This paper presents experimental results from three-point bending tests for a composite made of quadriaxial glass fiber fabrics and an epoxy resin. Two composites were tested, one with 8 layers and the other with 16 layers; both had the same matrix (the epoxy resin). Tests were carried out, using five different test rates from 10 mm/min to 1000 mm/min. The following parameters were recorded and calculated: Young’s modulus, flexural stress, flexural strain, energy, force, and all four for the first peak. The experimental data reveal no sensitivity for these materials based on the test rates, at least for the analyzed range; but, the characteristics for the thicker composite, with 16 layers of fabric, are slightly lower than those for the thinner composite, with 8 layers. The results pointed out that, for the same thickness of composite, certain characteristics, such as stress at the first peak, the flexural modulus, strain at the first peak, and energy at the first peak, are not sensitive to the test rate in the range 10–1000 mm/min. The energy at the first peak is double for the 16-layer composite compared to the 8-layer composite, but the specific energy (as energy on cross-sectional area) has close values: 103.47 kJ/m² for the 8-layer composite and 106.51 kJ/m² for the 16-layer composite. The results recommend this composite for applications in components with resistance to bending or for low-velocity impact protection.

In this study, the composition and mechanical properties of composites designed for shipbuilding are described. Four different composites were designed and fabricated by the research team, using quadriaxial glass fiber fabric (eight layers in all composites), two different resins (the epoxy resin SikaBiresin^® CR82 with the hardener CH80-2 or the polyester resin Enydyne H 68372 TA with Metox-50 W as the accelerator), and a middle layer of Coremat Xi 3 (only applied in some composites). The experimental results of low-velocity impact tests are also discussed, including the graphics force (displacement) and absorbed energy (displacement and velocity). The displacement and composite quality were evaluated through several parameters, such as maximum force, absorbed energy, and maximum displacement. Impact tests were carried out using four impact energy values (50–200 J), with an average impact velocity in the range of 4.37 ± 0.05 m/s. Only partial penetrations were obtained for all tested composites. For the low energy tests (50 J), the four composite materials were not well differentiated by graph shapes and parameter values, but for the higher energy tests, the composites containing Coremat Xi 3 displayed better behavior, having F_max reduced with 10.8% to 29.08%. The higher absorbed energy of these composites can be explained by the plateau generated by the force from a longer impactor displacement in contact with the composite. The results generated in this study confirm the suitability of the designed composites for shipbuilding applications. Still, the composites have light differences in terms of energy absorption in low-velocity impact and a significant reduction in maximum force.

This paper presents research on several factors influencing the stabbing behaviour of stratified panels made of aramid fabric Twaron^® SRM509 Teijin Aramid BV (Arnhem, The Netherlands). The inputs in the test campaign were the number of layers, the impact energy, and the sample size. Tests were performed on small samples (130 mm × 130 mm) on an Instron^® CEAST 9350 drop-tower impact system (Norwood, MA, USA) and on larger samples (400 mm × 400 mm) using a test installation with the same values of the impact energy. Knife type S1 was used, with the geometry recommended in NIJ Standard 0115.00 Stab Resistance of Body Armor SEM, and macro photography investigations revealed the failure mechanisms of panel, layers and fibres. A very important conclusion of this study regarding the stabbing performance of fabric Twaron^® SRM 509 in particular, but also in general for panels for body protection is that a research study could start on small size samples, with an accurately instrumented machine, in order to establish the influence of significant factors of stab resistance (energy level, number of layers in a panel, etc.), as these samples are less expensive and less time consuming, but the study should be continued to examine larger size samples. The obtained data are useful for the prototype.

This study focused on the development of a new concept for ablative thermal protection material, using a relatively new polymer matrix based on polysiloxane resin, which exhibits high-performance thermal properties. As a reinforcing element, graphite felt (GF/UHT) was selected. These new ablative materials were tested and characterized to evaluate their thermal properties through comparison with established/standard ablative materials based on phenolic resin and graphite felt (GF/Isophen). To evaluate them, two distinct types of thermal tests were performed. The first consisted of subjecting the ablative materials to a temperature of 1100 °C for a total duration of 10 min (with three different dwell times: 30 s, 120 s, and 300 s). A mass loss of 31% was recorded for the GF/UHT ablative material samples compared to the GF/Isophen material, where the mass loss reached approximately 68%. The second test consisted of exposure to an oxyacetylene flame at a temperature of 1600 °C. The GF/UHT samples had an improved behavior compared to the GF/Isophen samples, the latter being completely penetrated at the end of the test. Additionally, differential scanning calorimetry (DSC) tests were performed and characterized by FTIR spectroscopy and scanning electron microscopy.

In recent years, researchers have developed a new method of measuring the pressure on the surface using sensitive paints. This is an optical technique for determining surface pressure distributions by measuring changes in the intensity, emitted by certain excited molecules. The main advantage of the method over traditional techniques is the high resolution of the information. The only limitation of the resolution of a global map generated by the PSP (pressure-sensitive paint) technique is given by the capabilities of the image capture device. This paper describes the development of a technology for obtaining pressure-sensitive paint, in laboratory conditions, as an advanced measurement technique. The method has an application in many fields such as automotive, aerospace, or even medical.

Glass-fiber-reinforced polymer composites are of interest for lightweight structural applications, including marine structures, where accidental low-velocity impact is an important design consideration. This study investigates the low-velocity impact response of polyester-matrix composites reinforced with 4 layers, 6 layers, and 8 layers of biaxial glass fabric. A progressive test program, designed according to the number of fabric layers, used increasing impact-energy levels to cover both an indentation-dominated non-perforating regime and complete perforation, with the transition toward complete perforation in each configuration guiding the energy range selected for the configuration with the next higher number of fabric layers. Instrumented drop-weight tests with a 16 mm hemispherical impactor were analyzed using force, displacement, velocity, and energy histories. At the highest fully non-perforating energy levels of 30 J, 60 J, and 100 J, maximum contact forces were 7.25 kN, 13.05 kN, and 17.45 kN, while absorbed energies were approximately 28.7 J, 54.1 J, and 95.3 J. At 40 J, 80 J, and 120 J, respectively, the composite series entered the transition regime, with complete perforation observed for some of the tested specimens. The investigated parameters showed different diagnostic values: some were sensitive to the impactor mass–velocity combination, whereas displacement, energy, and velocity histories more clearly reflected the change in impact regime. The progressive test campaign, extended up to complete perforation, provides a practical means of identifying the transition between impact regimes and establishing application-specific impact limits. For design purposes, components exposed to accidental impact should therefore incorporate an adequate margin below the experimentally identified transition energy range.