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1

Experimental characterization of the AA7075 aluminum alloy using hot shear compression test

Bhujangrao Trunal, Veiga Fernando, Froustey Catherine, Guérard Sandra, Iriondo Edurne, Darnis Philippe, Mata Franck Girot

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

95--111

EN

The experimental characterization of the material under shear loading is essential for researchers to study the plastic behavior of materials during manufacturing processes. Indeed, regardless of the loading mode, ductile materials mainly deform plastically under shear loading. Thus, for such material behavior analysis, shear tests are very useful. In this paper, a test procedure is defined to characterize the shear deformation of AA7075 aluminum alloy at high strain under compression loading. The Finite Element (FE) simulation is used to select the suitable specimen geometry for the testing. Finally, the experimental tests are carried out using a conventional compression device at a constant strain rate of 0.1 s−1 and at an elevated temperature of 20–500 °C. The results show that the drop in the flow stress curved relative to the increase in temperature exhibits the softening mechanism. The homogeneous behavior of the shear strain along the shear region was also observed and shown by the macro and micro images. The effect of temperature and equivalent strain on the evolution of the microstructure is discussed in detail. It is discovered that, various dynamic recrystallization mechanisms were recorded for aluminum alloy AA7075 depending on the imposed strain conditions.

2

Localized failure analysis of internally pressurized laminated ellipsoidal woven GFRP composite domes: Analytical, numerical, and experimental studies

Gohari Soheil, Sharifi Shokrollah, Burvill Colin, Mouloodi Saeed, Izadifar Mohammadreza, Thissen Peter

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 4

1235--1250

EN

This paper presented a systematic approach toward localized failure inspection of internally pressurized laminated ellipsoidal woven composite domes. The domes were made of thin glass fiber reinforced polymer (GFRP) woven composite layups [0,0,0], [0,30,0], [0,45,0], and [0,75,0]. The analytical results demonstrated that the circumferential regions near meridian w = 458 in prolate ellipsoidal domes and near meridian w = 908 in oblate ellipsoidal domes sustain the highest deformation under internal pressure. This observation was then confirmed by the numerical and experimental results. In addition, the numerical and experimental results showed localized rather than uniform failure in those regions, irrespective of changes in laminate stacking sequence. It was observed that localized failure occurs since the woven fibers configuration in some areas of woven remains in initial geometry (square shape), while the rests are deformed into the rhombic shape. In other words, by moving along the circumferential direction from the area close to u = 08 to u = 458 and u = 458 to u = 908, the shape of woven fibers gradually changes from square (strong area) to rhombic (weak area), and rhombic to square, respectively. Thus, to minimize failure pressure, the meridian region vulnerable to failure must initially be identified. Afterwards, the rhombic regions in the circumference corresponding to that meridian must be strengthened.

3

Influence of friction condition on failure location of AA5754 aluminium sheet in Nakajima test

Slota J., Šiser M.

Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika

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2018

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z. 90 [298], nr 1

57--66

EN

This paper presents the results of numerical and experimental investigations on the influence of friction on failure location in Nakajima formability tests. Finite element (FE) simulations were performed using commercial explicit dynamic FE code. The numerical results obtained from the FE simulation were compared with experimental data from Nakajima tests. A 3D digital image correlation system ARAMIS was used in experiments. The location of failure on the sample was detected depending on friction conditions. The studies confirmed that the crack location near the centre of the specimen as required by the ISO standard could be obtained for low values of the friction coefficient. The numerical simulation combined with the inverse analysis was used to estimate a real value of the friction coefficient in the Nakajima formability test.

PL

W pracy przedstawiono numeryczne i eksperymentalne badania wpływu tarcia na lokalizację uszkodzeń w teście Nakajima. Symulację numeryczną testu przeprowadzono przy użyciu komercyjnego jawnego dynamicznego kodu FE. Wyniki uzyskane z symulacji FE porównano z danymi doświadczalnymi. W badaniach eksperymentalnych wykorzystano system ARAMIS do optycznej korelacji obrazu 3D. Lokalizacja uszkodzenia próbki wykazała zależność od warunków tarcia. Badania potwierdziły, że położenie pęknięcia w pobliżu środka próbki, zgodnie z wymaganiami normy ISO, można uzyskać dla niskich wartości współczynnika tarcia. Do oszacowania rzeczywistej wartości współczynnika tarcia w teście odkształcalności według Nakajima zastosowano symulację numeryczną połączoną z analizą odwrotną.

4

Geometric verification of the validity of Finite Element Method analysis of Abdominal Aortic Aneurysms based on Magnetic Resonance Imaging

Domagała Z., Stępak H., Drapikowski P., Kociemba A., Pyda M., Karmelita-Katulska K., Dzieciuchowicz Ł., Oszkinis G.

Biocybernetics and Biomedical Engineering

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2018

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Vol. 38, no. 3

544--555

EN

The currently used criterion of maximum transverse diameter for the Abdominal Aortic Aneurysm treatment has some limitations. Attempts to create individualized, therapeutic strategies are being conducted, including biomechanical assessment of rupture risk of an aneurysm based on the Finite Element Analysis of the geometric models. The usual approach is to use the results of the computed tomography imaging to build a three-dimensional model of the aneurysm. The FEA is then performed and the resulting stress is analysed to estimate the risk of rupture. Although such an approach brings significant improvements over the traditional maximum diameter method, it is difficult to ensure the validity of the assumptions made. This paper presents a method to evaluate the correctness of such an approach. The emergence of gated Magnetic Resonance Imaging allows registering aneurysm in both the systolic and diastolic phase of cardiac cycle. The corresponding geometric models are built and the results of the FEA applied to the diastolic model are compared with the actual deformation of the aneurysm observed in the patient's body. Thus, it is possible to verify whether the individualized diagnostic approach applied to a specific patient was correct. The geometry of the reference and the analysed models were compared using the Differential Surface Area Method. The average geometry error equals 1.65%. In the best case the error amounts to 1.04%, in the worst to 3.00%. The obtained results provide evidence that the Finite Element Analysis is a reliable method and can be potentially used for individualized diagnostics and treatment.

5

Fracture of laminated woven GFRP composite pressure vessels under combined low-velocity impact and internal pressure

Sharifi S., Gohari S., Sharifiteshnizi M., Alebrahim R., Burvill C., Yahya Y., Vrcelj Z.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 4

1715--1728

EN

Dome curvatures of pressure vessels often sustain highest level of stresses when subjected to various loading conditions. This research is aimed at investigating the effect of dome geometrical shape (hemispherical, torispherical, and ellipsoidal domes) on mechanical deformation and crack length of laminated woven reinforced polymer (GRP) composite pressure vessels under low-velocity impact (LVI) (case one) or combination of LVI and internal pressure (case two). The study is based on finite element (FE) simulations with laboratory-based experimental validation studies. It was observed that the maximum vertical displacements () and crack length along the diameter of deformation (a) are both of lower magnitude in case one. Damage intensity and fracture differ for different combinations of loading. Only matrix breakage and debonding occurs in case one and fiber breakage occurs in case two. The dome geometric shapes used in this study were found to be invariant to both damage intensity and failure modes. Irrespective of the type of load applied, the magnitude of and crack length correlate with dome geometric shape as the maximum and the minimum occur in torispherical and hemispherical domes, respectively. The maximum and the minimum crack lengths also take place in torispherical and hemispherical domes, respectively.

6

Non-linear viscoelastic constitutive model for bovine cortical bone tissue

Pawlikowski M., Barcz K.

Biocybernetics and Biomedical Engineering

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2016

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Vol. 36, no. 3

491--498

EN

In the paper a constitutive law formulation for bovine cortical bone tissue is presented. The formulation is based on experimental studies performed on bovine cortical bone samples. Bone tissue is regarded as a non-linear viscoelastic material. The constitutive law is derived from the postulated strain energy function. The model captures typical viscoelastic effects, i.e. hysteresis, stress relaxation and rate-dependence. The elastic and rheological constants were identified on the basis of experimental tests, i.e. relaxation tests and monotonic uniaxial tests at three different strain rates, i.e. [...] = 0:1 min_1, [...] = 0:5 min_1 and [...] = 1:0 min_1. In order to numerically validate the constitutive model the fourth-order stiffness tensor was analytically derived and introduced to Abaqus® finite element (FE) software by means of UMAT subroutine. The model was experimentally validated. The validation results show that the derived constitutive law is adequate to model stress–strain behaviour of the considered bone tissue. The constitutive model, although formulated in the strain rate range [...] = 0:1-1:0 min_1, is also valid for the strain rate values slightly higher than [...] = 1:0 min_1. The work presented in the paper proves that the formulated constitutive model is very useful in modelling compressive behaviour of bone under various ranges of load.

7

Determination of friction factor by ring compression testing and FE analysis

Gzyl M., Rosochowski A., Olejnik L., Sikora K., Jawad Qarni M.

Computer Methods in Materials Science

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2015

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Vol. 15, No.1

156--161

EN

The goal of this study was to examine performance of various lubricants for aluminium alloy AA5083. Conventional ring compression tests were conducted at 200°C. Samples were compressed to 50% of the initial height with a constant ram velocity 0.5 mm/s using a servo-controlled hydraulic press. The optimization procedure was implemented in self-developed software to identify friction factors from experiments. The application launches remotely finite element (FE) simulations of ring compression with a changing friction factor until a difference between experiment and numerical pre¬diction of the internal diameter of the sample is smaller than 0.5%). FE simulations were run using Forge3 commercial software. The obtained friction factor quantitatively describes performance of a lubricant and can be used as an input parameter in FE simulation of other processes. It was shown that application of calcium alumínate conversion coating as pre-lubrication surface treatment reduced friction factor from 0.28 to 0.18 for MoS2 paste. It was also revealed that com-mercially available graphite-based lubricant with an addition of calcium fluoride applied on conversion coating of calcium alumínate had even lower friction factor of 0.11

PL

Celem niniejszej pracy było zbadanie przydatności różnych smarów dla obróbki plastycznej stopu aluminium AA5083. Standardowe testy spęczania próbek pierścieniowych zostały wykonane w temperaturze 200°C. Próbki zostały spęczone do 50% początkowej wysokości ze stałą prędkością przesuwu narzędzia 0.5 mm/s. Testy zostały przeprowadzone na prasie hydraulicznej z serwonapędem. Procedura optymalizacyjna została zaimplementowana w samodzielnie opracowanej aplikacji w celu zidentyfikowania współczynników tarcia na podstawie wyników prób spęczania. Aplikacja zdalnie uruchamia symulację metodą elementów skończonych (MES) procesu spęczania próbki pierścieniowej ze zmieniającym się współczynnikiem tarcia dopóki różnica pomiędzy wewnętrzną średnicą próbki otrzymaną z eksperymentu oraz z symulacji numerycznej nie jest mniejsza niż 0.5%. Symulacje MES zostały wykonane w komercyjnym pakiecie Forge3. Otrzymane współczynniki tarcia pozwalają na ilościową ocenę przydatności użytego smaru oraz mogą być bezpośrednio użyte w symulacji MES. Wykazano, że dla smaru na bazie MoS2 zastosowanie powłoki konwersyjnej glinianu wapnia jako warstwy podsmarnej zmniejsza wartość współczynnika tarcia z 0.28 do 0.18. Zostało również pokazane, że dostępny na rynku smar grafitowy z domieszką fluorku wapnia nałożony na powłoce podsmarnej glinianu wapnia dał jeszcze mniejszy współczynnik tarcia, równy 0.11.

8

Analysis Of The Extrusion Process Of A Square Tube Multi-Channel Heat Pipe

Kim K. S., Kim J. Y.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1463--1466

EN

Heat pipes have been recently in use for cooling purposes in various fields, including electronic circuit boards and vehicle parts that generate large amounts of heat. In order to minimize the loss of heat transferred, there is a need to maximize the contact area of the working fluid. This study produced a square tube multi-channel heat pipe to replace the existing circular pipe type to maximize the internal surface area thereof. This expands the surface, allowing the working fluid to come into contact with a wider area and enhancing thermal radiation performance. A mold for the production for such a product was designed, and finite element simulation was performed to determine whether production is possible.

9

Effectiveness of the reverse bending and straightening tests in detecting laminations in wires for civil engineering applications

Adewole K. K., Bull S. J.

Archives of Civil Engineering

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2013

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Vol. 59, nr 4

423--439

EN

The reverse bending and straightening test is conducted on wires used for civil engineering applications to detect laminations which can pose a threat to the integrity of the wires. The FE simulations of the reverse bending and straightening of wires with laminations revealed that the reverse bending and straightening test is only effective in revealing or detecting near-surface laminations with lengths from 25mm located up to 30% of the wire’s thickness and may not be an effective test to detect mid-thickness, near-mid-thickness, and short near-surface laminations with lengths below 15mm. This is because wires with mid-thickness, near-mid-thickness and short nearsurface laminations will pass through the reverse bending and straightening procedures without fracturing and therefore mid-thickness, near-mid-thickness and short near-surface laminations may go undetected. Consequently, other in-line non destructive testing methods might have to be used to detect mid-thickness, near-mid-thickness and short near-surface laminations in the wires.

10

The effect of AZ31 alloy flow stress description on the accuracy of forward extrusion FE simulation results

Cyganek Z., Tkocz M.

Archives of Metallurgy and Materials

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2012

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Vol. 57, iss. 1

199-204

EN

Hot compression tests of the AZ31 magnesium alloy, performed for wide ranges of temperature and strain rate, revealed two different flow curve types for the material investigated. At higher strain rates and lower temperatures, flow curves exhibit a distinct peak. At lower strain rates and higher temperatures, flow stress values change less rapidly. This makes it difficult to find a single function able to accurately describe the deformation behaviour of AZ31 alloy in the entire forming range. The present study discusses an effect of the AZ31 magnesium alloy flow stress description on the accuracy of extrusion force prediction by means of FE simulation. A number of forward extrusion trials were carried out in order to acquire experimental data on AZ31 alloy deformation behavior in various forming conditions. Cylindrical billets of 40 mm in diameter and the tooling were initially heated to temperatures in the range of 200 to 400°C and placed in the working space of the 1500 kN hydraulic press to produce extruded rods of 12 mm in diameter. Numerical models for conducting corresponding extrusion simulations were prepared in Forge 2009 software and the selected form of Hensel-Spittel function was applied for the material flow stress description. Function coefficients were calculated both for the entire forming range of AZ31 alloy as well as for the ranges of parameters specific to a certain extrusion trial conditions. The numerical results were compared to the experimental ones and the accuracy of both approaches were estimated. It was found that the selected flow stress function, determined for the wide ranges of temperature and strain rate, allows to achieves a tis factory accuracy of AZ31 alloy extrusion force prediction by FE simulations.

PL

Dwa różne rodzaje krzywych płynięcia uzyskano w próbach ściskania na gorąco stopu magnezu AZ31, prowadzonych dla szerokiego zakresu temperatury i prędkości odkształcenia. Dla wyższych prędkości odkształcenia i niższych temperatur krzywe płynięcia wykazują wyraźne maksimum naprężenia uplastyczniającego. Dla niższych prędkości odkształcenia i wyższych temperatur zmiany wartości naprężenia uplastyczniającego są mniej gwałtowne. Z tego względu trudno jest znaleźć jedną funkcję opisującą zależność naprężenia uplastyczniającego dla całego zakresu warunków odkształcania stopu magnezu AZ31. W artykule przedstawiono wpływ zastosowanej funkcji naprężenia uplastyczniającego stopu AZ31 na dokładność wyznaczania siły wyciskania poprzez symulacje MES. Przeprowadzono szereg prób wyciskania współbieżnego w celu uzyskania danych doświadczalnych charakteryzujących zachowanie się stopu AZ31 w różnych warunkach kształtowania. Próbki walcowe o średnicy 40mm wraz z przyrządem do wyciskania były nagrzewane do temperatury w zakresie od 200 do 400°C i umieszczane w przestrzeni roboczej pionowej prasy hydraulicznej o nacisku 1500kN. Następnie wyciskano z nich pręty o średnicy 12mm. Próby wyciskania zostały zamodelowane w programie FORGE2009, a do opisu zmian naprężenia uplastyczniającego badanego stopu w zależności od warunków odkształcania wykorzystano wybraną postać funkcji Hensla-Spittla. Współczynniki funkcji zostały obliczone zarówno dla całego zakresu kształtowania stopu AZ31, jak i dla warunków występujących podczas określonej próby wyciskania. Wyniki obliczeń porównano z badaniami eksperymentalnymi, co pozwoliło na ocenę poprawności wyników symulacji numerycznych. Z badań wynika, że wybrana funkcja naprężenia uplastyczniającego, która została opracowana dla szerokiego zakresu temperatury i prędkości odkształcenia, pozwala na poprawne wyznaczanie siły wyciskania stopu magnezu AZ31 za pomocą symulacji MES.

11

Computer aided design of the manufacturing chain for fasteners

Kuziak R., Skóra M., Węglarczyk S., Paćko M., Pietrzyk M.

Computer Methods in Materials Science

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2011

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Vol. 11, No. 2

243-250

EN

Computer aided design of the forging technology for the fasteners made of bainitic steels is the objective of the paper. Three steels were tested and rheological models of these steels were developed. The models were implemented into the fmite element code for thermal-mechanical simulations of metal forming processes. The particular objectives of the work were twofold. Simulations of various variants of manufacturing chain were performed first. Operations, which were considered, include: cold drawing to reduce diameter and harden the material, forging in three operations, heat treatment. The best manufacturing chains were selected on the basis of numerical simulations. Industrial trials were performed at the for the selected cycles and the efficiency of these cycles was evaluated.

PL

Celem pracy jest wspomagane komputerowo projektowanie technologii wytwarzania elementów złącznych ze stali bainitycznych. Badano dwie stale, w tym jedną dla dwóch różnych temperatur końca walcowania. Opracowano modele reologiczne dla tych stali. Te modele zaimplementowano w programie z metody elementów skończonych dla termomechanicznej symulacji procesów kształtowania metali. Szczegółowe cele pracy były dwojakie. Pierwszym celem było wykonanie symulacji różnych wariantów wytwarzania elementów złącznych. Badaniami objęto operacje ciągnienia na zimno w celu zmniejszenia średnicy wsadu i umocnienia materiału, kucia na zimno w trzech etapach oraz obróbki cieplnej. Na podstawie wyników symulacji oceniono efektywność różnych wariantów technologii i wybrano najlepszy wariant technologiczny, dla którego przeprowadzono próby w warunkach przemysłowych.

12

Numeryczna symulacja zużycia narzędzi w procesie kucia stopów na bazie miedzi z zastosowaniem różnych technologii kucia

Nowak J., Węglarczyk S., Pietrzyk M.

Archiwum Technologii Maszyn i Automatyzacji

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2011

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Vol. 31, nr 1

77-91

PL

W artykule oceniono możliwości kucia odkuwek ze stopu CuCr na podstawie analizy różnych wariantów technologicznych. Szczególny nacisk położono na analizę zużycia narzędzi. Obliczenia numeryczne wykonano w programie Forge3 opartym na metodzie elementów skończonych. W obliczeniach wykorzystano dwa modele zużycia narzędzi: model Archarda i model zmęczeniowy. Na podstawie symulacji komputerowych oceniono różne warianty technologiczne pod względem zużycia narzędzi w procesie kucia.

EN

Copper alloys with chromium are widely used for manufacturing of electrodes and electric contacts. Due to their properties, they might find a much wider application, but the technological difficulties associated with metal forming limit these possibilities. In article the possibilities of forging of the CuCr alloy using different technological cycles are presented. The tool wear is particularly emphasized. Numerical calculations were performed in the program Forge3 based on the finite element method. Two die wear models have been used in simulations: Archard model and fatigue model. Estimation of the of tool wear for different technological variants was performed on the basis of simulations.

13

Wpływ luzów geometrycznych na stan naprężenia w otoczeniu nitu grzybkowego

Sławiński G., Szymczyk E., Niezgoda T., Jachimowicz J.

Górnictwo Odkrywkowe

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2010

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R. 51, nr 3

29-32

PL

W artykuleprzedstawiono wyniki symulacji numerycznych dotyczących wpływu wybranych imperfekcji geometrycznych naprężenia w otoczeniu nitu. W trakcie spęczania nitu do łączonych blach wprowadzane są naprężenia własne, których przekracza granicę plastyczności. Zjawisko to wpływa na poprawę trwałości zmęczeniowej połączenia. Jednak można się spodziewać, że niedokładności wykonania mogą wpłynąć na pogorszenie wytrzymałości połączenia nitowego.

EN

This paper deals with the numerical FE simulation of the geometrical imperfections influence on the residual stress fields around the rived hole. The residual stress state occurs in the rivet hole after the riveting process exceeds the yieldstress level. It has significant influence on the fatigue life improvement of aircraft structures, however, some geometrical imperfections can reduce the strength of the riveted joint.

14

Modelling the mechanical properties of multiphase steels

Thomser C., Prahl U., Vegter H., Bleck W.

Computer Methods in Materials Science

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2007

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Vol. 7, No. 1

42-46

EN

Modelling the mechanical properties of multiphase steels Corinna Thomser*, Ulrich Prahl*, Henk Vegter**, Wolfgang Bleck* *Institute of Ferrous Metallurgy, RWTH Aachen University, Germany **Corus RD&T, IJmuiden, Netherlands Due to economic, environmental and safety reasons the use of high strength steels for the automotive industry is increasing rapidly. For an optimal use of strength and formability of multiphase steels an accurate material model is required for forming simulations. At the moment the microstructure of multiphase steels, which is the most important factor influencing the strain hardening behaviour of multiphase steels, is not taken into account in FE simulations. In international projects like the ULSAB project, especially dual phase steels play an important role for the automotive industry. Their strain hardening behaviour is strongly influenced by the microstructure as is well known from several experimental investigations. Within this work an approach is presented which describes the microstructure evolution during intercritical annealing by thermodynamic calculations and predicts the strain hardening behaviour of dual phase steels by means of FE simulation of representative volume elements based on microstructural characterisations. After cold rolling, dual phase steels are intercritically annealed. The fractions and the carbon contents of austenite and ferrite depend on the annealing temperature and on the holding time. After a fast quenching, the austenite transforms to martensite, which yields a material of a soft ferrite matrix with strong martensite islands. For the determination of the phase fractions and the carbon partitioning between the two phases a DICTRA calculation was carried out, which considers thermodynamic and kinetic effects during intercritical annealing, thus taking into account that full equilibrium is not always reached. All other elements except of carbon are assumed to be uniformly distributed in both phases. The carbon content was used to calculate the strain hardening behaviour of ferrite and martensite based on dislocation theory models /1/-/2/ for different annealing temperatures. As well known from literature, the strain-hardening behaviour of martensite is mainly dependent on the carbon content, while for the prediction of the strain hardening behaviour of ferrite to the local chemical composition the grain size is needed additionally. A three-dimensional representative volume element is used to describe the interaction of ferrite and martensite in a dual phase steel during deformation in a FE simulation, done in Abaqus. The resulting strain hardening behaviour in simulation is in good agreement to the experimental determined strain hardening behaviour in tensile tests within the error range of the metallographical microstructural characterisation. Additionally to the strain hardening behaviour, the tensile strength and the uniform elongation can be determined in experiments and simulation by using the Considere criteria. References /1/ Rodriguez, R.; Gutierrez, I.: Proceeding of TMP ’04, B-Liege, 2004, p. 356-363 /2/ Rodriguez, R.; Gutierrez, I.: Materials Science Forum, Vols. 426-432, 2003, p. 4525-4530

PL

Z powodów ekonomicznych, środowiskowych oraz bezpieczeństwa gwałtownie wzrasta zapotrzebowanie na wytrzymałą stal dla przemysłu samochodowego. W celu otrzymania optymalnej kombinacji wytrzymałości i plastyczności dla wielofazowego, wymagany jest odpowiedni model materoiału, który następnie zostanie wykorzystany w symulacji. Obecnie mikrostruktura materiału wielofazowego nie jest brana pod uwagę, a w symulacjach procesów przeróbki plastycznej i elementów skończonych jest ona jednym z najważniejszych czynników wpływających na umocnienie materiału. Niniejsza praca przedstawia podejście opisujące rozwój mikrostruktury podczas etapu wyżarzania poprzez zastosowanie obliczeń modynamicznych oraz przewidujące efekt umacniania dwufazowej stali. Analizę prowadzono z zastosowaniem odpowiednich symulacji MES. Obliczone parametry wykorzystanezostaną w rzeczywistym procesie przeróbki.

15

An analysis of the evaluation of the fracture energy using the DCB-specimen

Biel A., Stigh U.

Archives of Mechanics

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2007

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Vol. 59, nr 4-5

311-327

EN

The methods to estimate the fracture energy using DCB-specimens as advocated in common standards. For instance, ASTM D 3433 and BS 7991:2001 are based on a compliance method, i.e. on linear elastic fracture mechanics (LEFM). Since the mechanical properties of almost all adhesives are non-linear, errors are generated. In some of the standards, the non-linear behaviour is compensated for by the use of correction terms generated from the experiments. An analysis of the methods of evaluation the fracture energy from experiments is performed. This analysis is performed first by simulating an experiment using realistic data for an engineering adhesive and then, by analysing the results with different methods. In this way, the correct fracture energy is known beforehand and the error in the evaluated fracture energy can be determined. In the present work it is shown that the magnitude of this error depends on the length of the crack. The results show that some commonly used methods generate substantial errors when a large region of non-linear deformation precedes the crack tip. It is also shown that methods based on nonlinear fracture methods do not produce this kind of error.

16

Symulacja MES i optymalizacja prędkości gięcia w procesie kucia ciężkich, jednolitych wałów korbowych z ciągłym przebiegiem włókien metodą N-TR

Zhang L. H., Zhang Z. C., Li S. Y., Cui H., Cui H. X.

Obróbka Plastyczna Metali

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2006

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T. 17, nr 2

3-13

PL

Autorzy przedstawili metodę N-TR (nowa TR) będącą nowym procesem kucia ciężkich, jednolitych wałów korbowych z ciągłym przebiegiem włókien. W metodzie N-TR mechaniczne sprzężenie spęczania z równoczesnym wyginaniem, spowodowane działaniem mechanizmu kolanowego w metodzie TR, zostało zlikwidowane dzięki zastosowaniu siłownika powodującego niezależne wyginanie, co umożliwia optymalizację procesu kucia. Przeprowadzono optymalizację procesu kucia ciężkiego wału korbowego typu 601 metodą N-TR korzystając z symulacji MES w programie DEFORM-3D. Badano związek stopnia wypełnienia wykrojów narzędzi z prędkością wyginania. Stwierdzono, że niższa prędkość wyginania na początku procesu i wyższa prędkość wyginania na końcu procesu sprzyjają wypełnieniu wykrojów. Uzyskano optymalne wypełnienie wykrojów narzędzi dla technicznie realnych prędkości wyginania.

EN

N-TR (new TR) is a new continuous grain flow forging process for solid heavy crankshafts forming proposed by the authors. In N-TR process, the mechanical coupling of upsetting and bending action via the toggle mechanism in TR process is decoupled by an independent additional cylinder to provide bending action, which provides the feasibility of process optimization. In this paper, a heavy crankshaft modeled 601 was selected as a case study to optimize the N-TR process with FE simulation in DEFORM-3D. Relationship of die filling versus bending speed-stroke parameters was set up from the simulations, which shows that lower bending speed in the beginning stage and higher speed in the ending stage benefit die filling. Optimum die filling and engineering feasible speed-stroke parameters was acquired.

17

Formability analysis of tube-hydroforming process

Chen F. K.

Applied Mechanics and Engineering

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1999

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Vol. 4, no 1

149-169

EN

A formability analysis for the tube-hydroforming process was investigated in the present study. The relationship between hydraulic pressure, outer corner radius of the deformed tube, the tube thickness and the tube yield stress was established based on a proposed theoretical model. Another theoretical model was also developed to calculate the die force generated in the tube-hydroforming process under frictionless condition. In order to validate the theoretical models developed, the two-dimensional finite element simulations were performed as well. The values predicted according to the proposed theoretical models are found to agree very well with those obtained from the finite element simulation results.