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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.13, #2)
Fracture Assessment of Carbon Fibre/Epoxy Reinforcing Rings through a Combination of Full-Scale Testing, Small-Scale Testing and Stress Modeling by Pieter Samyn; Ludo Van Schepdael; Wim Van Paepegem; J. S. Leendertz; Eric Suister; Patrick De Baets; Joris Degrieck (pp. 57-85).
Carbon fibre/epoxy rings are used as radial reinforcement for polymer bearing elements with nominal diameter 250 mm functioning under 150 MPa. Full-scale static and dynamic testing revealed no catastrophic failure for loading to 400 MPa, although there was circumferential splitting of carbon fibres at the machined top edge causing counterface wear under sliding. A combined numerical–experimental analysis was applied for design improvement with a representative small-scale qualification test on the real ring geometry, inducing additional stress concentrations compared to ASTM standards. Full-scale modelling revealed high radial–axial shear stresses (33 MPa) in non-hydrostatically loaded zones, while it increased towards 104 MPa under hydrostatic load conditions. The former is the most critical and should be simulated either on a small-scale unidirectional compression test or on a representative short beam shear test, respectively, measuring the radial–axial or radial–tangential shear strength. A relation between both small-scale states of stress was experimentally and numerically studied, experiencing that the composite ring has lower radial–tangential shear stress compared to radial–axial shear stress as a different hydrostatic stress state is observed in the bulk of the composite ring. As a compressive test is however more difficult to perform than a short-beam-shear test, a representative design criterion for shear fracture is determined from failure at 27 kN normal load in a short-beam-shear test. Finally, fracture is avoided by optimising the cross-sectional geometry of the composite reinforcing ring and close control of the processing parameters.
Keywords: finite elements; full-scale; shear failure; small-scale
Structural Health Monitoring of Cracked Aircraft Panels Repaired with Bonded Patches Using Fiber Bragg Grating Sensors by Hideki Sekine; Shin-Etsu Fujimoto; Tomonaga Okabe; Nobuo Takeda; Toshimitsu Yokobori Jr. (pp. 87-98).
Structural health monitoring of cracked aircraft panels repaired with bonded patches for extending the service life of aging aircraft has received wide attention. In this paper, the identification of the locations and shapes of fatigue crack and disbond fronts in aircraft panels repaired with double-sided bonded patches using fiber Bragg grating (FBG) sensors is studied. The identification is performed by minimizing the difference between the detected and calculated reflection spectra of FBG sensors at multiple positions on the free surface of patches. The validity and effectiveness of the identification in practical use is verified by comparing the identification results with the exact ones.
Keywords: patch repair; cracked aircraft panel; identification of crack and disbond fronts; reflection spectrum of FBG sensor; improved tunneling method; structural health monitoring
Structural Assessment of Externally Strengthened Bridge Deck Panels by Jongsung Sim; Hongseob Oh; Christian Meyer (pp. 99-114).
Deteriorated concrete bridge decks are strengthened with external bonding technique using either steel plate or various FRPs to enhance the decreased load carrying capacity and serviceability. But the failure characteristics of bridge decks strengthened with various materials can be changed according to mechanical properties of strengthening materials or strengthening scheme as well as the strengthening amount. In this paper, strengthening effect of deck strengthened with carbon fiber sheets, glass fiber sheets or steel plates is compared. And the theoretical load carrying capacity are evaluated using yield line theory and punching shear model properly modified for the strengthened RC member. The panels strengthened with sheet type FRP materials failed more often in a ductile mode, indicating that the failure developed after the rebar yielded.
Keywords: concrete bridge deck; yield line theory; punching shear model; strengthening effect
Interpenetrating Microstructure and Properties of Si3N4/Al–Mg Composites Fabricated by Pressureless Infiltration by Wang Shouren; Geng Haoran; Zhang Jingchun; Wang Yingzi (pp. 115-126).
Si3N4/Al–Mg composites based on Al–Mg alloy reinforced by ceramic interpenetrating network structure were fabricated via pressureless infiltration technology. Infiltration temperature and infiltration time are the key parameters distinctly effecting on infiltration processes. Moreover, the increasing of Mg content (2–8 wt.%) resulted in an increased amount of infiltration. Microstructural characterization of the composites reveals a special topology of skeleton and good integrity of metal/ceramic interface. The presence of second reinforced phase results in a significant increase in 0.2% offset yield and ultimate tensile strength of composites materials. However, when the volume fraction of reinforcement is large than 6%, there are a distinctly reduction of strength. The presence of additional secondary brittle phase in matrix results in the reduction in ductility and increase in hardness of 3-DNRMMCs. The failure features as cracking and void in reinforcement, interface cracking and interface debonding as well as matrix damage result in the decreases of fracture toughness. With the increases of volume fraction of reinforcement, 3-DRMMC exhibits excellent wear-resistance property.
Keywords: silicone nitride skeleton; metal matrix composites; pressureless infiltration; mechanical properties