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Wyszukujesz frazę "Hedayati, R." wg kryterium: Autor


Wyświetlanie 1-5 z 5
Tytuł:
Low-velocity impact behaviour of open-cell foams
Autorzy:
Hedayati, R.
Sadighi, M.
Powiązania:
https://bibliotekanauki.pl/articles/949323.pdf
Data publikacji:
2018
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
open-cell foam
low-velocity impact
biomaterial
mechanical properties
Opis:
Metal foams are cellular solids that show some unique properties which cannot be found in other natural or human-made materials. While the impact characteristics of closed-cell foams under static and impact loadings appear to be well-studied in the literature, the impact behaviour of open-cell foams is not yet well-understood. In this study, open-cell foams with two different densities are impacted by drop weights with different kinetic energies. The effects of foam density, impactor initial height, and impactor weight on the recorded stresstime, stress-strain, and energy-strain curves are investigated. While the stress-strain curve of closed-cell foams under impact loading usually consists of a single bell, the results of the current study showed that both the stress-time and stress-strain curves of most the samples consist of two consecutive bells. By increasing weight of the impacting weight, the number of bells increases which helps in increasing the impact period and keeping the maximum generated stress low. Compared to closed-cell foams, the open-cell foams can therefore better absorb the energy, as long as the impact energy is relatively small. The relatively low stiffness as well as the presence of large hollow space inside the open-cell foams also makes them favorable for being used as biomedical scaffolds.
Źródło:
Journal of Theoretical and Applied Mechanics; 2018, 56, 4; 939-949
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A micromechanical approach to numerical modeling of yielding of open-cell porous structures under compressive loads
Autorzy:
Hedayati, R.
Sadighi, M.
Powiązania:
https://bibliotekanauki.pl/articles/949311.pdf
Data publikacji:
2016
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
rhombic dodecahedron
additive manufacturing
micro-structure
porous biomaterials
implant
finite element
Opis:
Today, interconnected open-cell porous structures made of titanium and its alloys are replacing the prevalent solid metals used in bone substitute implants. The advent of additive manufacturing techniques has enabled manufacturing of open-cell structures with arbitrary micro-structural geometry. In this paper, rhombic dodecahedron structures manufactured using SLM technique and tested by Amin Yavari et al. (2014) are investigated numerically using ANSYS and LS-DYNA finite element codes for the modeling of the elastic and postyielding behavior of the lattice structure, respectively. Implementing a micro-mechanical approach to the numerical modeling of the yielding behavior of open-cell porous materials is the main contribution of this work.One of the advantages of micro-mechanical modeling of an open-cell structure is that, in contrast to the macro-mechanical finite element modeling, it is not necessary to obtain several material constants for different foam material models through heavy experimental tests. The results of the study showed that considering the irregularity in defining the cross-sections of the struts decreases both the yielding stress and densification strain of the numerical structure to the values obtained from the experimental tests. Moreover, the stress-strain curve of the irregular structure was much smoother in two points of yielding and densification, which is also observable in experimental plots. Considering the irregularity in the structure also decreased the elastic modulus of the lattice structure by about 20-30%. The post-densification modulus was more influenced by irregularity as it was decreased by more than 50%. In summary, it was demonstrated that using beam elements with variable cross-sections for constructing open-cell biomaterials could result in numerical results sufficiently close to the experimental data.
Źródło:
Journal of Theoretical and Applied Mechanics; 2016, 54, 3; 769-781
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Prediction of static crack propagation in adhesive joints
Autorzy:
Hedayati, R
Jahanbakhshi, M
Ghorbani Khouzani, S
Powiązania:
https://bibliotekanauki.pl/articles/280484.pdf
Data publikacji:
2014
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
fracture
adhesive joint
debonding
APDL
LEFM
Opis:
In this work, fracture mechanics methodology is used to predict crack propagation in the adhesive joining of aluminum and composite plates. Three types of loadings and two types of glass-epoxy composite sequences: [0/90]2s and [0/45/-45/90]s are considered for the composite plate. Therefore 2 × 3 = 6 cases are considered and their results are compared. The debonding initiation load, complete debonding load, crack face profile and load-displacement diagram have been compared for the six cases.
Źródło:
Journal of Theoretical and Applied Mechanics; 2014, 52, 4; 937-946
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical and experimental study of the mechanical response of aluminum foams under compressive loading using CT data
Autorzy:
Mohammadi Nasrabadi, A. A.
Hedayati, R.
Sadighi, M.
Powiązania:
https://bibliotekanauki.pl/articles/281633.pdf
Data publikacji:
2016
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
metal foam
image processing
compression test
finite element method
CT scan
Opis:
Metal foams are relatively novel materials that due to excellent mechanical, thermal, and insulation properties have found wide usage in different engineering applications such as energy absorbers, bone substitute implants, sandwich structure cores, etc. In common numerical studies, the mechanical properties of foams are usually introduced to FE models by considering homogenized uniform properties in different parts of a foamy structure. However, in highly irregular foams, due to complex micro-geometry, considering a uniform mechanical property for all portions of the foam leads to inaccurate results. Modeling the micro-architecture of foams enables better following of the mechanisms acting in micro-scale which would lead to more accurate numerical predictions. In this study, static mechanical behavior of several closed-cell foam samples has been simulated and validated against experimental results. The samples were first imaged using a multi-slice CT-Scan device. Subsequently, experimental compression tests were carried out on the samples using a uniaxial compression testing machine. The CT data were then used for creating micro-scale 3D models of the samples. According to the darkness or brightness of the CT images, different densities were assigned to different parts of the micro-scale FE models of the foam samples. Depending on density of the material at a point, the elastic modulus was considered for it. Three different formulas were considered in different simulations for relating the local elastic modulus of the foam material to density of the foam material at that point. ANSYS implicit solver was used for the simulations. Finally, the results of the FE models based on the three formulas were compared to each other and to the experimental results to show the best formula for modeling the closed-cell foams.
Źródło:
Journal of Theoretical and Applied Mechanics; 2016, 54, 4; 1357-1368
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effect of regular physical activity on non-lipid (novel) cardiovascular risk factors
Autorzy:
Naghii, Mohammad R.
Aref, Mraryam A.
Almadadi, Mehdi
Hedayati, Mehdi
Powiązania:
https://bibliotekanauki.pl/articles/2185376.pdf
Data publikacji:
2011-12-01
Wydawca:
Instytut Medycyny Pracy im. prof. dra Jerzego Nofera w Łodzi
Tematy:
physical activity
non-lipid cardiovascular risk factors
cytokines
military personnel
Opis:
Objectives: Cardiovascular — coronary heart disease, causing heart attack and heart failure is a leading cause of disability and death worldwide. The most important risk factors for CVD are well-established and physical activity has long been considered the cornerstone of interventions and has shown extremely important in reducing the burden of this disease. The aim of this study was to examine the association between activity and inactivity and non-lipid CVD risk factors in healthy military recruits. Materials and Methods: Selected hormones and variables such as testosterone, free testosterone, Vitamin D, homocysteine, folic acid, with the inflammatory cytokines such as hsCRP, TNF-α and IL-6 were assessed in two groups (active = 50, inactive = 50), randomly matched by a questionnaire. Relationships between some measured variables and CVD risk factors were determined using simple correlation procedures. Results: Physically active subjects had signifi cantly lower results of homocysteine (14.3±1.9 vs. 16.5±3.7, p < 0.000) and interleukin-6 (2.9.±5.3 vs. 6±8.2, p < 0.025) and tended to have a nearly signifi cantly higher free testosterone level (13.1±7.1 vs. 11±5.3, p = 0.08). Signifi cant correlations were found between BMI, WC, tHcy, and the corresponding risk factors; and also between hsCRP and IL-6, as well as TT and FT. Conclusions: Reducing the risk factors of developing CVD events such as homocysteine and interleukin-6, together with increasing free testosterone and signifi cantly preventing its progression, clearly serve to underscore the benefi cial properties of physical activity and to promote its effectiveness as a support means for healthier lifestyles in the community and, particularly, among military personnel.
Źródło:
International Journal of Occupational Medicine and Environmental Health; 2011, 24, 4; 380-390
1232-1087
1896-494X
Pojawia się w:
International Journal of Occupational Medicine and Environmental Health
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-5 z 5

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