Emerald | Multidiscipline Modeling in Materials and Structures | Table of Contents

Modeling of multi-cycle deformation of polymers with various deformation programs

literatinetwork@emeraldinsight.com (Aleksey D Drozdov, Necmi Dusunceli) — Fri, 21 Jun 2013 00:00:00 +0100

Abstract

Purpose - To compare mechanical response of polypropylene in multi-cycle tensile tests with strain-controlled and mixed deformation programs and to develop constitutive equations that describe quantitatively the experimental data.Design/methodology/approach - Multi-cycle tensile tests are performed on isotactic polypropylene with strain-controlled (oscillations between fixed maximum and minimum strains) and mixed (oscillations between a fixed maximum strain and the zero minimum stress) programs. A constitutive model is derived in cyclic viscoelasticity and viscoplasticity of semicrystalline polymers, and its parameters are found by fitting observations. The effect of damage accumulation of material parameters is analyzed numerically.Findings - The model predicts accurately mechanical behavior of polypropylene in tests with numbers of cycles strongly exceeding those used to determine its parameters. In the regime of developed damage, material constants in the stress–strain relations are independent of deformation program.Originality/value - A novel constitutive model in derived in cyclic viscoelastoplasticity of semicrystalline polymers and comparison of its adjustable parameters is performed for different deformation programs.

Wave propagation in Electro-Magneto-Elastic solid plate of polygonal cross-sections

literatinetwork@emeraldinsight.com (P. Ponnusamy) — Fri, 21 Jun 2013 00:00:00 +0100

Abstract

Purpose - This paper describes the method for solving vibration problem of electro–magneto -elastic plate of polygonal (Triangle, Square, Pentagon and Hexagon) cross-sections using Fourier Expansion Collocation Method (FECM). Design/methodology/approach - A mathematical model is developed to study the wave propagation in a electro-magneto-elastic plate of polygonal cross-sections using the theory of elasticity. The frequency equations are obtained from the arbitrary cross sectional boundary conditions, since the boundary is irregular in shape; it is difficult to satisfy the boundary conditions along the surface of the plate directly. Hence, the FECM is applied along the boundary to satisfy the boundary conditions. The roots of the frequency equations are obtained by using the secant method, applicable for complex roots.Findings - - From the literature survey, it is clear that the free vibration of electro-magneto-elastic plate of polygonal cross-sections have not been analyzed by any of the researchers, also the previous investigations in the vibration problems of electro-magneto-elastic plates are based on the traditional circular cross-sections only. So, in this paper, the wave propagation in electro-magneto-elastic plate of polygonal cross-sections are studied using the FECM. The computed non-dimensional frequencies are plotted in the form of dispersion curves and its characteristics are discussed.Originality/value - The researchers have discussed the circular, rectangular, triangular and square cross-sectional plates by the boundary conditions. In this problem, the author studied the vibrations of polygonal (triangle, square, pentagon and hexagon) cross-sectional plates using the geometrical relation which is applicable to all the cross-sections. The problem may be extended to any kinds of cross-sections by using the proper geometrical relations.

Thermal Model for Friction Stir Welding of Mild Steel

literatinetwork@emeraldinsight.com (Selvaraj M, Murali Vela, Rao SRK) — Fri, 21 Jun 2013 00:00:00 +0100

Abstract

Purpose - Purpose - Three dimensional thermal model for friction stir welding of AISI 1018 mild steel is proposed to predict the thermal cycle, temperature distribution, the effect of welding parameters on power required, heat generation and peak temperature during the friction stir welding process. Design/methodology/approach - Design / methodology / approach – The mathematical expressions for heat generation during the friction stir welding process were derived. The simulations for various welding and rotational speeds were carried out on ANSYS software employing temperature and radius dependent moving heat source and applying the boundary conditions. Findings - Findings - The predicted thermal cycle, torque required and temperatures were found to be in good agreement with the experimental results. The heat generation and peak temperatures were found to be directly proportional to rotational speed and inversely proportional to welding speed. The rate of increase in heat generation and peak temperature were found to be higher at lower rotational speeds and lower at higher rotational speeds. The heat generation during friction stir welding was found to be 71.4 % at shoulder, 23.1 % at pin side and 5.5 % at bottom of the pin.Originality/value - Originality / value – A new temperature dependent slip factor has been used to determine the contribution of slipping and sticking on total heat generation. A temperature and radius dependent moving heat source has been employed.

RECENT DEVELOPMENTS IN ANALYSIS OF DETERIORATING STIFFENED PANELS SUBJECTED TO STATIC AND EXPLOSIVE FORCES

literatinetwork@emeraldinsight.com (Osama Bedair) — Fri, 21 Jun 2013 00:00:00 +0100

Abstract

Purpose - The paper reviews recent developments for analysis of deteriorating stiffened panels subjected to static and explosive forces.Design/methodology/approach - The first part reviews numerical procedures developed for stiffened panels subjected explosive forces. The structural idealization, the theoretical basis, and the merits of these methods are discussed. The second part reviews the probabilistic procedures developed for analysis of deteriorating stiffened panels. The third part reviews recent work developed in several Finite element modelling philosophies for analysis of stiffened panels. The influence of various parameters affecting the structural performance, such as geometric and material imperfections, corrosion, residual stresses etc., is discussed. The fourth part reviews hybrid procedures developed to provide approximate solutions for the designers. Numerical procedure is presented using combination of energy formulations and mathematical programming techniques to model the interaction between the box girder componentsFindings - Localized damages largely affect the performance of stiffened panels and must be accounted for in the design phase. Little emphasis was given in the published literatures to develop simplified analytical models that can be used in practice to compute the residual strength of the stiffened panels under these types of loadings. Furthermore, analytical expressions are required to compute the reduction in the stiffness induced due to the structural or material defects. These expressions must be dependent on the type of damage. It must be noted that some these damages are localized in nature and must be accounted for by using specialized functions to assess the structural defect accurately. Research work is required in this direction.Originality/value - Very limited literature dealt with the ultimate strength of damaged stiffened structure under Static and Explosive Forces. No guidelines are available in current design codes to assess the damage in predicting the strength of deteriorating stiffened panels. The paper provides useful resource material for the engineers in practice regarding recent techniques developed to assess damaged stiffened panels subject to static and explosive loadings. The paper reviews work developed over the past 20 years that can be used as a baseline for future developments.

AN APPROACH FOR EXPLORING THE DYNAMICAL BEHAVIOUR OF INHOMOGENEOUS STRUCTURAL INCLUSIONS UNDER CONSIDERATION OF EPISTEMIC UNCERTAINTY

Fri, 21 Jun 2013 00:00:00 +0100

Abstract

Purpose - The purpose of this paper is to analyze the wave scattering behaviour of an inhomogeneous and eccentric inclusion in a homogeneous matrix material. Another purpose is to evaluate the influence of epistemic uncertainty to the wave scattering behaviour, particularly to the lack of knowledge about this eccentricity. This task calls for a multidisciplinary model.Design/methodology/approach - The inclusion is modelled as a multi-layered obstacle, with all layers being eccentric with respect to each other. The aterial behaviour of the embedding matrix is linear elastic and isotropic. In a multidisciplinary approach, the interaction of the inhomogeneous inclusion and the embedding matrix with respect to an incoming shear wave of arbitrary shape is solved analytically. The purely analytical solution process takes place in the frequency-domain. Due to the lack of knowledge about the eccentric configuration of the matrix inclusion and its influence on the total wave field inside the matrix material, the mechanical model is coupled with fuzzy set theory for modelling this non-stochastic uncertainty.Findings - An analytical model for describing the wave scattering behaviour of an elastic matrix inclusion with eccentric set-up is found and intimately connected with the framework of fuzzy set theory. Hence it is shown that the treatment of epistemic uncertainty with the derived analytical model is possible and fruitful. Additionally, it is shown that eccentric configurations lead to highly increased amplitudes with respect to the reference case of a concentric or even homogenous set-up of the inclusion.Practical implications - The results of this contribution do have implications to several practical applications for example in mechanical engineering and civil engineering, such as the design of subsequent reinforcement elements to existing structures, soundproof walls, the interaction of soil and building structures and so forth. In these areas, the reactions of structural elements or parts of them to dynamical loads are of great importance. The proposed method allows predictions of the dynamical behaviour of fibre-reinforced materials, whereas the geometric configuration of the (itself layered) fibre and the surrounding interphase is characterized by epistemic uncertainty.Originality/value - The value of this contribution is in the analytical model, which allows to predict the wave scattering behaviour of eccentric configurations of multilayered fibres including the surrounding interphase, and its coupling with fuzzy set theory to cope with the epistemic uncertainty inherent in the geometric set-up of the matrix inclusion.

MECHANICAL BEHAVIOUR AND DAMAGE EVALUATION BY ACOUSTIC EMISSION OF COMPOSITE MATERIALS

literatinetwork@emeraldinsight.com (chafik karra) — Fri, 21 Jun 2013 00:00:00 +0100

Abstract

Purpose - The aim of the present study is to investigate the mechanical behaviour of cross-ply laminates under static tensile and buckling loading. Different cross ply laminates constituting of carbon fibers (CFRP), hybrid fibers (HFRP) and glass ?bers (GFRP) in an epoxy matrix, were considered. This work is also interested in identifying and characterizing the local damage in the composites with the use of acoustic emission method (AE).Design/methodology/approach - The cross-ply laminates are differentiated by the stacking sequences, thickness of 90° oriented layers and reinforcement. They are subjected to the static tensile and buckling load. The damage investigation is reached by the analysis of acoustic emission signals collected from static buckling tests. Findings - The results show the effects of reinforcement type, stacking sequences and thicknesses ratio of 90° and 0° layers on the stiffness, failure load and displacement. A cluster analysis of acoustic emission data is achieved and the results are correlated to the damage mechanism of specimens under buckling tests.Originality/value - The analysis of acoustic emission signals collected from static buckling tests under loading levels of 40, 60 and 100% of the static failure load, allows the damage investigation in cross-ply laminates.

ADSORPTION-INDUCED FREQUENCY ANALYSIS USING NONLOCAL EULER-BERNOULLI BEAM THEORY WITH INITIAL AXIAL STRESS

literatinetwork@emeraldinsight.com (Xiao-Jian Xu, Zi-Chen Deng) — Fri, 21 Jun 2013 00:00:00 +0100

Abstract

Purpose - The purpose of this paper is to study the buckling and the vibration of the beam induced by atom/molecule adsorption using the nonlocal Euler-Bernoulli beam model with initial axial stress.Design/methodology/approach - The nonlocal parameter associated with adsorbed mass and bending rigidity variations of the beam induced by adsorbates are taken into account, the buckling and dynamic behaviors are obtained via the Hamilton’s principle, in which the potential energy between adsorbates and surfaces of the beam, the bending energy, the external work and the kinetic energy are summed as the Lagrangian function.Findings - The results show that, for both buckling and resonant frequency, the nonlocal effect should be considered when the beam scales down to several hundreds of nanometers, especially for higher mode numbers.Originality/value - The present paper gives the exact expressions for the buckling and resonant frequency of a simple-supported nonlocal beam with initial axial stress. Different from previous works, the mass increasing and bending rigidity of the beam are found size-dependent (nonlocal effect), resulting possible different static and dynamic behaviors of the beam when atom/molecular adsorption occurs. The exact expressions obtained for the buckling and resonant frequency may be helpful to the design and application of micro- and nanobeam based sensors/resonators.

Thermo-mechanical analysis of cold extrusion process using stream function and finite element methods

literatinetwork@emeraldinsight.com (S. Serajzadeh) — Fri, 21 Jun 2013 00:00:00 +0100

Abstract

Purpose - A mathematical model is proposed to estimate required energy and temperature distribution during cold extrusion process.Design/methodology/approach - An admissible velocity field is generated based on stream function technique. Then, the required energy and the temperature distributions in the metal and the extrusion die are determined by a coupled upper bound-finite element analysis. Findings - To examine the proposed model, cold extrusion of AA6061-10%SiCp is considered and the predicted extrusion force-displacement diagrams in different reductions are compared with the experimental ones and reasonable agreement is observed. Furthermore, it is found that there is a linear relationship between maximum temperature and logarithm of ram velocity for the examined composite.Originality/value - This approach requires shorter run-time as compared with fully finite element analyses while the model is particularly appropriate for high speed extrusion processes where the adiabatic heating is of importance.