Behzad Mohammadzadeh | Hongik University (original) (raw)

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Papers by Behzad Mohammadzadeh

AGU Fall Meeting Abstracts, Dec 1, 2019

Materials

This study presents a new ultra-high temperature composite fabricated by using zirconium diboride... more This study presents a new ultra-high temperature composite fabricated by using zirconium diboride (ZrB2), silicon carbide (SiC), and tantalum carbide (TaC) with the volume ratios of 70%, 20%, and 10%, respectively. To attain this novel composite, an advanced processing technique of spark plasma sintering (SPS) was applied to produce ZrB2–SiC–TaC. The SPS manufacturing process was achieved under pressure of 30 MPa, at 2000 °C for 5 min. The micro/nanostructure and mechanical characteristics of the composite were clarified using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and nano-indentation. For further investigations of the product and its characteristics, X-ray fluorescence (XRF) analysis and X-ray photoelectron spectroscopy (XPS) were undertaken, and the main constituting components were provided. The composite was densified to obtain a fully-dense ternary; the oxide pollutions were wiped out. The mean values of 23,356; 403.5 GPa; and 3100 °C wer...

Studies in the structural systems include two main approaches, design and analysis, which requir... more Studies in the structural systems include two main approaches, design and analysis, which require response evaluation of structures to the external loads including live and dead loads. Structures behave statically and dynamically for static and dynamic loads, respectively. One of the
most important dynamic loads acting on a structure is earthquake force. In order to find responses of structures subjected to earthquake, several schemes of direct integration can be used. This study deals with two methods of calculating dynamic responses of a single-degree of freedom oscillator, i.e., central difference method(CDM) and Newmark’s beta method(NBM), using recorded ground acceleration for 60seconds. The maximum relative acceleration is obtained to determine maximum
relative displacement by which estimation of quality and quantity of failure occurred to a structure for a given earthquake is provided. Firstly both CDM and NBM are discussed. Second, for a specific damping ratio dynamic responses are evaluated for periods of range in between 0.1sec to 1.5sec to evaluate the effects of period on responses of system. Third, the effects of damping on dynamic responses of SDOF system are evaluated by considering different damping coefficients from ζ=0 to
0.5. The results are compared and discussed to investigate the range of periods and damping factors where methods can provide a better estimation of responses.

To protect downstream of hydraulic structures against erosion and degradation must depress water ... more To protect downstream of hydraulic structures against erosion and degradation must depress water energy. one of the most common methods to achieve this purpose is constructing the
stilling basin at the downstream of such structures. In stilling basin, the water energy dissipated by taking place of hydraulic jump. When a hydraulic jump occurs, the hydrodynamic and hydrostatic forces effect on the stilling basin floor slab. These forces include the force due to water weight and the uplift force affected the slab below which these forces are classified under hydrostatic. also, the other force is hydrodynamic force due to pressure fluctuations below the hydraulic jump. To keep the stilling basin stability from lifting up and destruction must the resistant forces be equal to destroyer forces. In this study after discussion about the hydraulic jump and its resultant forces, an equation has been offered to determine the thickness of stilling basin floor slab using buckingham theory andsoftware DATAFIT. Finaly the slab which evaluated by physical model, simulated using mathematical model (software ANSYS 10) and studied. The stress and strain diagrams were extracted. Results showed that physical and mathematical models were matched very good.

Buckling analyses on plates with through-thickness holes are performed in order to find the buckl... more Buckling analyses on plates with through-thickness
holes are performed in order to find the buckling coefficient
which depends on the geometrical condition of individual
plates such as size of holes and thickness of plates. In order to
generalize the results, α is introduced. It is observed that the
buckling coefficient shows nonlinear trend in terms of the coefficient
α. The trend, however, is similar to each other for
plates with different thickness, having plateau region in the intermediate
values of alpha. The ratio of buckling coefficients
of plates with holes to that of the plates without holes is revealed
to be constant irrespective of the plate thickness. To
verify the generality of buckling coefficients, plates with different
dimensions from the original plates are analyzed. Buckling
stresses by using the suggested buckling coefficients show
good agreement with those obtained by numerical analyses
and errors are small enough to be ignored.

Buckling, a form of failure happened to plated structures, is investigated in this study. The mai... more Buckling, a form of failure happened to plated structures, is investigated in this study. The main focus is to investigate the effects of thickness of the plates having through-thickness holes on buckling when the plate is subjected to in-plane compression. Plates having length of 200mm and width of 100mm are chosen to have thickness in range from 0.50mm to 10mm. Two holes of diameters of 20mm are implemented in plates. The finite element procedure using ABAQUS is applied for analyses. Then using the Gerard and Becker equation compressive buckling coefficients, Kc, are calculated and presented to enable engineers to calculate buckling load for the desired plate with holes in specific dimension. In order to generalize the obtained results, verification analysis has been performed by taking plates having different dimensions from the original ones used in this study. The verification showed the capability of buckling coefficients to predict buckling stresses of plates in various dimensions.

Plate is one of the popular structural elements used in a wide range of industries and structures... more Plate is one of the popular structural elements used in a wide range of industries and structures. They may be subjected to blast loads during explosion events, missile attacks or aircraft attacks. This study is to investigate dynamic responses of the rectangular plate subjected to explosive loads. The effects of material properties and plate thickness on responses of the plate are to be investigated. The compressive pressure is applied to the surface of the plate. Different amounts of thickness in the range from 1mm to 30mm are considered for the plate to evaluate the changes in responses of the plate with respect to plate thickness. Two different properties are considered for the steel. First, the analysis is performed by considering only the elastic-plastic properties for the steel plate. Later on damping is considered to investigate its effects on the responses of the plate. To do analysis, numerical method using a finite element based package ABAQUS is applied. Finally, dynamic responses and graphs showing the relation between maximum displacement of the plate and aim parameters are provided.

This study involves an analytical approach to investigate the dynamic responses of plates subject... more This study involves an analytical approach to investigate the dynamic responses of plates subjected to blast and impulsive loads. Navier's approach was employed in order to obtain the equations for displacements and moments. The method validity was evaluated by making comparisons between the analytical and the numerical predictions of the plate time histories and the maximum displacement. A small discrepancy among the results proved the validity of the proposed analytical formulae. The effects of the plate aspect ratio, the thickness, and the charge weight on the plate deflection due to the blast loads were investigated by employing analytical and numerical approaches. The plate displacement changed linearly with respect to the charge weight, whereas it had a nonlinear variation for the plate thickness.

This study investigated the pull-out resistance of superelastic shape memory alloy (SMA) short fi... more This study investigated the pull-out resistance of superelastic shape memory alloy (SMA) short fibers in mortar with consideration of various end-anchorages that provide different anchoring actions. For the purpose, four types of SMA fibers were prepared using NiTi SMA wires with a diameter of 1.0 mm and the following four end shapes: straight (ST), L-shaped (LS), N-shaped (NS), and spearhead-shaped (SH). The straight-ended fiber was a reference with no working on the end, and the fiber with the spearhead-shaped end was crimped to make the end part flat. The fibers with Land N-shaped ends were bent with single or double bending. The results showed that only the spearhead-shaped fibers showed self-centering behavior because of the superelasticity of the SMA after slip occurred. This paper discusses the reasons that the ST, LS, and NS fibers do not show self-centering behavior and proposes a concept to induce superelastic behavior in SMA fibers in mortar or concrete.

Effect of superelastic SMA fibers end-shape on pullout resistance was investigated. Four end-shap... more Effect of superelastic SMA fibers end-shape on pullout resistance was investigated. Four end-shapes: straight end, L-shaped N-shaped, and crimped end were considered. Pullout test was done by displacement control to obtain hysteretic pullout behavior. Four cycling loadings were applied to each specimen during pullout test. a b s t r a c t This study investigated the effects of superelastic shape memory alloy (SMA) fibers end-shape on pullout resistance through hysteretic pullout testing. Superelastic NiTi SMA wire of 1.0 mm diameter was employed in manufacturing short fibers. SMAs were fabricated with four end-shapes: 1) prismatic and straight end, 2) L-shaped end, 3) N-shaped end, and 4) crimped end with a spearhead. The embedded length of a fiber into the mortar matrix having compressive strength of 50.0 MPa was 18.0 mm, except for the N-shaped end fiber for which the embedded length was 21.0 mm. The pullout test was conducted with displacement control to obtain hysteretic pullout behavior by four cycling loadings. The results showed that crimped-end fibers considerably magnified the pullout strength, and the deformation was recovered by their superelastic behavior. As N-shaped end fibers could not show flag-shaped behavior, another test was performed through which fibers were annealed to induce superelasticity, so, a perfect strain recovery was obtained. Results showed that additional annealing of the N-shaped fibers after the manufacturing improved superelastic behavior at the bended part.

A B S T R A C T This study assessed the performance of short fibers made of superelastic shape me... more A B S T R A C T This study assessed the performance of short fibers made of superelastic shape memory alloy (SE SMA) to close cracks in mortar beams. Four types of fibers were considered. Five types of cement mortar beams were manufactured. Four of these specimen types included superelastic SMA fibers such that each one was made with only one type of SMA fiber as well as steel bar, and the other specimen type was made with only a steel bar. The self-crack-closing capacity of the beams was investigated by comparing deflections upon loading and unloading through studying the post-cracking behavior. Results showed that the mortar beams resist flexural force until a crack is generated. Thereafter, the flexural load is sustained by the SE SMA fibers. Spearhead (SH) fiber provides the best self-centering behavior. A good crack recovery capacity cannot be achieved because there is a lake of flag-shaped behavior as the stress induced in the fiber does not hit the upper plateau stress due to fiber slip. The beam with only a steel bar showed a better recovery ratio than other types. For flexural crack control, a perfect bond between the SE SMA short fibers and the mortar matrix is needed to generate self-centering capacity.

An analytical approach is presented to investigate nonlinear dynamic responses of sandwich plates... more An analytical approach is presented to investigate nonlinear dynamic responses of sandwich plates. To obtain governing differential equations of motion, the higher order shear deformation theory is employed together with Hamilton’s principle. The Navier’s solution and Runge-Kutta method using available mathematical package software MAPLE 14 are used to solve the governing equations. This method can consider any required number of layers through the sandwich plate thickness. To evaluate the method validity a sandwich plate with FGM face sheets and the FRC core resting on an elastic foundation is subjected to the blast load due to the burst of 5 kg charge. The maximum plane-normal displacement is obtained by the analytical method and numerical approach. Comparison between results shows good agreement. Thereafter, time histories obtained from both analytical and numerical approaches are compared. The interlaminar stresses are obtained through the sandwich plate thickness. The results show
that neither material failure nor delamination occurs.

AGU Fall Meeting Abstracts, Dec 1, 2019

Materials