Fatigue resistance of ultra-high-modulus pitch-based carbon fiber/epoxy composites under tensile loading

Pitch-based carbon fiber reinforced epoxy composites are used in specialized applications for their high-modulus and thermal conductivity; however, little data on their fatigue performance are available in the open literature. In this study, fatigue behaviors of ultra-high-modulus pitch-based carbon fiber and standard-modulus polyacrylonitrile (PAN)-based carbon fiber were compared in woven quasi-isotropic epoxy matrix composites subject to uniaxial tension. It was found that the pitch fiber composite possessed higher normalized tensile fatigue strength and that its stress-life ( S-N) curve is less steep. Extrapolation suggests the pitch fiber composite is more fatigue-resistant in higher cycle regimes (specifically, N > 107). Cyclic loading of the pitch fiber composite resulted in minimal matrix damage, and the eventual fractures were localized and fiber-dominated for all stress levels. Cyclic loading of the PAN fiber composites resulted in widespread matrix cracking and delamination. The difference in fatigue behavior is attributed to the different strain levels attained at similar stress levels and the consequent difference in matrix damage development.

A numerical study for determining the effect of raffia, alfa and sisal fibers on the fiber-matrix interface damage of biocomposite materials

Background: : nowadays, the natural fibers are used in all industrial fields, particular in automotive technology and in civil engineering. this great emergence due to its biodegradability, recyclability and has no environmental effect. Objective: In this article, the effect of raffia, alfa and sisal fibers on the damage of biocomposite materials (raffia/PLA (polylactic acid), alfa/PLA and sisal/PLA), subjected to the same mechanical shear stress, has been investigated. Method: To calculate the damage to the interface, the genetic operator crossing are employed based on the fiber and matrix damage. Result: The results have shown that the raffia / PLA and alfa/PLA biocomposite materials are the better mechanical properties compared to sisal / PLA, this observation has been confirmed by the different values of interface damage of the biocomposite studied. Conclusion: The numerical results are similar and coincide perfectly with the results of Cox where he demonstrated that the Young's modulus of fibers improves the resistance of the interface. These conclusions are in very good agreement with our numerical data presented by the red cloud, and also in good agreement with the work presented by Antoine Le Duigou et al. and the work of Bodros et al. have shown that natural fibers greatly improve the physical characteristics of composite materials.

Temperature-Dependent Fracture Mechanics-Informed Damage Model for Ceramic Matrix Composites

This work presents a temperature-dependent reformulation of a multiscale fracture mechanics-informed matrix damage model previously developed by the authors. In this paper, internal state variable theory, fracture mechanics, and temperature-dependent material properties and model parameters are implemented to account for length scale-specific ceramic matrix composite (CMC) brittle matrix damage initiation and propagation behavior for temperatures ranging from room temperature (RT) to 1200°C. A unified damage internal state variable (ISV) is introduced to capture effects of matrix porosity, which occurs as a result of material diffusion around grain boundaries, as well as matrix property degradation due to matrix crack initiation and propagation. The porosity contribution to the unified damage ISV is related to the volumetric strain, and matrix cracking effects are captured using fracture mechanics and crack growth kinetics. A combination of temperature-dependent material properties and damage model parameters are included in the model to simulate effects of temperature on the deformation and damage behavior of 2D woven C/SiC CMC material systems. Model calibration is performed using experimental data from literature for plain weave C/SiC CMC at RT, 700°C, and 1200°C to determine how damage model parameters change in this temperature range. The nonlinear, temperature-dependent predictive capabilities of the reformulated model are demonstrated for 1000°C using interpolation to obtain expected damage model parameters at this temperature and the predictions are in good agreement with experimental results at 1000°C.

A progressive damage model of composite laminates under low-velocity impact

In this paper, a progressive damage model for studying the dynamic mechanical response and damage development of composite laminates under low-velocity impact was established. The model applied the Hashin and Hou failure criteria to predict the initiation of intra-laminar damage (fiber and matrix damage); a linear degradation scheme combined with the equivalent displacement method was adopted to simulate the damage development; a cohesive zone model with the bilinear traction-separation relationship was used to predict delamination. A user material subroutine VUMAT was coded, and the simulation analysis of carbon fiber reinforcement composite laminates subjected to 25 J impact was performed via commercial software ABAQUS. The predicted impact force-time curve, impact force-displacement curve, and damage distribution contours among the layers were in a good agreement with the experimental, which verified the proposed model. According to the simulation results, the fiber damage and matrix damage were analyzed, and the expansion of delamination was discussed.

Influence of gap filling on mechanical properties of composite-aluminum single-lap single-bolt hybrid joints

Composite-aluminum structures exist in aircraft structures generally. It is easy to cause gap between mating surfaces in composite-aluminum assembled structures with the curing deformation of composite. The composite-aluminum, single-lap, single-bolt joints were utilized to investigate the influence of forced assembly, liquid shim and peelable fiberglass shim on the mechanical properties of assembled structures. A steel gasket that removed the middle part was used in the joint to make a gap. The 3D Digital Imagine Correlation (3D-DIC) system was utilized to measure the strain field of specimens and the progressive damage model was created in ABAQUS. The results show that the shim filling can significantly increase the tension stiffness and peak load of the joint compare with forced assembly. As the shim thickness changes, the effects of the liquid shim and the peelable fiberglass shim on the tensile stiffness and peak load shows different. The liquid or peelable fiberglass shim can reduce the strain value around the hole and the peelable fiberglass shim has a better result than liquid shim. The squeeze between the bolt and composite laminate has a greater impact on matrix damage and fiber-matrix shear damage, while the secondary bending has a greater impact on matrix damage and fiber damage.

Celecoxib Attenuates Cartilage Matrix Damage in Arthritis Rats by Inhibiting NF-κ B

Objective: Celecoxib selectively inhibits the activity of COX-2 and the production of prostaglandin (PG), and plays a therapeutic role in treating osteoarthritis (OA). NF-κB signaling and IL-1α and TNFα are involved in OA pathogenesis. This study explored whether Celecoxib might exert therapeutic effects on OA through regulating NF-κB signaling and IL-1β and TNF release in OA rat model. Method : The contents of MMP-13, Hyp, IL-1β and TNFα in synovial fluid were detected by ELISA. The protein expressions of NF-κ B p-p65, COL2A1 and the activity of caspase-3 were detected. OA model rats were separated into OA group and OA+ Celecoxib group followed by analysis of MMP-13, Hyp, IL-1β and TNF level in articular fluid by ELISA and p-p65 and COL2A1 level and caspase-3 activity by western blot. Rat cartilage tissue was cultured and divided into control group, LPS group and LPS+ Celecoxib group followed by analysis of expressions of p-p65 and COL2A1 in cartilage tissue, IL-1 and TNF content in culture supernatant, and chondrocyte apoptosis. Results: Compared with Sham group, p-p65 expression and caspase-3 activity in cartilage tissue of OA rats was increased and COL2A1 level was reduced. Meanwhile the expression of MMP-13, Hyp, IL-1β and TNF in articular fluid of OA rats was increased. Compared to OA group, p-p65 expression and caspase-3 activity was decreased and COL2A1 expression was increased in OA+ Celecoxib treatment group along with decreased MMP-13, Hyp, IL-1β and TNF level in articular fluid. p-p65 expression and caspase-3 activity in LPS group was increased and COL2A1 expression was decreased with increased IL-beta; and TNF content. Compared to LPS group, p-p65 expression and caspase-3 activity was decreased and COL2A1 expression was increased in LPS+ Celecoxib group with decreased content of IL-1β and TNFα. Conclusion: Celecoxib can protect cartilage in OA by inhibiting NF-κB activation and IL-1β and TNF release, and decreasing cell apoptosis in inflammatory environment.