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- Austrell, Per Erik, et al.
(author)
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Survey of Design Methods and Material Characteristics in Rubber Engineering
- 1999
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Reports (other academic/artistic)abstract
- The unique properties of elastomeric materials are taken advantage of in many engineering applications. Elastomeric units are used as couplings or mountings between stiff structures. Examples of these are shock absorbers, vibration insulators, flexible joints, seals and suspensions.The development of computers and of analysis programs in this area has given engineers a new tool for the design of elastomeric components. Computer simulation by finite element analysis has become increasingly important, allowing the mechanical behavior of products with for complex geometries, as well as loading cases of different kinds to be evaluated. Computer simulations enable both static and dynamic aspects to be analyzed. These matters have been recognized by the manufacturers of rubber products and by their customers. The benefits are shorter time for product development and also quality improvements.However, the possibilities available for finding less complicated technical solutions at lower cost with the use of elastomers, has not been fully utilized. Rubber components could be employed more frequently in design if engineers were more familiar with materials of this sort.Part of the problem lies in education and in the dissemination of information. Engineers working in the design area tend to not be very familiar with elastomeric materials and their properties. The offerings of courses on the mechanics of polymers at schools and universities are very limited. Skillful engineers in this field have usually acquired their knowledge through many years of experience and not formal education.Moreover, the complicated nature of the material behavior involved makes it difficult to devise general design rules and design tools. Only recently have computers and analysis programs become powerful enough for the analysis of nonlinear elastic problems involving large strains.It is essential, if one is to become competitive in high-tech applications, to possess a thorough knowledge of computer methods, material models and test methods available.There has likewise been a lack of relevant data for the computer analysis of elastomeric materials. The design tools employed rely on the material models available and on the test data required for the calibration of these models. In many cases, the only information available for analysis is a value for the hardness of the rubber in question. The wide variety of rubber compounds is also a problem. The characterization of different materials is costly and time-consuming. There is thus a need for simple and reliable methods to characterize the different vulcanizates.
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- Gustavsson, Mats
(author)
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Methods for Aircraft Noise and Vibration Analysis
- 1999
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Licentiate thesis (other academic/artistic)abstract
- Aircraft noise control engineering is a challange both for experimentally based methods and for numerical analysis methods. Usually noise control installations are designed based on engineering judgement in combination with results from in-flight testing, rather than with nummerical methods, due to the absence of reliable and accurate models.For turbo-prop aircraft, such as the Saab 340 and Saab 2000, the low-frequency tonal noise generated by the propellers is a major reason for passenger discomfort. Two effective methods of reducing this propeller noise are tuned vibration absorbers/dampers and active noise control. The efficiency of both of these two methods is, to a great extent, determined by placement of the damper/absorber or active actuator (structural exciter or loudspeaker). Finding appropriate locations for such installations from experiments requires extensive testing, both in-flight and on ground. If alternative design methods requiring less, or ideally no, testing could be utilized this would allow significant cost reduction and the possibility of concurrent design for the noise control installations.That is the motivation for this study on methods for aircraft acoustic and structural vibration analysis.
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- Heyden, Susanne
(author)
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A Network Model Applied to Cellulose Fibre Materials
- 1996
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Licentiate thesis (other academic/artistic)abstract
- A network mechanics model for analysis of materials made of dry-shaped cellulose fibres is proposed. In terms of the model, the network is composed of fibres of arbitrary distribution in length, curvature, cross-section. stiffness and strength. The fibres are arranged in a random structure according to an arbitrary orientation distribution. Where fibres meet there may be fibre-to-fibre interaction, modelled by a linear or non-linear spring coupling representing stick-slip performance. The connection is of arbitrary distribution in stiffness and strength.The network geometry is periodic, any cell under observation being regarded as one of many identical cells that make up a global structure. A set of cyclic boundary and loading conditions facilities obtaining relevant results even in the case of small network cells.A two-dimensional implementation of the model was carried out, and several examples of simulation results are provided. The results concern geometrical properties of the network, and the effects on network stiffness and fracture behavior due to variations of sample size, boundary conditions and the various micro-level parameters mentioned above.
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- Olsson, Anders, et al.
(author)
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Parameter Studies on Pallet Racks
- 1998
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Reports (other academic/artistic)abstract
- Pallet racks used in industry are often exposed to large loads, and in some casesresistance to failure is reduced by damage or inadequate handling. The present study was undertaken with the aim of investigating a number of different parameters of importance for the load-carrying capacity of pallet racks. Mainly numerical studies, using the finite element method, are performed, but some experimental work is also presented.The first parameter studied was the influence of damage to upright, cold-formedproles with thin-walled, open cross-sections. Both numerical simulations and laboratory tests showed that small imperfections result in signicant reduction of the load-carrying capacity. A global pallet rack was modelled to investigate the global influence of damaged uprights. Probabilistic computations, containing up to 300 sets of damaged uprights, were performed. The different damage cases were generated with Latin hypercube sampling. Probabilistic computations were also performed to investigate the influence on the load-carrying capacity of uncertainties in the stiffnesses of the connectors between uprights and horizontal beams. The computational results show that the load-carrying capacity depends on the mean stiffness relation of the connectors, but is not very sensitive to the distribution of the connector stiffnesses around the mean stiffness relation. The last part of the work considers different situations where horizontal beams or cross-aisle bracing members are removed from a pallet rack. The influence of this type of handling, considering the load-carrying capacity, is evaluated.
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- Serrano, Erik
(author)
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Finger-Joints for Laminated Beams : Experimental and Numerical Studies of Mechanical Behaviour
- 1997
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Licentiate thesis (other academic/artistic)abstract
- The introduction of laminated timber, glulam being an example, allowed many of the disadvantages associated with solid wood to be overcome. The disadvantages in question are mainly those related to the size and shape limits of structural elements made of solid wood and to the large variability in such material properties of solid wood as strength and stiffness.In the present thesis, which comprises both experimental and numerical studies,such phenomena like the laminating effect and to some extent the size effect are investigated and discussed using the concept of fracture mechanics.The experimental part involved the testing of bond line strength, stress vs. deformation and fracture energy of three adhesives (resorcinol phenol, polyurethane and polyvinylacetate) and tensile testing of finger-jointed laminations. The results from bond line tests were used as input data in a nonlinear fracture mechanics model based on the concept of a fictitious crack. The model was verified by simulating both the bond line tests and the lamination tests. Parameter studies on the influence of bond line characteristics on the strength of finger-joints were also performed, together with analyses of the sensitivity of a finger-joint to defects in the bond line. The influenceof finger-jointing pieces of lumber dissimilar in stiffness was also investigated. These parameter studies showed the brittleness of the bond line to be an important parameter in governing the strength of the finger-joint. For brittle resorcinol-phenol adhesive, the approach adopted, one based on nonlinear fracture mechanics, predicted the strength of a finger-jointed lamination to differ considerably from the strength predicted by such classical theories as single point maximum stress theory and perfect elastic plastic theory. The complete load displacement response of a finger-joint was determined using anumerical solution procedure that allowed so-called snap-back behaviour to be traced. The behaviour of a laminated beam in bending was also simulated. This showed the laminating effect to partly be explainable on the basis of fracture mechanics.
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| 30. |
- Ormarsson, Sigurdur, 1963-
(author)
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A Finite Element Study of the Shape Stability of Sawn Timber Subjected to Moisture Variations
- 1995
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Licentiate thesis (other academic/artistic)abstract
- Shape instability in timber products exposed to moisture variation is a serious problem since it can make wood products unsuitable for construction purposes. In this thesis the finite element method has been used to simulate deformations during the drying process.….….…To investigate the influence of different parameters on drying deformations a parameter study was performed, the influence of different material parameters and of different constitutive models being studied. In addition, the influence of the spiral grain angle, the conical angle, the orientation of the growth rings, the cross section dimension and the drying profile was examined.
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