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  • 1.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Shen, Hayley
    Clarkson University, Potsdam, NY.
    Onset of transition for cohesive and viscous granular flows1998Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 124, nr 10, s. 1073-1079Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A theory for determining the onset of rapid flow or termination of quasi-static flow in a cohesive granular material mixed in a viscous interstitial fluid is presented. This theory is based on a one-dimensional model introduced in an earlier paper. Linear stability analysis is used to find the combination of material properties and flow rate for which a quasi-static flow becomes unstable, indicating the onset of rapid flow. This theory yields a quantitative criterion to select appropriate constitutive laws for viscous and cohesive granular material. This criterion is a linear approximation of the theoretical result. While it provides the critical condition for quasi-static flow to terminate, it does not give the transitional constitutive law before a rapid flow is fully developed, for which a second power law dependence on the strain rate applies. Nonetheless, the analysis and modeling effort presented in this work are necessary first steps toward a general quantification of how granular materials, with identical physical composition, can behave in drastically different ways.

  • 2.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Shen, Hayley H.
    Gupta, Ram B.
    Uppsala universitet.
    Experimental and numerical studies of shear layers in granular shear cell1996Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 122, nr 3, s. 187-196Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stability of a shear layer inside a granular material in a gravity field is studied experimentally and numerically. A shear cell is built of transparent acrylic to visualize the motion of the granular material. This shear cell consists of two concentric cylinders containing layers of uniform spheres in the annular space between the cylinders. The shearing motion of the spheres is produced by rotating the bottom boundary of the cell. Friction of the cylinder walls resists the shear motion, thus creating a single shear layer adjacent to the bottom boundary, while the rest of the layers above move with constant speed as a solid body. As the rotation speed of the bottom boundary increases, two layers adjacent to the bottom boundary begin to shear. This shearing zone quickly thickens and dilates as the rotational speed increases. The transition of this shear motion from a single layer to many layers of shearing is studied by video recording. The initiation of this transition is observed to depend on the material properties and the number of layers overlaying the shear layer. A one-dimensional numerical model is constructed to bring insight into this transitional phenomenon.

  • 3.
    Challamel, Noël
    et al.
    Mechanics Division, Department of Mathematics, University of Oslo.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Lateral-torsional buckling of partially composite horizontally layered or sandwich-type beams under uniform moment2013Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 139, nr 8, s. 1047-1064Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper is devoted to the analytical and numerical modeling of the lateral-torsional stability of horizontally layered composite beams. Composite beams are classified as horizontally layered beams with interlayer slip or sandwich beams with a weak shear core. The governing differential equations of the out-of-plane behavior of horizontally layered composite beams are supported by variational arguments. In the theoretical analysis, a distinction is made between the influence of the shear connection at the interface with respect to the in-plane or transversal deformations and to the out-of-plane or lateral deformations, respectively. Some engineering results are presented for a partially composite beam under pure bending moment. In the case of noncomposite in-plane action (orthotropic connection), a simple closed-form solution is derived for the lateral-torsional buckling moment, and it is shown that the exact dimensionless buckling moment depends only on two structural parameters for beams composed of two identical subelements. The results are analogous to those obtained for the in-plane buckling of partially composite or sandwich-type beams, where the buckling moment increases with the stiffness of the shear connection. Prandtl’s valid solution for lateral-torsional buckling of ordinary beams is also found for composite beams in the case of noncomposite action in both the transversal and lateral directions. A generalization of Prandtl’s valid solution for composite beams with partial composite action in the lateral direction and noncomposite action in the transversal direction is derived. It is shown that the lateral-torsional buckling formulas are strongly affected by the kinematics of the connected shear layer. Also, the lateral-torsional buckling of partially composite beams with both in-plane and out-of-plane slip behavior is analyzed using the Rayleigh-Ritz method. This mathematical problem leads to a system of differential equations with nonuniform coefficients. An approximated solution is derived for the isotropic connection with isotropic noncomposite actions, whereas an exact solution is presented for the orthotropic connection with noncomposite in-plane action. Finally, the Rayleigh-Ritz approach is compared with some numerical results associated with the exact resolution of the differential equations with nonuniform coefficients. The Rayleigh-Ritz approach appears to be efficient to capture the main phenomena, including the nonmonotonic dependence of the buckling load to the connection parameter.Read More: http://ascelibrary.org/doi/abs/10.1061/(ASCE)EM.1943-7889.0000489

  • 4.
    Gustafsson, Lennart
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Gustafsson, Peter
    Luleå tekniska universitet.
    Studying disk movements by novel image-analysis method1995Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 121, nr 8, s. 931-934Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An image-analysis method developed to study granular flow, the accumulating particle trajectories (APT) method, is shown to be a versatile tool to study the movements of disks. The moving disks, which are provided with suitable dot patterns, are video-recorded and the recorded sequences are analyzed to provide trajectories of the disks and the dots, thus making it possible to study both translational and rotational movements. It is also possible to introduce time markers in the trajectories. Up to eight images per second can be analyzed. The filtering necessary to attenuate electronic noise in the video equipment is performed as time filtering between consecutive images and is very efficient. The method's demands for processing power are very moderate and, therefore, particle movements during time spans corresponding with thousands of video frames can be easily presented as analysis results. The method can be implemented at relatively low cost.

  • 5.
    Klisinski, Marek
    et al.
    Luleå tekniska universitet.
    Moström, Annika
    Luleå tekniska universitet.
    On stability of multitime step integration procedures1998Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 124, nr 7, s. 783-793Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Stability of multitime step integration methods for finite-element computations in structural dynamics is analyzed. Multitime step procedures based on the Newmark family of methods are described. The basic idea of multitime step methods is to utilize various time step sizes in different domains of an element mesh. Interpolated nodal values from the large time step domain are used in the computation of displacements, velocities, and accelerations in the small time step domain. An analytical study of the errors introduced by the interpolation is given. The analysis shows instability because of the resonance phenomena and because of the propagation of spurious high frequencies caused by unbalanced forces originating from interpolation errors. Numerical results exhibiting instability problems are presented. To complete the study, examples of solutions stabilized with numerical damping of high frequencies are included in the presentation. The conclusion from the present study is that multitime step methods are unstable in their nature. Numerical damping can stabilize the computations but alters the response of free vibrating undamped systems.

  • 6.
    Lundberg, Jan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Shen, Hayley H.
    Clarkson University, Potsdam, NY.
    Collisional restitution dependence on viscosity1992Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 118, nr 5, s. 979-989Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dense two-phase flows occur in many material processing situations. In these flows, particle collision presents a mechanism for internal resistance. In the literature, restitution coefficients are given for collisions between dry objects. Little is known about two colliding objects placed in a fluid. Thus, although two-phase flow models exist for dense mixtures, realistic values of the required restitution coefficient are not available. Recent theoretical and experimental analyses of colliding spheres in a viscous fluid show that collisional rebound depends greatly on the interstitial fluid. At very high viscosity, contact may not occur. This paper presents an experimental study of collisional restitution between steel and nylon, and a range of Newtonian viscous fluids. The fluids have a viscosity range from 27 mm2/s to 2,600 mm2/s. The normal impact velocity ranges from 0.015 m/s to 0.75 m/s. Preliminary results show that the behaviour of the impact and the resulting restitution coefficient depend on the interstitial fluid. These results will be useful to the mathematical modeling of dense two-phase flows.

  • 7.
    Noghabai, Keivan
    Luleå tekniska universitet.
    Discrete versus smeared versus element-embedded crack models on ring problem1999Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 125, nr 3, s. 307-314Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three different concepts in finite-element modeling are compared by analyzing a thick-walled concrete ring subjected to an internal pressure. These are the discrete crack, the fixed smeared crack, and an element-embedded crack model called the inner softening band (ISB) model. The results are compared with experimental studies on rings of both normal- and high-strength concrete mixtures with and without spiral reinforcement. The ISB analysis gives the best results with respect to explaining the fracture mechanism as well as consistency in prediction of the ring capacity. The smeared crack model also provides satisfactory results, but in the light of robustness in geometrical modeling and requirement of minimum amount of input data (which all have a physical relevance) the ISB concept in this case is more reliable. The study exposed some deficiencies of the discrete crack method based on the fact that the localization processes and the strain redistribution in the body are often unknown. This also underlines caution in assuming symmetry when softening occurs on a structural level

  • 8.
    Ohlsson, Ulf
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Olofsson, Thomas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Mixed-mode fracture and anchor bolts in concrete analysis with inner softening bands1997Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 123, nr 10, s. 1027-1033Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper presents a nonlinear fracture mechanics analysis of mixed-mode fracture and anchor pullout in concrete. The analysis is based on elements with inner softening bands (ISB). A major advantage of the ISB approach is that discrete cracks can be introduced anywhere and in any direction within the finite-element mesh. Calculated loads, deformations, and crack patterns are compared to experimental results. A good correspondence is achieved.

  • 9.
    Stehn, Lars
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    DeFranco, S.J.
    Amoco Production Co, Tulsa, Oklahoma.
    Dempsey, J.P.
    Clarkson University, Potsdam, NY.
    Specimen geometry effects on fracture of warm pond (S1) ice1995Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 121, nr 1, s. 16-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fracture toughness tests were performed on S1 type freshwater ice to investigate if similarities exist in the local K I fields for three different fracture geometries. The ice was tested using a handheld loading device called the FIFT (Field Instrument for Fracture Toughness Tests on ice). The geometries tested were the short rod chevron notched (SRCN) specimen, the reverse tapered (RT) specimen and the square plate (SP) geometry. All tests were performed at –4°C. The results indicate that under comparable conditions (loading rate, temperature, crack orientation, and propagation direction), the apparent fracture toughness K Q is similar for all of the geometries. The toughness was computed assuming the initiation of a stationary macrocrack from linear elastic, isotropic K I solutions. Scatter of the experimental results is accounted for in part by the large grain size of S1 ice. However, it is important to note that the results may be an artifact of subsized tests. Even though the ice was warm, the crack extended unstably in each experiment and the fracture surfaces of the split specimens showed evidence of brittle fracture. The test geometry had a marked influence on the character of the fracture surface.

  • 10. Talreja, Ramesh
    et al.
    Niu, Kangmin
    Optimal CAE, 39555 Orchard Hill Place, Ste. 200, Novi, MI.
    Modeling of wrinkling in sandwich panels under compression1999Ingår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 125, nr 8, s. 875-883Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A wrinkling model for sandwich panels in compression is developed with the assumption of a continuous isotropic linear elastic core. Wrinkling stresses for the three modes, defined in a well-known book by H. G. Allen, are expressed by a unified, single expression. The expression depends linearly on a case parameter η, defined to specify the three cases of wrinkling: η = 0 for single-sided face wrinkling (case 1), η = 1 for in-phase wrinkling (case 2), and η = - 1 for out-of-phase wrinkling (case 3). It is shown that the stresses in all three cases are almost identical for short wavelength wrinkling and car be expressed by a single simplified analytical expression; however, they may differ significantly in moderate and long wavelength wrinkling, and for these cases they are given by simplified analytical expressions. It is proved that the in-phase wrinkling stress is the lowest among the three cases. Based on the analysis conducted, limitations of the commonly used Winkler and two-parameter models are discussed. Finally, engineering design procedures are recommended for the wrinkling effect in sandwich panels under compression.

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