Wyniki wyszukiwania - Biblioteka Nauki

1

Comparative evaluation of various experimental and numerical simulation methods for determination of t8/5 cooling times in HPAW process weldments

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Sajek A. , Nowacki J.

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tom Vol. 18, no. 2

583--591

EN

The aim of this article is to provide a quantitative comparison and efficiency verification of the methods of estimating t8/5 cooling time in the process of HPAW of S960QL steel. The measurements of t8/5 welding time were conducted at the face of weld with the use of thermoelectric, pyrometric and thermovision methods. A FEM model of the joint was made, and welding simulation was done. The results of the calculations were then confronted with experimental data, and measuring methods were evaluated. Differences in the results of t8/5 time measurements were determined for the analysed methods and arranged according to the precision of results presented; the applicability of FEM for predicting the value of t8/5 time was investigated. The usability of temperature measuring methods for determining cooling time was determined, the weaknesses of non-contact measurement in terms of diversification of cooling time in a section of a welded joint were shown, and the advantages of numerical method were demonstrated. It was established that joining experimental methods for measuring cooling time of a joint with FEM analysis allows to obtain a desired resolution of prediction. In this way, the technology for hybrid welding of advanced high-strength steels can be designed more efficiently.

2

Verification of Properties of Joints Made of Advances High Strength Steels in the Conditions of the Complex Thermal Cycles of the HPAW Process

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Nowacki J. , Sajek A.

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tom Vol. 62, No. 5

167--173

EN

The article discusses the primary issue related to the verification of properties of joints made in AHSS in relation to conventional structural steels and based on the identification of cooling time t8/5. The solution suggested in the study involving the application of the Finite Element Method is based on two computational models. In addition the article presents a material model allowing for properties of single metallic phases and their interaction during the welding cycle. The study also describes the numerical model of the HPAW (plasma + MAG) heat source composed of two models predefined in the Simufact.Welding software programme corresponding to the nature of constituent processes. The research-related tests also involved welding simulations and experimental verification. The tests demonstrated the conformity of simulation results and the high usability of simulation when verifying properties of joints.

PL

Scharakteryzowano podstawowy problem kontroli właściwości złączy wykonanych ze stali AHSS w odniesieniu do konwencjonalnych stali konstrukcyjnych, bazujący na wyznaczaniu czasu stygnięcia t8/5. Zaproponowane rozwiązanie w postaci zastosowania metody elementów skończonych bazuje na dwóch modelach obliczeniowych. Przedstawiono model materiałowy, który uwzględnia właściwości pojedynczych faz metalicznych oraz ich interakcje w trakcie cyklu spawania. Jako drugi, opisano numeryczny model hybrydowego źródła ciepła HPAW (plazma + MAG) składający się z dwóch predefiniowanych w oprogramowaniu Simufact.Welding modeli, adekwatnych do charakterów procesów składowych. Przeprowadzono symulację spawania oraz eksperyment weryfikujący. Wykazano zgodność wyników symulacji i jej wysoką przydatność w zakresie kontroli właściwości analizowanych złączy.

3

Mechanical analysis and numerical simulation of modified bone cements in the hip joint alloplasty

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Nowacki J. , Sajek A.

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tom Vol. 46, nr 1

57--64

EN

Purpose: The paper aims at verifying the stress values in bone-cement-implant system during human movement cycle and determining the amount of bone cement admixture which induces a drop in mechanical properties to acceptable level. Design/methodology/approach: In the first place, mechanical tests of modified cements were carried out. These tests are a basis for mathematical description of mechanical properties which will be used during numerical simulations. Numerical simulations were carried out using the geometry obtained by computer tomography. Findings: A drop in mechanical properties induced by modification depends on admixture size. During movement, cement bond is affected by considerable forces. These forces operate cyclically, i.e. momentarily (when setting a foot on the ground) within the elastic range of examined material. From the point of view of mechanical parameters, an optimum admixture of the aqueous solution of biologically active modifying agent is that inducing porosity at a level of 8%. Research limitations/implications: The paper constitutes a beginning of examinations on modified cement junctures which may be expanded in future by testing the dynamics basing on the analysis of fatigue strength. Practical implications: Modifying agent amount was determined and verified that does not induce a decrease in the bending strength and the longitudinal modulus of elasticity during bending below the level specified in ISO 5833 standard. Originality/value: Modification of cement with aqueous solution of salmon calcitionin, as well as examination and verification of the effect of admixture on mechanical properties.

4

Modified bone cement microstructure numeric simulation

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Nowacki J. , Sajek A.

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2010

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tom Vol. 43, nr 2

533--541

EN

Purpose: The paper aimed at determining the strength of modified bone cement microstructure. Modification with aqueous hormone solution stimulates the growth of bone at a hip-joint endoprosthesis implantation site. Design/methodology/approach: In the first place, microstructure of modified cements was examined. This examination was a basis for statistical description of porosity obtained as a result of modification. Statistical data were used to create microstructure models in a programme being in agreement with FEM technique. Simulations were carried out on structures of 2 types of pores, i.e. those containing water and empty ones. Findings: Modification with aqueous solutions of modifying agents affects the structure and properties of bone cements. This is caused by formation of pores filled with aqueous solutions of modifying agents. This type of porosity decreases mechanical properties less than air-filled pores. Research limitations/implications: Numerical simulation of the stress and displacement pattern in juncture microstructure should be expanded with a simulation of bone-cement-implant system operation, which will allow estimation of an optimum value of modifying agent admixture, i.e. a value enabling the improvement of juncture biocompatibility not lowering at the same time its mechanical properties below a level set up in standard specifications. Practical implications: Microstructure simulations performed confirmed a manner of modified cement cracking observed on fractures. They showed formation of pore agglomerations where concentrating stresses may bring about the appearance of dangerous micro-fractures. Originality/value: Cement modification with aqueous solution and examination of the effect of admixture on microstructure mechanical properties.

5

Zastosowania metody elementów skończonych w analizie spawania hybrydowego PAW-MAG

100%

Nowacki J. , Sajek A.

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tom nr 9-10

26--30

PL

W artykule przedstawiono problematykę symulacji procesu spawania przy użyciu metody elementów skończonych i dedykowanego do tego procesu specjalistycznego oprogramowania simufact.welding. Zaprezentowano przykładowe wyniki obliczeń numerycznych stali o zróżnicowanych właściwościach spawanych metodą hybrydową PAW-MAG oraz zakres możliwości symulacji nowoczesnej i innowacyjnej metody spawania hybrydowego PAW-MAG, wspomagające optymalny dobór parametrów we wczesnej fazie wprowadzania nowego produktu. Zaprezentowano wyniki modelowania rozkładu temperatury, struktury, twardości, naprężeń i odkształceń w złączu oraz duże zróżnicowanie modeli materiałowych zaimplementowanych w wykorzystanym w badaniach środowisku obliczeniowym oraz określono możliwości Metody Elementów Skończonych w analizie historii cieplnej dowolnego obszaru złącza spawanego, dowodzące, że stanowi ona innowacyjne narzędzie projektowania złączy spawanych stali.

EN

The article presents the issue of simulating the welding process using the finite element method and the specialized software simufact.welding dedicated to this process, as well as the exemplary results of the numerical calculations of steels of different properties welded using PAW-MAG – a modern and innovative method of hybrid welding – and the range of its simulation capabilities supporting the optimal selection of parameters in the early phase of a product introduction. Moreover, it addresses the results of the modelling of temperature distribution, structure, hardness, stress and strain in the joint and a large diversity of material models implemented in the computing environment used in the research and identifies the possibilities of the element method in the analysis of the thermal history of any area of the welded joint proving that it constitutes an innovative tool for the design of welded joints of steel.

6

Impact Tests of UHSS Steel Welded Joints Using the Drop - Tower Impact Drop Method

80%

Dorożyński J. , Nowacki J. , Sajek A.

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tom Vol. 19, nr 3(61)

19--31

EN

The article characterizes the impact test method using Drop-Tower Impact Test with the registration of the value of force and energy of breaking. Based on sources, the possibilities and scope of the current application of this method were determined and the current state of knowledge on the results of these tests was reviewed. In order to determine the possibility of using the method in impact tests of high strength steel joints, investigations of hybrid PTA - GMA welding conditions on impact strength of joints of MART S1300QL steel were carried out. In particular, the influence of t8/5 cooling time on the impact strength of welded joints by the Drop - Tower Impact Test method was determined. It has been shown that the use of dropping machine with computer-based registration of breaking force and energy values was possible in the case of impact strength testing of UHSS welded joints and enabled precise analysis of the energy distribution dynamics absorbed by the tested.