Toshiko Osada

Initial fracture behavior of satin woven fabric composites

Abstract Final fractures of composites is considered to be caused by cumulation of the microfractures, so that, the initiation of microfracture, namely, initial fracture is important factor to know the mechanical properties. Microfracture behaviors in textile composites were regarded to be decided by the geometry of textile fabric quantitatively. In this study, initial fracture in plain and satin woven fabric composites was investigated and the effect of weaving structure on initial fracture behavior was clarified. First, in order to investigate the geometry of textile fabric, crimp ratio and aspect ratio were measured. Tensile testing was performed and knee point on the stress–strain curve was identified. Fracture process of composites was observed by replica method. Initial fracture in plain woven fabric composite was confirmed as transverse crack in weft fiber bundle, on the other hand, in satin woven fabric composites both transverse crack and filament fracture at the same time was observed. The effects of changes in crimp ratio and aspect ratio on the initial fracture of woven fabric composites were discussed.

Strain monitoring of braided composites by using embedded fiber-optic strain sensors

Recently, fiber optic strain sensors have been applied to internal strain and damage monitoring of composites because of their small size, light weight and flexibility. Braided fiber reinforced plastics (FRP) are compatible with fiber optic sensors because optical fibers can be integrated directly and easily into fabrics. In the present paper, the strain monitoring of braided glass fiber reinforced plastics (GFRP) was conducted by using embedded fiber Bragg grating (FBG) and extrinsic Fabry–Perot interferometric (EFPI) sensors during the cure process, tensile tests and fatigue tests. From the experimental results of cure monitoring, it was found that both sensors can be used only for monitoring of thermal residual strain during cooling process. From the results of tensile tests, it was found that both sensors could measure strain correctly until damage initiation of braided GFRP. It also appeared that FBG sensors could monitor damage to FRP by observing the reflected spectral shape. From the fatigue tests, it appeared that the strain measured by embedded FBG sensors was affected by fatigue damage. Therefore, it is concluded that internal strain monitoring of braided FRP using fiber optic strain sensors is very useful for cure and health monitoring.

Role of surface treatment in textile composites

Abstract It is well known that glass fibers are treated with both binding and coupling agents. The role of the binding agent is to act as a lubricant to reduce friction during textile processing, in addition to “binding” the filaments within a fiber bundle. In the present study, the role of the binding agent in braided composites was investigated from the point of view of fiber bundle strength and interface around the fiber bundle. The strength of normal flat braided composites was found to be affected by filament strength, whereas flat braided composites, whose fiber bundles at the side edges had been cut, were affected by both filament and interfacial strength.

Effect of Nesting of Fiber Bundles on Micro Fracture of Laminated Woven Fabric Composite

In laminated woven fabric composites, fiber bundles do not pack tightly because there are resin rich regions caused by crimp of fiber bundles. The fiber bundles in one layer are often fitted into the neighboring layer, which is called nesting. In this study, the effect of nesting by laminating on mechanical properties and micro fracture behavior of composites was investigated. Tensile testing of woven fabric composites with different number of layers and observation using optical microscopy were performed. With the increase of number of layers, nesting is more likely to occur, resulting in a decrease in thickness per layer increase in fiber volume fraction. This also lead to an increase in modulus and strength but a decrease in knee point stress. The locations at which cracks occurred were different in specimens with and without nesting.Copyright

Mechanical properties of flat braided composite with flexible interphase

Textile composites have been used extensively as industrial materials because of the excellent mechanical properties resulting from the continuously oriented fiber bundle. In a study of the mechanical properties, it is important to consider the fiber/matrix interface property as for other composite materials. In a recent study, the fiber/matrix interface is regarded as an interphase that has its own material constants and thickness; consequently, the mechanical properties of a composite can be controlled by specifically designing the interphase. In this study, we applied this concept to braided composites with flexible resin as interphase for the purpose of designing the interphase. In a static tensile test, though there were no improvements in Noncut specimens (normal braided composites), but a Cut specimen (each side of the Noncut specimen was cut) with flexible interphase was improved in fracture load and displacement. The observation of the specimen edge was carried out and it was confirmed that the progress of debonding at the fiber bundle intersection was interrupted by a flexible interphase, and a matrix crack did not occur in the Cut specimen with flexible interphase. In a fiber bundle pull-out test, it was confirmed that debonding progressed not into the fiber/resin interface but into the flexible interphase in the specimen with flexible interphase, and the interfacial property at the fiber bundle intersection was improved.

Study on Initial Failure in Tension of Glass Woven Fabric/Epoxy Composite with Functional Interphase

Recently the term of interphase is recognized and mainly used instead of the term of interface because the interphase should be considered not only for two dimensional boundary plane between fiber and matrix but also the three dimensional volume containing the region of matrix resin modified by silane coupling agent. In this paper, the functional interphase as a new concept of composites interphase was suggested. It is expected that the functional interphase could improve the performance of composites and add the farther function such as strengthening, toughening and so on. In this study the static tensile properties and initial failure behavior of glass woven fabric/epoxy composite plate with flexible interphase were investigated. The modulus and the strength were kept the same in any thickness of flexible interphase. The thickness of flexible interphase was well controlled by changing the concentration of flexible resin to the chemical solvent of acetone. The first and second Knee Points were identified by least squires method on tensile stress-strain curves. The Knee Point stress was maximized at 1.0 wt.% and decreased with increase in concentration. Accordingly the optimum concentration, namely optimum thickness exists to improve the initial failing stress.