| 1. |
- Al-Ramahi, Nawres J., 1980-, et al.
(författare)
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Numerical analysis of stresses in double-lap adhesive joint under thermo-mechanical load
- 2021
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 233
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study for the double-lap adhesive joint made of similar adherends subjected to tensile and thermal loads is presented. A novel displacement coupling conditions which are able to correctly represent monoclinic materials (off-axis layers of composite laminates) are used to build a comprehensive numerical model. Two types of double-lap joints are considered in this study: metal–metal and composite-composite. In case of composite laminates, four lay-ups are evaluated: unidirectional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/−45]S and [90/45/0/−45]S). The effect of different parameters (adherend stiffness, ply stacking sequence, adherend thickness, one-step or two-step manufacturing of the joint) on peel and shear stress distribution in the middle of the adhesive is studied. The comparison of the behaviour of single-lap and double-lap joint in relation to these parameters is made. The maximum peel and shear stress at the ends of the overlap with respect to the axial modulus of the adherends are presented in a form of the master curves. The analyses of results show that: the maximum peel and shear stress concentration at the overlap ends is reduced with the increase of the axial modulus of the adherend; the stress distribution in the adhesive layer can be improved (lower stress concentrations and level-out the curve) by changing the fibre orientation (which affect the stiffness) in plies connected to the adhesive layer.
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| 2. |
- Al-Ramahi, Nawres J., 1980-, et al.
(författare)
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Numerical stress analysis for single-lap adhesive joint under thermo-mechanical load using non-linear material
- 2020
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Ingår i: The 3rd International Conference on Sustainable Engineering Techniques (ICSET20). - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- A comprehensive stress analysis by means of Finite Element Method (FEM) for single-lap joint subjected to thermal and mechanical loads is presented in this paper. Simulation is used to predict the effect of residual thermal stresses (caused by difference of temperature of use and elevated temperature during the assembly of the joint) on stress distribution within adhesive layer. The residual thermal stresses are assigned to joint members as initial condition before the mechanical load is applied. The FEM model employs linear and nonlinear material model and accounts for geometrical nonlinearity. It is confirmed that the difference between the manufacturing and the ambient temperature results in high residual thermal stresses, especially in axial and lateral directions of the joint. The calculation of total stress as superposition of thermal and mechanical stresses works only for linear materials. Moreover, simultaneous application of temperature and mechanical load (applied strain in case of displacement controlled test) in FEM produces inaccurate results, since in real situation the strain is applied to already thermally loaded structure. It is also found that the residual thermal stresses may reduce the peel and shear stress concentration in the adhesive at the ends of overlap and the shear stress within the overlap.
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| 3. |
- Al-Ramahi, Nawres J, 1980-, et al.
(författare)
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Numerical stress analysis in adhesively bonded joints under thermo-mechanical loading
- 2020
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Ingår i: Advances in Mechanical Engineering. - : Sage Publications. - 1687-8132 .- 1687-8140. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work is to evaluate the effect of residual thermal stresses, arising after assembling a single-lap joint at elevated temperature, on the inelastic thermo-mechanical stress state in the adhesive layer. The numerical analysis (FEM) employing linear and non-linear material models, with geometrical nonlinearity accounted for, is carried out. Simulating the mechanical response, the calculated thermal stresses are assigned as initial conditions to polymeric, composite and metallic joint members to reflect the loading sequence where the mechanical strain is applied to cooled-down structure. It is shown that the sequence of application matters and simulations with simultaneous application of temperature and strain give different result. Two scenarios for adhesive joints with composites are studied: joining by adhesive curing of already cured composite parts (two-step process) and curing the adhesive and the composite simultaneously in one-step (co-curing). Results show that while in-plane stresses in the adhesive are higher, the peaks of out-of-plane shear stress and peel stress (most responsible for the joint failure) at the end of the overlap are reduced due to thermal effects. In joints containing composite parts, the one-step joining scenario is more favorable than the two-step. The ply stacking sequence in the composite has significant effect on stress concentrations as well as on the plateau value of the shear stress in the adhesive.
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| 4. |
- Freire, Rodrigo T.S., et al.
(författare)
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On Determination of the Linear Viscoelastic Compliance and Relaxation Functions for Polymers in One Tensile Test : [Об определении функций линейной вязкоупругой податливости и релаксации полимеров в одном испытании на растяжение]
- 2023
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Ingår i: Mechanics of composite materials. - : Springer Nature. - 0191-5665 .- 1573-8922. ; 58:6, s. 765-786
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Tidskriftsartikel (refereegranskat)abstract
- Usually, the viscoelastic (VE) response of polymers for applications in composites is obtained in uniaxial strainor stress-controlled tests. However, analyzing multimaterial structures by the Finite Element Method (FEM) or by other numerical or analytical tools, a material model in terms of a complete set of compliance functions and/or relaxation functions is required. In this paper, a methodology and exact analytical expressions for calculating the whole set of VE functions is presented based on the relaxation modulus E(t)and Poisson’s ratio v (t) determined in strain-controlled tests. The method is based on Laplace transforms, where an exact inversion is possible if a linear VE model with functions in Prony series is used. Results of the analytical model are compared with the FEM simulation, where specific boundary conditions to determine each particular VE function are used. Finally, the applicability of the so-called quasi-elastic method is investigated, where the expressions of elasticity theory are used to calculate a given viscoelastic function at an instant of time tk using the instant values of E(tk) and v(tk). For isotropic materials, the three approaches render almost coinciding results.
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