Marcin Gajewski

The buckling resistance of welded plate girders taking into account the influence of post-welding imperfections - Part 1: Parameter study

Abstract Welding is the most important joining technique and offers the advantage of customizable plate thicknesses. On the other hand, welding causes residual stresses and deformations influencing the load carrying capacity. Their consideration in the design requires simple and fast models. Though welding simulation has contributed to accurately access to these values nowadays, their application to large components remains still in a less practicable range. Nevertheless, many studies emphasized the need to make corrections in recently available simplified models. Especially the influence of residual stresses seems somewhat overestimated in many cases if comparing conventional structural steel S355 and high-strength steel S690. In times of computer-aided design, an improved procedure to implement weld-inducted imperfections appears overdue. This will be presented in two parts. The first part illustrates the potential influence of post-welding imperfections exemplified for weak axis buckling in comparison with the general method in accordance with Eurocode 3. Residual stresses and initial crookedness were varied systematically in order to produce a scatter band of capacities. An approach to characterize the borders of these imperfections was untertaken before that. The excessive scattering of reduction factors for the load bearing capacity demonstrates the importance of these variables. Results were finally evaluated against advanced simulation models which will be further detailed in part two of this contribution.

Inverse analysis and DIC as tools to determine material parameters in isotropic metal plasticity models with isotropic strain hardening

Abstract The main objective of this study is to estimate the accuracy of the method for the determination of material parameters based on laboratory data from a single experiment conducted on a sample working in a nonuniform stress state, registered by the digital image correlation system (DIC). The idea of the method is based on the inverse analysis, in which the material parameters are determined by the optimization procedures using the cost function being the result of comparison of the laboratory data with the results of FEM simulation, wherein the whole deformation areas are taken into account. This paper presents the method described above applied on the determination of isotropic hardening parameters for an aluminum alloy material. Tests were carried out on the aluminum plates with nonuniform geometry subjected to tensile deformation. A comparison of the effect of sample geometry on the results was made, and an analysis of the impact of variation of material parameters on the value of the cost function was carried out.

Verification of Plasticity Theory with Isotropic Hardening and Additive Decomposition of Left Deformation Tensor Using Digital Image Correlation System

The development of measurement methods, and in particular digital image correlation (DIC) systems, which are designed to measure of entire displacements and deformations fields, opens up new areas of research. In general, the materials constitutive relations are formulated in such a way that material parameters could be determined with relatively simple experimental tests carried out on samples with uniform (approximately) stress and strain fields. Then it is possible to apply them to complex boundary value problems formulated e.g. in the small or large deformation theories. The application of DIC allows to verify the accuracy of their predictions by comparing the results of the experiment with solutions to boundary value problems obtained using the finite element method (FEM).

Orthotropic composite constitutive model of mineral–asphalt mix reinforced with grid and its approximation with an isotropic model

A theoretical model for an elastic anisotropic composite of road mixtures reinforced with grids together with its isotropic approximation is proposed. In the considered models, some elements of the mechanics of fibrous composite materials and optimisation theory are used. A composite model is an energy model; that is, constitutive relationships result from the differentiation of the stored energy function arising from two summed parts corresponding to the matrix and reinforcement grid energy via mixture theory. The obtained model is incorporated into the commercial finite element program ABAQUS via a user subroutine written in Fortran. The correctness of the proposed composite constitutive model has been tested by a numerical solution (with the application of a finite element program) of the structure, in which the matrix is modelled as a three-dimensional continuum region and the reinforcement as working in one dimension a set of truss elements. In addition, in the paper the proposition of approximation of the composite orthotropic model with an isotropic one is presented. The interpretation and application of this approximation are analysed. The energetically equivalent isotropic model for the layer with grid reinforcement can be directly used in standard programs used for designing road pavements with mechanistic methods.