Mechanics of Composite Materials最新文献

A special case of the structural model of a hybrid composite multidirectional-reinforced in the plane was considered, which makes it possible to calculate the yield curve of a composite in the space of principal averageв stresses in a plane stress state (PSS). The composite contains an even number of reinforcing fiber families, which are divided into pairs of families. In each pair of the families, the fibers are made of the same material and are laid symmetrically with respect to the directions of principal stresses in the composite. The constituents of the reinforced composite are isotropic and have different tensile–compressive yield strengths. The mechanical behavior of composition constituents was described by the associated flow rule of an ideal rigid-plastic body with piecewise quadratic and piecewise linear yield curves in the space of principal stresses. The influence of approximation parameters of yield curves of composition constituents in the principal stresses and reinforcement parameters on the shape and dimensions of the yield curves of compositions was studied. It was demonstrated that the plastic flow in a fibrous medium is associated with the calculated yield curves of compositions.

The rapid growth in population, consumption, and economy have led to an increase in the extraction of natural resources, directly influencing the environment by generating waste and CO₂ emissions, particularly in the civil construction industry. The study aimed to evaluate the use of coarse and fragmented tire rubber waste, without chemical treatment, as a replacement for fine aggregate in geopolymeric mortar specimens. The central composite design, coupled with the response surface methodology, was used to determine the optimized values for compressive strength, water absorption, void index, and specific gravity. X-ray diffraction and scanning electron microscopy were used to characterize the geopolymeric mortar specimens. The optimized parameters for the best results were 1% replacement of fine aggregate with tire rubber waste, 0% coarse rubber, and approximately a 6-day curing time. This combination resulted in optimal values of 17.75 MPa for compressive strength, 10.48% for water absorption, 18.58% for void index, and 1.77 g/cm³ for specific gravity. The experimental validation of the models had an error of less than 10%.

The heterogeneous structure of polymer and aluminum alloy is an effective way to meet the dual technical indicators of structural performance and lightweight design. Friction stir welding (FSW) is a solid-phase welding technology characterized by low temperature and large plastic deformation. It is basically not affected by the crystal structure and physical-chemical properties of materials and can realize polymer and aluminum alloy-specific materials quality connection. This paper presents a comprehensive review of the current advancements in FSW between polymers and aluminum alloys with a focus on optimizing welding parameters, joint formation, defect identification, and mitigation. The results showed that the most important details are that high rotation speed combined with low welding speed that is beneficial to increase welding heat input, improve joint forming and mechanical properties, and form aluminum riveting structure. Welding defects are the main reason for the low FSW performance of polymer and aluminum alloy heterogeneous structures. To improve the forming and load-bearing capacity of heterogeneous structures, welding tool structure design, surface pretreatment, and welding structure optimization can be utilized.

Longitudinal wave propagation in axially graded nanotubes was explored. The effect of shear deformation and lateral inertia on nanorods was considered using the nonlocal Raylegh–Bishop rod theory. As a novel approach, a nonlocal parameter was assumed in the graded formulation. The higher order Haar wavelet method was utilized for solving the governing equation of motion. The effects of material grading power-law index and nonlocal parameters on the longitudinal wave response of axially graded nanorods were investigated. Phase and group velocity variations of the axially graded nanorod were obtained. The present study may be useful in the modeling of advanced functional composite nanowires.

The effect of glass fiber-reinforcement polymer Polyamide 66 on the uniaxial compressive mechanical response was measured over a wide strain-rate range from quasi-static tests with strain rate of 5×10^–3 s^–1 to impact tests with strain rate of 2×10³ s^–1. Dynamic compressive load was applied using a split Hopkinson pressure bar, whereas an electromechanical testing machine was used to carry out quasi-static experiments in displacement control to determine strain-rate sensitivity. The results demonstrate that strain rate significantly influences yield stress, post-yield behavior, and ductility of the two polymers under study. The yield stress experimental data are consistent with thermally activated processes.

An effective numerical analysis process was carried out to simulate an impact event based on the Hashin failure criterion and the Camanho degradation rule. The middle and shoulder of a cylinder were impacted by the edge of square-shaped impactors, and the remaining burst pressure was predicted. The accuracy of the numerical analysis was verified by results of two experiments that proved that the numerical analysis was reliable. The impact damage at different impact energies (20-200 J) was evaluated. According to the analysis carried out, the impact damage of gas cylinders intensified with increasing impact energy, and there existed a critical value of this energy. The damaged area of gas cylinders under the same impact energy first decreases and then increases from the inner to outer layer, and the maximum increase in the residual bursting pressure could reach 9.6%.

Tensile tests were carried out on carbon fiber high-entropy alloy, carbon fiber aluminum alloy, carbon fiber titanium alloy, and carbon fiber-reinforced composite laminates. Their mechanical properties were investigated at the tensile strain rates of 3·10^–3, 1·10^–3, and 1·10^–4 s^–1. Compression tests on carbon fiber high entropy alloy (HEA) and carbon fiber-reinforced composite laminates were carried out at the strain rates of 3·10^–3 and 1·10^–3 s^–1, respectively. Results showed that the carbon fiber high-entropy alloy composite laminate was more elastic than the carbon fiber-reinforced composite laminate at the strain rates of 3·10^–3, 1·10^–1, and 1·10^–4 s^–1. Their strength increased by 27, 16, and 10%, and the breaking strength by 18, 12, and 14%, respectively. Compared with the carbon fiber-reinforced composite laminate, the compressive strength of the carbon fiber HEA composite laminate increased by 44 and 29% at the compressive strain rates of 3·10^–3 and 1·10^–3s^–1, respectively.

A dynamic constitutive model of fiber-reinforced resin matrix composites considering temperature effect was proposed. It was used to predict the impact limit speed of composite laminates. High-speed bullet impact tests of fiber-reinforced resin matrix composite laminates were carried out at 25, 160, and 200°C, and the impact limit speed V_c was calculated using the test results. The test results showed that V_c of carbon-fiber-reinforced resin matrix composite laminates decreased with increasing ambient temperature. On this basis, a dynamic failure model of fiber-reinforced resin matrix composites was established considering the influence of ambient temperature. A VUMAT user subroutine was also developed to embed the failure model into the finite-element analysis software package. Then, the high-speed impacts of composite laminates at different temperatures were simulated numerically. The magnitude of V_c was predicted by the bisection method. A comparison of simulation results with test data showed that the error was smaller than 5%.

A novel generic workflow to predict homogenized material parameters of tensile behavior of a steel fiber-reinforced concrete (SFRC) using artificial neural networks (ANNs) was proposed. The neural network estimated the homogenized parameters of composite materials linked to finite-element (FE) models. An advantage of this approach is its flexibility in obtaining model parameters, which often have no physical interpretation. Moreover, the joint application of ANNs to estimate the model parameters and FE simulations to obtain the global mechanical behavior of SFRC is an innovation. An experimental database was constructed from the tests available in the literature and provided the ANN input data: the water-cement ratio, the fiber volume fraction, and the diameter and length of steel fibers. The outputs were Young’s modulus, the tensile strength, and the fracture energy of the composite. Three different networks were trained for each output dataset. The ANN configuration consisted of an input layer with four nodes and an output layer with one node. Blind tests with five experimental test sets checked the solution accuracy, presenting relative errors lower than 10%. Finally, a FE model of a direct tensile test was built, adopting the parameters obtained through the workflow. The load–displacement curve of the numerical solution showed a good agreement with the experimental curve, and peak–load errors were smaller than 5%.