Six-directional Braided Composites Research Articles

Comparison study on bending properties and failure of 3D5d and 3D6d carbon/phenolic braided composites at room and elevated temperatures

Three-dimensional five-directional and six-directional braided composites (3D5dBCs and 3D6dBCs) are widely used in aerospace industry for their excellent axial and transverse properties. This work successfully fabricated 3D5dBCs and 3D6dBCs with carbon/phenolic, and compared their bending properties and failure mechanisms at room and high temperatures (RT and HT). The influences of braiding structure and temperature on bending properties and failure mechanisms of 3D5dBCs and 3D6dBCs were analyzed. The load/deflection curves are linear elastic at RT, showing prominent plastic characteristics at HT. From RT to HT, the bending properties decrease, but 3D5dBCs always have higher bending properties than 3D6dBCs. The 3D5dBCs and 3D6dBCs are primarily damaged near the surface at RT; fiber shearing fracture feature becomes apparent and the interior damage worsens at HT. 3D5dBCs exhibit obvious shear failure mode, where the fracture is bent and rough, and the damage patterns are braiding and axial fibers shearing fracture, matrix softening, and interface debonding. 3D6dBCs show transverse sawtooth fracture cracks, and the damage mechanisms are braiding fiber shearing fracture, fifth fiber tearing, sixth fiber shedding and pulling-off, matrix plasticization, and interface debonding.

Liquid nitrogen temperature effects on the mechanical behaviors of three-dimensional seven-directional braided composites

Three-dimensional (3D) braided composites are broadly adopted in aerospace cryogenic fuel tanks. This work designed and fabricated 3D seven-directional braided composites (3D7dBCs) with different braiding angles, and their compression properties at room and liquid nitrogen temperatures (RT and LNT) were explored and discussed, while the mechanical properties were compared with other braided structural composites. Temperatures and braiding angles considerably influenced the properties of 3D braided composites. The multi-directional compression strength of 3D7d21-LNT and 3D7d34-LNT was 392.7 MPa, 426.1 MPa, 270.3 MPa, 210.3 MPa, and 268.8 MPa, 204.1 MPa, which was 18.1% and 18.6% higher than that of 3D7d21-RT and 3D7d34-RT in the out-of-plane direction, 5.1% and 6.5% in the longitudinal direction, 74.2% and 9.7% in the transverse direction, whereas the longitudinal strength decreased as braiding angles increased, and the out-of-plane and transverse compression strength increased. Additionally, shear cracking was the main reason for the failure of 3D7dBCs at RT, while fiber loosening, pulling-out, and interfacial debonding were exhibited at LNT. Compared to 3D five-directional and 3D six-directional braided composites (3D5dBCs and 3D6dBCs), the incorporation of seventh yarns significantly improved the out-of-plane properties of 3D7dBCs.

Fatigue behavior and failure of three-dimensional six-directional braided composites under tension

Carbon/epoxy-three-dimensional (3D) six-directional braided composites are fabricated and tensile fatigue behavior are reported. The results show that the composites have good fatigue properties and limit with small braiding angle. Fatigue life decreases with increasing the stress level. Dynamic modulus decreases and rate of stiffness degradation is also restricted by cycle number. Moreover, there are two regions on the hysteretic curve where the failure strain suddenly increases. Fracture morphology indicates that fatigue cracks spread from the outside to inside of the material and enter fiber/matrix interface, then to the fibers. The damage degree becomes more serious with increasing the stress level. At low stress levels, composite shows small damage and flush fracture. At high stress levels, it exhibits shear fracture along the braiding angle.

A novel mechanical behavior and failure mechanism analysis of 3D six-directional braided composites in liquid nitrogen subjected to compression

The influence of temperature, braiding angle, and braided structure on compressive mechanical properties and failure mechanisms of three-dimensional six-directional braided composites (3D6DBCs) were comprehensively analyzed. At low temperature, the out-of-plane and transverse strength increased by 16.2% and 50.1%, respectively. Interfacial damage caused a 25.3% decrease in longitudinal strength. The increase in braiding angle leads to a decrease in longitudinal and transverse strengths. At room temperature, the failure of the yarn-matrix interface and the deformation of the composites are the main reasons for the failure of 3D6DBCs. At low temperature, 3D6DBCs exhibits brittle fracture and shear failure modes. The braiding angle affects the deformation of 3D6DBCs. The composites with different braided structures have significant property differences. The addition of axial and transverse yarns significantly improves the longitudinal and transverse properties of 3D6DBCs.

Numerical investigation on tensile behavior of three-dimensional six-directional braided composites

Based on the mesostructure, a parametric finite element (FE) model of the three-dimensional six-directional (3D6d) braided composites was developed considering the real cross-sectional shape of the yarn and its contact relationship. The 3D Hashin criterion and maximum stress criterion were used for failure determination and periodic displacement boundary conditions were imposed on the model to numerically simulate the initiation, propagation and final failure of yarns and matrix damage. The FE model accurately predicts the longitudinal tensile strength of 3D6d braided composites and simulates the progressive damage process associated with the stress-strain behavior. The longitudinal mechanical properties of the 3D6d braided composites decrease with increasing braiding angle, while increasing the fiber volume fraction leads to enhancement of these properties. Furthermore, the change rate of longitudinal mechanical properties with braiding angle is relatively stable, and the influence of fiber volume fraction on longitudinal properties decreases with the increase of braiding angle. For the damage mode, the increase of braiding angle makes the damage of braiding and sixth-directional yarns gradually change from single direction to multiple directions, and the decrease of fiber volume fraction makes the damage of braiding and fifth-directional yarns at the peak stress more serious.

Influence of moisture absorption on mechanical properties and damage mechanisms of three-dimensional six-directional braided composites under hydrostatic pressure

Fibre-reinforced composites have shown a growing interest in pressure-resistant materials for deep-sea use due to their excellent properties. This paper presents the influence of the moisture absorption on the mechanical properties and damage mechanisms of three-dimensional six-directional (3D6D) braided composites under hydrostatic pressure. The bisphenol A epoxy resin, bisphenol F epoxy resin, and hydrogenated bisphenol A epoxy resin, are chosen. SEM and X-ray Micro-CT are employed to investigate the moisture absorption, tensile and compressive damage before and after subjecting to the hydrostatic pressure. Results show that the bisphenol F carbon/epoxy composite has the lowest porosity at 0.082% among the three composite materials. The average moisture absorption was the lowest at 0.3755%. Furthermore, moisture is mainly transported along micro cracks in the matrix and the fiber-matrix interface under hydrostatic pressure. After the composites absorb moisture, the average tensile strength retention rates of bisphenol A carbon/epoxy composite, bisphenol F carbon/epoxy composite, and hydrogenated bisphenol A carbon/epoxy composites drop to 88.282%, 76.34%, and 66.43%, respectively. Moreover, their average compressive strength retention rates drop to 53.15%, 74.26%, and 83.45%, respectively. The tensile and compressive strengths of the 3D6D braided composites decreased significantly after moisture absorption, mainly due to fiber-matrix debonding and matrix cracking.

On the tensile properties and failure mechanisms of 3D six-directional braided composites at elevated temperatures

Three-dimensional six-directional (3D6d) braided composites with different braiding angles were prepared, and the influences of temperature and braiding angle on tensile properties and failure mechanisms were studied. The results show that both temperature and braiding angle have significant effects on the tensile properties of 3D6d braided composites. As temperature increases, due to the weakening of the fiber/matrix interface, the stress-strain curve shows a nonlinear upward trend and the tensile properties decrease. As braiding angle increases, the curve declines, and both the tensile strength and modulus diminish. At high temperatures, the damage pattern is mainly braiding fibers multiple shear fracture, fifth fibers tensile fracture, sixth fibers torn, showing expansion outwards, matrix softening and peeling off from the fiber bundles. At 150 °C, the composite shows shear fracture, as the braiding angle increases, the shear fracture characteristics along the braiding angle become prominent. At 200 °C, the composite distorts and expands outwards overall. The fibers pull-out feature become obvious with increasing the braiding angle.

High strain rate impact effect and failure behavior of 3D six-directional braided composites

The high strain rate impact effect and failure behavior of three-dimensional six-directional (3D6d) braided composites with different braiding angles are reported in this paper. The results show that 3D6d braided composites exhibit typical strain rate sensitivity. Under out-of-plane dynamic compression, the stress–strain curves rise linearly and present obvious softening characteristics. With the increase of strain rate, both the strength and modulus of composites increase, while the failure strain decreases. Moreover, the composites with larger braiding angle exhibit higher dynamic curves and better out-of-plane high strain rate properties. The fracture morphology shows that composites exhibit different dynamic damage and failure modes at different strain rates and braiding angles. As the strain rate increases, the composites show clearer shear fracture feature and more severe brittle failure. The damage is mainly manifested as shear of the sixth and braiding fibers, tear of the fifth fibers on the shear plane, interfacial debonding and matrix cracking. As the braiding angle increases, the damage and fracture of composites are reduced obviously and the composites become less brittle failure at high stain rates.

Experimental and numerical study of in-plane compressive properties and failure of 3D six-directional braided composites with large braiding angle

Three-dimensional (3D) six-directional braided carbon/epoxy composites are widely used in aerospace field and this is successfully fabricated in this study. The composite is thoroughly analyzed with regard to both mechanical properties and failure mechanism in connection with the affecting factors, i.e., loading direction and temperature. At room and elevated temperatures, the in-plane compressive properties of such composites are obtained, and their failure mechanism is evaluated. A progressive damage model is established to predict the mechanical properties and to quantitatively interpret the failure behavior. At room temperature, longitudinal curve increases linearly and then drops suddenly, indicating brittle characteristics; the transverse curve is linear up to the failure point and drops gradually after the peak point. At elevated temperatures, the curves become non-linear up and the mechanical properties of composites decrease. At room temperature, the longitudinal compression presents shear fracture and shear plane exfoliation. Meanwhile, failure is observed in fiber rupture in various directions and matrix cracks. The transverse failure is observed in shear cracks and braiding fibers shedding. At elevated temperatures, 45° shear cracks are developed, the fibers are pulled out, the texture of matrix softens and exfoliates, and a noticeable debonding of the interface occurs.

Mechanical properties and failure mechanisms of 3D six-directional braided composites at elevated and liquid nitrogen temperatures

3D six-directional braided carbon/epoxy composites are fabricated successfully, and their mechanical properties and failure mechanisms at room, elevated and liquid nitrogen temperatures are reported. The results show the temperature has an important influence on load-deflection curves and bending properties. All the curves are divided into three stages: initial linear elastic, nonlinear and final fracture stage. At room temperature, the linear characteristic is obvious and properties are excellent. The failure is a gradual process from external to internal due to good reinforcement of transverse yarns, and fibers are sheared and pulled out. At elevated temperatures, the curves decline successively and nonlinear features increase, with decrease of bending properties. The damage is matrix softening and plasticization, interface debonding. At liquid nitrogen temperature, zigzagged fluctuation feature increases and linear elastic characteristic strengthens. Bending properties have been improved significantly and failure is fibers shear fracture and formation of shear bands among fiber/matrix interface.

Internal damage detection of three-dimensional four-step six-directional braided composites based on carbon nanotube thread sensor

Internal damage detection of three-dimensional four-step six-directional braided composites based on carbon nanotube thread sensor

Mechanical and failure behavior of three-dimensional six-directional braided composites bolted joint

Experiments and finite element simulation were used to investigate the influence of geometric parameters on failure response of a single-lap bolted joint. Single- and double-bolt joints in three-dimensional six-directional braided composites were tested. The failure modes and mechanisms of the joints were evaluated. To accurately predict bearing strength, a three-dimensional composite damage model was used, which included the Yamada–Sun failure criteria based on the characteristic curve method. The finite element method (FEM) was validated by experimental results. The geometric reference value and failure envelope for the single-lap bolted joint were obtained. The results showed that the carrying capacity of the single-lap bolted joint decreased and the failure mode also changed owing to the secondary bending. It can also be obtained that increased the number of bolt rows can effectively reduce the secondary bending of the plates and thus generated less severe net tensile stresses.

Microstructure analysis and solid unit cell modeling of three dimensionally six-directional braided composites

A new solid unit cell model is developed based on the microstructure analysis of three-dimensional (3D) six-directional braided composite (6DBC) produced by four-step 1 × 1 procedures in this research. First, the volume control method is applied to analyze the spatial movement traces of yarns. Then the microstructure configuration and squeezing condition of yarns is analyzed in detail by the mathematical modeling. The relationships between the microstructure parameters of unit cell and the braiding process parameters are derived. The parametrical solid unit cell model for modeling the microstructure of 6DBC is established. Finally, the main microstructure parameters of specimens are calculated to validate the effectiveness of the model. The predicted results agree well with the available experimental data. In addition, the squeezing conditions of the braiding yarns and the axial yarns are analyzed in detail, respectively. The variations of the key microstructure parameters with the braiding angle are discussed. Results indicate that the parametrical unit cell model has provided a better understanding of the relationship between the microstructure and the braiding process parameters for 3D 6DBC.

Studies on Tensile and Shear Properties of 3D Six-Directional SiO<sub>2f</sub>/SiO<sub>2</sub> Composites

SiO2f/SiO2 composites reinforced with 3D six-directional preform were fabricated by silicasol-infiltration-sintering method. To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile and shear loading. All of the testing curves exhibited highly nonlinear behavior. The results indicated that the 3D six-directional braided SiO2f/SiO2 composites exhibited superior tensile properties and good shear resistant. Therefore, the 3D six-directional braided composites developed can well meet the demands of the thermal structure component.

Experimental Study of Effect of Adhesives on Strength of Composites Adhesive Joints

Tension tests on T700/EXOPY unidirectional laminates and 3-D and six-directional braided composites single-lap adhesive joints with different adhesive types under uniaxial tensile loading are performed in the presented paper. Failure modes, strengths and load-displacement curves of two kinds of different adhesive joints are compared and analyzed. According to the experimental results, it is found that the strength of the joints of the smaller adhesive shear strength is less, in contrast, the strength of the joints of the bigger adhesive shear strength is greater, Failure shear strength average is grown 27% relatively. And the starting position of the crack is appeared at the overlap ends, and the whole joint is failed with propagation of the crack.

Mechanical properties and mechanical behavior of (SiO2)f/SiO2 composites with 3D six-directional braided quartz fiber preform

Abstract(SiO2)f/SiO2 composites reinforced with three-dimensional (3D) six-directional preform were fabricated by the silicasol-infiltration-sintering method. The nominal fiber volume fraction was 47%. To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile, flexural, and shear loading. The composite exhibited highly nonlinear stress-strain behavior under all the three types of loading. The results indicated that the 3D six-directional braided (SiO2)f/SiO2 composites exhibited superior flexural properties and good shear resistant as compared with other types of preform (2.5D and 3D four-directional)-reinforced (SiO2)f/SiO2 composites. 3D six-directional braided (SiO2)f/SiO2 composite exhibited graceful failure behavior under loading. The addition of 5th and 6th yarns resulted in controlled fracture and hence these 3D six-directional braided composites could possibly be suitable for thermal structure components.

Finite Element Analysis of 4-Step 3-Dimensional Braided Composite Structure under High Velocity Impact

The finite element method was used to simulate and analyze I-shaped beam which was made of the three-dimensional braided composite and suffered from bird impact. The models contained five braiding modes, two kinds of three-dimensional three-directional braiding and three kinds of three-dimensional six-directional braiding. Three kinds of thickness (10 mm, 15 mm and 20 mm), and all of these models were impacted by three different velocities (80 m/s, 150 m/s and 200 m/s) respectively. The bird has different mechanical properties in different velocities; therefore, different finite element models were used. Also, the stiffness of the braided composites degraded while damaged was absolutely considered. The numerical results indicated that, the capability of anti-bird impact was best when the beam was made of three-dimensional six-directional braided composites with sizes proportion of braiding yarn 1:1:1 for the four-directional, five-directional and six-directional. After analysis, the most reasonable braiding mode and structure dimension was obtained, in which condition the I-shaped beam was strong enough to resist bird impact and less weight.

Experimental Researches on the Mechanical Properties of Three Dimensional Multidirectional Braided Composites

This paper investigated the mechanical properties and the relationships between fiber architecture and the composites properties of three-dimensional multidirectional braided composites made of Toray@T700 carbon fiber impregnated with TDE 86# epoxy resin using RTM. The strength and stiffness properties measured here include tension, compression, flexure and short beam shear, all of these in both the longitudinal and transverse directions. It is found that the 3D six-directional braided composites with 55 % fiber volume fraction and 25°surface braiding angle represent quasi-isotropic in-plane elastic behaviors due to their symmetric, intertwined architecture and unidirectional reinforcements in both the longitudinal and transverse directions. Compared with the tension strength and modulus, those for compressions in the same directions descend near 40% and 10% respectively. The cut-edge on the width destroys the integrity of microstructure and inevitably cuts down the carrying capacity of composites under the longitudinal tension.