Effect of agitation speed on microencapsulation of healing agent in PMMA shell and study on the mechanical properties of epoxy/PMMA microcapsules

Ramin Jahadi,Hamid Beheshti,Mohammad Heidari-Rarani,Amir H Navarchian 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.27 No.6

In this study, the effect of agitation speed as a key process parameter on the morphology and particle size of epoxy-Poly (methyl methacrylate) (PMMA) microcapsules was investigated. Thus, a new interpretation is presented to relate between the microcapsule size to rotational speed so as to predict the particle size at different agitation speeds from the initial capsule size. The PMMA shell capsules containing EC 157 epoxy and hardener as healing materials were fabricated through the internal phase separation method. The process was performed at 600 and 1000 rpm mechanical mixing rates. Scanning electron microscopy (SEM) revealed the formation of spherical microcapsules with smooth surfaces. According to static light scattering (SLS) results, the average diameter size of the epoxy/PMMA capsules at two mixing rates were 7.49 and 5.11 μm for 600 and 1000 rpm, respectively, indicating that the mean size increased as the mixing rates of the process increased. The D₅₀, D₉₀ and mean particle size values were the lowest for hardener/PMMA microcapsules at 1000 rpm. Moreover, the Fourier transform infrared (FTIR) spectroscopy was conducted to describe the chemical structure of epoxy and hardener PMMA capsules. To investigate the reinforcing role of microcapsules, they embedded in EPL-1012 epoxy resin with various amounts of 1 and 2.5 wt.% epoxy/PMMA capsules. The investigation also involved the effect of microcapsules on mechanical behavior as well as the reinforcement of polymer composite material. Experimental results showed that the tensile strength of the self-healing polymer composite slightly increased by 1 wt.% PMMA microcapsules prepared at 1000 rpm and then reduced with an increase in the concentration and mean size diameter of PMMA microcapsules. In addition, a similar trend of Young's modulus was seen for pristine epoxy matrix and microcapsule-loaded epoxy composite.

Experimental study of collapse mode and crashworthiness response of tempered and annealed aluminum tubes under axial compression

Majid Emadi,Hamid Beheshti,Mohammad Heidari-Rarani,Farhad Haji Aboutalebi 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5

Thin-walled aluminum tubes have been widely used in engineering structures, aerospace and transportation industries due to their excellent properties. In this paper, the effect of tempering and annealing on the crushing behavior of aluminum alloy tubes, in brittle or ductile manner, under quasi-static compression were investigated. The chemical composition, the Brinell hardness number and the tensile stress-strain curves of various types of Al alloys, i.e., Al 2024, Al 7075 and Al 6061 were obtained in both tempered and annealed state. Then, the axial compression tests were performed on the tubes by a universal testing machine at a controlled displacement rate of 5 mm/min. The crushing mode, load-displacement curve, and crashworthiness characteristics were achieved to obtain specifications of mentioned aluminum tubes. Annealing process, apart from changing the deformation mode and material strength, has often reduced energy absorption in the ductile alloy, Al 6061, and increased in brittle alloys, Al 2024-T3, T4 and Al 7075-T651. This process could also be used as a triggering mechanism to decrease the initial peak force. These experimental results give useful information regarding the material behavior of aluminum alloys to be utilized in the design process of crashworthy components.

A comparative study for beams on elastic foundation models to analysis of mode-I delamination in DCB specimens

Mahmood Mehrdad Shokrieh,Mohammad Heidari-Rarani 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.2

The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus (E_fx) and out-of-plane extensional stiffness (E_z) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ([0˚]_6) and antisymmetric angle-ply ([±30˚]_5, and [±45˚]_5) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.

Experimental and analytical studies on one-way concrete slabs reinforced with GFRP molded gratings

Shokrieh Mahmood Mehrdad,Heidari-Rarani Mohammad 국제구조공학회 2009 Steel and Composite Structures, An International J Vol.9 No.6

Corrosion of steel rebars in bridge decks which are faced to harsh conditions, is a common problem in construction industries due to the porosity of concrete. In this research, the behavior of one-way concrete slabs reinforced with Glass fiber reinforced polymer (GFRP) molded grating is investigated both theoretically and experimentally. In the analytical method, a closed-form solution for load-deflection behavior of a slab under four-point bending condition is developed by considering a concrete slab as an orthotropic plate and defining stiffness coefficients in principal directions. The available formulation for concrete reinforced with steel is expanded for concrete reinforced with GFRP molded grating to predict ultimate failure load. In finite element modeling, an exact nonlinear behavior of concrete along with a 3-D failure criterion for cracking and crushing are considered in order to estimate the ultimate failure load and the initial cracking load. Eight concrete slabs reinforced with steel and GFRP grating in various thicknesses are also tested to verify the results. The obtained results from the models and experiments are relatively satisfactory.

Axial buckling response of fiber metal laminate circular cylindrical shells

Ali M. Moniri Bidgoli,Mohammad Heidari-Rarani 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.57 No.1

Fiber metal laminates (FMLs) represent a high-performance family of hybrid materials which consist of thin metal sheets bonded together with alternating unidirectional fiber layers .In this study, the buckling behavior of a FML circular cylindrical shell under axial compression is investigated via both analytical and finite element approaches. The governing equations are derived based on the first-order shear deformation theory and solved by the Navier solution method. Also, the buckling load of a FML cylindrical shell is calculated using linear eigenvalue analysis in commercial finite element software, ABAQUS. Due to lack of experimental and analytical data for buckling behavior of FML cylindrical shells in the literature, the proposed model is simplified to the full-composite and full-metal cylindrical shells and buckling loads are compared with the available results. Afterwards, the effects of FML parameters such as metal volume fraction (MVF), composite fiber orientation, stacking sequence of layers and geometric parameters are studied on the buckling loads. Results show that the FML layup has the significant effect on the buckling loads of FML cylindrical shells in comparison to the full-composite and full-metal shells. Results of this paper hopefully provide a useful guideline for engineers to design an efficient and economical structure.

A comparative study for beams on elastic foundation models to analysis of mode-I delamination in DCB specimens

Shokrieh, Mahmood Mehrdad,Heidari-Rarani, Mohammad Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.2

The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus ($E_{fx}$) and out-of-plane extensional stiffness ($E_z$) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ($[0^{\circ}]_6$) and antisymmetric angle-ply ($[{\pm}30^{\circ}]_5$, and $[{\pm}45^{\circ}]_5$) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.