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  • 1. Fällström, Karl-Evert
    A nondestructive method to detect delaminations and defects in plates1991In: NDT & E international, ISSN 0963-8695, E-ISSN 1879-1174, Vol. 24, no 2, p. 67-76Article in journal (Refereed)
    Abstract [en]

    Double exposure holographic interferometry, with a ruby laser as the light source, is used to study the influence of local changes in thickness, of delaminations and variations in damping upon propagating transient bending waves in plates and shells. The bending waves are created by the impact of a pendulum. Defects cause changes in the wave impedance of the plate, which will give rise to changes relative to the undisturbed fringe pattern, by reflected and transmitted waves. The size of a defect has to be of the same size or larger than the wavelength of the bending wave to be visible. Since bending waves are dispersive, high frequency components travelling faster than low frequency ones, a small defect is most likely to be observed shortly after impact. The influence of local changes in thickness and delaminations upon the fringe pattern is presented, together with a method to interpret the fringe pattern when several defects are present

  • 2. Fällström, Karl-Evert
    Determining material properties in anisotropic plates using Rayleigh's method1991In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 12, no 5, p. 306-314Article in journal (Refereed)
    Abstract [en]

    Material parameters of anisotropic plates are determined. Rectangular anisotropic plates are tuned by changing the quotient between the length of the sides, so that the second and third modes of vibration, for free-free boundary conditions, degenerate into the well-known cross-shaped and ring-shaped modes, respectively. The first three modes of vibrations for these plates are determined by optical methods. The propagation of bending waves, generated by the impact of a ballistic pendulum on the plates, has also been optically studied. It is found that bending waves generated in the middle of the tuned plates will reach the boundaries of the plates simultaneously. This gives a relationship between main material parameters. Using this relation and Rayleigh's method for the first three modes of vibrations, the main material parameters for the plates, that is, the effective two Young's moduli, the shear modulus, and the Poisson's ratio, are determined

  • 3. Fällström, Karl-Evert
    Icke förstörande materialprovning: förstudie1986Report (Other academic)
  • 4. Fällström, Karl-Evert
    Material parameters and defects in anisotropic plates determined by hologram interferometry1990Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Material parameters and defects in composite plates are determined in a non-contacting and nondestructive way by use of optical methods. Material parameters are determined from TV-holography images, and defects are detected by holographic interferometry with a double pulsed laser as the light source. A plate excited into harmonic vibration will be in resonance for certain frequencies. At each such frequency the plate vibrates in a certain manner, called a mode. Experimentally determined frequencies and shapes of these modes of vibration for rectangular orthotropic and anisotropic plates are compared with the results of FE-calculations or calculations using Rayleigh's method. In both cases it is possible to estimate the two Young's moduli, the in-plane shear modulus and Poisson's ratio of the orthotropic and the anisotropic plates. Defects are detected by impacting the plates with a small pendulum. This creates propagating transient bending waves in the plates. These waves are recorded using holographic interferometry. A defect gives rise to anomalies in the interference pattern. Large defects can be examined in the interferograms with the naked eye. Small defects, such as delaminations with a diameter of 15 mm, could be discovered using a proposal method. The impacted plate problem is solved analytically for an isotropic plate. A similarity parameter depending upon thickness, density and effective material parameters is found. The existence of this variable brings new understanding to the importance of specific parameters for wave propagation in plates.

  • 5. Fällström, Karl-Evert
    Material parameters in anisotropic plates1991In: Mechanical identification of composites: [proceedings of the European Mechanics Colloquium 269, "Experimental Identification of the Mechanical Characteristics of Composite Materials and Structures" held in Saint-Étienne, France, 3 - 6 December, 1990], Elsevier, 1991, p. 117-124Conference paper (Refereed)
    Abstract [en]

    Material parameters, that is, the two Youngs moduli, the in-plane shear modulus and the Poisson's ratio, in anisotropic rectangular GFRP plates are determined in three different ways using modes of vibration, Rayleigh's method and transient bending waves

  • 6. Fällström, Karl-Evert
    Solfångare med luftburen värme1983Report (Other academic)
  • 7. Fällström, Karl-Evert
    et al.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mattsson, Roger
    Luleå tekniska universitet.
    Determination of paper stiffness and anisotropy from recorded bending waves in paper subjected to tensile forces2002In: NDT & E international, ISSN 0963-8695, E-ISSN 1879-1174, Vol. 35, no 7, p. 465-472Article in journal (Refereed)
    Abstract [en]

    Experiments and theory for bending wave propagation of paper sheets in tension are presented. An all-electronic pulsed TV holography technique is used to record the bending wave field initiated by a laser pulse. A theory for bending wave propagation in tensile-loaded paper is developed. The bending waves are influenced by mechanical properties such as density, thickness, bending stiffness, anisotropy and also by tensile forces in the paper. The paper stiffnesses are determined by matching the measured deformation field with the calculated theoretical field. The results show that the bending wave pattern is strongly influenced by the tensile force. For a non-destructive on-line measurement of, e.g. stiffnesses and anisotropy in the paper machine the tensile force must be considered

  • 8. Fällström, Karl-Evert
    et al.
    Gustavsson, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Molin, Nils-Erik
    Wåhlin, Anders
    Transient bending waves in plates studied by hologram interferometry1989In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 29, no 4, p. 378-387Article in journal (Refereed)
    Abstract [en]

    Propagating bending waves are studied in plates made of aluminum and wood. The waves are generated by the impact of a ballistic pendulum. Hologram interferometry, with a double pulsed ruby laser as the light source, is used to record the out of plane motion of the waves. Elliptic-like fringes visualize differences in wave speed for different directions in the anisotropic plate and circular ones are obtained for the isotropic plate. The experimental data for the isotropic plate compare favorably with analytical results derived from the Kirchhoff-plate equation with a point impact of finite duration. A similarity variable is found when starting conditions are modeled as a Dirac pulse in space and time, that brings new understanding to the importance of specific parameters for wave propagation in plates. A formal solution is obtained for a point force with an arbitrary time dependence. For times much larger than the contact time, the plate deflection is shown to be identical to that from a Dirac pulse applied at the mean contact time. A method for determining material parameters, and the mean contact time, from the interferograms is hence developed.

  • 9. Fällström, Karl-Evert
    et al.
    Jonsson, Mikael
    A nondestructive method to determine material properties in anisotropic plates1991In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 12, no 5, p. 293-305Article in journal (Refereed)
    Abstract [en]

    Material parameters in anisotropic rectangular plates are determined in a nondestructive way. Real-time, TV-holography is used to determine frequencies and shapes of the first five modes of vibration of plates with free-free boundary conditions. According to rules given in the paper, finite element analysis is then used to determine two effective Young's moduli, the shear modulus, and the Poisson's ratio

  • 10. Fällström, Karl-Evert
    et al.
    Lindblom, O.
    Luleå tekniska universitet.
    Transient bending wave propagation in anisotropic plates1998In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 65, no 4, p. 930-938Article in journal (Refereed)
    Abstract [en]

    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

  • 11. Fällström, Karl-Evert
    et al.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Molin, Nils-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Transient bending waves in anisotropic plates studied by hologram interferometry1989In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 29, no 4, p. 409-413Article in journal (Refereed)
    Abstract [en]

    Propagating bending waves are studied in plates made of glass-fiber reinforced polyester. The waves are generated by the impact of a ballistic pendulum. Hologram interferometry, with a double pulsed ruby laser as light source, is used to record the out of plane motion of the waves. The interferograms have an elliptic-like symmetry for an orthotropic plate, while the wave pattern for a symmetric angle-ply reinforced plate has a symmetry about the axes of reinforcements. Experimental data are compared on one hand to analytical results obtained by assuming that the orthotropic plate can be described as if isotropic along the main axes, and on the other hand to numerical results from calculations using the finite-element method. The effective Young's modulus raised to power 1/4 is shown to be an important parameter for the description of the dispersive wave pattern. A defect in the plate alters the wave pattern in the interferograms significantly. This may have technical use.

  • 12. Fällström, Karl-Evert
    et al.
    Molin, Nils-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nondestructive method to determine material properties in orthotropic plates1987In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 8, no 2, p. 103-108Article in journal (Refereed)
    Abstract [en]

    An electronic speckle pattern interferometer (ESPI) is used to determine modes of vibration in rectangular, orthotropic, free-free-plates; that is using a noncontact, nondestructive, optical method. It is shown, using the finite element method (FEM), that each of the first three modes of vibration in rectangular orthotropic plates has a strong dependence upon only one of the main material parameters, namely the in-plane shear modulus and the two Young's moduli, respectively. With this one-variable dependence it is a simple task to determine the effective material parameters. This method has several obvious advantages compared to the use of test bars and it can be extended to give a measure of the damping parameters and probably also be used for production control. Preliminary results are presented and discussed

  • 13. Fällström, Karl-Evert
    et al.
    Molin, Nils-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Olofsson, Kenneth
    Luleå tekniska universitet.
    Schedin, Staffan
    Luleå tekniska universitet.
    Wåhlin, Anders
    Mechanical and thermal effects in a steel plate impacted by a focused laser pulse1997In: Nondestructive Testing and Evaluation, ISSN 1058-9759, E-ISSN 1477-2671, Vol. 13, no 5, p. 293-307Article in journal (Refereed)
    Abstract [en]

    A short laser pulse from a 1 J ruby laser is focused at a steel plate. The effect will be that the material surface at the impact point becomes very rapidly heated. Metal vapour leaves the surface at a very high velocity. That is, both a mechanical impulse and local thermal energy are transferred to the plate. The mechanical impulse creates propagating bending waves in the plate, which in turn creates transient sound waves in the surrounding air. The heated spot at the plate surface creates thermal stresses in the plate which give rise to an out-of-plane deformation of the plate. This deformation is added up to the propagating bending waves. These effects are studied in experiments using pulsed holographic interferometry.

  • 14. Fällström, Karl-Evert
    et al.
    Olofsson, Kenneth
    Luleå tekniska universitet.
    Saldner, Henrik O.
    Luleå tekniska universitet.
    Schedin, Staffan
    Luleå tekniska universitet.
    Dynamic material parameters in an anisotropic plate estimated by phase-stepped holographic interferometry1996In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 24, no 5-6, p. 429-454Article in journal (Refereed)
    Abstract [en]

    Material parameters in an anisotropic plate are determined using two non-destructive measuring techniques: real-time phase-stepped electronic speckle pattern interferometry and dual-reference-beam pulsed holographic interferometry. The first technique is used to measure the lower modes of vibration of the plate with free-free boundary conditions. Finite element analysis is then used to determine two effective Young's moduli and the in-plane shear modulus. The second technique is used to detect transient bending waves propagating in the plate and acoustic waves propagating in the surrounding air. A double-pulsed laser is used both to generate the waves and to make holographic recordings of the wave fields. The stiffness of the plate is estimated using the measured deformation field and an analytical solution to the plate impact problem.

  • 15. Fällström, Karl-Evert
    et al.
    Olofsson, Kenneth
    Luleå tekniska universitet.
    Sarady, Istvan
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Generating and recording transient bending waves in plates by pulsed lasers1996In: Experimental techniques (Westport, Conn.), ISSN 0732-8818, E-ISSN 1747-1567, Vol. 20, no 1, p. 15-19Article in journal (Refereed)
    Abstract [en]

    We have presented a method to generate bending waves in a plate by focusing a Q-switched Nd:YAG-laser pulse on its surface. These waves are recorded by double pulsed hologram interferometry. Evaluation of the interferograms show that the bending wave pattern is very similar to what is predicted by the Kirchhoff plate equation assuming a point impact of infinitesimally short duration. This indicates that a short Nd:YAG-laser pulse may be considered as a Dirac pulse in space and time. Future investigations will be performed with a more powerful and "cleaner" laser to get a higher energy and impulse transfer to the plate thus giving bending waves of larger amplitude. Promising preliminary experiments have also begun using a double pulsed ruby laser both for generating and recording of bending waves

  • 16. Fällström, Karl-Evert
    et al.
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Generating and recording transient bending waves in plates with a double pulsed laser1993In: 16th Congress of the International Commission for Optics :: optics as a key to high technology : 9-13, August, 1993, Budapest Convention Centre, Budapest, Hungary / [ed] Ákos Gy, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 1993, p. 984-985Conference paper (Refereed)
  • 17.
    Lindblom, Ove
    et al.
    Luleå tekniska universitet.
    Näslund, Reinhold
    Persson, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Fällström, Karl-Evert
    A study of bending waves in infinite and anisotropic plates1997In: Applications of Mathematics, ISSN 0862-7940, E-ISSN 1572-9109, Vol. 42, no 3, p. 213-232Article in journal (Refereed)
    Abstract [en]

    In this paper we present a unified approach to obtain integral representation formulas for describing the propagation of bending waves in infinite plates. The general anisotropic case is included and both new and well-known formulas are obtained in special cases (e.g. the classical Boussinesq formula). The formulas we have derived have been compared with experimental data and the coincidence is very good in all cases

  • 18.
    Molin, Nils-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Fällström, Karl-Evert
    Wåhlin, Anders
    On Bending Wave Propagation and Thermal Deformation of Laser Impacted Plates1995In: Proceedings of the International Symposium on Advanced Technology in Experimental Mechanics '95: ATEM '95, 1995Conference paper (Refereed)
  • 19.
    Olofsson, Kenneth
    et al.
    Swedish Pulp and Paper Research Institute, STF1.
    Fällström, Karl-Evert
    Palágyi, P.
    Forsmarks kraftgrupp AB.
    Laser generated and recorded transient bending waves in composite tubes1996In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 36, no 3, p. 224-231Article in journal (Refereed)
    Abstract [en]

    Propagating bending waves are studied in three different composite tubes by holographic interferometry. A conical mirror is placed axially inside the tubes. Axial illumination and observation directions make it possible to view the circumference of the tube, with a high sensitivity to radial deformation. It is shown how the deformation field can be numerically evaluated using a phase stepping and unwrapping technique. Transient bending waves in the tubes are both generated and recorded by the same pulsed laser, which makes the experiments easy to perform. Finite element simulations of the impacted tubes are compared to corresponding experiments. Both the geometry and the material properties of the tubes affect the wave propagation. For unidirectional composite tubes, the 0-deg and 90-deg directions have different dynamic behavior. The proposed method could be used in nondestructive testing of tubes.

  • 20.
    Runnemalm, Anna
    et al.
    Luleå tekniska universitet.
    Fällström, Karl-Evert
    Varför låter en orgelpipa som den gör?1997In: Övertorneåprojektet: om dokumentationen av orgeln i Övertorneå och rekonstruktionen av 1684 års orgel i Tyska kyrkan, Piteå: Luleå tekniska universitet, 1997, p. 115-127Chapter in book (Other (popular science, discussion, etc.))
  • 21.
    Runnemalm, Anna
    et al.
    Luleå tekniska universitet.
    Saldner, Henrik
    Luleå tekniska universitet.
    Fällström, Karl-Evert
    Material, structural modes and air modes of an open organ pipe1997Report (Other academic)
  • 22.
    Wåhlin, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Fällström, Karl-Evert
    Gustavsson, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Molin, Nils-Erik
    Wave propagation in plates studied by pulsed hologram interferometry1989In: The Sixth Meeting in Israel on Optical Engineering: proceedings : 19-21 December 1988, Tel Aviv, Israel / [ed] Rami Finkler; Joseph Shamir, Bellingham, Wash: SPIE - International Society for Optical Engineering, 1989, p. 146-53Conference paper (Refereed)
    Abstract [en]

    Isotropic and non-isotropic plates are impacted by a ballistic pendulum. The bending waves that are generated are studied with holographic interferometry using a double pulsed ruby laser as light source. The pulse shape changes with time because of the dispersivity of the waves. Initially the fringe pattern in the isotropic case is cylindrically symmetric and determined from an initial value problem. Later, when the waves have reached the plate rim, in- and outgoing waves gradually develop fringe patterns which in the end will be a combination of eigenmodes of the plate. A solution to the corresponding Kirchhoff plate equation is presented, which in the special case when the impact is modelled as a Dirac-pulse in space and time, is shown to depend only of the distance to the impact point divided by the square root of the time after impact and a parameter containing plate parameters. From the slope of the central deflection material parameters can be determined. Another solution, assuming a finite impact time, is shown to agree better with experiments. Results from investigations of non-isotropic materials are also presented.

1 - 22 of 22
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