Wyniki wyszukiwania - BazTech

1

The energy approach for prediction of the behaviour of the notched specimens and components

Buczynski A., Glinka G., Baum Ch.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2002

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z. 73

27-45

EN

The stress-strain behaviour in the notch tip of elastic-plastic bodies is discussed in the presentation. The approach is based on the incremental formulation which relates hypothetical elastic energy density to elastic-plastic energy density at the notch root. The Mróz-Garud multisurface cyclic plasticity theory is employed for simulation of the material response due to the current load increments. The equations of the energy density balance in the notch root together with constitutive relations formulate a set of algebraic equations. The fictitious elastic load history at the notch root and the material constitutive relations provide the parameters, so that the set of equations can be easily solved for the stress and strain increments. A shaft with a circumferential notch subjected to random load events is addressed to as an example of a component specified to predict the material stress-strain behaviour. The calculation results, obtained for general non-proportional load paths, are compared to the corresponding finite element data.

2

Further Development of the creep-fatigue prediction methods frequency separation method and strain range partitioning method and crack propagation prediction for the recent titanium alloy Timetal TI 834

Nowack H., Kordisch T., Baum Ch.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2002

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z. 73

47-74

EN

The original Strain Range Partitioning (SRP) method and the Frequency Separation (FS) method for predictions of the creep-fatigue behaviour of thermome-chanically loaded structures have been proposed a long time ago. However, they are still of interest because they explicitly consider the combined action of time independent and time dependent contributions to the creep-fatigue life behaviour. Meanwhile these methods have reached a high state in development. In the present paper some proposals for a further improvement of the prediction capability of these methods are included. For an application of high temperature materials in practise a careful consideration of the microstructure has also to be performed. Typical microscopical phenomena and processes are briefly described in the first part of the paper. The material that has been considered in more detail in the paper is the new titanium alloy Timetal 834. The properties and the thermomechanical behaviour of this alloy are presented. The alloy is sensitive to the environment at higher temperatures. Various engineering tools to predict the time dependent mechanical behaviour are presented including the SRP method and the FS method as mentioned above. The third part of the paper deals with the crack extension behaviour under high temperature conditions. It is shown that predictions for long time applications still include some risk. In the crack stage the environmental condition is also important.

3

Computer visualization of the material stress-strain behaviour after Mróz model and typical effects

Buczynski A., Baum Ch.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2002

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z. 73

11-25

EN

The discussion addresses the description of material behaviour due to stress-controlled load histories. It is restricted to 2D-problems, and a principal stress piane will be employed to demonstrate specified load events, assuming that the principal stress components are fixed to the material element. In order to tracę the general rules of the model evolution, due to the current load development, the assumptions postulated in the original formulation are described. As it was originally composed, the plastic module field and its variations, in respect to the actual load event of the considered load path, will be demonstrated. The attention will be paid to the ability to reproduce the Bausch-inger effect, and the plastic strain accumulation occurring under specific nonpropor-tional load conditions.

4

Single yield surface model for cyclic plasticity

Buczyński A., Baum Ch.

Zeszyty Naukowe Politechniki Białostockiej. Mechanika

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2001

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Z. 24

91--100

EN

The paper deals with the ratchetting effect as observed under general nonproportional loading. Multisurface models, most frequently used for prediction of material behaviour under random loadings, account for the plastic strain progression. However, the predicted rates of strain, in general, differ from the experimental observations. The authors´ attention was addressed to reduce the effect of the plastic strain accumulation in one direction. For this purpose a plasticity constitutive model for prediction of stress-strain behaviour of cyclically loaded metallic materials, based on the one yield surface, is presented. The Prager rule for the yield surface translation and the Ramberg-Osgood stress-strain curve for hardening modulus distribution were incorporated. The numerical simulations made for selected load paths were compared to results obtained by using the most popular multisurface model.

PL

W pracy podjęto próbę stabilizacji efektu kumulacji odkształceń plastycznych powstajacych w materiale w wyniku działania wieloosiowych obciążeń. W tym celu opracowano jednopowierzchniowy model przeznaczony do symulacji zachowania materiału w warunkach losowych obciążeń zewnętrznych. Wyniki obliczeń porównano z odpowiednimi rezultatami uzyskanymi przy zastosowaniu wielopowierzchniowego modelu Garuda.