on a composite T-joint to simulate the pull out test conditions. A simplified plane strain model coupled with CZM is proposed, which can evaluate the failure initiation and progression accurately with lesser computational efforts. The final failure occurs at a displacement of 8.04 mm and the computed failure load is 2240 N. The results obtained by the proposed numerical model are validated by experimental results and it is observed that predicted regions of failure, failure displacements and failure load calculated are correlating reasonably well with the experiment.

Interaction Analysis of Infilled Frame Structures under Lateral Loads

Filler stiffness and confinement effect on the frame structure under horizontal loads, making the earthquake severely damaged in recent years with filler frame structure. Research shows that the actual stiffness frame structure with infill walls and internal force distribution and pure framework significantly different. In this paper, the equivalent model analysis bracing frame structure filler with actual stiffness, elasticity and structure from stage to stage of the internal forces shaping the distribution were analyzed. The results show that the stiffness of the contribution and the confinement effect filler by factors geometry, masonry materials, the impact of the framework is not the same, need to consider the specific analysis and structural design.

Two-Dimensional Stress Analysis of Adhesive Butt Joints Filled With Elastic Circular Fillers in the Adhesive Subjected to Static Tensile Loadings

This paper deals with a two-dimensional stress analysis of adhesive butt joints with elastic circular fillers in the adhesive subjected to external tensile loadings. Similar adherends and an adhesive including elastic circular fillers were replaced with finite strips in the analyses. Stress distributions in the adhesive butt joints were analyzed exactly using a two-dimensional theory of elasticity. The effects of stiffness, location of filler particles and number of filler particles on the interface stress distributions and at the periphery of the filler particles were examined in the numerical calculations. It was seen that as the amount of filler particles increased, the stiffness of filler increased and the location of filler approached the edges of interfaces, and the joint strengths were assumed to increase. For verification of the analyses, experiments were carried out to measure the strains. The analytical results were in fairly good agreement with the experimental results. In addition, the analytical results were also compared with those obtained from 2-D and 3-D FEM calculations. Fairly good agreements were seen among the analytical, the 2-D and 3-D FEM results. However, it was observed that the difference in the interface stress distributions between the present analysis and 3-D FEM calculation was substantial due to the stress singularity at the interfaces in the z-direction obtained from 3-D FEM. Rupture tests were conducted, and joint strengths were shown to be improved by adding the elastic fillers.

Vibration isolation using buckled or pre-bent columns—Part 1: Two-dimensional motions of horizontal rigid bar

The use of buckled columns, or pairs of pre-bent columns bonded with a viscoelastic filler, as vibration isolators is analyzed. They support a horizontal rigid bar at its ends, and harmonic vertical motion is applied at the base of the isolators. The displacement transmissibility is analyzed for both symmetric and asymmetric bars. In the latter case, the bar exhibits rotational as well as translational motion. Each column is modeled as an elastica, allowing for large deflections. Small steady-state vibrations about the equilibrium configuration of the system are analyzed. After formulation of the governing equations, a shooting method is utilized to obtain numerical solutions in Mathematica. The transmissibility is plotted as a function of the excitation frequency, and vibration shapes associated with peaks in the transmissibility plots are shown. For the buckled single-column isolators, the effect of the amount of asymmetry of the bar is examined. For the bonded two-column pre-bent isolators, the effects of the filler stiffness, amount of initial curvature, and supported weight are determined. The isolators can be effective for a large range of excitation frequencies.

Influence of filler stiffness on the thermoplastic stress state of cylindrical sandwich shells

UDC 629.%023: 539~ Depending on the stiffness properties of the filler of a circular cylindrical sandwich shell, its a~symmetric thermoelastic--p lastic stress state is analyzed. To clarify the fundamental singularities of this state, the solutions which are obtained on the basis of two fundamental versions of the theory of laminar shells using the kinematic hypotheses of a rigid normal for the whole packet and the hypothesis of the broken line [5-9] are compared. It is considered that the layer materials have different mechanical properties, are incompressible, and initially isotropie. The layer thicknesses are constant along the coordinates of the reduction surface, but distinct from each other. In the first case the reduction surface is superposed on the inner surface of the shell wall, and in the second case on the filler middle surface. We neglect creep strains, and the temperature is considered given. Let us elucidate the algorithm and write down the fundamental equations by which the problem formulated will be solved. The plastic deformations are taken into account in the physical equations as follows in the general case [3]: