نشریه علوم و فناوری کامپوزیت
سال یازدهم شماره 2 (پیاپی 40، تابستان 1403)

In this paper, an experimental investigation was conducted to study the ballistic properties of sandwich structures with fiber-metal laminate skins and reinforced syntactic foam core with carbon nanotubes. The syntactic foam was produced using epoxy resin and glass microballoon with volume fractions of 30%, 40%, and 55%. In addition, a series of reinforced samples was created using 40% volume fraction of microballoon and 4% multi-walled carbon nanotubes. The composite fiber-metal laminate skins on each side of the cores were made of one aluminum layer sheet and two layers of glass fiber reinforced polymer composite (GFRP). The structures were subjected to high-velocity impact tests using a gas gun and a conical head projectile. The results were analyzed to determine the effects of microballoon volume fraction and carbon nanotubes reinforced foam on the ballistic behavior of sandwich structures. The experiments showed that increasing microballoon volume fraction up to 40% decreased the projectile residual velocity and increased the ballistic limit velocity and penetration energy. Furthermore, reinforcing syntactic foam with carbon nanotubes significantly affected the ballistic properties of the structure.

In this research, the free vibration of poroelastic composite rectangular plates has been investigated considering Biot's theory of proelasticity and based on modified shear deformation theories. The governing equations of the vibration behavior of poroelastic composite rectangular plate are solved using the Galerkin method and with the help of Mathematica software, which results in obtaining dimensionless natural frequencies and the shape of vibration modes for poroelastic composite rectangular plates. In this study, modified theories of exponential, trigonometric, hyperbolic, parabolic and two high-order shear deformation theories have been used to approximate plate displacements, in which the effect of rotational inertia and transverse shear deformation have been considered. Biot's theory of poroelasticity has also been used to describe the relations governing poroelastic materials. The theories used in this study do not have the shortcomings of classical theories, and hence improve the static and dynamic responses. The innovation of the current study is the use of the theory of poroelasticity based on the theory of modified shear deformation and the solution of the governing equations using the Galerkin method. Three non-uniform symmetric, non-uniform asymmetric and uniform distributions are considered for porosity modeling and poroelasticity theory is used to investigate fluid behavior inside cavities. Also, the influences of different parameters including porosity coefficient, Biot’s effective stress coefficient, Skempton coefficient and length-to-width ratio have been investigated. To check the accuracy of the method used in this research, the numerical results were compared with the results in the references.

Due to the characteristics of thermoplastic composites, their use has received increasing attention. The present research proposes a novel micromechanics-based method for predicting the long-term creep behavior of thermoplastics reinforced with unidirectional continuous fibers (UD) and long fibers (LFT), such as carbon/PEEK and glass/polyethylene composites. Polyethylene and PEEK thermoplastic materials exhibit nonlinear viscoelastic properties, which are modeled using the four-element Berger's model. Experimental results have demonstrated that Berger's four-element model accurately predicts both the short-term and long-term behavior of thermoplastic polyethylene and PEEK matrices. Additionally, the behavior of glass and carbon fibers is considered elastic in this study. Using the micromechanical model of the bridging matrix, the influence of the nonlinear viscoelastic matrix on the long-term creep behavior of composites has been predicted and validated. A comparison of the modeling results with available experimental data shows a maximum difference of 12% in predicting the long-term creep behavior of thermoplastic composites reinforced with continuous fibers (UD) and a maximum difference of 10% in thermoplastic composites reinforced with long fibers (LFT).

Continuous ultrasonic welding is one of the new and very fast methods for joining thermoplastic composites, in which by using high power ultrasonic waves with a frequency of 20kHz and transferring it to the interface of the composite plates that have a certain overlap, the viscoelastic heat produced leads to the melting of the polymer and at the same time as the pressure is applied, the welding process of the composite plates in the desired direction is done continuously. In this research, the effect of three main parameters of this process, i.e., welding power, welding speed and pressure, on the lap shear strength of continuous ultrasonic welding is investigated by making glass-polyamide 6 composite plates and planning continuous ultrasonic welding experiments. To justify the effect of each parameter on the welding strength, The images of the fracture surface of the weld joint were used by optical and scanning electron microscopes. Finally, it was found that the power parameter has a direct relationship and the speed and pressure parameters have an inverse relationship with the lap shear strength of continuous ultrasonic welding glass-polyamide6 composite.additionally, power has the greatest effect and pressure has the least effect on weld strength.

In this research, the high-velocity impact behavior of sandwich structures with FML skins and glass fiber-reinforced syntactic foam core was conducted, experimentally. The syntactic foam was produced using epoxy resin and glass microballoon with 30%, 40%, and 60% volume fractions. The FML skins on each side of the cores comprised two layers of glass fiber-reinforced polymer composite (GFRP) and one aluminum layer sheet. In addition, a series of reinforced samples were created using 30% volume fraction of microballoon and 15% chopped glass fibers. The samples were subjected to high-velocity impact tests using a one-stage gas gun and a conical-head aluminum projectile. The results were used to investigate the effects of microballoon volume fraction and glass fiber-reinforced syntactic foam core on the high-velocity impact behavior of structures. The results showed that increasing the microballoon volume fraction from 20% to 30% decreased the projectile residual velocity and increased the ballistic limit velocity and penetration energy. Furthermore, reinforcing syntactic foam with glass fiber significantly affected the high-velocity impact behavior of the structure.

This research introduces a novel gradient honeycomb structure as an energy absorber inspired by the sunflower pattern. It evaluates and compares the crashworthiness parameters and deformation mode of this structure with traditional honeycomb structures. In this research, the effect of filling the honeycomb lattice structure with rigid polyurethane foam on energy absorption and structural strength is investigated. Initially, four types of honeycomb samples with dimensions of 70×70×70 mm were fabricated using an FDM 3D printer with polylactic acid (PLA) material. Subsequently, two-component polyurethane foam was injected into the space between the cells. Next, the samples were subjected to quasi-static compressive loading, and the force-displacement diagram obtained from the test was extracted. Finally, crashworthiness parameters such as energy absorption, specific energy absorption, and crushing force efficiency have been investigated. Experimental results demonstrated that the proposed sunflower-inspired honeycomb structure exhibited a 4% and 6% increase in specific energy absorption and crushing force efficiency, respectively, compared to traditional honeycomb structures in energy absorption applications. Additionally, the use of polyurethane foam in both conventional and sunflower-inspired honeycomb lattice structures led to a 16% and 10% increase in energy absorption and average crushing force, respectively, indicating increased strength and improved performance.