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1.	Alkhagen, M., et al. (författare) Micromechanics of a compressed fiber mass 2007 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 74:4, s. 723-731 Tidskriftsartikel (refereegranskat)abstract A theory is presented for the rate modeling of flexible granular solids based on affine average motion of interparticle contacts. We allow contacts to form and break continually but assume the existence of a finite friction coefficient rendering contacts force free as they form or break. The resulting constitutive equations are of the hypoelastic type. A specific model for the deformation of a fiber mass is then developed. The model improves on previous theories for fiber masses in at least two respects: First, it is more general in that it is not restricted to uniaxial compression, although it is restricted to predominantly compressive deformations histories, due to neglect of frictional dissipation. Second, by allowing torsion as well as bending of fibers, this theory covers a larger deformation range. Compression experiments are performed on carded slivers of PA6 fibers under various conditions. The measured response is found to be in close agreement with that predicted by the model.
2.	Alkhagen, M., et al. (författare) The effect of fiber diameter distribution on the elasticity of a fiber mass 2009 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 76:4 Tidskriftsartikel (refereegranskat)abstract A random mass of loose fibers interacting by fiber-fiber contact is considered. As proposed in a previous paper, the elastic response is modeled based on the statistical mechanics of bending and torsion of fiber segments between fiber-fiber contact points. Presently we show how the statistical approach can be used to account for a distribution of fiber diameters rather than just a single diameter. The resulting expression has the same form and the same set of parameters as its single-diameter counterpart, except for two dimensionless reduction factors, which depend on the fiber diameter distribution only and reduce to unity for monodisperse fibers. Uniaxial compressibility experiments are performed on several materials with different bimodal fiber diameter distributions and are compared to model predictions. Even though no additional parameters were introduced to model the effect of mixed fiber diameters, the behavior is accurately predicted. Notably, the effect of the nonuniform fiber diameter is strong: A mixture of two fiber diameters differing by a factor of 2 can reduce the response by an order of magnitude, compared to the case of uniform diameter.
3.	Appelgren, Patrik, et al. (författare) Disruption mechanisms in electrified solid copper jets 2011 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 78:2 Tidskriftsartikel (refereegranskat)abstract Interaction between a solid copper jet and an electric current pulse is a complex process that has been experimentally studied by letting a jet created by a shaped charge device pass through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. When the jet bridged the electrodes, which are connected to a charged pulsed power supply, current pulses with amplitude up to 250 kA were passed through the jet. By using flash X-ray diagnostics, the disruption of the electrified jets could be studied. In this paper, the disruption of the electrified jets is discussed and compared with disruption phenomena observed in electrically exploded metal rods in a static setup. Necks are naturally formed along a stretching jet, and in the experiments with current interaction these necks explode electrically. In the static experiments, the metal rods have small notches distributed along the rod to resemble the necks of the jet. When two neighboring necks or notches explode, the shock of the explosion compresses the intermediate jet or rod segment axially and the material is forced out radially. The disruption phenomena in the jet and rod experiments are similar with rapid expansion of the metal at explosion and at comparable velocities.
4.	Appelgren, Patrik, et al. (författare) Experimental Study of Electromagnetic Effects on Solid Copper Jets 2010 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:1, s. 011010- Tidskriftsartikel (refereegranskat)abstract In this paper we present a study of the interaction between all electric current pulse and a solid copper jet. Experiments were performed using a dedicated pulsed power supply delivering a current pulse of such amplitude, rise little, and duration that the jet is efficiently affected. The copper jet was created by using a shaped charge warhead. All electrode configuration consisting of two aluminum plates with a separation distance of 150 mm was used. The discharge current pulse and the voltages at the capacitors and at the electrodes were measured to obtain data oil energy deposition in and the resistance of the jet and electrode contact region. X-ray diagnostics were used to radiograph the jet, and by analyzing the radiograph, the degree of disruption of the electrified jet could be obtained. It was found that a current pulse with an amplitude of 200-250 kA and a rise time of 16 mu s could strongly enhance the natural fragmentation of the jet. In this case, the initial electric energy was 100 kJ and about 90% of the electric energy was deposited in the jet and electrodes. At the exit of the electrode region, the jet fragments formed rings with a radial velocity of up to 200 m/s, depending oil the initial electric energy in the pulsed power supply. [DOI: 10.1115/1.3172251]
5.	Appelgren, Patrik, et al. (författare) Interaction between solid copper jets and powerful electrical current pulses 2011 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 78:2 Tidskriftsartikel (refereegranskat)abstract The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped-charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed-power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region, which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor 5 compared with the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet breakup. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared with other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.
6.	Bahaloo, Hassan, 1983-, et al. (författare) Micropolar Modeling of Auxetic Chiral Lattices With Tunable Internal Rotation 2019 Ingår i: Journal of applied mechanics. - : ASME. - 0021-8936 .- 1528-9036. ; 86:4 Tidskriftsartikel (refereegranskat)abstract Based on micropolar continuum theory, the closed-form stiffness tensor of auxetic chiral lattices with V-shaped wings and rotational joints were derived. Representative volume element (RVE) of the chiral lattice was decomposed into V-shape wings with fourfold symmetry. A unified V-beam finite element was developed to reduce the nodal degrees of freedoms of the RVE to enable closed-form analytical solutions. The elasticity constants were derived as functions of the angle of the V-shaped wings, nondimensional in-plane thickness of the ribs, and the stiffness of the rotational joints. The influences of these parameters on the coupled chiral and auxetic effects were systematically explored. The results show that the elastic moduli were significantly influenced by all three parameters, while Poisson's ratio was barely influenced by the in-plane thickness of the ribs but is sensitive to the angle of the V-shaped wings and the stiffness of the rotational springs. There is a transition region out of which the spring stiffness does not considerably affect the auxeticity and the overall lattice stiffness.
7.	Bonnaud, Etienne L., et al. (författare) Proper Boundary Conditions for Infinitely Layered Orthotropic Media 2000 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 67, s. 629-632 Tidskriftsartikel (refereegranskat)abstract A stress analysis of a plane infinitely layered medium subjected to surface loadings is performed using Airy stress functions, integral transforms, and a revised transfer matrix approach. Proper boundary conditions at infinity are for the first time established, which reduces the problem size by one half. Methods and approximations are also presented to enable numerical treatment and to overcome difficulties inherent to such formulations.
8.	Boström, Anders E, 1951, et al. (författare) Point-force excitation of an elastic plate with n embedded cavity 1985 Ingår i: Journal of Applied Mechanics, Transactions ASME. - : ASME International. - 0021-8936 .- 1528-9036. ; 52:4, s. 937-942 Tidskriftsartikel (refereegranskat)abstract The propagation of elastic waves in a thick plate containing an embedded cavity is considered. The full elastodynamic equations are solved and both time-harmonic and pulse propagation are treated. The time-harmonic problem is solved using the null field approach, a method whose main characteristics are surface integral representations and expansions in spherical and planar vector wave functions. To obtain the pulse response, a Fourier integral in frequency is employed. Numerical examples are given showing the fields in both the time and frequency domains at a few selectd locations on the plate surfaces when the plate is excited by a point force. Only low and intermediate frequencies are included and the pulse width is thus somewhat larger than the dimensions of the spheroidal cavity.
9.	Collet, Pierre, et al. (författare) Noise-corrected Estimation of Complex Modulus in Accord With Causality and Thermodynamics : Application to an Impact test 2013 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 80:1, s. 011018- Tidskriftsartikel (refereegranskat)abstract Methods for estimation of the complex modulus generally produce data from which discrete results can be obtained for a set of frequencies. As these results are normally afflicted by noise, they are not necessarily consistent with the principle of causality and requirements of thermodynamics. A method is established for noise-corrected estimation of the complex modulus, subject to the constraints of causality, positivity of dissipation rate and reality of relaxation function, given a finite set of angular frequencies and corresponding complex moduli obtained experimentally. Noise reduction is achieved by requiring that two self-adjoint matrices formed from the experimental data should be positive semidefinite. The method provides a rheological model that corresponds to a specific configuration of springs and dashpots. The poles of the complex modulus on the positive imaginary frequency axis are determined by a subset of parameters obtained as the common positive zeros of certain rational functions, while the remaining parameters are obtained from a least squares fit. If the set of experimental data is sufficiently large, the level of refinement of the rheological model is in accordance with the material behavior and the quality of the experimental data. The method was applied to an impact test with a Nylon bar specimen. In this case, data at the 29 lowest resonance frequencies resulted in a rheological model with 14 parameters. The method has added improvements to the identification of rheological models as follows: (1) Noise reduction is fully integrated. (2) A rheological model is provided with a number of elements in accordance with the complexity of the material behavior and the quality of the experimental data. (3) Parameters determining poles of the complex modulus are obtained without use of a least squares fit.
10.	Cullis, Ian G., et al. (författare) The International Symposium on Ballistics 2010 Ingår i: Journal of applied mechanics. - : ASME-AMER SOC MECHANICAL ENG. - 0021-8936 .- 1528-9036. ; 77:5 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
11.	Dahlberg, Carl F. O., et al. (författare) Size Scaling of Plastic Deformation in Simple Shear : Fractional Strain-Gradient Plasticity and Boundary Effects in Conventional Strain-Gradient Plasticity 2020 Ingår i: Journal of applied mechanics. - : ASME. - 0021-8936 .- 1528-9036. ; 87:3 Tidskriftsartikel (refereegranskat)abstract A recently developed model based on fractional derivatives of plastic strain is compared with conventional strain-gradient plasticity (SGP) models. Specifically, the experimental data and observed model discrepancies in the study by Mu et al. (2016, "Dependence of Confined Plastic Flow of Polycrystalline Cu Thin Films on Microstructure," MRS Com. Res. Let. 20, pp. 1-6) are considered by solving the constrained simple shear problem. Solutions are presented both for a conventional SGP model and a model extension introducing an energetic interface. The interface allows us to relax the Dirichlet boundary condition usually assumed to prevail when solving this problem with the SGP model. We show that the particular form of a relaxed boundary condition does not change the underlying size scaling of the yield stress and consequently does not resolve the scaling issue. Furthermore, we show that the fractional strain-gradient plasticity model predicts a yield stress with a scaling exponent that is equal to the fractional order of differentiation.
12.	Dhavale, Nikhil N., et al. (författare) Finite Inflation Analysis of Two Circumferentially Bonded Hyperelastic Circular Flat Membranes 2014 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 81:9 Tidskriftsartikel (refereegranskat)abstract A finite inflation analysis of two circumferentially bonded hyperelastic circular flat membranes with uniform internal pressure is presented. The governing equations of equilibrium are obtained using the variational formulation. By making a suitable change in the field variables, the problem is formulated as a set of two coupled nonlinear two point boundary value problem (TPBVP) and is solved using the shooting method. Membranes of identical and dissimilar material properties are considered in the analysis. For dissimilar membranes, asymmetric inflation, and remarkably, deflation (after an initial phase of inflation) in one of the membranes in certain cases, has been observed. The effect of inflation pressure and material properties on the geometry of inflated configuration, state of stress, and the impending wrinkling condition of the membranes are also studied. This work has relevance to tunable inflated reflectors and lenses among other applications.
13.	Digby, Peter J., et al. (författare) Wave propagation through elastically-anisotropic fluid-saturated porous rocks 1989 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 56:4, s. 744-750 Tidskriftsartikel (refereegranskat)abstract An elastically-anisotropic sedimentary rock is modeled by a simple cubic packing of identical, contacting spherical particles. The connected pore space is filled with an inviscid, compressible fluid. A set of averaged equations is derived to relate the constitutive and dynamic coupling coefficients, and hence also the effective wave speeds in any given direction explicitly to the microstructural properties of the rock considered. Simple, explicit results are obtained when the propagation of either a purely longitudinal or a purely transverse wave is considered.
14.	Edvardsson, Sverker, et al. (författare) System dynamics of the open draw with web adhesion: Particle approach 2010 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:2, s. 1-11 Tidskriftsartikel (refereegranskat)abstract In the present work we propose a particle approach, which is designedto treat complex mechanics and dynamics of the open-draw sections thatare still present in many of today's paper machines. First, knownsteady-state continuous solutions are successfully reproduced. However,it is shown that since the boundary conditions depend on the solutionitself, the solutions for web strain and web path in the open-drawsection are generally time-dependent. With a certain set of systemparameters, the nonsteady solutions are common. A temporal fluctuationof Young's modulus, for example, destabilizes the system irreversibly,resulting in the continuous growth of web strain, i.e., break. Finallywe exemplify with some strategic draw countermeasures how to prevent adangerous evolution in the web strain.
15.	Edvardsson, Sverker, 1964-, et al. (författare) The dynamical functional particle method: an approach for boundary value problems 2012 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 79:2, s. art. no. 021012- Tidskriftsartikel (refereegranskat)abstract The present work is concerned with new ideas of potential value for solving differential equations. First, a brief introduction to particle methods in mechanics is made by revisiting the vibrating string. The full case of nonlinear motion is studied and the corresponding nonlinear differential equations are derived. It is suggested that the particle origin of these equations is of more general interest than usually considered. A novel possibility to develop particle methods for solving differential equations in a direct way is investigated. The dynamical functional particle method (DFPM) is developed as a solution method for boundary value problems. DFPM is based on the concept of an interaction functional as a dynamical force field acting on quasi particles. The approach is not limited to linear equations. We exemplify by applying DFPM to several linear Schrödinger type of problems as well as a nonlinear case. It is seen that DFPM performs very well in comparison with some standard numerical libraries. In all cases, the convergence rates are exponential in time. © 2012 American Society of Mechanical Engineers.
16.	Ekneligoda, Thushan C., et al. (författare) Boundary perturbation solution for nearly circular holes and rigid inclusions in an infinite elastic medium 2008 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 75:1, s. 011015- Tidskriftsartikel (refereegranskat)abstract The boundary perturbation method is used to solve the problem of a nearly circular rigid inclusion in a two-dimensional elastic medium subjected to hydrostatic stress at infinity. The solution is taken to the fourth order in the small parameter epsilon that quantifies the magnitude of the variation of the radius of the inclusion. This result is then used to find the effective bulk modulus of a body that contains a dilute concentration of such inclusions. The corresponding results for a cavity are obtained by setting the Muskhelishvili coefficient K equal to -1, as specified by the Dundurs correspondence principle. The results for nearly circular pores can be expressed in terms of the pore compressibility. The pore compressibilities given by the perturbation solution are tested against numerical values obtained using the boundary element method, and are shown to have good accuracy over a substantial range of roughness values.
17.	Eriksson, Kjell (författare) The support reaction of a simply supported and uniformly loaded thin circular aeolotropic plate 2008 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 75:2, s. 10021-10028 Tidskriftsartikel (refereegranskat)abstract A previous analytical solution of the deflection of a thin circular aeolotropic plate, with simply supported edge and uniform lateral load, has been used to derive approximate series expressions for the plate support reaction, which are directly applicable in practice. The support reaction, which has been calculated for some typical anisotropic materials of varying degree of anisotropy, varies significantly along the plate perimeter and strongly anisotropic materials require in general a higher order series solution. Certain solution constants of previous deflection approximations were not found to harmonize and are therefore recalculated.
18.	Fällström, Karl-Evert, et al. (författare) Transient bending wave propagation in anisotropic plates 1998 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 65:4, s. 930-938 Tidskriftsartikel (refereegranskat)abstract We study transient propagating bending waves. We use the equations of orthotropic plate dynamics, derived by Chow about 25 years ago, where both transverse shear and rotary inertia are included. These equations are extended to include anisotropic plates and an integral representation formula for the bending waves is derived. Chow's model is compared with the classical Kirchoff's model. We also investigate the influence of the rotary inertia. Comparisons with experimental data are made as well
19.	Ghaddar, Nesreen, et al. (författare) Experimental and Theoretical Study of Ventilation and Heat Loss From Isothermally Heated Clothed Vertical Cylinder in Uniform Flow Field 2010 Ingår i: Journal of Applied Mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:3 Tidskriftsartikel (refereegranskat)abstract The flow characteristics and heat transfer are studied in a vertical annulus of a heated cylinder surrounded by a permeable cylinder, subject to cross uniform wind with open end to the environment and in the presence of natural convection. The objective here is to develop a computationally efficient model capable of capturing the physics of the flow and heat transport to predict air renewal rates in the vertical annulus. The small quantities of air infiltrating/exfiltrating through the porous cylinder over its upstream/downstream regions do not substantially affect the external flow pattern around the clothed cylinder. The air annulus flow and heat transport model predicted the radial and vertical mass fluxes and the mass flow rate at the opening as a function of environment conditions, porous cylinder thermal properties, wind speed, and annulus geometry. Experiments were performed in a low speed wind tunnel (0.5-5 m/s), in which an isothermally heated vertical cylinder surrounded by a clothed outer cylinder was placed in uniform cross wind. The tracer gas method is used to predict total ventilation flow rates through the fabric and the opening. Good agreement was found between the model and experimental measurements of air renewal rate and predicted heat loss from the inner cylinder at steady conditions. A parametric study is performed to study the effect of wind speed and temperature difference between the wind and skin temperature on induced ventilation through the clothing and the opening. It is found that natural convection enhances ventilation of the annulus air at wind speed, less than 3 m/s, while at higher speeds, natural convection effect is negligible. As the temperature difference between external wind and inner cylinder surface increases, the vertical air temperature gradient and total upward airflow through the opening increase.
20.	Gil-Negrete, N., et al. (författare) A Nonlinear Rubber Material Model Combining Fractional Order Viscoelasticity and Amplitude Dependent Effects 2009 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 76:1, s. 1-9 Tidskriftsartikel (refereegranskat)abstract A nonlinear rubber material model is presented, where influences of frequency and dynamic amplitude are taken into account through fractional order viscoelasticity and plasticity, respectively. The problem of simultaneously modeling elastic, viscoelastic, and friction contributions is removed by additively splitting them. Due to the fractional order representation mainly, the number of parameters of the model remains low, rendering an easy fitting of the values from tests on material samples. The proposed model is implemented in a general-purpose finite element (FE) code. Since commercial FE codes do not contain any suitable constitutive model that represents the full dynamic behavior of rubber compounds (including frequency and amplitude dependent effects), a simple approach is used based on the idea of adding stress contributions from simple constitutive models: a mesh overlay technique, whose basic idea is to create a different FE model for each material definition (fractional derivative viscoelastic and elastoplastic), all with identical meshes but with different material definition, and sharing the same nodes. Fractional-derivative viscoelasticity is implemented through user routines and the algorithm for that purpose is described, while available von Mises' elastoplastic models are adopted to take rate-independent effects into account. Satisfactory results are obtained when comparing the model results with tests carried out in two rubber bushings at a frequency range up to 500 Hz, showing the ability of the material model to accurately describe the complex dynamic behavior of carbon-black filled rubber compounds.
21.	Gradin, Per, 1952-, et al. (författare) A Note on the Co-linearity of forces and Displacements in an Elastic Structure 2011 Ingår i: Journal of Applied Fluid Mechanics. - : ASME International. - 1735-3572 .- 1735-3645 .- 0021-8936 .- 1528-9036. ; 78:6, s. Art. no. 4003912- Tidskriftsartikel (refereegranskat)abstract Theconditions under which force vectors and corresponding displacement vectors becomeco-linear are investigated under the assumption of a linear elasticstructure and for an arbitrary number of loading points. Itis shown that there exist an infinite number of directionsalong which the load and displacement vectors in each loadingpoint coincide. Moreover, the problem of co-linearity is analogous tothe problem of finding the extreme values of the workperformed on an elastic structure under the constraint that eachforce has a given magnitude. The result for a finitenumber of loading points is extended to a continuous loaddistribution on the boundary of an elastic structure, i.e., itis possible to find an infinite number of load distributionssuch that the displacement in a point on the boundaryis co-linear with the boundary stress vector in that samepoint.
22.	Grenestedt, Joakim L, et al. (författare) Crack initiation from homogeneous and bimaterial corners 1997 Ingår i: Journal of applied mechanics. - 0021-8936 .- 1528-9036. ; 64:4, s. 811-818 Tidskriftsartikel (refereegranskat)abstract Fracture initiated at a corner between two different isotropic materials is considered. A "small" crack, well within the region dominated by the asymptotic stress fields of the non-cracked corner, is modelled and the stress intensities associated with the tip of the small crack are determined. Different criteria for the direction of crack propagation are studied.
23.	Gudmundson, Peter, et al. (författare) Stress Singularity At The Free-Surface Of A Dynamically Growing Crack. 1990 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 57:1, s. 112-116 Tidskriftsartikel (refereegranskat)abstract The stress singularity at the intersection between the crack front and the free surface of a dynamically growing crack in a linear elastic isotropic material has been numerically evaluated by an especially developed finite element program. The singularity parameter (), defined by ~ R−1, is presented as a function of the crack-tip velocity and the angle (ß)between the crack front and the free surface. The angle (ß) at which the singularity () equals 0.5 was found to be 101 deg almost independently of the crack-tip velocity.
24.	Gupta, R. B. (författare) Propagation Of Elastic-Waves In Rods With Variable Cross-Section 1979 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 46:4, s. 951-951 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
25.	Helsing, Johan, et al. (författare) On the accuracy of benchmark tables and graphical results in the applied mechanics literature 2002 Ingår i: Journal of Applied Mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 69:1, s. 88-90 Tidskriftsartikel (refereegranskat)abstract Converged normalized stress intensity factors for a matrix crack interacting with an elastic cylinder are presented. The new results differ from previously published results in several examples. The need for better error analysis in computational fracture mechanics is emphasized.
26.	Helte, Andreas, et al. (författare) The role of Kelvin-Helmholz instabilities on shaped charge jet interaction with reactive armour plates 2010 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:5, s. 051805- Tidskriftsartikel (refereegranskat)abstract Reactive armor panels have been used for many years as very efficient add-on armoragainst shaped charge warheads. The main features of the defeat mechanisms of thearmor are therefore well known. The origin of the irregular disturbances on the shapedcharge jet, which leads to the severe fragmentation and scattering of the jet, is howevernot described in literature. As this scattering of the jet provides the main protectionmechanism of the armor, it is of interest to understand the details of the interaction andthe origin of the disturbances. Some experimental observations have been made showingthat the backward moving plate often displaces the jet relatively smoothly while it is theinteraction with the forward moving plate that causes the disturbances that leads tofragmentation and scattering of the jet. In this work, a mechanism for the interaction isproposed based on the theory of Kelvin–Helmholtz instabilities, which explains the originof the disturbances on the jet due to the interaction with the forward moving plate.Numerical simulations have been performed to show the difference in the mechanisms ofbackward and forward moving plates when interacting with the jet. The impact angle ofthe plate seems to be the dominant parameter for the onset of instabilities. A parametricstudy has also been performed on how different interaction and material parametersinfluence the development of instabilities of the interface between the jet and the armorplate. The parametric study shows that low-strength jets promote development of instabilities,a tendency that is amplified by frictional forces between the materials. Theinfluence of the plate strength is more complex due to the influence of the structuralstability on the contact forces. The effect of friction and melting of the metals in theboundary layer to the development of the instabilities is discussed. A microscopic study ofthe edge of the penetration channel has been made, which shows that the materials havebeen melted during the interaction between the plate and the jet.
27.	Hild, Francois, et al. (författare) Localization due to damage in two-direction fiber-reinforced composites 1996 Ingår i: Journal of applied mechanics. - 0021-8936 .- 1528-9036. ; 63:2, s. 321-325 Tidskriftsartikel (refereegranskat)
28.	Johansson, Leif, et al. (författare) Study of frictional impact using a nonsmooth equations solver 2000 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 67:2, s. 267-273 Tidskriftsartikel (refereegranskat)abstract In this paper a mathematical formulation and a numerical algorithm for the analysis of impact of rigid bodies against rigid obstacles are developed. The paper concentrates on three-dimensional motion using a direct approach where the impenetrability condition and Coulomb's law of friction are formulated as equations, which are not differentiable in the usual sense, and solved together with the equations of motion and necessary kinematical relations using Newton's method. An experiment has also been performed and compared with predictions of the algorithm, with favorable results.
29.	Karlsson, Lennart, et al. (författare) Plane stress field induced by a concentrated heat source moving perpendicularly toward free edge of semi-infinite plate 1974 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 41:3, s. 825-827 Tidskriftsartikel (refereegranskat)abstract This study of a simplified mathematical model of the process aims at explaining the tendency of hot cracking in the weld metal near that end of a joint where the (submerged-arc) welding is finished and the welding set leaves the panel.
30.	Karlsson, Lennart (författare) Plane stress fields induced by moving heat sources in butt-welding 1977 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 44:2, s. 231-236 Tidskriftsartikel (refereegranskat)abstract Mathematical models of the cooling of large butt-welded plates are investigated. One thermoelastic infinite plate and one thermoelastic semi-infinite plate are considered. On the infinite plate two concentrated heat sources of constant power move with constant velocity along a straight line toward each other. They meet and are then immediately removed from the plate. On the semi-infinite plate one concentrated heat source of constant power moves with constant velocity along a straight line perpendicularly toward the edge and is removed as it reaches the plate edge. The straight plate boundary is thermally adiabatic and mechanically free. It is shown that after removal of the heat source(s) such tensile stresses remain much longer in the semi-infinite plate than in the infinite plate. The transverse tensile stresses may explain the tendency of hot cracking in the end portion of a butt-weld.
31.	Karlsson, Martin, et al. (författare) Rotor Dynamic Analysis of an Eccentric Hydropower Generator With Damper Winding for Reactive Load 2007 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 74:6, s. 1178-1186 Tidskriftsartikel (refereegranskat)abstract Asymmetry in the magnetic circuit, around the air gap circumference, in a hydroelectric generator will give rise to a unbalanced magnetic pull. In this paper a hydropower rotor system is modeled and the influence of electro-mechanical forces due to overexcitation is analyzed The active power has been kept constant and the rotor excitation has been changed in order to vary the output of reactive power The electromagnetic field is solved with the finite element method Two electromagnetic models are compared: one with and one without damper winding. The mechanical model of the generator consists of a four id disk connected to an elastic shaft su orted b two bearin s de rees of freedom ri pp y g g g with linear properties. It has been found that the unbalanced magnetic pull slightly increasesfor reactive loads resulting in a decrease of natural frequencies and an increase of unbalance response. When the damper winding is included, the magnetic pull will decrease compared to the model without damper winding, and the pull force has two components: one radial and one tangential. The tangential component can influence the stability of the mechanical system for a range of design parameters.
32.	Li, Y. Q., et al. (författare) Modeling of advanced combat helmet under ballistic impact 2015 Ingår i: Journal of applied mechanics. - : ASME Press. - 0021-8936 .- 1528-9036. ; 82:11 Tidskriftsartikel (refereegranskat)abstract The use of combat helmets has greatly reduced penetrating injuries and saved lives of many soldiers. However, behind helmet blunt trauma (BHBT) has emerged as a serious injury type experienced by soldiers in battlefields. BHBT results from nonpenetrating ballistic impacts and is often associated with helmet back face deformation (BFD). In the current study, a finite element-based computational model is developed for simulating the ballistic performance of the Advanced Combat Helmet (ACH), which is validated against the experimental data obtained at the Army Research Laboratory. Both the maximum value and time history of the BFD are considered, unlike existing studies focusing on the maximum BFD only. The simulation results show that the maximum BFD, the time history of the BFD, and the shape and size of the effective area of the helmet shell agree fairly well with the experimental findings. In addition, it is found that ballistic impacts on the helmet at different locations and in different directions result in different BFD values. The largest BFD value is obtained for a frontal impact, which is followed by that for a crown impact and then by that for a lateral impact. Also, the BFD value is seen to decrease as the oblique impact angle decreases. Furthermore, helmets of four different sizes - extra large, large, medium, and small - are simulated and compared. It is shown that at the same bullet impact velocity the small-size helmet has the largest BFD, which is followed by the medium-size helmet, then by the large-size helmet, and finally by the extra large-size helmet. Moreover, ballistic impact simulations are performed for an ACH placed on a ballistic dummy head form embedded with clay as specified in the current ACH testing standard by using the validated helmet model. It is observed that the BFD values as recorded by the clay in the head form are in good agreement with the experimental data.
33.	Löfstrand Grip, Rasmus (författare) A dynamical model of an axial piston machine 2009 Ingår i: Journal of applied mechanics. - 0021-8936 .- 1528-9036. Tidskriftsartikel (refereegranskat)
34.	Mao, Huina, et al. (författare) Design and Analysis of Laminates for Self-Deployment of Viscoelastic Bistable Tape Springs after Long-Term Stowage 2017 Ingår i: Journal of applied mechanics. - : ASME Press. - 0021-8936 .- 1528-9036. ; 84:7 Tidskriftsartikel (refereegranskat)abstract Bistable tape springs are ultrathin fiber-reinforced polymer composites, which could self-deploy through releasing stored strain energy. Strain energy relaxation is observed after long-term stowage of bistable tape springs due to viscoelastic effects and the tape springs might lose their self-deployment abilities. In order to mitigate the viscoelastic effects and thus ensure self-deployment, different tape springs were designed, manufactured, and tested. Deployment experiments show that a four-layer, [â '45/0/90/45], plain weave glass fiber tape spring has a high capability to mitigate the strain energy relaxation effects to ensure self-deployment after long-term stowage in a coiled configuration. The two inner layers increase the deployment force and the outer layers are used to generate the bistability. The presented four-layer tape spring can self-deploy after more than six months of stowage at room temperature. A numerical model was used to assess the long-term stowage effects on the deployment capability of bistable tape springs. The experiments and modeling results show that the viscoelastic strain energy relaxation starts after only a few minutes after coiling. The relaxation shear stiffness decreases as the shear strain increases and is further reduced by strain energy relaxation when a constant shear strain is applied. The numerical model and experiments could be applied in design to predict the deployment force of other types of tape springs with viscoelastic and friction effects included.
35.	Melin, Solveig (författare) Accurate data for stress intensity factors at infinitesimal kinks 1994 Ingår i: Journal of Applied Mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 61:2, s. 467-470 Tidskriftsartikel (refereegranskat)
36.	Olsson, Erik, et al. (författare) On the effect of particle size distribution in cold powder compaction 2012 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 79:5, s. 051017- Tidskriftsartikel (refereegranskat)abstract The effect of particle size distribution in powder compaction has been studied using the discrete element method. Both isostatic compaction and closed die compaction are studied together during the entire loading process. Particle rotation and frictional effects are accounted for in the analysis. The particles are, constitutively described by rigid plasticity, assumed to be spherical with the size of the radii that follows a truncated normal distribution. The results show that size distribution effects are small on global compaction properties like compaction pressure if the size distribution is small. Furthermore, the size distribution had no influence at all on the macroscopic behavior at unloading. To verify the model, comparisons were made on two different sets of experiment found in the literature where the particles were of varying sizes. Good agreement was found both on fundamental properties like the average number of contacts per particle and on more important properties from a practical point of view, like the compaction pressure.
37.	Olsson, Peter, 1956, et al. (författare) Elastodynamic scattering from inclusions surrounded by thin interface layers 1990 Ingår i: Journal of Applied Mechanics. ; 57:3, s. 672-676 Tidskriftsartikel (refereegranskat)
38.	Olsson, Peter, 1956 (författare) Elastodynamic scattering from pennyshaped and nonplanar cracklike flaws with dissipation and restoring forces 1990 Ingår i: Journal of Applied Mechanics. ; 57:3, s. 661-666 Tidskriftsartikel (refereegranskat)
39.	Ottosen, Niels Saabye (författare) Relaxation of Thick-Walled Cylinders and Spheres 1982 Ingår i: Journal of Applied Mechanics, ASME. - : ASME International. - 0021-8936 .- 1528-9036. ; 49:3, s. 487-491 Tidskriftsartikel (refereegranskat)abstract Using the nonlinear creep law proposed by Soderberg, closed-form solutions are derived for the relaxation of incompressible thick-walled spheres and cylinders in plane strain. These solutions involve series expressions which, however, converge very quickly. By simply ignoring these series expressions, extremely simple approximate solutions are obtained. Despite their simplicity these approximations possess an accuracy that is superior to approximations currently in use. Finally, several physical aspects related to the relaxation of cylinders and spheres are discussed.
40.	Pons, Arion, 1995, et al. (författare) Aeroelastic flutter of continuous systems: a generalized Laplace Transform Method 2016 Ingår i: Journal of Applied Mechanics, Transactions ASME. - : ASME International. - 0021-8936 .- 1528-9036. ; 83:8 Tidskriftsartikel (refereegranskat)abstract This paper presents a generalization of the Laplace transform method (LTM) for determining the flutter points of a linear ordinary-differential aeroelastic system-a linear system involving a spatial derivative as well as a time-eigenvalue parameter. Current implementations of the LTM have two major problems: they are unable to solve systems of arbitrary size, order, and boundary conditions, and they require certain key operations to be performed by hand or with symbolic manipulation libraries. Our generalized method overcomes both these problems. We also devise a new method for solving and visualizing the algebraic system that arises from the LTM procedure. We validate our generalized LTM and novel solution method against both the Goland wing model and a large system of high differential order, as a demonstration of their effectiveness for solving such systems
41.	Pons, Arion, 1995, et al. (författare) Multiparameter Spectral analysis for aeroelastic instability problems 2018 Ingår i: Journal of Applied Mechanics, Transactions ASME. - : ASME International. - 0021-8936 .- 1528-9036. ; 85:6 Tidskriftsartikel (refereegranskat)abstract This paper presents a novel application of multiparameter spectral theory to the study of structural stability, with particular emphasis on aeroelastic flutter. Methods of multiparameter analysis allow the development of significant new solution and analysis algorithms for aeroelastic flutter problems; including direct solvers for polynomial problems of arbitrary order and size, and a pseudospectral method for characterizing the nature of the flutter point and its local modal damping gradient. Two variants of the flutter point direct solver are presented, their computational characteristics are compared, and an efficient hybrid method of direct spectral solution and iterative pseudospectral solution is developed. This method is well suited to the analysis of problems arising in reduced-order modeling and preliminary design optimization and has the advantage of computing all the system flutter points and their characteristics with minimal user oversight. The aeroelastic inverse problem, with applications in parameter identification and system optimization, is also shown to be solvable via multiparameter analysis. Extensions and improvements to this new conceptual framework and associated solvers are discussed.
42.	Skrinjar, Olle, et al. (författare) Local contact compliance relations at compaction of composite powders 2007 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 74:1, s. 164-168 Tidskriftsartikel (refereegranskat)abstract Local contact behavior of composite powders has been investigated by using the finite element method. In previous analyses of such problems it has in general been assumed that one of the powder materials is rigid while the other deforms at loading as in such a case self-similarity prevails. This is a very good approximation for ceramic/metallic composites but may not be so when the composite consists of two materials of roughly equal hardness. An approximate compliance formula for describing this feature is proposed showing good agreement with corresponding finite element results for representative cases.
43.	Stigh, Ulf (författare) Continuum Damage Mechanics and the Life-Fraction rule 2006 Ingår i: Journal of applied mechanics. - : American Society of Mechanical Engineers. - 0021-8936 .- 1528-9036. ; 73:4, s. 702-704 Tidskriftsartikel (refereegranskat)abstract This paper gives a short review of two different methods for life prediction at high temperature; namely continuum damage mechanics (CDM) and the linear life-fraction rule (LFR). It is well known that the class of CDM theories with a separable evolution law gives a life prediction in accordance with the LFR. However, it appears to be an open question if this is a necessary condition. It is here shown that in order for a CDM theory to comply with the LFR it must have a separable evolution law. That is, if we can assume that a material follows the LFR, it is necessary to chose a separable evolution law for this material. The reverse is also true, to get a life-fraction different from unity, we must chose a nonseparable evolution law.
44.	Storåkers, Bertil, et al. (författare) On delamination growth in shallow shells 2004 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 71:2, s. 247-254 Tidskriftsartikel (refereegranskat)abstract A theoretical and computational study has been carried out for compressive loading of a thin circular embedded delamination located below a cylindrical surface. The delaminated member is subjected to nominally uniaxial and balanced biaxial loading with the main objective to analyze its influence on surface curvature especially as regards imminent crack growth. The analysis is based on nonlinear shell theory combined with linear fracture mechanics. A finite element program earlier developed for delaminated plates has been generalized to apply also for shells and used to determine energy release rates and mode intensities along the delaminated front. A parameter study, is made of the influence of curvature of the delaminated shell in particular as regards initiation and stability of crack growth.
45.	Westerling, Lars, et al. (författare) Stresses in a long cylindrical conductor moving axially through a pair of electrode plates under stationary conditions 2013 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 80:2, s. 021013- Tidskriftsartikel (refereegranskat)abstract In a conductor carrying electric current, the Lorentz force gives rise to mechanical stresses. Here, we study a long elastic cylindrical conductor that moves axially with constant velocity through two electrode plates. The aims are to explore how the stresses in the conductor depend on the velocity in the stationary case of constant current and to assess the validity of the analytic method used. The diffusion equation for the magnetic flux density is solved by use of Fourier transform, and the current density is determined. The stresses, due to the Lorentz force, are found by use of an analytic method combining the solutions of a quasi-static radial problem of plane deformation and a dynamic axial problem of uniaxial stress. They are also determined through FE analysis. Radial field profiles between the plates indicate a velocity skin effect signifying that the current and the magnetic field are concentrated near the cylindrical surface up-stream and are more uniformly distributed downstream. The radial and hoop stresses are compressive, while the axial stress is tensile. The von Mises effective stress increases towards the symmetry axis, in the downstream direction, and with velocity. There are circumstances under which a large current can produce an effective stress in a copper conductor of the order of the yield stress without causing a significant temperature rise. The stresses obtained with the two methods agree well, even relatively near the electrode plates. The analytical method should be useful in similar cases as well as for the provision of test cases for more general simulation tools.
46.	Wikström, Adam, et al. (författare) Thermal deformation of initially curved substrates coated by thin inhomogeneous layers 2001 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 68:2, s. 298-303 Tidskriftsartikel (refereegranskat)abstract Thermal curvature changes and membrane strains are analyzed for elastic shallow shell substrates which are coated by thin, generally inelastic, inhomogeneous and anisotropic layers. The analysis is restricted to linear kinematics. It is shown that the deformation is governed by the corresponding solution for a flat substrate and a correction due to the initial curvature. The correction is determined from a shallow shell problem for the bare substrate with a loading expressed by the coefficients of thermal curvature for the substrate/layer system. For constant initial curvature, certain analytic solutions are presented. For situations when the initial deflection of the substrate is much larger than the substrate thickness, a boundary layer solution is derived. In the particular case of a circular isotropic substrate with a spherical initial curvature and a coating of arbitrary anisotropy, the solution is presented in closed form. For nonflat substrates, measured curvatures can generally not be used to extract layer stresses without a proper compensation for the initial curvature. In this paper, it is explicitly presented how to accurately compensate for a spherical initial curvature. The results are particularly discussed in relation to curvature measurements on Silicon substrates.
47.	Åberg, Mats, et al. (författare) Dispersion of waves in composite laminates with transverse matrix cracks, finite element and plate theory computations 1998 Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 65:3, s. 588-595 Tidskriftsartikel (refereegranskat)abstract Dispersion relations for laminated composite plates with transverse matrix cracks have been computed using two methods. In the first approach it is assumed that the matrix cracks appear periodically and hence it is possible to consider a periodic cell of the the structure using Bloch-type boundary conditions. This problem was formulated in complex notation and solved in a standard finite element program (ABAQUS) using two identical finite element meshes, one for the real part and one for the imaginary part of the displacements. The two meshes were coupled by the boundary conditions on the cell. The code then computed the eigenfrequencies of the system for a given wave vector. It was then possible to compute the phase velocities. The second approach used may be viewed as a two step homogenization. First the cracked layers are homogenized and replaced by weaker uncracked layers and then the standard first-order shear-deformation laminate theory is used to compute dispersion relations. Dispersion relations were computed using both methods for three glass-fiber/epoxy laminates ([0/90](2), [0/90](2) and [0/45/-45](s) with cracks in the 90 and +/-45 deg plies). For the lowest flexural mode the difference in phase velocity between the methods was less then five percent for wavelengths longer than two times the plate thickness. For the extensional merle a wavelength of ten plate thicknesses gave a five percent difference.
48.	Boström, Anders E, 1951 (författare) Elastic wave scattering from an interface crack: antiplane strain 1987 Ingår i: Journal of Applied Mechanics, Transactions ASME. - 0021-8936. ; 54, s. 503-508 Tidskriftsartikel (refereegranskat)abstract The two-dimensional scalar problem of scattering of elastic waves under antiplane strain from an interface crack between two elastic half-spaces is considered. The method used is a direct integral equation method with the crack-opening displacement as the unknown. Chebyshev polynomials are used as expansion functions and the matrix in the resulting equations is simplified by contour integration techniques. The scattered far field is expressed explicitly in simple functions and the expansion coefficients. The consequences of energy conservation are explored and are used as a check in the numerical implementation. For incoming plane waves numerical results are given for the total scattered energy and the far field amplitude.
49.	Toll, Staffan, et al. (författare) Elastic compression of a fiber network 1995 Ingår i: Journal of Applied Mechanics, Transactions ASME. - 0021-8936. ; 62:1, s. 223-226 Tidskriftsartikel (refereegranskat)abstract A constitutive equation for a planar fiber network under transverse compression is derived allowing for an in-plane fiber orientation distribution. The fibers are assumed to be well dispersed in space and to have a large aspect ratio and uniform diameter. A compression experiment, performed on a glass-fiber network obtained by ashing a commercial composite preform, is accurately described by the theory.

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