Load Bearing Capacity Of Composite Research Articles

Effects of microvoids on strength of unidirectional fiber-reinforced composite materials

Microvoids are common defects generated during manufacturing or prolonged services of composites. Depending on the local physical environment, microvoids may form as two types, namely, matrix voids and interfiber voids. These voids are known to have detrimental effects on the load bearing capacity of composites. However, it is relatively unknown the quantitative influence of these voids on the mechanical strength of composites. Without a direct mapping between defects and ply-level constitutive behavior, high-fidelity progressive failure predictions of composite structures is challenging. To bridge the gap, a micromechanics-based finite element framework is developed to investigate composites failure in the presence of three interfiber voids and the matrix void under transverse compression, tension, shearing, and longitudinal shearing. Mechanical strengths under these four loading modes are correlated with microstructural parameters including the void volume fraction, fiber-to-void number ratio, and void orientation. In general, at the same void volume fraction, the pentagonal interfiber void lowers strength the most, followed by the square interfiber void, the triangular interfiber void, and the circular matrix void. The weakening effect is strongly associated with stress concentration in the vicinity of voids, making the fiber-to-void number ratio an important parameter as it determines the local geometry. While void orientation shows limited influence, void size is found to play an important role. Results are expected to guide design and manufacturing of composite materials to achieve less critical flaws and higher strengths. Quantitative understanding of the criticality of voids of various configurations will also assist in-situ evaluation of composite materials.

Atomistic investigation of mechanical behavior for CNT reinforced nanocrystalline aluminum under biaxial tensile loading

In this paper, the mechanical behavior of nanocrystalline aluminum and carbon nanotube reinforced NC Al composites have been examined by using molecular dynamics simulations under biaxial tensile loading. Armchair type of (5,5) CNT, (15,15) CNT, (30,30) CNT and three different temperatures (10 K, 300 K and 681 K) have been considered to perform tensile test at a strain rate of 109 s−1. CNT reinforced NC Al composites have exhibited diminished in ultimate tensile strengths and fracture strains compared to NC Al without CNT specimen, corresponding to simulated temperatures. On the other hand, only (15,15) CNT incorporated NC Al specimen exhibited higher fracture strain in contrast to NC Al specimen at room temperature in which load bearing capacity of composite has been enriched through CNT. The thermal fluctuations have increased with increase in temperature and which leads to reduce in mechanical properties. Dislocation density analysis and Centrosymmetry parameter analysis have been carried out to evaluate the structure evolution of the composites at different strains during biaxial tensile loading. The deformation behavior of NC Al and CNT reinforced NC Al composites have been analysed at various temperatures with respect to three different CNT diameters.

Friction Properties of PTFE Matrix Composites Reinforced by PPS and PPTA Fibers

The polytetrafluoroethylene (PTFE) matrix composites reinforced by polyphenylene sulfide (PPS) fiber and poly-p-phenelenferephthalamide (PPTA) fiber were prepared by the processes of mechanical blending, compression molding and sintering. The fractured surfaces of impacting specimens were examined by scanning electron microscopy (SEM). The tribological properties of the composites were investigated on M-2000 wear tester at dry friction condition. The wear mechanism was also discussed and the wear surfaces were examined by SEM. The result indicates that fibers which diffused in PTFE matrix wind with PTFE molecule chain, and then form grid structure. The load-bearing capacity of composites can be obviously enhanced and the trend of block fragmentation’s slide is inhibited, so that the tribological properties are improved markedly. The friction coefficient of composites is reduced by adding graphite which also prevents fibers leaving. The tribological properties of PTFE matrix composites is greatly improved because of the synergistic effect between fibers and graphite, which has good prospect for low loading application.

Comparison of Mechanical and Frictional Properties of PTFE Matrix Composites Reinforced by Different Fibers and Graphite

The polytetrafluoroethylene (PTFE) matrix composites which filled with polyphenylene sulfide (PPS) fiber, poly-p-phenelenferephthalamide (PPTA) fibre or glass fiber (GF)) and graphite at various mass fractions were prepared by the processes of mechanical blending, compression molding and sintering. The mechanical properties of the composites, such as tensile strength, impact strength and hardness were investigated. The results show that tensile strength and elongation at break markedly decrease but elasticity increases by filling with fibers. Impact strength decreases by filling with PPS and GF, and the composite displays brittle characteristic. However, the impact strength rapidly increases by filling with PPTA fiber. Hardness increases with the fibers content increases, and decreases with graphite content increases. Filling graphite into PTFE has light effect on the impact and tensile strength of composites. The tribological properties of the composites were investigated on M-2000 wear tester at dry friction condition. The wear mechanism was also discussed and the wear surfaces were examined by SEM. The result indicates that fibers which diffused in PTFE matrix wind with PTFE molecule chain, and then form grid structure. The load-bearing capacity of composites can be obviously enhanced and the trend of block fragmentations slide is inhibited, so that the tribological properties are improved markedly.