This paper presents an analytical solution for the thermomechanical buckling of functionally graded material (FGM) sandwich plates. The solution is obtained using a four-variable equivalent-single-layer (ESL) plate theory. Two types of sandwich plates are included: one with FGM facesheets and homogeneous core, and vice versa for the other. The governing equations are derived based on the principle of minimum total potential energy. For simply supported boundary conditions, these equations are solved via the Navier method. The results on critical buckling load and temperature increment of simply supported FGM sandwich plates are compared with the available solutions in the literature. Several results are presented considering various material and geometrical parameters as well as their effect on the thermomechanical buckling response of FGM sandwich plates. The relationship between the mechanical load and the temperature increment for uniform/linear temperature rise of FGM sandwich plates under combined mechanical and thermal loads is studied.

To contribute to the development of sustainable composites, this work investigates the effects of moisture on the key AE characteristics related to the damage mechanisms of a bio-based balsa wood core sandwich in 4-point bending tests, including cumulative counts, amplitude, peak frequency, and duration. Novel triple dog-bone balsa wood core sandwich specimens with different MC (moisture content) were studied by comparing microscopic observations and a proposed two-step clustering approach in AE analysis. Three MC states, i.e., dry, 50% MC, and 120% MC, are discussed. GFRP (glass-fiber-reinforced polymer) laminate skin damages were found to be predominant in most GFRP–balsa sandwich specimens, but balsa wood core damages play a more important role as MC increases. The degradation of the bending stiffness of the sandwich was proven to be faster in the first linear stage of the moisture absorption curve, while the decrease in bending strength was more pronounced at the MC saturation level. Finally, for all of the dry and wet sandwich specimens, peak frequency and duration were proven to be more helpful in identifying damages associated with the lighter bio-based balsa wood core, such as balsa core damages and skin/core debonding.

This article presents the results of research on sandwich materials manufactured by liquid resin infusion and designed to resist in low-velocity/low-energy impact applications. The sandwich plates are made of composites skins [glass fiber reinforced plastic (GFRP)] on a foam core. A manufacturing method was designed to produce samples in a one-shot process. Four manufacturing parameters were selected and combined: resin’s temperature, preform’s temperature, hardener type, and presence of nanoscaled additives. Their influences on the behavior of the samples during impact and the resulting damages were investigated. For each manufactured plate, nine samples were impacted with a 10 J drop-weight tower. Impacted samples were inspected with two nondestructive testing methods, visual inspection and infrared thermography. Samples were cut afterward to confirm conclusions and observe in-depth damages. Two impact behaviors and three damage types have been identified among all tested samples. The impact properties of the samples can be directly linked to the processing conditions. To ensure uniform mechanical properties, plates should be manufactured with isothermal conditions (same temperature in the preform and in the resin). If the manufacturing temperature is high enough, there is no significant influence on the impact behavior of the sandwich samples using slow or standard hardener. The higher the infusion temperature is, the more brittle the resulting composite. With nanoadditives in isothermal conditions, the resin’s viscosity is much higher, leading to a longer infusion and nonuniform properties.

Aiming at the low-speed impact load localization and vibration testing requirements of aerospace composite flexible structure, The Fiber Bragg Grating sensor network monitoring system is established. The increasing sampling technique is used to process the impact response signal, then the generalized cross-correlation delay estimation method is used to extract the time difference relationship between the sensor response signals. On this basis, the rapid identification of the impact position of the composite flexible structure is realized by considering the position information of the sensor comprehensively. The experimental results show that the area of six impact sample points and the specific coordinates of the location can be accurately identify respectively by this method. The average error of the coordinate positioning is about 3cm. The self-vibration mode and the natural frequency of the composite structure are achieved by using Fiber Bragg Grating sensor network monitoring system simultaneously. The finite element model of the composite structure with triangular section is established by using Patran. The natural frequency of the simulation is in good agreement with the experimental result, which proves that the Fiber Bragg Grating sensor has good vibration test performance.