Yazar "Choupani, Naghdali" seçeneğine göre listele

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    A finite element approach for addressing the interphase modulus and size interdependency and its integration into micromechanical elastic modulus prediction in polystyrene/SiO2 nanocomposites
    (Elsevier Sci Ltd, 2024) Soudmand, Behzad Hashemi; Biglari, Hasan; Fotouhi, Mohammad; Seyedzavvar, Mirsadegh; Choupani, Naghdali
    The perturbed transitional area between the nanoparticle and matrix shapes the properties of polymer nanocomposites. Due to the stochastic nature of these interphase regions, their size and physical properties are intricately linked. For instance, a higher interphase modulus, Eint, might result from a thinner interphase, and vice versa. The inherent randomness can introduce variability in the interphase modulus with respect to interphase thickness, tint. This challenges the practicality of conventional micromechanical approaches, which assume the interphase modulus to be either a constant or a function of filler and matrix properties when predicting the elastic modulus of polymer nanocomposites. Unlike conventional approaches, which simply used interphase quantification to predict global stiffness and treated the interphase modulus independently of its thickness, this study aims, for the first time, to consider the stochastic nature of the interphase, seeking to exclusively explore the interdependencies within the Eint - tint relationship in polystyrene/SiO2 nanocomposites. Simulations were conducted using finite element analysis, FEA, providing high accuracy and flexibility. To manage the large number of simulations, FEA was streamlined with a customized Python scripting, generating a spectrum of (Eint, tint) solutions for varying SiO2 contents based on experimental measurements and a rigorous methodology. Subsequently, empirical equations were formulated, unveiling the relationship between Eint and tintper composition. The FEA-driven interphase intercorrelation scheme was compared to the results obtained from a modified three-phase Halpin-Tsai model. Additionally, the FEA scheme was utilized to modulate the HT model by adjusting its relevant interphase terms.
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    Assessing the safety and reliability of type-3 high-pressure composite tanks: a comprehensive analysis of failure metrics
    (Springer India, 2024) Avcu, Adem; Seyedzavvar, Mirsadegh; Boga, Cem; Choupani, Naghdali
    Pressure tanks play a pivotal role in various industrial applications, serving as vessels for the storage of gases under different pressures and environmental conditions. The burgeoning interest in hydrogen gas as a clean energy source has necessitated a comprehensive assessment of pressure tank structural integrity, particularly under high-pressure demands exceeding 700 bar. In this study, we systematically investigate the influence of different aluminum alloys, including AL6061, AL7075, and AL7178, reinforced with various fiber/epoxy composite materials. Our primary objective is to identify the optimal combination of liner and composite materials, along with the number of composite layers and fiber winding orientations that minimize distortion energy within the tank's liner and composite layers while maximizing safety factors. Our results indicate that distortion energy decreases as the fiber angle increases from zero to 75 degrees, with the ideal fiber orientation angle shifting with the number of composite layers. The lowest distortion energy levels in the liner were achieved in composite tanks comprising 60 laminates of reinforcing composite material, wound at an orientation angle of [+/- 55 degrees/90 degrees]. Across various internal pressure levels, pressure tanks reinforced with boron/epoxy composite material consistently outperformed other fiber materials. In terms of aluminum liner materials, AL6061 exhibited a remarkable 10.5% reduction in distortion energy on average when compared to AL7075. Safety indices revealed that pressure tanks reinforced with aramid/epoxy composite material provided the highest level of reliability, particularly when applying the maximum principal stress criterion. Carbon/epoxy and graphite/epoxy composites followed closely. In contrast, glass/epoxy and Kevlar/epoxy composites did not meet the stringent safety requirements for high-pressure storage tanks. These findings offer invaluable guidance for designing high-pressure composite tanks, ensuring their structural integrity and safety when storing hydrogen gas at elevated pressures, and exemplify the importance of materials and design considerations for such critical applications.
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    Characterizing the effects of liner and fiber-reinforced resin composite shell on fracture energy in type-III high-pressure composite tanks
    (Springer Heidelberg, 2024) Avcu, Adem; Seyedzavvar, Mirsadegh; Boga, Cem; Choupani, Naghdali
    The increasing adoption of fuel-cell vehicles, driven by their environmentally friendly zero-emission features, is a crucial step towards reducing environmental damage. However, current research primarily focuses on stress-related aspects of pressurized tanks, leaving a critical knowledge gap regarding potential fractures within the tank's body, which can accelerate pressure tank failure. This study aims to address this concern by analyzing alternative fiber materials beyond carbon fiber in a finite element analysis model, with the primary objective of enhancing the durability of pressurized tanks for hydrogen-fueled vehicles against fracture loading. The investigation revolves around the fracture behavior of type-III high-pressure composite tanks, pivotal components for the secure operation of hydrogen-powered fuel cell vehicles. Various configurations of Al6061 and Al7178 liners coupled with six distinct fiber materials and six different winding orientations [(+/- 15/90)n]T, (+/- 30/90)n, [(+/- 45/90)n]T, [(+/- 55/90)n]T, [(+/- 60/90)n]T, and [(+/- 75/90)n]T have been meticulously assessed to provide an in-depth analysis of fracture energy behavior in composite tanks. The stress intensity factor (GI) was computed using a compact tension model developed in Abaqus, for all composite variations under consistent conditions, providing a robust foundation for understanding the fracture behavior. Additionally, MATLAB was utilized to calculate the effective elastic modulus for the selected composite materials. Subsequently, the strain energy release rate was derived from the relationship between the GI and the effective elastic modulus of composite tanks. The derived GI revealed notable improvements in fracture resistance for specific composite shells and liner materials, particularly at higher winding orientations. The results emphasized the superior performance of boron-epoxy composite shells for type-III pressure vessels, exhibiting the lowest GI values and exceptional crack resistance. Notably, Al7178 combined with boron-epoxy outperformed Al6061 composites at higher winding orientations, while glass-epoxy shells exhibited greater susceptibility to crack propagation, especially in specific ply orientations.
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    Evaluation of recycled Al-LDPE-Al sandwich panels as ballistic protection material
    (Ice Publishing, 2020) Torun, Ahmet Refah; Kaya, Seyma Helin; Choupani, Naghdali
    Metal-polymer-metal hybrid sandwich panels are gaining importance in civil, automotive and aerospace applications due to their light weight and damping properties. Compared with composite materials, hybrid materials consisting of separate metal and thermoplastic parts can be recycled much more easily. Besides their applications as covering material on buildings as well as general insulation material, recycled aluminum (Al)-low-density polyethylene (LDPE)-aluminum hybrid panels yield a potential usage of light ballistic protection. In this study, a standard hybrid panel of 3.2mm polyethylene filling and two 0.4mm aluminum metal sheets was experimentally tested under ballistic impact. A finite-element model was used with a commercial software program and validated against the experimental results. The finite-element results show that stacking of multiple layers of panels absorbs more energy than an equivalent single-layer panel. Six layers of stacked hybrid aluminum-LDPE-aluminum panels are capable of absorbing the impact energy of a 9mm pistol projectile, and they can be utilized as recyclable inexpensive ballistic protection materials.
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    Experimental investigation and numerical analysis: fracture mechanics and microstructural development in Ni55.8Ti superalloy under mixed-mode loading at different temperatures
    (Springer, 2022) Seyedzavvar, Mirsadegh; Boga, Cem; Choupani, Naghdali
    Shape memory alloys (SMAs) and specifically NiTi superalloys have gained significant attention in different industries for their excellent mechanical properties and superior material characteristics including processability, corrosion resistance, cyclic stability and bio-compatibility. Static and dynamic properties of NiTi SMAs, mainly under tensile loadings, have been widely evaluated in pseudoelastic and pseudoplastic states in many studies. However, there is a gap in the literature concerning the fracture failure of these materials under mixed-mode loadings, as these types of loadings are responsible for the most of the material failures in practical applications. This study is aimed at investigating the fracture toughness and microstructure of NiTi ASTM F2063 shape memory superalloy under mixed-mode fracture conditions and various temperatures, ranging from below the A/M phase transformation temperature to above the temperature at which the material behaves pseudoplastically. The material has been characterized using differential scanning calorimetry (DSC) and uniaxial tensile test apparatus under varying temperature to determine the mechanical and metallurgical characteristics before the mixed-mode fracture experiments. The fracture tests have been conducted using a tensile test machine equipped with a temperature control chamber and an in-lab developed special fixture to make the application of mixed-mode loading on a butterfly shaped specimen, known as Arcan sample, feasible. X-ray diffractometry and fractography using scanning electron microscope have been conducted to characterize the mechanism of failure and development of microstructure under different loading modes and temperatures. Finite element analyses were conducted to determine the fracture toughness and strain energy release rate of NiTi superalloy at different loading conditions.
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    Fracture characteristics of mixed-mode toughness of dissimilar adherends (cohesive and interfacial fracture)
    (Taylor & Francis Ltd, 2020) Abadi, Ramak Hossein; Torun, Ahmet Refah; Fard, Arash Mohammadali Zadeh; Choupani, Naghdali
    This paper investigates the fracture behavior of aluminum/polymer dissimilar adhesively bonded joints at different mixed-mode ratios. For this purpose, a series of experiments were carried out using a modified Arcan fixture to obtain critical fracture load in mode I, mode II and mixed-mode, for two types of cohesive and interface starter cracks. Experimental data, along with the Virtual Crack Closure Technique (VCCT) were employed to extract the strain energy release rates. The average values of strain energy release rates were found and for cohesive cracks, and and for interface cracks. Considering the relations between the strain energy release rate and the stress intensity factor, and were also calculated for cohesive and interface starter cracks.
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    Fracture characterization and modeling of Gyroid filled 3D printed PLA structures
    (Walter De Gruyter Gmbh, 2021) Torun, Ahmet Refah; Dike, Ali Sinan; Yildiz, Ege Can; Saglam, Ismail; Choupani, Naghdali
    Polylactic acid (PLA) is a commonly used biodegradable material in medical and increasingly in industrial applications. These materials are often exposed to various flaws and faults due to working and production conditions, and increasing the demand for PLA for various applications requires a full understanding of its fracture behavior. In addition to ABS, PLA is a widely used polymeric material in 3D printing. The gyroid type of filling is advantageous for overcoming the relatively higher brittleness of PLA in comparison with conventional thermoplastic polymers. In this study, the effects of various filling ratios on the fracture toughness of 3D printed PLA samples with gyroid pattern were investigated numerically and experimentally for pure mode I, combined mode I/II, and pure mode II. Two-dimensional finite element modeling was created, and the two-dimensional functions of stress intensity coefficients were extracted in loading mode I, mode I/II, and mode II at varied filling ratios of the gyroid PLA samples. Mixed-mode fracture tests for 3D printed PLA samples with a gyroid pattern at various filling ratios were performed by using a specially developed fracture testing fixture. The results showed that the amount of fracture toughness of the samples under study in tensile mode was much higher than those values in shear mode. Also, as the percentages of the filling ratios in the samples increased, both tensile and shear fracture toughness improved.
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    Fracture characterization of bonded composites: A comparative study
    (Growing Science, 2022) Choupani, Naghdali; Torun, Ahmet Refah
    Bonded joints have important benefits over conventional joining techniques such as rivets, welding, bolts and nuts in structural applications, particularly for components prepared of composite or polymeric materials. Due to the involvement of many geometric, material and construction variables, and the complex fracture and mechanical modes offered in the bonded joints, a proper consideration of fracture behavior is required to fully achieve their benefits. The fractures in bonded joints are mainly of three types; interlaminar (delamination), adhesive (interfacial) and cohesive crack. For a particular defect, crack propagation may occur in the tensile (mode I), the shear (mode II), and the tear (mode III) and their combinations (mixed mode). This study deals with topics such as theories of bonded composite joints and repairs, finite element analysis and fracture-based analysis and tests of mixed-mode cohesive, interfacial and interlaminar fracture mechanics. By employing geometrical factors extracted from finite element analysis and experimental results obtained from a modified Arcan test fixture, the mixed-mode cohesive, interfacial, and interlaminar fracture toughness are determined and fracture surfaces obtained are discussed. © 2022 Growing Science Ltd. All rights reserved.
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    Fracture Toughness Assessment of Longitudinally Seam-Welded Gas Pipelines at Low Temperatures
    (Asce-Amer Soc Civil Engineers, 2020) Yengejeh, Ehsan Alipour; Torun, Ahmet Refah; Khajedezfouli, Mohammadreza; Choupani, Naghdali
    American Petroleum Institute (API) 5L X65 and X70 steel pipelines are employed widely for natural gas transportation and typically experience internal high transmission pressures and low temperatures in cold regions. Investigations show that in spite of strict inspections and controls, welding joints are commonly subjected to the presence of defects, with cracking being the most important one. Due to the many geometrical, material, and manufacturing variables involved, the failure mechanisms and procedures presented in the welded gas pipelines are complex. In order to achieve the benefits of gas pipelines, a deep understanding of the failure behavior is needed, especially in mixed mode loading conditions and at low temperatures. In this work, fracture toughness evaluation of longitudinal seam-welded gas transportation pipes at low temperatures and under mixed mode loading was studied based on experimental and numerical analysis. The experimental procedure included preparing the API X65 steel pipes, making the butterfly shaped experimental specimens, and encapsulating and insulating specimens in order to control and stabilize the temperature of test. By utilizing the Arcan fixture, the experiments carried out under different loading conditions at low temperatures and fracture forces by using force-displacement diagrams were obtained. Stress intensity factors (SIFs) for tensile and shear loading were found by numerical analysis and geometry correction factors were determined. The results indicated that the fracture toughness of the seam-welded samples decreased at lower temperatures, and it is strong to the tensile mode loading but weak to the shearing mode loading. The tensile and shear values of fracture toughness of seam weld under consideration for the temperature of -25 degrees C were found 203.3 and 11.8 kJ/m(2), respectively. (c) 2020 American Society of Civil Engineers.
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    Mixed-mode fracture behavior of 3D-printed PLA with zigzag filling
    (Ice Publishing, 2021) Torun, Ahmet Refah; Yildiz, Ege Can; Kaya, Seyma Helin; Choupani, Naghdali
    Polylactic acid (PLA) is a widely used biomaterial in medical applications as a biodegradable and renewable aliphatic polyester type of material. This material is often subjected to different defects and damages from in-service and manufacturing conditions, and the increasing demand for PLA for different applications requires a thorough understanding of its fracture behavior. In this work, a numerical and experimental study of the mixed-mode fracture behaviors of three-dimensional (3D)-printed PLA samples with a zigzag pattern of different filling ratios was performed using a recently developed special loading fixture. The 3D-printed samples were produced with a 200 degrees C nozzle at 60 degrees C bed temperature and 50mm/s printing speed. Mixed-mode fracture tests from pure tensile to pure shear loading were performed by varying the loading angle, alpha, from 0 to 90 degrees. Finite-element analyses were conducted by using the Abaqus software program, and geometrical factors were obtained at different loading angles. As a result, the fracture toughness values of pure tensile loading, pure shear loading and mixed modes were determined.
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    Oblique impact behavior of Al-LDPE-Al sandwich plates
    (Walter De Gruyter Gmbh, 2020) Kaya, Seyma Helin; Karaoglu, Furkan Nuri; Saglam, Ismail; Choupani, Naghdali; Torun, Ahmet Refah
    Metal-polymer-metal hybrid sandwich panels are gaining importance in various industrial applications due to their light weight and damping properties. When compared with composite materials, hybrid materials consisting of separate metal and thermoplastic parts can be recycled more easily. In addition to their applications in civil engineering, the aluminum-low density polyethylene-aluminum (Al-LDPE-Al) sandwich panels yield a potential use as light ballistic protection material. In this study, a standard hybrid panel of 3.2 mm polyethylene filling and 0.4 mm of two aluminum metal sheets was experimentally tested under ballistic impact. A finite element model was constructed via commercial software and validated through shooting experiments with a rifle under real conditions. The finite element model was used to simulate the oblique impact behavior of Al-LDPE-Al sandwich panels as a single layer, as 5 layers stacking and as a single layer equivalent of the stacked 5 layer. Results showed that the oblique impact does not have a significant effect on the single layer panel. Stacked layers, however, and the equivalent single layer of a stacked layer have the highest energy absorption under a 30 degrees hitting angle.