| 1. |
- Agmell, Mathias, et al.
(author)
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Identification of plasticity constants from orthogonal cutting and inverse analysis
- 2014
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In: Mechanics of Materials. - : Elsevier BV. - 0167-6636. ; 77, s. 43-51
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Journal article (peer-reviewed)abstract
- The aim of this work is that from experimental determined cutting process parameters be able to predict the plasticity input constants to Finite Element Method (FEM) models. In the present study the Johnson-Cook constitutive model constants are determined on the basis of cutting process parameters in orthogonal cutting and by use of inverse analysis. Previously established links between Johnson-Cook constitutive model constants and cutting process parameters in the cutting process such as primary cutting force and chip compression ratio is used serve as a starting point in the inverse analysis. As a reference material AISI 4140 has been chosen in this study, which is a tempered steel. The Johnson-Cook constitutive model constants in the reference material are being changed within an interval of ±30 %. The inverse analysis is performed using a Kalman filter. The material model for the reference material is validated on the basis of the experimental results in previous work. The model showed to predict the cutting process parameters with a high level of accuracy. The predicted Johnson-Cook constitutive model constants in the present study achieve an error between simulated- and experimental cutting process parameters of maximum 2%. The method described in this study is not limited to identify Johnson-Cook constitutive model constants, but the method can also be used for other constitutive models. The same applies to the process itself and the selected cutting process parameters, but orthogonal cutting has been used to illustrate and validate this method.
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| 2. |
- Ask, Anna, et al.
(author)
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Electrostriction in electro-viscoelastic polymers
- 2012
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In: Mechanics of Materials. - : Elsevier BV. - 0167-6636. ; 50, s. 9-21
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Journal article (peer-reviewed)abstract
- Electrostrictive polyurethane (PU) elastomers belong to the class of materials commonly referred to as electroactive polymers (EAP). These materials have their use in a variety of applications, including biomimetics and microrobotics where traditional engineering components may fall short. PU is one of the materials considered for so called dielectric actuators, where the electromechanical response is generally due to Coulomb forces on the actuator electrodes, giving rise to a compressive pressure and thereby large deformations of the polymer. On the other hand, for more moderate electric fields, which may be more attractive in certain applications, a large part of the electroactive response for PU elastomers is due to inherent electrostriction. The latter phenomena is the focus of this work. As is common in elastomers, PU elastomers are viscoelastic. A coupled electro-viscoelastic phenomenological constitutive model for electrostrictive PU is proposed and fitted to experimental data available in the literature. The possibility of performing simulations of EAP is of interest as the number of applications grow. Considering this, the computational model is embedded in a coupled finite element formulation and, based on this, representative simulations of inhomogeneous boundary value problems are presented.
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| 3. |
- Drescher, A, et al.
(author)
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On the Behavior of a Parallel Elasto-Visco-Plastic Model for Asphaltic Materials
- 2010
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In: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 42:2, s. 109-117
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Journal article (peer-reviewed)abstract
- The paper considers a dissipation energy based elasto-visco-plastic constitutive modelformulated by coupling in parallel visco-elastic and elasto-plastic components, which has been developed at Delft University of Technology for the response prediction ofasphaltic materials. To discuss the various aspects of the model under different creep loads, a simplified one-dimensional analytical solution is derived. Three different analytical cases are treated: visco-elastic response, elasto-visco-plastic response in which plasticity develops during the loading and instantaneous plasticity. The analyses show that the interaction between the parallel visco-elastic and elasto-plasticcomponents of the model are an important aspect of the predictive capabilities of themodel. A case is derived in which short duration loading of the model could lead to aprediction of increasing strains during the unloading phase. Care should be taken when choosing the material parameters of the model to avoid this erroneous prediction.
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| 4. |
- Gamstedt, E. Kristofer, et al.
(author)
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Characterization of interfacial stress transfer ability of particulate cellulose composite materials
- 2011
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In: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 43:11, s. 693-704
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Journal article (peer-reviewed)abstract
- Composites with cellulose reinforcements are steadily gaining increased use. The stress transfer ability between reinforcement and polymer matrix has a strong influence on mechanical properties like strength and fracture toughness. This work presents a method to assess the stress transfer ability between cellulose and polymer matrix from a model material with cellulose spheres embedded in a polymer matrix. Such a material show smaller variability compared with composites based on natural cellulose fibres, and is less cumbersome than single fibre tests with regard to interfacial characterization. Measured elastic moduli of particulate composites is compared with predicted values from a micromechanical model based on a composite sphere assembly in a self-consistent scheme with only a spring constant of an imperfect interface as fitting parameter expressed in Pa/m. This interface parameter is identified through inverse modelling and used to quantify stress-transfer ability of cellulose/polylactide and cellulose/polystyrene composite interfaces. A higher degree of interfacial interaction was found for the former. This ranking was corroborated by adhesive force measurements using a micrometre sized cellulose sphere attached to the end of a cantilever in an atomic force microscope. With the model microstructure of a cellulose-sphere composite, an interfacial efficiency parameter can be backed out from stiffness measurements to be used in e.g. ranking of different fibre surface treatments and choice of matrix in the development of stronger natural-fibre composites.
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| 5. |
- Huang, Hui, et al.
(author)
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Quasi static analysis of creasing and folding for three paperboards
- 2014
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In: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 69:1, s. 11-34
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Journal article (peer-reviewed)abstract
- The creasing and folding behavior of three paperboards have been studied both experimentally and numerically. Creasing and folding studies were performed on strips in both the machine direction and the cross machine direction. A finite element model that mimicked the experimental creasing and folding setup was developed, and the creasing and folding behavior could be well predicted for all three paperboards. An experimental characterization scheme consisting of three experiments was proposed, and was shown to be sufficient to predict the creasing and folding behavior. For the whole paperboard the shear strength profiles in the through thickness direction was determined with the notched shear test. Each ply was laid free by grinding, and density measurements and in-plane tension tests were performed on the bottom, middle and top plies of each paperboard. Instead of assuming uniform properties in each ply, the shear strength profiles were used to map the measured properties in the through thickness direction. Numerical simulations were performed when the ply and interface properties of the paperboards were altered to follow different shear strength profiles. This was done in order to mimic different production strategies. It was shown that the interface strengths mainly influenced the folding behavior. Whereas altered the ply properties affected the creasing force needed.
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| 6. |
- Joffre, Thomas, et al.
(author)
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Effects of defects on the tensile strength of short-fibre composite materials
- 2014
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In: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 75, s. 125-134
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Journal article (peer-reviewed)abstract
- Heterogeneous materials tend to fail at the weakest cross-section, where the presence of microstructural heterogeneities or defects controls the tensile strength. Short-fibre composites are an example of heterogeneous materials, where unwanted fibre agglomerates are likely to initiate tensile failure. In this study, the dimensions and orientation of fibre agglomerates have been analysed from three-dimensional images obtained by X-ray microtomography. The geometry of the specific agglomerate responsible for failure initiation has been identified and correlated with the strength. At the plane of fracture, a defect in the form of a large fibre agglomerate was almost inevitably found. These new experimental findings highlight a problem of some existing strength criteria, which are principally based on a rule of mixture of the strengths of constituent phases, and not on the weakest link. Only a weak correlation was found between stress concentration induced by the critical agglomerate and the strength. A strong correlation was however found between the stress intensity and the strength, which underlines the importance of the size of largest defects in formulation of improved failure criteria for short-fibre composites. The increased use of three-dimensional imaging will facilitate the quantification of dimensions of the critical flaws.
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| 7. |
- Kroon, Martin
(author)
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A constitutive model for strain-crystallising Rubber-like materials
- 2010
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In: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 42:9, s. 873-885
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Journal article (peer-reviewed)abstract
- In the present paper, a constitutive model for strain-crystallising rubber is proposed. The constitutive behaviour is formulated in terms of a strain energy function, where the full network approach is adopted. The Arrhenius equation provides the basis for the crystallite nucleation law. The full network approach allows for the development of an anisotropic crystal structure. The model was applied to experimental results from uniaxial tensile tests. Strain-crystallisation causes a hysteresis in the stress-stretch relation, but according to the model predictions, the effect of crystallisation is not sufficient to explain the mechanical hysteresis observed in the tensile tests. Hence, additional viscoelasticity associated with amorphous polymer chains must be included. The model was fully able to predict both the stress vs. stretch relations and the crystallinity vs. stretch relations from the experiments.
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| 8. |
- Kulachenko, Artem, 1978-, et al.
(author)
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Direct simulations of fiber network deformation and failure
- 2012
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In: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 51, s. 1-14
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Journal article (peer-reviewed)abstract
- A finite element model for 3D random fiber networks was constructed to simulate deformation and failure behavior of networks with dynamic bonding/debonding properties. Such fiber networks are ubiquitous among many living systems, soft matters, bio-materials, and engineering materials (papers and non-woven). A key feature of this new network model is the fiber–fiber interaction model that is based on AFM measurements from our earlier study. A series of simulations have been performed to investigate strain localization behavior, strength statistics, in particular, the variations of strength, strain-to-failure and elastic modulus, and their size dependence. Other variables investigated are fiber geometries. The result showed that, in spite of its disordered structure, strength and elastic modulus of a fiber network varied very little statistically, as long as the average number of fibers in the simulated specimen and the degree of fiber orientation are kept constant. However, strain-to-failure showed very significant statistical variations, and thus more sensitivity to the disordered structures.
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| 9. |
- Notta-Cuvier, D., et al.
(author)
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Damage of short-fibre reinforced materials with anisotropy induced by complex fibres orientations
- 2014
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In: Mechanics of materials. - : Elsevier. - 0167-6636 .- 1872-7743. ; 68, s. 193-206
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Journal article (peer-reviewed)abstract
- In this paper, a behaviour model for damageable elastoplastic materials reinforced with short fibres that have complex orientations is. proposed. The composite material is seen as the assembly of the matrix medium and several linear elastic fibre media. Its macroscopic behaviour is computed thanks to an additive decomposition of the state potential, with no need to implement complex methods of homogenisation. A 4th-order tensor that depends on the characteristics of each fibre medium is introduced to model the anisotropic damage of the matrix material induced by the reinforcement, as well as the progressive degradation of the fibre-matrix interface. The division of short fibres into several families means that complex distributions of orientation or random orientation can be easily modelled. The model is tested for the case of a polyamide reinforced with different contents of short-glass fibres with distributed orientations and subjected to uniaxial tensile tests in different loading directions. The comparison of the results with experimental data (extracted from the literature) demonstrates the efficiency of the model.
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