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Yield strength modelling of formed material using evolutionary computational method
Leo Gusel, Rebeka Rudolf, 2009, original scientific article

Abstract: In this paper we propose an evolutionary computation approach for the modelling of yield strength in formed material. One of the most general evolutionary computation methods is genetic programming, which was used in our research. Genetic programming is an automated method for creating a working computer program from a problemćs high-level statement. Genetic programming does this by genetically breeding a population of computer programs using the principles of Darwinianćs natural selection and biologically inspired operations. During our research, material was cold formed by drawing using different process parameters and then determining yield strengths (dependent variable) of the specimens. On the basis of a training data set, various different genetic models for yield strength distribution were developed during simulated evolution. The accuracies of the best models were proved by a testing data set and comparing between the genetic and regression models. The research showed that very accurate genetic models can be developed by the proposed approach.
Keywords: metal forming, yield strength, genetic programming, modelling
Published: 31.05.2012; Views: 1275; Downloads: 23
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The impact of structure on the undrained shear strength of cohesive soils
Bojana Dolinar, Ludvik Trauner, 2007, original scientific article

Abstract: The relationship between the undrained shear strength and the water content ofcohesive soils can be described with a two parameter non-linear function. Parameter a is the water content at the undrained shear strength su=1 kPa, andb is the slope of the linear function which represents the ratio between the water content logarithm and the undrained shear strength logarithm. These parameters depend mainly on the type and amount of clay minerals in the soils,the particle sizes and shapes, their arrangements, the forces between the clay particles, and the chemical composition of the pore water. The impactof quantity, type and size of clay grains on the water content at a uniform undrained shear strength in different soils has been studied previously, whilst the impact of structure is less understood. Particle associations and arrangements (i.e. fabric), and the interparticle forces determine the structure of soil. This paper focuses on an investigation of therelationship between water content and undrained shear strength in kaolinite samples with different structures. The various arrangements of clay particles that resulted from the changed of interparticle forces were obtainedby salt addition (NaCl). Microfabrics of wet kaolinite samples were studied using a field emission scanning electron microscope. The results showed that clay structure exerts a strong influence on the relationship between the quantity of water and undrained shear strength. This was reflectedin the values of both soil-dependent parameters, a and b. Values of parameter a varied between 39.16% and 62.96%, and b between 0.100 and 0.139, for well crystallized kaolinite with salt concentrations of 0- 175 mmol/l. Forpoorly crystallized kaolinite with salt concentrations of 0-300 mmol/l, thevalues of a range between 46.96% and 100.30%, and b between 0.090% and 0.148%.
Keywords: geomechanics, clay, kaolonite, structure, fabric, undrained shear strength
Published: 31.05.2012; Views: 1346; Downloads: 64
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The total colorant sensitivity of a color matching recipe : an approach to colorant weighting and tinctorial strength errors
Shahram Peyvandi, Seyed Hossein Amirshahi, Boris Sluban, 2008, original scientific article

Abstract: The repeatability of the recipe color can be affected by several different types of inevitable inaccuracies in the coloration process. Two of the major causes of poor target-color reproducibility are the (random) weighing and (proportional) strength errors. This article describes alternative definitions of colorant strength sensitivity and total colorant sensitivity of a dyeing recipe. The influences of the maximal colorant weighing and strength errors are taken into account in order to bring the magnitudes of the two treated types of sensitivity into a mutually realistic balance between each other. The quantifications of precision and accuracy of a color matching recipe are also developed and combined into a single-number measure of recipe quality. The listed quantities are expected to be useful in selecting the most reliable one(s) among the different formulations for the same standard color. The methods are presented for calculating numerical estimates of the newly introduced quantities. The precision and accuracy of the coloration process are investigated in laboratory experiments involving repeated dyeings.
Keywords: color formulation, color matching, color sensitivity, color strength
Published: 31.05.2012; Views: 845; Downloads: 51
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Determination of lower bound fracture toughness of a high strength low alloy steel welded joint
Nenad Gubeljak, 2005, original scientific article

Abstract: The use of high-strength low-alloy steels for high performance structures (e.g. pressure vessels and pipelines) requires high strength consumables to produce an overmatched welded joint. This globally overmatched multipass welded joint contains two significantly different microstructures, as welded and reheated. In this paper, the influence of weld metal microstructure on fracture behaviour is estimated in comparison with the fracture behaviour of composite microstructures (as welded and reheated). The lower bound of fracture toughness for different microstructures was evaluated by using the modified Weibull distortion. The results, obtained using specimens with crack front through the thickness, indicated low fracture toughness, caused by strength mismatching interaction along thevcrck front. In the case of through thickness specimens, at least one local brittle microstructure is incorporatedin the process zone at the vicinity of the crck tip. Hence, unstable fracture occurred with small or without stable crack propagation. Despite the fact that the differences between the impact toughness of a weld metal and that of base metal are insignificant, the future toughness of a weld metal can be significantly lower.
Keywords: welded joints, fracture mechanics, Crack tip opening displacement, high strength seeel weld, mismatch effects, fracture toughness, resistance curves
Published: 01.06.2012; Views: 1194; Downloads: 63
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Relationship between the undrained shear strength, water content, and mineralogical properties of fine-grained soils
Ludvik Trauner, Bojana Dolinar, Miha Mišič, 2005, original scientific article

Abstract: The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soilsč these relationships, however, have not yet been investigated. The findings describedin this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals,their quantity in soil composition, and the interlayer water quantityin the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.
Keywords: soil mechanics, clays, fine-grained soils, shear strength, water content, mineralogy
Published: 01.06.2012; Views: 1742; Downloads: 68
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Micromechanical analysis of constraint effect on fracture initiation in strength mis-matched welded joints
Miloš Dobrojević, Marko Rakin, Nenad Gubeljak, I. Cvijović, Milorad Zrilić, N. Krunich, Aleksandar Sedmak, 2007, original scientific article

Abstract: In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect crack growth initiation in mismatched welded joints. The single edged- notched bend specimens (precrack length ▫$a_o/W=0.32$▫) were experimentally and numerically analysed. The coupled micromechanical model prposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18 mm). HSLA steel was used as the base metal in a quenched and tempered condition. The flux-cored arx-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smmoth specimen. The difference in fracture behaviour between over- and undermatched welded joints obtained in experimental results was followed by numerical computationsof void volume fraction in front of the crack tip.
Keywords: fracture mechanics, ductile fracture, high strength low alloyed steel, cracks, micromechanical model, mismatched welded joints, constraint effect, void growth
Published: 01.06.2012; Views: 1106; Downloads: 57
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Strength mismatch effect on yield load in X-shaped weldment with centre crack
Dražan Kozak, Nenad Gubeljak, Jožef Predan, Franjo Matejiček, 2004, published scientific conference contribution

Abstract: This paper provides yield load solutions for single edged fracture toughness specimen subjected to bending SE (B) with present X-shaped weld joint. The weld centre crack is located in the overmatch weld part. The corresponding fully plastic yield loads were obtained directly by plain strain FEM analysis for five characteristic a/W ratios: 0,1;0,2;0,3;0,4 and 0,5. Also, the influence of the sistematically varied weld root width 2H on the fracture behaviour has been evaluated. It was found that yield load decreases with the increasing weld root, because the undermatched region ahead the crack tip plays the dominant role.
Keywords: fracture mechanics, X-shaped welded joints, centre crack, strength mismatching, plastic yield load, constraint effects
Published: 01.06.2012; Views: 940; Downloads: 23
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The fracture behaviour of global/local mis-matched weld joints provided on HSLA steels
Inoslav Rak, Nenad Gubeljak, Zdravko Praunseis, 2001, original scientific article

Abstract: The fracture behaviour of thick section high strength steel weldments, that contain soft root passes, has been studied. Two different weld consumables with different strength mismatch (1>M>1) and fracture toughness properties in the WM have significantly increased the complexity of the mis-match effect and failure behaviour of weld joints, depending on the crack location and the thickness of the soft root layer. The aim was to explain the effect of strength heterogeneity between BM and WM and between different regions in WM (global/local mismatching). R-curves of WM and HAZ regions were also discussed. The conclusion is that the application of a welding procedure with a two-pass soft root layer, introduced for the purpose of reducing or even omitting preheating, can be recommended in mis-matched weld joints on steel grade HT80. Nevertheless, the alloying from BM, and the tempering effect of subsequent weld passes, have to be taken into account. They can cause reduction of the root region ductility and affect the local mismatch in WM and HAZ. The deterioration by providing a soft root layer can probably be reduced by a selected consumable and proper welding procedure. The final conclusion is that the application of a mismatched weld joint with a soft root layer can be recommended only if high root toughness can be provided.
Keywords: welding, welded joints, strength mismatching, fracture toughness, CTOD, hardness, impact toughness, HSLA steels
Published: 01.06.2012; Views: 1191; Downloads: 60
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Vloga in nastanek mikrostrukturnih sestavin M-A v zvarnih spojih maloogljičnih visokotrdnostnih konstrukcijskih jekel
Zdravko Praunseis, Masao Toyoda, Alojz Križman, Mitsuru Ohata, 2001, review article

Abstract: The existence of martensite-austenite constituents in the weld metal and heat-affected zone seriously reduces the fracture toughness of the welded joint. Therefore, we have investigated the formation of the martensite-austenite constituents when high-strength low-alloy steel is welded with a high heat input or using multi-pass welding. This paper deals with the effects of martensite-austenite constituents on the fracture toughness, the metallurgical features of the martensite-austenite constituents, and the prevention and elimination of the martensite-austenite constituents in the welded joints.
Keywords: arc welding, high-strength low-alloy steels, microstructure, martensite-austenite constituents, weld metal, heat-affected zone, cooling rate
Published: 01.06.2012; Views: 1111; Downloads: 58
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The transferability of fracture-mechanics parameters to fracture performance evaluation of welds with mismatching
Masao Toyoda, Zdravko Praunseis, 2000, original scientific article

Abstract: The differences in the mechanical properties between different weld-metal regions obviously affect the strain distribution around the crack tip during a fracture test and hence influence the fracture toughness value. The variation in plastic constraint during fracture mechanics testing has an additional effect on the ductile and brittle fracture initiation behaviour of any weld joint. This paper deals with the transferability of fracture toughness results to the fracture performance evaluation of the strenght of mismatch welded joints based on the two-parameter criterion and the local approach. It was found that the numerical simulations based on the transferrable fracture concept are effective in practice.
Keywords: welding, welded joints, strength mismatching, plastic constraint, transferability concept
Published: 01.06.2012; Views: 1122; Downloads: 184
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