| 1. |
- Bekele, Abiy, et al.
(författare)
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Automated Non‑contact Resonance Excitation Method to Assess Low Temperature Dynamic Modulus of Asphalt Concrete
- 2019
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Ingår i: Journal of nondestructive evaluation. - : Springer Nature. - 0195-9298 .- 1573-4862. ; 38:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the applicability of an automated non-destructive testing method to monitor the stiffness of asphalt concrete at low temperatures. A loudspeaker is used as a source of non-contact excitation of the axially symmetric fundamental resonant frequencies of a disc-shaped asphalt concrete specimen positioned inside an environmental chamber. Measured resonant frequencies are used to calculate the dynamic moduli of the specimen at different temperatures. The repeatability of the method as well as the effect of loudspeaker height above the sample are studied. Results show that the main advantage of the non-contact excitation method, compared to manually applied impact hammer excitation, is that repeatable automated measurements can be performed while the specimen is placed inside an environmental temperature chamber. This methodology enables to study the effect of only low temperature conditioning on the dynamic modulus of asphalt concrete without interference from mechanical loading.
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| 2. |
- Boström, Anders E, 1951, et al.
(författare)
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On the boundary conditions for ultrasonic transmission by partially closed cracks
- 1991
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Ingår i: Journal of Nondestructive Evaluation. - 1573-4862 .- 0195-9298. ; 10, s. 139-149
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Tidskriftsartikel (refereegranskat)abstract
- The probability of detecting crack-like defects using ultrasonic techniques can be severly reduced if the crack is closed by a static background pressure. In this paper, we model the contacting faces of a partially closed crack by an array of circular spot-welds randomly distributed over an infinite plane. We give an exact derivation of the reflection and transmission coefficients for a plane elastic wave at such a boundary in terms of the mean interfacial stresses. The latter are estimated in the limit when the contact radius is much smaller than the wavelength and the contacts are sparsely distributed. This calculation is then related to a distributed spring model of the interface. The latter replaces the real interface by an effective homogeneous linear boundary condition which relates the crack opening displacement to the boundary stresses by effective stiffnesses. These unknown parameters are chosen to ensure that the model condition predicts the exact values of the mean interfacial stresses and the reflection and transmission coefficients in the limit already described. Our results are consistent with and complement thoses of Baik and Thompson who introduced the distributed spring model in this and a number of other contexts. Our analysis provides a systematic assessment of the range of validity of the model and suggests ways in which the present estimates may be improved.
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| 3. |
- Boström, Anders E, 1951, et al.
(författare)
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Ultrasonic Attenuation in Polycrystalline Materials in 2D
- 2019
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Ingår i: Journal of Nondestructive Evaluation. - : Springer Science and Business Media LLC. - 1573-4862 .- 0195-9298. ; 38:2
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Tidskriftsartikel (refereegranskat)abstract
- Grains in a polycrystalline material, typically a metal, act as scatterers of ultrasonic waves and thus give rise to attenuation of the waves. Grains have anisotropic stiffness properties, typically orthotropic or cubic. A new approach is proposed to calculate attenuation in a 2D setting starting from the scattering by an anisotropic circle in an isotropic surrounding. This problem has recently been solved, giving explicit, simple expressions for the elements of the transition (T) matrix (which gives the relation between the the incoming and scattered fields) when the circle is small compared to the ultrasonic wavelengths. The T matrix can be used to calculate the total scattering cross section, which in turn can be used to estimate the attenuation in the material. Explicit expressions for the attenuation coefficient for longitudinal and transverse waves are obtained for a cubic material, and contrary to results in the literature these expressions are valid also for strong anisotropy. For the longitudinal attenuation coefficient a comparison with recent FEM results for Inconel 600 gives excellent agreement.
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| 4. |
- Gudmarsson, Anders, 1983-, et al.
(författare)
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Comparing Linear Viscoelastic Properties of Asphalt Concrete Measured by Laboratory Seismic and Tension–Compression Tests
- 2014
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Ingår i: Journal of nondestructive evaluation. - : Springer Science+Business Media B.V.. - 0195-9298 .- 1573-4862. ; 33:4, s. 571-582
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Tidskriftsartikel (refereegranskat)abstract
- Seismic measurements and conventional cyclic loading have been applied to a cylindrical asphalt concrete specimen to compare the complex modulus and complex Poisson’s ratio between the two testing methods. The seismic moduli and Poisson’s ratio have been characterized by optimizing finite element calculated frequency response functions to measurements performed at different temperatures. An impact hammer and an accelerometer were used to measure the frequency response functions of the specimen which was placed on soft foam for free boundary conditions. The cyclic loading was performed by applying both tension and compression to the specimen while measuring the displacements in the axial and radial direction. The Havriliak–Negami and the 2S2P1D model have been used to estimate master curves of the complex modulus and complex Poisson’s ratio from the seismic and the tension–compression tests. The seismic measurements performed at a lower strain level than the tension–compression test give a higher absolute value of the complex moduli (e.g.∼12% at 100 Hz) and a lower phase angle compared to the tension–compression results.
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| 5. |
- Krasnova, Tatiana, 1967, et al.
(författare)
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Wave Scattering from a Slightly Wavy Interface Between two Anisotropic Media
- 2006
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Ingår i: Journal of Nondestructive Evaluation. - : Springer Science and Business Media LLC. - 1573-4862 .- 0195-9298. ; 25:4, s. 155-164
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Tidskriftsartikel (refereegranskat)abstract
- Wave scattering from a periodic interface separating two anisotropic layers in a thick elastic plate is studied in the two-dimensional case. The problem is solved by replacing the exact boundary conditions, i.e. continuous displacement and traction on the wavy interface, by approximate first order conditions on a flat reference surface. Numerical results are presented for a number of cases and compared to the exact solution obtained by the null field approach. The conclusion is that the approximate method gives reasonably accurate results as long as the slope of the surface is small and the amplitude of the wavy surface is not too large compared to the wavelength of the incident wave.
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| 6. |
- Larsson, Lars, 1984, et al.
(författare)
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Integral Equation Method for Evaluation of Eddy-Current Impedance of a Rectangular, Near Surface Crack Inside a Cylindrical Hole
- 2016
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Ingår i: Journal of Nondestructive Evaluation. - : Springer Science and Business Media LLC. - 1573-4862 .- 0195-9298. ; 35:2
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Tidskriftsartikel (refereegranskat)abstract
- An integral equation method for solving the eddy-current nondestructive evaluation problem of a flat, rectangular, near surface crack inside of a cylindrical hole in a conducting material is presented. The method involves expanding the Green’s tensor, the incoming field, and the jump in electric potential over the crack in suitable basis functions. Here, plane waves, cylindrical waves, and basis functions related to the Chebyshev polynomials, are used. The way of discretization in this method leads to a formulation where the scattering is defined by a scattering matrix, independent of the incoming field. This presents an advantage, when conducting numerical simulations, since the scattering matrix does not have to be recalculated for every probe position. The numerical calculations are straightforward to perform and model predictions are compared with finite element results.
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| 7. |
- Lei, Xiangyu, 1992, et al.
(författare)
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Model-Based Parametric Study of Surface-Breaking Defect Characterization Using Half-Skip Total Focusing Method
- 2023
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Ingår i: Journal of nondestructive evaluation. - : Springer Nature. - 0195-9298 .- 1573-4862. ; 42:2
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Tidskriftsartikel (refereegranskat)abstract
- As the demand of structural integrity in manufacturing industries is increasing, the ultrasonic array technique has drawn more attention thanks to its inspection flexibility and versatility. By taking advantage of the possibility of individual triggering of each array element, full matrix capture (FMC) data acquisition strategy has been developed that contains the entire information of an inspection scenario. Total focusing method (TFM) as one of the ultrasonic imaging algorithms, is preferably applied to FMC dataset since it uses all information in FMC to synthetically focus the sound energy at every image pixel in the region of interest. Half-skip TFM (HSTFM) is proposed in multi-mode TFM imaging that involves a backwall reflection wave path, so that the defect profile could be reconstructed for accurate defect characterization. In this paper, a method involving Snell’s law-based wave mode conversion is proposed to account for more reasonable wave propagation time when wave mode conversion happens at backwall reflection in HSTFM. A series of model based simulations (in software simSUNDT) are performed for parametric studies, with the intention of investigating the capability of defect characterization using HSTFM with varying tilt angle and relative position of surface-breaking notch to array probe. The results show that certain TFM modes could help with defect characterization, but the effectiveness is limited with varying defect features. It is inappropriate to address a certain mode for all characterization perspectives but rather a combination, i.e., multi-mode TFM, should be adopted for possible interpretation and characterization of defect features.
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| 8. |
- Lei, Xiangyu, 1992, et al.
(författare)
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Simulation-Based Investigation of a Probability of Detection (POD) Model Using Phased Array Ultrasonic Testing (PAUT) Technique
- 2022
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Ingår i: Journal of Nondestructive Evaluation. - : Springer Science and Business Media LLC. - 1573-4862 .- 0195-9298. ; 41:2
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Tidskriftsartikel (refereegranskat)abstract
- Probability of detection (POD) as a metric for quantifying the capability of inspection procedures in nondestructive evaluation (NDE), has been applied and evolved in industries since 1970s. Progress had been noted when certain statistical functions were brought up to model POD behavior, including log-normal model (also referred as Probit model). This model had been concluded to be the best fit and therefore has been widely used in many studies, while the involved assumptions and conditions were not carefully addressed and explored. To make flexible POD datasets available for specific inspection procedures and reduce the number of expensive experiments needed, model-assisted POD (MAPOD) is an alternative. This paper addresses a pure simulation-based POD procedure of an inspection scenario involving phased array ultrasonic testing (PAUT) on lack-of-fusion defects in additive manufactured (AM) components. The mathematical simulations are performed by an ultrasonic testing (UT) simulation software, simSUNDT, developed at Chalmers University of Technology in Sweden. Resulted inspection datasets with the proposed data processing steps are evaluated in terms of the assumptions and conditions of log-normal POD model, with the purpose of discussing the POD model validity under different circumstances. Simulation-based POD curves are finally compared with several discrete POD values at some defect sizes, calculated through massive computations from physics-model based metamodel. Comparisons and observations confirm satisfactory application of log-normal POD model despite some violations in model hypotheses.
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| 9. |
- Lidén, Peter, 1982, et al.
(författare)
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Development of a Non-destructive Testing Method for Assessing Thermal Status of District Heating Pipes
- 2020
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Ingår i: Journal of Nondestructive Evaluation. - : Springer Science and Business Media LLC. - 1573-4862 .- 0195-9298. ; 39:1
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Tidskriftsartikel (refereegranskat)abstract
- Pre-insulated district heating (DH) pipes have been in use for more than 40 years. The thermal performance of these pipes decreases over time as a result of thermal and mechanical aging, which leads to higher heat energy losses. A non-destructive method based on a cooling method is under development for assessing the thermal performance of a DH network. The method utilizes the copper wire, which is already embedded in the polyurethane insulation for detection of water leakage, as a sensor for measuring the temperature at the position of the copper wire. The method involves a shutdown of a selected part of a network for less than 2 h and evaluating the cooling process by measuring the supply pipe temperature and the temperature of the copper wire. The method was applied in a DH network during heating season. The thermal conductivity calculated by the method [0.027 W/(m K)] was in good agreement with the reference value [0.026 W/(m K)]. The cooling of the network can be measured at a valve or at other more easily accessible steel parts. It was also shown that the method is applicable for DH networks without a copper wire. However, a temperature measurement is needed on the casing pipe.
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| 10. |
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