Modeling The Creep Behavior Of Wood Cantilever Loaded At Free End During Drying

A new approach to modeling the creep behavior of a wood cantilever loaded at free end under constant moisture content and under drying conditions is developed. This approach is based on equilibrium equations of cantilever beam theory and allows the computation of stress, strain, and displacement fields through the thickness without any assumption on stress distribution. The analysis is restrained to a modified Burger model that takes into account a moisture content change in wood, although it can be extended to any type of rheological model. In constant hygrothermal conditions, the computed stress field is the same as the one based on equations of elastic cantilever. In drying conditions, a moisture gradient takes place through the thickness, and thus, a nonlinear stress distribution appears and the location of the neutral axis moves away from the geometrical center of the cross-section. The main advantage of the proposed approach is that it can be used to simulate experimental creep bending tests in the presence of moisture content gradients. Accordingly, bending tests should be appropriate to identify both viscoelastic and mechano-sorptive creep parameters

STR-818: THE EFFECT OF RELAXATION ON THE SLIP RESISTANCE OF METALLIZED FAYING SURFACES IN SLIP-CRITICAL CONNECTIONS

Metallizing has emerged as an effective protective coating for steel bridge members, providing a physical barrier and a galvanic protection. Recent research has shown that metallized faying surfaces used in high strength bolted connections provide higher slip resistance than specified values for uncoated blast-cleaned faying surfaces in North American design standards. As a particularity, relaxation of the clamping force is observed in the slip-critical connections with metallized faying surfaces. In this study, tests were designed to evaluate the effect of relaxation on the slip resistance of metallized faying surfaces in high strength bolted connections. Some design parameters included in this study are the coating thickness, the amount of bolt preload, the type of bolt and the presence of burrs. Test results showed that the relaxation of the clamping force does not adversely affect the slip resistance of connections with metallized faying surfaces

Experimental exploration of the aluminum tube drawing process for producing variable wall thickness components used in light structural applications

Tube drawing is a well known process involving at room temperature the reduction of diameter and wall thickness to obtain specified values. The initial tube is drawn into a die of a smaller opening and its thickness achieved by use of a mandrel. Usually, the mandrel has a land area which diameter defines by sizing the inside diameter of the final tube. Some structural components found in cars, aircrafts and other vehicles require bent or hydroformed tubes of lower weight. It is of interest to have tubes of varying axial or circumferential thickness so that to reduce overweight in low stressed areas and reinforce it otherwise. However, the production of tubes of varying thickness is more difficult in reason notably of higher metal flow stresses in the deformation zone and the need to control precisely the mandrel position during drawing. Axial thickness variation is obtained using a mandrel with stepped lands or with a slight taper while circumferential variation is achieved with a mandrel of desired internal or external shape (e.g. oval). In this paper, two techniques for axial tube wall thickness variation and one technique for circumferential variations are introduced and tested. First, the techniques to produce drawn tubes with thickness variations are presented. For testing, a small (335 kN) instrumented tube drawing machine is used. Details on this machine, process lubrication, monitored data and on the tooling implemented are also presented. Initial tubes are mainly AA6063 extrusions of 63.5mm O.D. and 2.6mm thick and the final outside diameter, i.e. the inside diameter of the die, is about 47.5 mm. AA6061 tubes are also drawn. Starting with drawing tests without mandrel, the natural flow of the tube and the drawing force involved are measured. Secondly, tubes of 4 different thicknesses are produced with a stepped mandrel and the strain hardening effect on mechanical properties established. Using a tapered mandrel, tubes of continuously varying wall thickness are tested. Higher local pressure in the die corner radius restricts proper lubrication in certain conditions but results are promising in most cases. We also study the effect of thickness rate of change along the tube. Finally, tests with a stepped oval mandrel provided good results for circumferential thickness variations. The dimensional quality is measured using a coordinate measuring machine and mechanical properties obtained from tensile tests in both initial and drawn tubes. Finally, despite some minor problems, the techniques proposed can efficiently produce tubes with thickness variations and have a very strong potential for industrial use

Full thermo-mechanical coupling using eXtended finite element method in quasi-transient crack propagation

Abstract This work aims to present a complete full coupling eXtended finite element formulation of the thermo-mechanical problem of cracked bodies. The basic concept of the extended finite element method is discussed in the context of mechanical and thermal discontinuities. Benchmarks are presented to validate at the same time the implementation of stress intensity factors and numerical mechanical and thermal responses. A quasi-transient crack propagation model, subjected to transient thermal load combined with a quasi-static crack growth was presented and implemented into a home-made object-oriented code. The developed eXtended finite element tool for modeling two-dimensional thermo-mechanical problem involving multiple cracks and defects are confirmed through selected examples by estimating the stress intensity factors with remarkable accuracy and robustness

Constitutive laws of carboneous materials of aluminium electrolysis cell : Current knowledge and future development

The Hall-H\ue9roult cell behaviour at different stages of the electrolysis process is an important point to take into consideration in the design and the optimization the cell. Nowadays, numerical simulation has become a powerful and essential tool since in situ measurements are difficult to perform and cost expensive. For those numerical simulations, constitutive laws and their parameters\u2019 identification in laboratory are required for all the relevant physics of the cell materials. For the mechanical behaviour of the cell, many efforts have been done to characterize, to understand and to develop constitutive laws for the carboneous materials. Plasticity, viscosity, visco-elasticity, baking, etc., are examples of phenomena which have been addressed up to date, on both transient and steady state situations. This paper presents an overview on various level of modeling of the mechanical behaviour of the carbon cell lining material, from elastic to more complex like a thermo-(chemo)-visco-elasto-plactic one.NRC publication: Ye