Applied Composite Materials最新文献

This study employed a high-extrusion-rate Fused Deposition Modeling (HFDM) 3D printer, with the nozzle diameter enlarged from 0.4 mm to 1.0 mm. The increase in nozzle diameter (from 0.4 mm to 1.0 mm) significantly enhanced the volumetric deposition rate, thereby reducing the time required to print each layer and shortening the overall manufacturing cycle. In addition, the larger nozzle diameter increased the width and height of each printed bead, which shortened the required path length per layer, further improving printing efficiency. Short-carbon-fiber filled polyamide 12 (PA12-CF) is used as the test material. The three-point bending test samples are prepared with the HFDM system, where the effects of extrusion width and layer height, as printing parameters, on the flexural properties are investigated. Furthermore, the fiber orientation within the deposited beads is measured using optical microscopy and imaging process software ImageJ. Experimental results indicate that with an increased layer height and extrusion width, PA12-CF samples exhibit improved mechanical properties, where the bending strength and stiffness can be increased up to ~ 20%, and ~ 30%, respectively. The fiber orientation angle measurements indicate that with smaller values of layer height and extrusion width, the fibers tend to align more parallel to the material extrusion direction. As these printing parameters increased, the fibers tend to align more diversely to the transverse directions, which ultimately benefits the increment of the flexural resistance of the entire samples. Additionally, isothermal annealing process improves the bending strength and bending modulus of the samples by approximately 12% and 13%, respectively.

Polyurethane foam (PUF) is widely utilized in cushioning and energy absorption applications, owing to its cellular structure, that provides high damage tolerance under compression. This study explores the dynamic mechanical properties of PUF with varying densities under different strain rates. Uniaxial compression tests were conducted on PUF samples with densities of 120, 200, and 300 kg/m³ using an improved Split Hopkinson Pressure Bar (SHPB) system and a universal testing machine, with loading rates ranging from 10^–4 to 2000s⁻¹. Results show that PUF properties are influenced by density and strain rate. Higher density foams have higher strength but lower densification strain. All samples demonstrated strain rate sensitivity, where higher rates leading to increased strength and decreased densification strain. Based on the aforementioned findings, a dynamic constitutive model was developed to incorporate the influences of density, strain, and strain rate. This model effectively predicts the mechanical behavior of PUF and offers valuable insights for engineering applications requiring impact protection and energy absorption.

Aluminum/epoxy resin interpenetrating phase composites (IPCs) were directly strengthened by adding glass fiber of varying content (80 wt%, 100 wt%, 120 wt% and 140 wt%) inside the epoxy resin. The macro and micro structures of IPCs were intact, and the interface between aluminum and epoxy resin was well combined. As the content of glass fiber increased, the compressive strength of epoxy resin increased, but the failure was advanced, while IPCs displayed the opposite trend. IPCs exhibited three compression deformation modes, namely plastic deformation of aluminum, resin fracture and interface debonding. The digital image correlation and infrared thermal imager were used to characterize the apparent principal strain distribution and temperature distribution of IPCs to verify the deformation modes. The surface temperature damage evolution of IPCs included the rapid temperature rise stage, steady temperature stage and slight temperature drop stage, respectively, mainly corresponding to the linear elastic stage, plateau stage and densification stage in the stress-strain curves.

Three-dimensional woven tubular composites (3DWTCs) exhibit exceptional structural integrity and superior interlaminar shear resistance, making them highly promising candidates for energy absorption components in a wide range of applications. This paper aims to evaluate the impact response of 3DWTCs with varying structures through low-velocity impact experiments. Three types of 3DWTCs, namely shallow cross-linked (SCL), shallow-crossed curved joint (SCCL), and through orthogonal (TO), were fabricated using basalt fiber bundles and epoxy resin via the vacuum-assisted resin transfer molding (VARTM) process. Low-velocity impact tests were conducted at energy levels of 5, 10, and 20 J. To evaluate the damage characteristics of 3DWTCs, the observations were analyzed in terms of load-time curves, load-displacement curves, energy-time curves, and failure morphologies. The results indicate that the SCL structure exhibits superior impact resistance, followed by SCCL, while the TO structure displays the lowest. This study provides valuable insights into the potential applications of 3DWTCs in the aerospace industry and other sectors.

This study presents an analytical model of low-velocity impact on composite plates, possessing either flat or cylindrical shapes. The overall plate`s stiffness properties are varied with an additionally assembled Ω-stringer and embedded shape memory alloy wires in the composite material, using only the shape memory effect. This analytical approach enables a low-effort but sufficiently accurate design of low-energy-impacted structures. Comprehensive analytical equations are developed based on the inclusion of the stringer effect on the curved panels. For both stringer-stiffened and non-stiffened plate models, parameter variations regarding the impact and shape memory alloy (SMA) wire integration are conducted. The effects can be classified as changes in essential and acquired stiffness. Our results indicate that SMAs improve the energy absorption capability of stiffened composite panels.

The production of high-quality fiber reinforced polymer parts is an important aspect in several industrial areas. However, due to unavoidable uncertainties in material and manufacturing processes, the part quality scatters. One important aspect here is the fiber orientation, being crucial for the thermo-mechanical properties of the part and being influenced by the uncertain material state and process conditions. Process simulations are an important tool for predicting the fiber orientation, but state-of-the-art simulations are normally deterministic and represent only one specific case. Performing enough deterministic simulations to model manufacturing uncertainties requires high numerical effort. Therefore, this work presents methods to quickly and efficiently approximate the fiber orientation under varying material and process parameters, requiring only a few simulations as input. Different schemes for approximation are evaluated and compared with each other and with 3D process simulations.

Combination of experimental testing and numerical analysis is suggested to determine static mechanical properties of the auxetic honeycombs realized via material extrusion. Special specimens, which consist of two honeycombs plates and three steel plates, are used to analyze experimentally shear mechanical properties of honeycombs. Shear testing is simulated using the finite elements software ANSYS. The tests on tension of honeycombs are carried out. These tests are simulated by finite elements software. Plasticity of the honeycomb material and geometrically nonlinear deformations of the honeycomb walls are accounted in honeycomb model. The experimental data and calculations results are close.

Herein, a coupled elastoplastic-damage analytical model is developed to analyze the effect of the plasticity of the resin on the failure behavior of 3D woven composites (3DWC). The proposed model is numerically simulated using different unit-cells of 3DWC and is verified by experimental data. The results show that under warp loading, the plasticity of the resin has a greater effect on component damage, and both the plasticity and the damage show an alternating iterative propagation mode; in contrast, under weft loading, the plasticity of the resin has a lesser effect on component damage, and both show an independent extension pattern. This work provides a guidance for the strength design of 3DWC structures such as aero-engine fan blades, which demonstrates significant engineering implications.

In recent years, laminated composites reinforced with natural fibers have extensively used in the various industries. One of the most important failure modes of laminated composite materials is translaminar fracture under different loading conditions. In this research, the effect of temperature on the translaminar critical strain energy release rate (CSERR) of the composites reinforced with cotton fibers was investigated. The cotton/epoxy samples were placed at different temperature conditions of 30, 0, and -30 °C. The translaminar CSERR values of cotton/epoxy laminated composites were obtained under pure mode I, mixed mode I/II with two different loading angles, and pure mode II loading conditions. To calculate the translaminar CSERR based on experimental results, numerical modeling was also performed. Besides, a modified version of Mixed Mode Fracture Envelope criterion was proposed to predict the mixed mode I/II translaminar fracture behavior of the cotton/epoxy laminated composites at the mentioned temperatures. The results showed that lowering the temperature has a great impact on the translaminar CSERR. It was also concluded that the change in the temperature had the greatest effect on the value of the mode I translaminar CSERR. Moreover, as the temperature decreased from 30 to 0 and -30 °C, the value of the mode I translaminar CSERR decreased around 80 and 90%, respectively.

This study focuses on the spring-back as a function of the degree of cure on single-curved metal-composite laminates. The manufacturing through a hot-pressing process involves different (curing) stages and can reduce the spring-back with the proper combination of forming and curing. The cure-dependent spring-back is measured and analysed as a function of material constituents, fibre directions, laminate layups, and the process parameters including temperature, holding time and pressure. The results demonstrate that the spring-back ratio after full-cured process is relatively small and mainly depends on the mechanical properties of the metal sheet in laminates. However, temperature and time have a significant effect on the spring-back of partially-cured laminates and the same type of fibre prepreg combined with two different metal sheets have similar trends of spring-back reduction. Moreover, the study found that the hybrid laminates with aluminium sheet delaminate at low pressure after full-cured, while the delamination disappears as the pressure increases. The characterisation on cure-dependency of the spring-back contributes to a better understanding of the deformability of the metal-composite laminates during the hot-pressing process and offers an opportunity to tune the spring-back of these laminates.