ENGINEERING TRANSACTIONS
ROZPRAWY INŻYNIERSKIE

A QUARTERLY JOURNAL

Abstracts of papers for

Previous issue vol. 49, no. 2-3 (2001)

vol. 49, no. 4 (2001)

Next issue vol. 50, no. 1-2 (2002)

Contents of issue 4, vol. 49

1. K. Doliński and R. Stocki: Reliability-based structural optimization accounting for manufacturing and material quality
2. J.Z. Malinowski and J. Ostapkowicz: On the behavior of a bolt-nut joint with plastically deformed thread
3. J.M. Fragomeni: Characterizing the brittle fracture and the ductile to brittle to ductile transition of heat-treated binary aluminum-lithium alloys
4. M.N. Ichchou and L. Jezequel: Direct stiffness energy model for a one-dimensional complex system
5. M. Kowal and J. Mielniczuk: Yield criterion of the softwood under conditions of variable humidity
6. K. Kowalczyk: Evolution of plastic anisotropy for the polycrystalline materials in large deformation processes
7. J. Maciejewski, A. Jarzębowski and W. Trąmpczyński: On the efficiency of the soil digging processes
8. Z. Nowak and A. Stachurski: Nonlinear regression problem of material functions identification for porous media plastic flow
9. W. Trzciński, S. Cudziło and L. Szymańczyk: Determination of the detonation pressure from a water test
10. A. Wysokowski: Method of assessing fatigue hazard to steel railway bridges

K. Doliński and R. Stocki: Reliability-based structural optimization accounting for manufacturing and material quality

The reliability-based optimization problem in which the structural material and manufacturing quality is assumed to be uncertain is considered. Moreover, the quality cost is appropriately taken into consideration in the formula determining the total cost of the structure. Some parameters describing the quality, namely the means and variances of the material properties and the variances of the precision of assembling of the structure are considered as the design parameters in the optimization procedure, in which the required structural reliability level determines some constrains to be satisfied in searching for the minimum structural cost.

Contents

J.Z. Malinowski and J. Ostapkowicz: On the behavior of a bolt-nut joint with plastically deformed thread

The results of investigations connected with influence of tightening bolts above their yield stress on the fatigue life and loosening of the bolt-nut joints are presented. From numerical approach by the FEM, the dependence of the load distribution at the threads and maximal value of stress at the roots of thread on the tightening level of bolts is determined. The obtained results indicate, that tightening of a joint above its yield stress gives more uniform load distribution at the bolt thread, and stress distribution at the roots in part of the bolt screwed with the nut. Experimental investigations of the fatigue life of the bolt-nut joint with the tightening of the bolts below and above their yield stress are presented. The results indicate that tightening above the yield stress considerably increases the fatigue life of the joint. Experimental test of creep in the fatigue process and introductory test on dynamic loosening of the joint have been carried out. It was stated that the phenomenon of creep during the fatigue has no greater influence on the joint, and that the resistance to loosening of the joint increases with tightening of the bolt above its yield stress.

Contents

J.M. Fragomeni: Characterizing the brittle fracture and the ductile to brittle to ductile transition of heat-treated binary aluminum-lithium alloys

An aluminum alloy containing 2.6wt.% Li and 0.09wt.% Zr exhibited a very low value in tensile ductility consistently prior to the peakaged strength independent of thermal treatment. A transition was characterized by very low ductility in the slightly underaged condition up to the near peakaged condition, then followed by a substantial increase in ductility with aging after the peakaged treatment. In order to better understand the deformation and fracture, a scanning electron microscopy study of the fracture surfaces of Al-2.6wt.% Li-0.09wt.% Zr tensile samples solution heat-treated and artificially aged was performed to relate the mechanical behavior to microstructure in the precipitation hardened Al-Li alloy. SEM analysis of the surface features and fracture morphology of the alloy was performed to understand the mechanisms of fracture in relation to the ductile-to-brittle transition that resulted in the alloy from precipitation hardening. TEM analysis was also performed to characterize the deformation behavior, and revealed the distribution of precipitates (both Al₃Li (a') and Al₃Zr-Al₃Li) in the microstructure at very high magnifications as well as the dislocation subgrain structure of the alloy at lower magnification. It follows from this study that the presence of a' particles in the matrix promotes intense planar slip which was believed to be responsible for the ultra-low ductility prior to the peakaged temper. Based on a detailed quantitative microscopy study, it was proposed that the increase in the ductility of the alloy after aging was a consequence of particle coarsening with aging and thus resulting in the Orowan process due to the transition from dislocation particle shearing to dislocation particle bypassing.

Contents

M.N. Ichchou and L. Jezequel: Direct stiffness energy model for a one-dimensional complex system

This paper deals with the high frequency analysis of one-dimensional waveguides. In this frequency range, this paper proposes a numerical implementation and tests of an alternative to the classical predictive dynamical methods. The originality of this approach consists in the fact that it is solely an energy density description. A numerical scheme very similar to the well-known direct stiffness method is employed here. This leads to a numerical code capable of predicting the mean value energy density for complex beam-like structure up to high frequencies. A twenty-four components plane truss, including both the bending and extension motion is used as a verification test, and shows the ability of the proposed code to predict the high frequency dynamics of complex beam-like structures.

Contents

M. Kowal and J. Mielniczuk: Yield criterion of the softwood under conditions of variable humidity

Wood is a porous material. In a dry state the unit volume of wood consists of water-free volume of the wood substance, the so-called wood skeleton, and of the air-filled pores. The variable humidity produces the internal forces within the loaded wood bulk loading to destruction in the form of loosening wood fibers, cracks and twists. In the paper the yield criterion or the transition of the softwood into the plastic state is discussed. The outset of yielding is examined in accordance with the Hill criterion for anisotropy with various ratios of humidity. The case of plane stress with the orthotropic structure is used as an example for which the material constants are identified, resulting in a special form of the yield criterion.

Contents

K. Kowalczyk: Evolution of plastic anisotropy for the polycrystalline materials in large deformation processes

Model of evolution of plastic anisotropy due to crystallographic texture development in metals subjected to large deformation processes is presented. The rigid-plastic model of single grain with regularized Schmid law proposed by Gambin is used. Phenomenological and physical descriptions of plastic flow of polycrystals are discussed. Properties of any yield function for orthotropic material subjected to the plane stress state are outlined. Yield conditions of degree m proposed by Hill and Barlat with Lian are analyzed. Finally, phenomenological texture-dependent yield surface is proposed. Evolution of this yield surface is compared with phenomenological yield conditions for two processes: rolling and pure shear.

Contents

J. Maciejewski, A. Jarzębowski and W. Trąmpczyński: On the efficiency of the soil digging processes

In the first part of the paper, an experimental verification of correctness of the common assumption that the plane strain conditions occur in the tests performed in soil bins is presented. An experimental program was executed basing on the soil cutting problem, with the application of vertical rigid walls of various widths as the working tools. It turned out that in the case of the tool width equal to the width of the soil bin, the soil cutting problems may be treated as the plane strain processes. The influence of the friction phenomena on the side walls of the bin was estimated. For the tools for which no interaction with the side walls of the bin was observed, the zone of the plane strain deformation occurred in the central part of the tools. Then the characteristic deformation patterns and force-displacement relations for the L-shaped tool are determined. Finally, the new idea of the optimization of digging be means of the earth-working machinery is presented and experimentally verified. Dividing the whole excavation task into several repeatable cycles for which the soil free boundary before and after the experiment are similar, the optimization of the single cycle plays a significant role in the energetic efficiency of the whole task. The single cycle of the working process is defined using several basic parameters. The influence of each parameter on the specific unit energy of the process is experimentally verified. The set of values of the discussed parameters is recommended for the particular soil and tool shape. The disadvantages of other soil cutting strategies are discussed.

Contents

Z. Nowak and A. Stachurski: Nonlinear regression problem of material functions identification for porous media plastic flow

In the paper we present the identification problem arising in modelling the processes of nucleation and growth of voids in the elastic-plastic media. Identification is carried out on the basis of Fisher's data measured on the cylindrical steel specimens subjected to the uniaxial tension. The identification problem is formulated as the standard nonlinear regression problem. Our aim was to select appropriate formulae of the material functions appearing in the porosity model in the right-hand side of the differential equation, and to identify their unknown parameters. The resulting nonlinear regression problem was solved by means of the global optimization method of Boender et al. As the local minimizer we have implemented the modified famous BFGS quasi-Newton method. Modifications were necessary to take into account box constraints posed on the parameters. As the directional minimizer we have prepared a special procedure joining quadratic and cubic approximations and including a new switching condition. We have tested two variants of the porosity model; in the first one with variable shape of the material function g, and the second one - with constant g. The results suggest that the model with material function g ş 1 describes well the nucleation and growth of voids. However, our attempt to identify that constant has brought an unexpected value smaller than 1, and approximately equal to 0.84.

Contents

W. Trzciński, S. Cudziło and L. Szymańczyk: Determination of the detonation pressure from a water test

In the paper, a semi-empirical method of determining the detonation pressure of high explosives from the so-called water test is proposed. X-ray photographs of expansion of a water envelope being accelerated by the detonation products of a cylindrical charge and results of numerical modelling of the process of water expansion are the basis of the method. The pressure is estimated by comparison of the calculated and recorded profiles of an oblique shock wave propagating in water. The method is applied to determine the detonation pressure for selected high explosives used for military purposes. The results obtained are compared with the experimental values of pressure given in the literature and with the pressures obtained from thermochemical calculations. The estimated detonation pressures differ by less than 5% from those given in literature. It is proved that the accuracy of estimation of the detonation pressure depends generally on the measurement precision of the position of the shock wave front in water. A simplified variant of the method is also proposed in which the numerical modelling of the detonation in water is not needed.

Contents

A. Wysokowski: Method of assessing fatigue hazard to steel railway bridges

This research has been carried out as part of the ministerial R & D program: "Improvement of the condition of roads and highway and railway bridges". This paper deals with the establishment of guidelines relating to "Checking the fatigue hazard to railway bridges". Its aim is to provide a relatively simple and coherent method of assessing the fatigue hazard to steel structural elements in both newly designed bridges and those being in service under different conditions of traffic on Polish Railways lines. This is proposed to be done on the basis of the latest results of fatigue studies. Another aim is to develop a method of assessing the allowable - from the point of view of fatigue - the service life of railway bridges in service. Finally, examples of checking the fatigue hazard to structural elements of railway bridges by means of the proposed method are given.

Contents

Abstracts for 49, 2-3, 2001 (previous issue)

Abstracts for 50, 1-2, 2002 (next issue)

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