| 1. |
- Christensen, Peter
(författare)
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A semi-smooth newton method for elasto-plastic contact problems
- 2002
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 39:8, s. 2323-2341
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we reformulate the frictional contact problem for elasto-plastic bodies as a set of unconstrained, non-smooth equations. The equations are semi-smooth so that Pang's Newton method for B-differentiable equations can be applied. An algorithm based on this method is described in detail. An example demonstrating the efficiency of the algorithm is presented. © 2002 Elsevier Science Ltd. All rights reserved.
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| 2. |
- Ciavarella, M., et al.
(författare)
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Interaction of thermal contact resistance and frictional heating in thermoelastic instability
- 2003
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 40:21, s. 5583-5597
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelastic contact problems can posess non-unique and/or unstable steady-state solutions if there is frictional heating or if there is a pressure-dependent thermal contact resistance at the interface. These two effects have been extensively studied in isolation, but their possible interaction has never been investigated. In this paper, we consider an idealized problem in which a thermoelastic rod slides against a rigid plane with both frictional heating and a contact resistance. For sufficiently low sliding speeds, the results are qualitatively similar to those with no sliding. In particular, there is always an odd number of steady-state solutions, if the steady-state is unique it is stable and if it is non-unique, stable and unstable solutions alternate, with the outlying solutions being stable. However, we identify a sliding speed V0 above which the number of steady states is always even (including zero, implying possible non-existence of a steady-state) and again stable and unstable states alternate. A parallel numerical study shows that for V > V0 there are some initial conditions from which the contact pressure grows without limit in time, whereas for V < V0 the system will always tend to one of the stable steady states. © 2003 Elsevier Ltd. All rights reserved.
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| 3. |
- Ireman, Peter, et al.
(författare)
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A model of damage coupled to wear
- 2003
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 40:12, s. 2957-2974
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Tidskriftsartikel (refereegranskat)abstract
- The present paper presents a model of damage coupled to wear. The damage model is based on a continuum model including the gradient of the damage variable. Such a model is non-local in the sense that the evolution of damage is governed by a boundary-value problem instead of a local evolution law. Thereby, the well-known mesh-dependency observed for local damage models is removed. Another feature is that the boundary conditions can be used to introduce couplings between bulk damage and processes at the boundary. In this work such a coupling is suggested between bulk damage and wear at the contact interface. The model is regarded as a first attempt to formulate a continuum damage model for studying crack initiation in fretting fatigue. The model is given within a thermodynamic framework, where it is assured that the principles of thermodynamics are satisfied. Furthermore, two variational formulations of the full initial boundary value problem, serving as starting points for finite element discretization, are presented. Finally, preliminary numerical results for a simple one-dimensional example are presented and discussed. It is qualitatively shown how the evolution of damage may influence the wear behaviour and how damage may be initiated by the wear process. © 2003 Elsevier Science Ltd. All rights reserved.
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| 4. |
- Isaksson, Per, et al.
(författare)
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Directional crack path criterion for crack growth in ductile materials subjected to shear and compressive loading under plane strain conditions
- 2003
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 40:13-14, s. 3523-3536
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Tidskriftsartikel (refereegranskat)abstract
- A directional crack growth criterion in a compressed elastic perfectly plastic material is considered. The conditions at the crack-tip are evaluated for a straight stationary crack with a small incipient kink. Remote load is a combined hydrostatic pressure and pure shear applied via a boundary layer. Crack surfaces in contact are assumed to develop homogenous Coulomb friction. The crack opening displacement of an extended kink is examined in a finite element analysis to judge the risk of opening mode failure. It has been found that the direction that maximizes the crack opening displacement of an extended kink tip coincides very well with a prediction of the crack growth direction obtained by using a criterion for continued crack growth direction discussed by the authors elsewhere [Int. J. Fract. 108 (2001) 351]. Moreover, the by the model predicted incipient crack growth directions are qualitatively comparable with reported crack paths obtained in ductile materials in a limited number of experiments performed under a combined load of inplane shear and compression.
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| 5. |
- Isaksson, Per, et al.
(författare)
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Mode II crack paths under compression in brittle solids : A theory and experimental comparison
- 2002
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 39:8, s. 2281-2297
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Tidskriftsartikel (refereegranskat)abstract
- A study of crack propagation paths in the situation where the crack is suppressed to open during growth due to high compressive forces has been performed. This problem was analyzed theoretically very recently by the authors and is here extended to involve a limited number of illustrative experimental results reported elsewhere in the literature. By analyzing the experimental crack growth patterns, the conclusion is that the model cannot describe the more realistic microscopic failure in detail. Since shear crack growth on the microscale strongly depend on inhomogenities in the material, like cavities, grains or inclusions; the closed crack growth patterns observed are not smooth or free of kinks. Nevertheless, the model show good agreement with the reported experimental observations of the paths of closed macroscopic mode II cracks on samples in brittle materials, induced under overall compression. Failure patterns experimentally observed supports the theory that the growth of mode II cracks under compression in brittle materials follow a propagation path described by a function y ¼ kxb, where b ¼ 3=2. This is strongly supported by the measured values obtained from various experiments. In all the studied experiments, the exponent b was found in the interval [1.43–1.58]. Further, an investigation of the curvature parameter k has been performed and the conclusion is that k does also agree with the simplified model, even though not as good as the exponent b. However, k differs in general <15% from the theoretical value predicted by the model. The process of crack growth is in the simplified model assumed to be controlled by the mode II stress intensity factor KII of the main crack and the difference between the compressive remote normal stress parallel with the crack plane (r111) and the compressive remote normal stress perpendicular to the crack plane (r122).
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| 6. |
- Makela, P., et al.
(författare)
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Orthotropic elastic-plastic material model for paper materials
- 2003
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 40:21, s. 5599-5620
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Tidskriftsartikel (refereegranskat)abstract
- Paper and paperboard generally exhibit anisotropic and non-linear mechanical material behaviour. In this work, the development of an orthotropic elastic plastic constitutive model, suitable for modelling of the material behaviour of paper is presented. The anisotropic material behaviour is introduced into the model by orthotropic elasticity and an isotropic plasticity equivalent transformation tensor. A parabolic stress-strain relation is adopted to describe the hardening of the material. The experimental and numerical procedures for evaluation of the required material parameters for the model are described. Uniaxial tensile testing in three different inplane material directions provides the calibration of the material parameters under plane stress conditions. The numerical implementation of the material model is presented and the model is shown to perform well in agreement with experimentally observed mechanical behaviour of paper.
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| 7. |
- Nilsson, K.-F., et al.
(författare)
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Delamination buckling and growth for delaminations at different depths in a slender composite panel
- 2001
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 38:17, s. 3039-3071
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Tidskriftsartikel (refereegranskat)abstract
- A numerical and experimental investigation for delamination buckling and growth for slender composite panels loaded in compression is presented. The investigated panels consisted of 35 plies in a cross-ply layup with artificially embedded delaminations inserted after three, five or seven plies from the upper surface. The tests clearly and consistently showed that for all delamination depths, delaminated panels failed by delamination growth slightly below the global buckling load of the undamaged panel, whereas the undelaminated panels failed in compression at global buckling. The analysis was done with a finite element based computational model that accounts for contact between delaminated members and fracture mode separation and where crack propagation was simulated with a moving mesh scheme. For all delamination depths, the analysis showed a dramatic increase in the energy release rate when global buckling takes place. Features seen in the tests were captured in the computational analysis. Excellent agreement with tests was found for loads at which delaminated members buckle, the load for onset of delamination growth and the evolution of delamination, e.g., delamination shape and out-of-plane displacements.
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| 8. |
- Nilsson, K.F., et al.
(författare)
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On transition of delamination growth behaviour for compression loaded composite panels
- 2001
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 38:46-47, s. 8407-8440
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a combined numerical and experimental study of slender composite panels loaded in compression with artificial delaminations at two different depths. The study was motivated by finite element analyses where this change in delamination depth induced a transition in the direction of delamination growth along with a change in the basic fracture modes and stability. Tests were then carried out to verify the transition in delamination growth. The predicted transitions were to a large extent also seen in the tests. The paper gives an outline of the computational model, which includes contact between delaminated members, calculation of energy release rate with fracture mode separation by an approximate as well as a reliable method for general layups, and moving mesh scheme to account for delamination growth. The experimental work includes monitoring of delamination growth by C-scan and acoustic emission along with a detailed fractographical study. The correlation between experimental observations and computed results are discussed in detail.
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| 9. |
- Semb, G., et al.
(författare)
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Stresses and Strains in a Race Track Strap with a radical clearance
- 2002
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 39:3, s. 699-708
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Tidskriftsartikel (refereegranskat)abstract
- In certain situations it is desirable to transfer only tensile loads between two points in a structure whilst minimising any stress concentrations. In such circumstances a so-called race track starp can be utilised. The strap consists of two semi-circular elements that transfer the load, from bolts at each end, to two parallel flexible elements joining the whole together. The strap is loaded in tension by means of these bolts. This paper considers the situation where there is clearance between the bolts and the semi-circular elements of the strap. To develop an analytical model, it is assumed that engineering beam theory is applicable, that the influence of the membrane strains can be ignored and that the clearance is small as compared with the bolt and strap radii. It was found that the simple analytical model compared well with both finite element calculations and experiments.
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| 10. |
- Åberg, Mats, et al.
(författare)
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Micromechanical modeling of transient waves from matrix cracking and fiber fracture in laminated beams
- 2000
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 37:30, s. 4083-4102
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Tidskriftsartikel (refereegranskat)abstract
- A micromechanical model for excitation of waves resulting from fiber fracture and matrix cracking in laminated beams is presented. The source is described as a time dependent displacement discontinuity and the wave propagation in the beam is modeled by a higher-order beam theory. The equations of motion defined by the beam model are then formally solved by employing integral transforms. Asymptotically valid solutions are subsequently found using residue calculus and the stationary phase method. As an example, a [90/0(2)/90] beam with a width to thickness ratio of 10 is considered. The dispersion curves resulting from the beam theory and three-dimensional finite element computations are compared and a maximum frequency for applicability of the beam theory is determined. The time response from fiber fracture and transverse matrix cracking is presented. The applications of the results to the analysis of acoustic emission experiments are also discussed.
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