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  • 1.
    Al-Ramahi, Nawres
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Failure Impact Energy in Curved Composite Plates2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An investigation of low velocity impact characteristics of curved composite plates have been presented. The plates represent parts of car's bumpers with radii of curvature of 120mm,200mm, 300mm, 450mm and infinity.

    Two types of composite materials are used, unidirectional 0° and woven 0°/90° types with five layers of 3mm thickness and ten layers of 6mm thickness of each type.

    The results showed that larger plates curvatures can absorb more impact energy and the ten layer woven 0°/90° composite are superior to similar unidirectional 0° composite. On the other hand the five layer unidirectional 0° plates are superior in absorbing energy compared to similar woven 0°/90° plates.

    An investigation of the failure patterns and development for both types of composite has been presented and discussed.

    The effects of multi-strike on the energy absorbtion of both type of composite have showed different pattern of energy absorbtion behavior.

  • 2.
    Al-Ramahi, Nawres
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Numerical stress analysis in hybrid adhesive joint with non-linear materials2018Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis presents systematic numerical study of stresses in the adhesive of a single-lap joint subjected to various loading scenarios (mechanical and thermal loading). The main objective of this work is to improve understanding of the main material and geometrical parameters determining performance of adhesive joint for the future analysis of failure initiation and development in these structures.

    The first part of the thesis deals with development of a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates). The model takes into account the nonlinearity of materials (adherend and adhesive) with geometrical nonlinearity also accounted for. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criteria and it allows separation of edge and end effects. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters is carefully examined by analyzing peel and shear stress distributions in the adhesive layer. Discussion and conclusions with respect to the magnitude of the stress concentration at the ends of the joint overlap as well as overall level of stresses within overlap are presented. Recommendations concerning use of nonlinear material model are given.

    The rest of the work is related to the various methods of manufacturing of joint (curing) and application of thermo-mechanical loading suitable to these scenarios. The appropriate sequences of application of thermal and mechanical loads for the analysis of the residual thermal stresses developed due to manufacturing of joints at elevated temperature required to cure polymer (adhesive/composite) are proposed. It is shown that the most common approach used in many studies of simple superposition of thermal and mechanical stresses works well only for linear materials and produces wrong results if material is non-linear. The model and simulation technique presented in the current thesis rectifies this issue and accurate stress distributions are obtained. Based on the analysis of these stress distributions the following conclusions can be made: joint processing at elevated temperature causes high stresses inside the adhesive layer; the residual thermal stresses will reduce the peel stress concentration at the ends of overlap joint and the shear stress within the overlap, moreover, this effect is more pronounced for the case of the one-step joint manufacturing in comparison with two-step processing technique.

    This study has generated a lot of results for better understand of behavior of adhesive joints and it will help in design of stronger, more durable adhesive single-lap joints in the future.

  • 3.
    Al-Ramahi, Nawres
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Institute of Technology, Middle Technical University, Baghdad.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Swerea SICOMP AB.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Fem analysis of stresses in adhesive single-lap joints with non-linear materials under thermo-mechanical loading2018Inngår i: ECCM18, 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This study presents comprehensive numerical stress analysis in the adhesive layer of a single-lap joint subjected to various loading scenarios (mechanical and thermal loading). For this purpose numerical model (finite element method) with novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates) has been developed. This model includes nonlinear material model and geometrical nonlinearity is also accounted for. The effect of thermal residual stresses (in adhesive) is analysed for various methods of manufacturing of single lap joint. The sequences of application of thermal and mechanical loads for the analysis of the thermal residual stresses in joints are proposed. It is shown that the most common approach used in many studies of linear superposition of thermal and mechanical stresses works well only for linear materials and produces wrong results if material is non-linear. The present study demonstrates suitable method to apply combined thermal and mechanical loads to get accurate stress distributions. Based on the analysis of these stress distributions the conclusions concerning the effect of the thermal residual stresses on peel and shear stress concentrations are made. The comparison between effect of thermal stresses in case of the one-step and two-step joint manufacturing techniques is made.

  • 4.
    Al-Ramahi, Nawres
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Institute of Technology / Baghdad, Middle Technical University, Baghdad, Iraq.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Swerea SICOMP AB, Piteå, Sweden.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Investigation of end and edge effects on results of numerical simulation of single lap adhesive joint with non-linear materials2018Inngår i: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 87, s. 191-204Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents systematic numerical study of stresses in the adhesive of a single-lap joint with the objective to improve understanding of the main material and geometrical parameters determining performance of adhesive joints. For this purpose a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates), are employed. The model accounts for non-linearity of materials (adherend and adhesive) as well as geometrical non-linearity. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint allowing to separate edge effect from end effects is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criterion. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters on peel and shear stress distributions in the adhesive layer is examined carefully and mechanical parameters governing the stress concentrations in the joint have been identified, this dependence can be described by simple but accurate fitting function. The effect of the used material model (linear vs non-linear) on results is also demonstrated.

  • 5.
    Al-Ramahi, Nawres
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Model for numerical simulation and parametric analysis of composite adhesive joints under thermo-mechanical loading2017Inngår i: ICCS20: Proceedings : 20th International Conference on Composite Structures / [ed] Antonio J.M. Ferreira, W. Larbi, J.F. Deu, F. Tornabene, N. Fantuzzi, Paris: Società Editrice Esculapio, 2017 , 2017, , s. 662s. 234-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Abstract: The current investigation focuses on development and verification of a modelfor numerical simulation of performance of adhesive joints under tensile loading. Differentcombination of materials in joints is considered: metal-metal, composite-composite andcomposite-metal. The objective of this paper is to present simulation results of joints usingan accurate finite element model including non-linear behaviour and large deformation.Moreover, several loading scenarios are analysed, including simultaneous application oftemperature and mechanical load. Not only the effect of temperature on mechanicalperformance of materials (adhesive as well as adherents) is analysed but also built up ofresidual thermal stresses during the manufacturing of joints are taken into account. Thisapproach is demonstrated by simulation of tensile tests of joints at several temperatures.Two scenarios of application of temperature and mechanical load using large deformationtheory are considered: 1) the thermal and mechanical loads are applied simultaneously (theproperties of the materials are adjusted accordingly to their performance at differenttemperatures); 2) temperature is applied on specimen which is not macroscopicallyconstrained and the obtained stress distribution is used as initial state for the nextsimulation of mechanical loaded joint. The influence of edge effects (due to limited widthof the joint) on the stress distribution within the joint are studied. In order to eliminatethese effects the periodic boundary conditions (BC) are used in the numerical model.These BC are adjusted to optimize numerical model and obtain efficient calculation routinefor analysis of stresses within interior part of the structure. The validity of these BCs isevaluated and verified by analysing number of case studies. The comparison between full3D FEM model and simplified 2D model is carried out. The resulting stress distributions inthe overlap region of joints are presented for different joints (the parameters are: materialcombinations, material models, geometry of adhesive layer, constraints and BCs) withcomprehensive analysis and recommendations for optimal numerical model that can beused in joint design.

  • 6.
    Al-Ramahi, Nawres
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Numerical stress analysis in adhesive joints under thermo-mechanical load using model with special boundary conditions2019Inngår i: 2nd International Conference on Sustainable Engineering Techniques (ICSET 2019)6–7 March 2019, Baghdad, Iraq, Institute of Physics (IOP), 2019, Vol. 3, artikkel-id 032061Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A numerical study of the adhesive joint made of similar and dissimilar adherends subjected to thermo-mechanical loading is presented. A comprehensive numerical model was used for this purpose with the novel displacement coupling conditions which are able to correctly represent monoclinic materials (off-axis layers of composite laminates). The geometrical nonlinearity as well as nonlinear material model are also taken into account. Three different types of single-lap and double-lap adhesive joints are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). This paper focuses on the parameters which have the major effect on the peel and shear stress distribution within adhesive layer at the overlap ends. The comparison of behaviour of single- and double- lap joints in relation to these parameters is made. The master curves for maximum stress (peel and shear) at the ends of the overlap with respect to the bending stiffness and axial modulus of the adherends are constructed by analysing stress distributions in the middle of the adhesive. The main conclusions of this paper are: the maximum peel stress value for SLJ is reduced with increase of the adherend bending stiffness and for DLJ, similar behaviour was observed at the end next to the inner plate corner, while, at the end next to the outer plate corner peel stress is reduced with increase of adherend axial modulus.

  • 7.
    Jabar Nasser, Nawres
    Institute of Technology, Baghdad, Iraq.
    Investigation of fatigue life of 6061-T6 aluminum alloys welded by metal inert gas welding2015Inngår i: Journal of Engineering and Development, ISSN 1813-7822, Vol. 19, nr 3, s. 1-15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present research aims to investigate the effects of Metal Inert Gas (MIG) weldingprocess on the mechanical properties and fatigue life of AA 6061 T6. A series ofexperimental techniques has been conducted to evaluate the mechanical and fatigue life.metal inert gas (MIG) have been carried out on Rolled sheet of 12mm thickness to obtainmany butt welding joints with dimensions of (200 *100* 12) mm and with geometry ofsingle and double V at (70⁰) and square using ER- 5356 as a filler metal and argon asshielding gas. The welded pieces were tested by X-ray radiography and Faulty pieceswere excluded Welding joints were subjected to heat treatment including heating thejoints in furnace to (150 °C) for one hour then air cooling to relief heating stress.Allspecimens subjected to Vickers hardness, tensile test and microstructure examination.The examinations were carried out to show the effect of MIG weld method on the jointmicrostructure. The fatigue test of the welds and base alloy were examined to obtain theS-N curve.Results showed a general decay of mechanical properties of MIG weld jointthat is due to heat input during the welding process and low cooling rate.

  • 8.
    Jabar Nasser, Nawres
    Institute of Technology, Baghdad, Iraq.
    Mechanical Properties of MIG Joints for Dissimilar Aluminum Alloys (2024-T351 and 6061-T651)2016Inngår i: Al-Khwarizmi Engineering Journal, ISSN 1818-1171, Vol. 12, nr 3, s. 121-128Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The research aims to investigate the effects of GMAW or MIG welding process on the mechanical properties ofdissimilar aluminum alloys 2024-T351 and AA 6061- T651. A series of experimental techniques have been conductedto evaluate mechanical properties of the alloys, by carrying out hardness, tensile and bending tests for welded and unweldedspecimens.Metal inert gas (MIG) has been carried out on sheet metal using ER- 4043(AlSi5) as a filler metal and argon asshielded gas. The welded joints were tested by X-ray radiography and Faulty pieces were excluded.Welding joints without defects are subjected to heat treatment including heating the joints in furnace to 170 °C forhalf an hour then air cooling to relief welding stress.Tensile test was implemented for all specimens which prepared in the dimensions according to ASTM 17500 byusing Testing machine smart series with preload value 100 kN. Vickers hardness test and microstructure examinationwere made, the last test was bending test which implemented on the welded and un welded specimens which machinedinto standard test specimen dimensions.Results of mechanical properties Using MIG welding process appear a general decay compared with un welded andin the dissimilar joint comparing with parent metal that is due to the microstructure change during the welding process.The location of the failure for welded specimens after all mechanical test was found predominantly along the heataffected zone ( HAZ ).but Unwedded specimens were failed near the center line of the specimen.

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