| 1. |
- Hägglund, R, et al.
(författare)
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Some Aspects on the Zero-span tensile test
- 2004
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Ingår i: Experimental mechanics. - : Springer Science and Business Media LLC. - 0014-4851 .- 1741-2765. ; 44:4, s. 365-374
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present some analytical and numerical results concerning the zero-span testing method, frequently used for quality control of cellulose fiber for papermaking. Of particular interest is the relationship between an apparent modulus obtained from the zero-span testing method and the elastic properties of the fibers. The apparent elasticity modulus is estimated using two energy theorems in elasto-statics in which the role of span length is explored. Analytical results, derived under the assumption that slippage between specimen and clamps does not occur, clearly show that the apparent modulus strongly depends on the span length. This is verified by the numerical results obtained using the finite element method. In addition to the above analysis, the effect of slippage is investigated, also by utilizing the finite element method, and it is found that for a specific case, the contribution from slippage to the total displacement depends strongly on the length of the span. Tensile tests at nominal zero span were conducted in an effort to further validate the analysis with relevant experimental data and it was concluded that there is qualitative agreement between the experimental results and the result of the analysis.
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| 2. |
- Johansson, Sten, et al.
(författare)
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Errors in crack closure measurements caused by flexure test fixture support effects
- 2001
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Ingår i: Experimental mechanics. - 0014-4851 .- 1741-2765. ; 41:1, s. 47-51
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Tidskriftsartikel (refereegranskat)abstract
- Flexural tests are sometimes used for the evaluation of fatigue and fracture properties, especially for thin cross sections such as plate material where compact tension specimens cannot be used, or where material thickness is limited in the direction required for data generation. The method is also useful for evaluation of crack closure provided the force transfer occurs correctly. This paper shows how the influence of incorrect test fixture supports, which are outside the standard testing arrangement for such test specimens, can affect the force-displacement curves as evidenced using the back-face strain method, The results show that incorrect test fixture supports may cause deviations in the force-displacement trace as an artifact of the testing conditions. This effect can severely influence crack closure measurements. The effect was also modeled with finite element analysis.
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| 3. |
- Widehammar, Svante
(författare)
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Stress-strain relationships for spruce wood : Influence of strain rate, moisture content and loading direction
- 2004
-
Ingår i: Experimental mechanics. - 0014-4851 .- 1741-2765. ; 44:1, s. 44-48
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Tidskriftsartikel (refereegranskat)abstract
- The influence of strain rate, moisture content and loading direction on the stress-strain relationships for spruce wood has been investigated. The strain rates were approximately 8 x 10(-3) s(-1), 17 s(-1) and 1000 s(-1), and the states of moisture content were those corresponding to oven dry, fiber saturated and fully saturated. Compressive loads were applied along the principal directions of the stem of the tree, i.e., radially, tangentially and axially. The low and medium strain-rate tests were performed with the aid of a servohydraulic testing machine, while the high strain-rate tests were carried out using the split Hopkinson pressure bar (SHPB) technique. Magnesium or steel bars were used in the different SHPB tests in order to reduce impedance mismatch for the different directions of the wood specimens. The strain rate was found to have large influence on the behavior of the wood, especially under the condition of full saturation, where water transport in the deforming specimen is of major importance.
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| 4. |
- Widehammar, Svante
(författare)
-
Stress-strain relationships for spruce wood : influence of strain rate, moisture content and loading direction
- 2004
-
Ingår i: Experimental mechanics. - 0014-4851 .- 1741-2765. ; 44:1, s. 44-48
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of strain rate, moisture content and loading direction on the stress-strain relationships for spruce wood has been investigated. The strain rates were approximately 8×10−3 s−1, 17s−1 and 1000 s−1, and the states of moisture content were those corresponding to oven dry, fiber saturated and fully saturated. Compressive loads were applied along the principal directions of the stem of the tree, i.e., radially, tangentially and axially. The low and medium strain-rate tests were performed with the aid of a servohydraulic testing machine, while the high strain-rate tests were carried out using the split Hopkinson pressure bar (SHPB) technique. Magnesium or steel bars were used in the different SHPB tests in order to reduce impedance mismatch for the different directions of the wood specimens. The strain rate was found to have large influence on the behavior of the wood, especially under the condition of full saturation, where water transport in the deforming specimen is of major importance.
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| 5. |
- Åberg, Jonas, et al.
(författare)
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Uniaxial material damping measurements using a fiber optic lattice: a discussion of its performance envelope
- 2004
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Ingår i: Experimental mechanics. - 0014-4851 .- 1741-2765. ; 44:1, s. 33-36
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Tidskriftsartikel (refereegranskat)abstract
- Damping is the internal transfer of kinetic energy to other forms of energy. Today, most methods use either bending or torsional vibration to measure damping. This means that the strain field in the specimen is nonhomogeneous. If the damping of the tested material is linear, strain-independent, the values acquired with these traditional methods will be equal to the intrinsic material damping of the material. If, however, the damping is strain-dependent, nonlinear, the measured value will be an average of the damping of the specimen, and not equal to its intrinsic material damping. To address this problem, a method is required to experimentally determine the damping in uniaxial tension in order to produce the same strain level in all parts of the test specimen and hence obtain a measurement of the intrinsic material damping. Using such a method, it is possible to view the material damping as the phase angle between the stress and the strain in a harmonic oscillation. In this paper, a method is suggested for measuring this phase shift in uniaxial tension to determine the material damping properties. It uses a tensile test machine, an optical fiber Bragg grating technique and a lock-in amplifier. Measurements with the phase shift technique have been suggested previously, but its performance envelope has been overestimated. In this paper, the performance envelope is discussed and restricted. It is shown that the envelope depends on the specimen length, loss factor and test frequency. An optical strain measurement method is also believed to help avoid many electrical measurement problems seen with the originally proposed method.
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