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Licentiate seminar

Combined shear and compression analysis using a modification of the losipescu shear test device


Defendant Main Advisor Extra Advisor Date
Federica De Magistris Anders Eriksson 2003-09-03

Opponent
Myat Htun, Mitthögskolan

Evaluation committee

Abstract

The mechanical treatment of wood in a refiner is a complex combination of shear and compression forces. To obtain more knowledge on this mechanical treatment, a new fixture was developed to test the behavior of wood under a combined shear and compression load. In this fixture different combinations of shear and compression load were possible to achieve by different rotations of the shear test device. Measurements were made using both an original (Wyoming version) and an in­house modified fixture based on the Iosipescu shear test. A medium density fiberboard (MDF) was used in order to examine the behavior of the modified device with an orthotropic material without the complexity of the annual ring structure of wood. The MDF was tested in the three main orientations both in tension and in shear. Numerical simulation of the combined shear and compression test was carried out to verify the reliability of the modified device. The numerical results showed good agreement with the experimental results for the shear test in all the three material directions tested. The shapes as well as the values of the strain fields were similar in the numerical and experimental results. Different rotations of the combined shear and compression device were studied using the Finite Element model to find the combinations that gave reliable results in shear and compression. It was found that the 45 degrees rotation gave the most uniform strain fields in the section between the notches. This rotation was then tested on the fiberboard and, again, the experimental results were compared with the numerical ones. Experiments were then made on dry wood using the modified device in the 45 degrees rotation. Numerical simulations of the combined shear and compression test were carried out to verify the reliability of the modified device applied to wood. The analysis showed that wood exhibits a non­linear material behavior under combined shear and compression load. Probably non­linear material behavior of the wood cells appears in the supposedly elastic range of the material due to this combination of shear and compression forces.
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