http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Amer Darvishvand,Asghar Zajkani 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
Present study investigates a comparative study of lower and higher-order strain gradient plasticity (SGP) theories involvingthe size-dependent micromechanically flexural behaviors of crystalline thin plates. The investigation includes the Mechanism-Based and the Chen–Wang SGP models established on the Taylor dislocation hardening by evoking the statistically storeddislocations and geometrically necessary dislocations. In addition, these models are conjugated with a multiple plasticwork-hardening law proposed for the microstructural applications of the SGP. An analytical approach based on energyminimizing method is used for obtaining deflection values in terms of the length scale, exponent of the work-hardening andthe tangential module. The obtained results indicate a meaningful dependence of the deflections to the length scale, plasticwork hardening and other parameters as well.
Amer Darvishvand,Asghar Zajkani 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.3
Since the actuators with small- scale structures may be exposed to external reciprocal actions lead to create undesirable loads causing instability, the buckling behaviors of them are interested to make reliable or accurate actions. Therefore, the purpose of this paper is to analyze plastic buckling behavior of the micro beam structures by adopting a Conventional Mechanism-based Strain Gradient plasticity (CMSG) theory. The effect of length scale on critical force is considered for three types of boundary conditions, i.e. the simply supported, cantilever and clamped - simply supported micro beams. For each case, the stability equations of the buckling are calculated to obtain related critical forces. The constitutive equation involves work hardening phenomenon through defining an index of multiple plastic hardening exponent. In addition, the Euler-Bernoulli hypothesis is used for kinematic of deflection. Corresponding to each length scale and index of the plastic work hardening, the critical forces are determined to compare them together.
Vakil Saeed,Zajkani Asghar 한국물리학회 2023 Current Applied Physics Vol.48 No.-
A self-consistent higher order couple stress model is based on Fleck - Hutchinson Strain Gradient Plasticity to consider flexural behavior of brittle - ductile microscale structures. The dual phasic functionally graded material made of Titanium-boride/Titanium structure is modeled by defining a material flow stress which reflects a parameter of combined effective length scale, dependent on Geometrically Necessary Dislocations. The dual phasic crystalline micro-beam is built with the properties having continuously and non-linearly variation along the thickness. The perfectly plastic behavior of micropolar functionally graded material is described by incorporating a ductile –like mixture law, so-called TTO model, possessing a simple possibility of transition through defining a graded phase acting as an equilibrium mixed phase. Further, the effects of the elastic foundation and temperature rise on the plastic deformations are investigated. While an energy method is used to derive governing equations, the obtained results are verified individually in three steps.
Peyman Rashidpour,Majid Ghadiri,Asghar Zajkani 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.3
The present research aims to analyze the response of viscoelastic laminated composite microplate under microparticle low-velocity impact. Hertz contact law is used to model the impact phenomenon between the microparticle and the microplate. According to Kelvin-Voigt theory, the realistic behavior of the structure is considered by considering the viscoelastic properties. The governing equations of the system are derived based on the first-order shear deformation plate theory (FSDT) and the nonlocal strain gradient theory (NSGT) by employing Hamilton’s principle. Galerkin’s method is employed to solve differential equations of microplate with different boundary conditions. Afterward, the system of time-dependent equations by applying the Newmark’s method is solved. The parametric study is presented to examine the effect of particle radius, particle initial velocity, nonlocal parameter, length scale
Masir, Amin Nouroozi,Darvizeh, Abolfazl,Zajkani, Asghar Techno-Press 2018 Advances in materials research Vol.7 No.3
The mechanism of biological materials structure is very complex and has optimal properties compared to engineering materials. Top Neck mollusks shells, as an example of biological materials, have hierarchical structure, which 95 percent of its structure is Aragonite and 5 percent organic materials. This article detected mechanical properties of the Top Neck mollusks shell as a Nano composite using Nano-indentation method in different situations. Research findings indicate that mechanical properties of the Top Neck mollusks shell including elastic modulus and hardness are higher than a fresh one preserved in -50 centigrade and also a Top Neck mollusks shell preserved in environmental conditions. Nano-indentation test results are so close in range, overall, that hardness degree is 3900 to 5200 MPa and elastic modulus is 70 to 85 GPa.