Sharif Digital Repository

The theoretical need to recognize the link between the basic microstructure of nonlinear porous materials and their macroscopic mechanical behavior is continuously rising owing to the existing engineering applications. In this regard, a semi-analytical homogenization model is proposed to establish an overall, continuum-level constitutive law for nonlinear elastic materials containing prolate/oblate spheroidal voids undergoing finite axisymmetric deformations. The microgeometry of the porous materials is taken to be voided spheroid assemblage consisting of confocally voided spheroids of all sizes having the same orientation. Following a kinematically admissible deformation field for a... 

Rapid prototyping is a promising technique for producing tissue engineering scaffolds due to its capacity to generate predetermined forms and structures featuring distinct pore architectures. The objective of this study is to investigate the influences of different pore geometries and their orientation with respect to the compressive loading direction on mechanical responses of scaffolds. Plastic models of scaffolds with cubic and hexagonal unit cells were fabricated by three-dimensional (3-D) printing. An in situ imaging technique was utilized to study the progressive compressive deformation of the scaffold models. In both cubic and hexagonal geometries, organized buckling patterns relevant... 

Today, structural Health monitoring is a major concern in the engineering community. Multisite fatigue damage, hidden cracks and corrosion in hard-to-reach locations are among the major flaws encountered in today's extensive diagnosis and/or prognosis of aircraft structures. Ultrasonic waves, lamb waves are particularly advantageous because of their propagation at large distances with little damp in thin-wall structures. In this paper a new rectangular shape array of embedded piezoelectric sensors is developed to detect some damages in large planar structures. An artificial neural network is trained to identify the damage state and its location. Output signals of each sensor due to various... 

In this paper, the fluid-structure interaction problem in mechanical systems in which a high frequency vibrating solid structure interacts with the surrounding fluid flow is considered. Such a situation normally appears in many microelectromechanical systems like a wide variety of microfluidic devices. A different implementation of the residual-based variational multiscale flow method is employed within the arbitrary Lagrangian-Eulerian formulation. The combination of the variational multiscale method with appropriate stabilization parameters is used to handle the so-called small time step instability in the finite element analysis of the fluid part in the coupled fluid-structure interaction... 

In this paper, the so-called small time-step instability in finite element simulation of the fluid part is considered in fluid-structure interaction (FSI) problems in which a high-frequency vibrating structure interacts with an incompressible fluid. Such a situation is common in many microfluid manipulating devices. A treatment has been proposed that uses the dimensionless set of FSI governing equations in order to scale up the problem time step to a proper level that precludes the potential small time-step instability. Two-dimensional and three-dimensional finite element simulations of a mechanical micropumping device are performed to verify the efficiency of the presented approach. Solid... 

A new design for a valveless micropumping device has been proposed that integrates two existing pumping technologies, namely, the wall induced traveling wave and the obstacle-type valveless micropump. The liquid in the microchannel is transported by generating a traveling wave on the channel, while the placing of two asymmetric trapezoid obstacles, along the centerline of the channel inlet and outlet, leads to a significant (up to seven times) increase of the net flow rate of the device. The effectiveness of this innovative design has been proved through a verified three-dimensional finite element model. FluidStructure Interaction (FSI) analysis is performed in the framework of an Arbitrary... 

Flow sensors play a critical role in monitoring flow parameters, including rate, velocity, direction, and rotation frequency. In this paper, inspired by biological hair cells in the human vestibular system, an innovative flow sensor is developed based on polyvinyl alcohol (PVA) hydrogel nanocomposites with a maze-like network of vertically grown graphene nanosheets (VGNs). The VGNs/PVA hydrogel absorbs a copious amount of water when immersed in water, making the sensor highly sensitive to tiny stimuli underwater. The sensor demonstrates a high sensitivity (5.755 mV (mm s−1)−1) and extremely low velocity detection (0.022 mm s−1). It also reveals outstanding performance in detecting... 

Flow sensors play a critical role in monitoring flow parameters, including rate, velocity, direction, and rotation frequency. In this paper, inspired by biological hair cells in the human vestibular system, an innovative flow sensor is developed based on polyvinyl alcohol (PVA) hydrogel nanocomposites with a maze-like network of vertically grown graphene nanosheets (VGNs). The VGNs/PVA hydrogel absorbs a copious amount of water when immersed in water, making the sensor highly sensitive to tiny stimuli underwater. The sensor demonstrates a high sensitivity (5.755 mV (mm s−1)−1) and extremely low velocity detection (0.022 mm s−1). It also reveals outstanding performance in detecting... 

Flow sensors play a critical role in monitoring flow parameters, including rate, velocity, direction, and rotation frequency. In this paper, inspired by biological hair cells in the human vestibular system, an innovative flow sensor is developed based on polyvinyl alcohol (PVA) hydrogel nanocomposites with a maze-like network of vertically grown graphene nanosheets (VGNs). The VGNs/PVA hydrogel absorbs a copious amount of water when immersed in water, making the sensor highly sensitive to tiny stimuli underwater. The sensor demonstrates a high sensitivity (5.755 mV (mm s−1)−1) and extremely low velocity detection (0.022 mm s−1). It also reveals outstanding performance in detecting... 

Forming limit diagrams (FLDs) are extensively used in industries, particularly the auto industry. The establishment of these diagrams using a predictive approach can lead to reduction in both cost and time. In the present work, Gurson-Tvergaard-Needleman (GTN), a porosity-based model, was used to predict the FLD of an interstitial-free steel via finite element simulation. Optimum values of the GTN model were obtained by applying a response surface methodology (RSM) based on central composite design. Results show that RSM is a good method for an appropriate determination of the GTN model parameters, such as initial void volume fraction, effective void volume fraction, critical void volume... 

Analysis and investigation of the relation between different parts of biological cells such as biomembrane, cytoplasm and nucleus can help to better understand their behaviors and material properties. In this paper, first, the whole elastic properties of mouse oocyte and embryo cells have been computed by inverse finite element and Levenberg-Marquardt optimization algorithm and second, using the derived mechanical properties and the mechanical properties of its bio membrane from the literature, the mechanical properties of its cytoplasm has been characterized. It has been assumed that the cell behavior is as continues, isotropic, nonlinear and homogenous material for modeling. Matching the... 

In order to better understand the mechanical properties of biological cells, characterization and investigation of their material behavior is necessary. In this paper hyperelastic Neo-Hookean material is used to characterize the mechanicalproperties of mouse oocyte cell. It has been assumed that the cell behavior is continues, isotropic, nonlinear and homogenous material. Then, by matching the experimental data with finite element (FE) simulation result and using the LevenbergâMarquardt optimization algorithm, the nonlinear hyperelastic model parameters have been extracted. Experimental data of mouse oocyte captured from literatures. Advantage of the developed model is that it can be used to... 

In this paper seven different multiaxial fatigue criteria based on stress, strain and energy were employed to estimate the fatigue lives of double shear lap joint specimens of aluminum 2024-T3 with bolt clamped and interference fitted-bolt clamped fastener holes. Detailed finite element (FE) simulations were conducted to obtain the stress and strain distributions in the joint to be used to as basic data in estimating the fatigue lives using multiaxial fatigue criteria. The estimated lives were compared with available experimental fatigue test results to investigate the capability of the criteria in predicting the fatigue lives. The results showed that the accuracy of life estimation for any...