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1

Comparison of different failure approaches in knotty wood

Guindos P.

Drewno : prace naukowe, doniesienia, komunikaty

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2014

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vol. 57, nr 193

51--68

EN

This article presents and assesses 64 different ways for predicting the failure onset in knotty wooden beams. The aim is to provide engineers and modellers a general view of how to evaluate the failure in wooden structural members with knots. The studied criteria included both the conventional point-based and average stress theories. Special attention was paid to the effect of the elements of the wood mesostructure, i.e. knots and fiber deviation, which can generate singular stress concentrations as notches or cracks would do in fracture mechanics. The case study consisted of predicting the failure onset of bending in structural wooden beams. A previously validated finite element model was used in order to compute the heterogeneous stresses. It was found that the knots caused considerable stress singularities so that the size of the average stress theory influenced the failure predictions by up to 23%. However, the variations generated by distinct phenomenological criteria were in general much smaller. The application of the average stress theory in large stress integration volumes is strongly recommended when predicting the failure in wood members.

2

Wieloskalowy numeryczny model ciągnienia na zimno drutów z niskoplastycznych stopów magnezu z uwzględnieniem mechanizmu utraty spójności

Milenin A., Byrska-Wójcik D. J.

Rudy i Metale Nieżelazne

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2013

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R. 58, nr 11

731--736

PL

Rozpatrywane stopy Mg zostały opracowane w celu wytworzenia resorbowalnych bio implantów. Ich skład chemiczny cechuje się dodatkami takimi jak Ca i Li (MgCa0,8, A×30, LA63). Te dodatki zwiększają biozgodność stopu, optymalizują intensywność korozji, ale obniżają technologiczną plastyczność przy przeróbce plastycznej [1, 2]. Technologia produkcji nici chirurgicznych zawiera etapy wyciskania półwyrobu, ciągnienia w podgrzewanych ciągadłach oraz przewiduje ciągnienie na zimno w celu kształtowania odpowiedniej jakości powierzchni i własności. Problem stanowi jednak niska plastyczność rozpatrywanych stopów w temperaturze pokojowej, co utrudnia ostatni etap cyklu produkcyjnego [3]. Celem pracy jest opracowanie numerycznego modelu ciągnienia na zimno niskoplastycznych stopów magnezu z uwzględnieniem mechanizmu utraty spójności w skali mezo i wykorzystanie go do optymalizacji technologicznych parametrów procesu. Model utraty spójności opracowano za pomocą metody elementów brzegowych. Model został skalibrowany za pomocą badań in situ. Walidacja wykonana została na podstawie porównania mikrostruktury i powstających defektów w drucie z wynikami symulacji.

EN

Magnesium alloys with high biocompatibility containing Ca, Li and rare earths are the alternative for nowadays used materials for implants and surgical threads. The main advantage of those alloys are properties similar to properties of human bones. However the low ductility in cold deformation of this alloys is a problem [1-3]. In the case of production of surgical threads the high temperature causes an oxidation of the surface, but cold deformation is very difficult because of the low plasticity. In work [4] the technology of thin surgical threads production from magnesium alloys is proposed. The described technology contains: extrusion to diameter 1 mm, hot drawing to diameter 0.1-0.2 mm and cold drawing to diameter 0.1-0.05 mm to improve the surface quality. The last stage of presented technology requires the development of the mathematical model of the process, because identification of the parameters is very difficult for materials with such low plasticity. Furthermore, the experimental research proved, that the model in the macro scale is not adequate [5, 6]. The developed model in macro scale use the finite element method, and the model in meso scale use the boundary element method and considers the microstructure mechanisms: intergranular fracture mechanism, grain orientation and the effect of micro cracks on the plasticity restoring during annealing. The macro and meso models are coupled and finally the multiscale model is obtained.

3

Identiﬁcation in multiscale thermoelastic problems

Długosz A., Burczyński T.

Computer Assisted Methods in Engineering and Science

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2013

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Vol. 20, no. 4

325--336

EN

The paper deals with the identiﬁcation in multiscale analysis of structures under thermal and mechanical loads. A two-scale model of porous materials is examined. Direct thermoelastic analyses with representative volume element (RVE) and ﬁnite element method (FEM) are taken into account. Identiﬁcation of material constants of the microstructure and identiﬁcation of the shape of the voids in the microstructure are considered. Identiﬁcation functional is formulated on the basis of information obtained from measurements in mechanical and thermal ﬁelds. Evolutionary algorithm is used for the identiﬁcation as the optimization technique. Numerical examples of identiﬁcation for porous aluminum models are enclosed.