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1
Content available remote Numerical simulation of non-linear loading– unloading hysteresis behavior of blood clots
Tashiro Koichiro, Shobayashi Yasuhiro, Hotta Atsushi
Biocybernetics and Biomedical Engineering
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2022
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Vol. 42, no. 4
1205--1217
EN
The stress-strain characteristics of a clot during loading/unloading mechanical cycles are significant features to assess the underlying mechanisms of thrombectomy, especially when multiple thrombectomy attempts are required. We investigated a damage model to predict loading/unloading response of clots. To study the validity of the model, we tested theoretical models to reproduce the experimentally obtained mechanical characteristics of clots under various conditions. Three types of clot analogs with different red blood cell (RBC) compositions were prepared. Cylindrical clot analogs were formed for the tensile and compression tests. Loading/unloading tests at 80% of strain were conducted, where the material parameters were determined by fitting the results to a theoretical curve combining the damage model and the elasto-plastic constitutive model. Through the computation for theoretical curves, unique characteristics of clots were revealed such that the hysteresis loss rate did not change by varying RBC contents, except for the clot created with 0% RBC composition, under compressive loading. In addition, the plastic strain decreased as the RBC content decreased under tensile loading, whereas it increased as the RBC content decreased under compressive loading. A three-dimensional finite element method (FEM) was employed with the determined parameters. The FEM could accurately reproduce the experimental stress-strain curves for all types of clot analogs and for both loading types up to a strain of 80%. The results indicate that the theoretical model which incorporates and combines the damage model and the elasto-plastic constitutive model is applicable to predict the non-linear stress–strain behavior of clots under loading and unloading.
2
Content available remote Numerical and experimental investigations on Mannesmann effect of nickel‑based superalloy
Zhang Zhe, Liu Dong, Man Tongchi, Li Nan, Yang Yanhui, Pang Yuhua, Wang Jianguo
Archives of Civil and Mechanical Engineering
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2022
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Vol. 22, no. 3
art. no. e133
EN
The preparation of nickel-based superalloy tubes by rotary tube piercing (RTP) process is still difficult due to the Mannesmann effect (central cracking phenomenon) has not been clarified. The combinations of numerical analysis and experiment verifications method were adopted in the study. The critical parameters for central cracking were determined by experiments. It was found that the evolution process of central cracking for nickel-based superalloy includes voids nucleation, growth and aggregation. Based on the obtained critical parameters, the evolutions of stress, strain, strain rate, temperature and damage were discussed by numerical simulation. By comparing the experiment results and simulation results, the Normalized Cockcroft and Latham (NCL) model was determined as the most suitable model. Considering the influences of temperature and strain rate on the damage threshold, the NCL model of Inconel 718 alloy was established by high-temperature tensile test. Based on the above results, it is found that the maximum shear stress promotes the plastic deformation, which provides necessary conditions for the generation of defects, and the maximum principal stress induces the generation of voids and expansion of micro-cracks, which directly leads to the central cracking. The essence of central cracking is ductile fracture under tensile stress.
3
Content available Mesoscale modeling of fracture in cement and asphalt concrete
Al-Jelawy Haider M., Al-Rumaithi Ayad, Fadhil Aqeel T., Naji Alaa J.
Przegląd Naukowy Inżynieria i Kształtowanie Środowiska
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2021
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Vol. 30, No. 3
439--450
EN
In this paper, mesoscale modeling is performed to simulate and understand fracture behavior of two concrete composites: cement and asphalt concrete using disk-shaped compact tension (DCT) tests. Mesoscale models are used as alternative to macroscale models to obtain better realistic behavior of composite and heterogeneous materials such as cement and asphalt concrete. In mesoscale models, aggregate and matrix are represented as distinct materials and each material has its characteristic properties. Disk-shaped compact tension test is used to obtain tensile strength and fracture energy of materials. This test can be used as a better alternative to other tests such as three points bending tests because it is more convenient for both field and laboratory specimens in addition to its accurate results. Comparing the numerical results of the mesoscale models of cement and asphalt concrete specimens with experimental data shows that these models can predict the behavior of these composite materials very well as seen in the curves of load-crack mouth opening displacement (CMOD). Also, the mesoscale modeling highlights the variability of crack direction where it is dependent on the random distribution of aggregate.
4
Content available A Pressure-Dependent Plasticity Model for Polymer Bonded Explosives under Confined Conditions
Wei Qiang, Huang Xi-cheng, Chen Peng-wan, Liu Rui
Central European Journal of Energetic Materials
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2021
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Vol. 18, no. 3
339--368
EN
The safety of explosives is closely related to the stress state of the explosives. Under some stress stimulation, explosives may detonate abnormally. It is of great significance to accurately describe the mechanical response of explosives for the safety evaluation of explosives. The mechanical properties of polymer bonded explosives (PBXs) strongly depend on pressure. In this study, the mechanical behaviour of PBXs under confined conditions was investigated. It was found that the stress-plastic strain response of a PBX under high confining pressures is a combination of the non-linear and linear hardening portions. However, the linear hardening portion has often been neglected in characterizing the mechanical behaviour of a PBX under such pressures. The Karagozian and Case (K&C) model was applied to characterize the mechanical behaviour of PBXs. The numerical results demonstrated that when the confining pressure was high, the K&C model could not adequately match the experimental data due to the limitation of the damage model. Therefore, a new damage model was developed by means of considering intragranular damage and transgranular damage. This modification made it possible to introduce a linear hardening process into the original K&C model. The method proposed to describe the stress-strain results under high confining pressures was to consider the stress-plastic strain curve, including the nonlinear and linear hardening portions. The damage evolution of the original K&C model and a linear hardening model were applied for the nonlinear and linear hardening portions respectively. The influence of the linear hardening model on the damage evolution of the original K&C model was included when describing the nonlinear hardening portion. A comparison between simulation and experiment showed that the modified K&C model could well describe the mechanical response of PBXs under different confining pressures.
5
Content available Seismic damage behaviour of aeolian sand reinforced concrete columns with I-shaped structural steel
Wang Y. H., Wang H. Y., Wang Y. P., Zhao M., Qi J., Huo G. Z., Liu P. Q.
Archives of Civil Engineering
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2020
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Vol. 66, nr 4
633--650
EN
To promote the application of aeolian sand resources for steel-concrete composite structures, an aeolian sand reinforced concrete column with I-shaped structural steel is proposed in this study. Four specimens are designed and manufactured with different replacement rates of aeolian sand. The seismic behaviour and damage evolution process of the specimens are studied by low-cycle repeated loading tests. Based on the test results, the mechanical characteristics, failure modes, hysteresis curves, skeleton curves, energy dissipation capacity, displacement ductility, and stiffness degradation of the specimens with different replacement rates of aeolian sand are analysed. In addition, the effects of the design parameters on the seismic behaviour of the specimens are also studied. The results show that the indexes of the seismic behaviour can be significantly improved by adding steel. Moreover, a revised damage model is proposed, to better reflect the evolution law of seismic damage of aeolian sand reinforced concrete columns with steel. The proposed model can provide an important reference for seismic damage assessment of the columns.
6
Content available remote Wpływ obciążenia śniegiem na konstrukcje drewniane w polskich regionach górskich
Domański T., Kmiecik K.
Materiały Budowlane
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2018
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nr 6
22--24
PL
Wartości parametrów mechanicznych drewna zmniejszają się w czasie pod wpływem działania obciążeń zewnętrznych. Redukcja nośności zależy od typu obciążenia i od klasy drewna. Ze względu na obciążenie długotrwałe, przy wysokich poziomach naprężeń, występują efekty redukcji wytrzymałości zwane pełzaniem. W artykule przedstawiono kalibrację współczynnika modyfikacji kmod za pomocą metod probabilistycznych. Pod uwagę wzięto trzy modele zniszczenia: Gerhardsa, Barretta-Foschi oraz Foschi-Yao. Parametry w tych modelach przyjęto zgodnie z metodą największej wiarygodności, wykorzystując dane istotne dla polskiego drewna konstrukcyjnego. Parametry obciążenia śniegiem zostały oszacowane na podstawie danych meteorologicznych. Dane zawierają obciążenie śniegiem polskich stref górskich: Zakopanego, Świeradowa i Leska z przeszło 45 lat. Do oceny niezawodności wykorzystano reprezentatywne stany krótko- i długoterminowe. Następnie dokonano estymacji współczynnika kmod dotyczącego polskich warunków górskich.
EN
The values of mechanical parameters of wood decrease in time under the influence of external loads. It depends on the type of load and timber. Due to long term loading at high stress ratio levels, there are strength reduction effects, referred to as creep-rupture effects. The paper presents the calibration of the modification factor kmod using probabilistic methods. Three damage accumulation models are considered: Gerhards, Barrett- Foschi and Foschi-Yao. The parameters in this models are fitted by the Maximum Likelihood Method using the data relevant for Polish structural timber. The snow load process parameters have been estimated based on Polish snow data over 45 years from mountain zones: Zakopane, Świeradów and Lesko. Representative short-and long-term states are used for evaluate the reliability. Then, the kmod coefficient was estimated for Polish mountain zones.
7
Content available remote The effect of aggregate characteristics on the fracture behaviour of fine-grained concrete under tensile loading
Skarżyński Ł., Tejchman J.
Architecture Civil Engineering Environment
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2012
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Vol. 5, no. 2
55-66
EN
This paper presents the effect of the aggregate characteristics on the fracture behaviour of fine-grained concrete under quasi-static three-point bending. Concrete was modelled as a random heterogeneous three-phase material. The 2D simulations for notched concrete beams were carried out with the finite element method using an isotropic damage constitutive model enhanced by a characteristic length of micro-structure by means of a non-local theory. The effect of the volume fraction, shape, size and statistical distribution of aggregate was analysed. The numerical results were compared with own laboratory test results and other meso-scale calculations for three-phase concrete elements.
PL
Artykuł przedstawia analizę wpływu kruszywa na zjawisko pękania drobnoziarnistego betonu podczas quasi-statycznego trzypunktowego zginania. Beton został opisany jako stochastyczny i niejednorodny materiał trzyfazowy. Dwuwymiarowe obliczenia numeryczne dla betonowych belek z nacięciem wykonano metodą elementów skończonych stosując izotropowy materiałowy model z degradacją sztywności rozszerzony o długość charakterystyczną mikrostruktury przy zastosowaniu teorii nielokalnej. Analizowano wpływ procentowej zawartości, kształtu, wielkości i rozkładu losowego ziaren kruszywa. Wyniki obliczeń numerycznych porównano z wynikami własnych badań laboratoryjnych oraz podobnych obliczeń numerycznych dla trzyfazowych elementów betonowych.
8
Content available Modelling of concrete behaviour with a non-local continuum damage approach
Bobiński J., Tejchman J.
Archives of Hydro-Engineering and Environmental Mechanics
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2005
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Vol. 52, nr 3
243-263
EN
The paper presents FE-results on the behaviour of concrete under plane strain conditions. The material was modelled using a simple isotropic damage continuum model. The model was enriched by non-local terms to avoid a pathological mesh-sensitivity and to obtain a well-posed rate boundary value problem. The constitutive model was used to simulate localization of deformation in 3 benchmark problems: a double-edge notched specimen under uniaxial tension and a notched beam under three- and four-point bending. Attention was laid on the effect of a characteristic length on the load-displacement curves and strain localization. The FE-results were compared with experiments and other numerical studies.
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