Akio Ohtani

Prediction Method for Temporal Change in Fiber Orientation on Cylindrical Braided Preforms

An advantage of braided fabrics is that the fiber bundle orientation angle, called the “braiding angle,” can be changed. Because the braiding angle affects the fabric’s mechanical properties, changing the angle is an important means of adjusting the stiffness distribution as required. However, when the braiding angle is changing from an initial braiding angle to a targeted braiding angle designated by the longitudinal velocity of the mandrel, some delay occurs before the actual braiding angle reaches the targeted braiding angle. Previously, several models have been developed in order to predict braiding angles, although a prediction method for a temporal change in braiding angle caused by the mandrel velocity change has not been presented. In order to obtain the temporal change in braiding angle under unsteady-state conditions, this paper presents a step response model in braiding angle on a cylindrical braided fabric. Furthermore, the method is verified with the experimental data. As a consequence, the model has proved effective for predicting fiber orientation on a cylindrical braided preform under unsteady-state conditions.

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.

Effect of Needle Punching Process on a Chopped Strand Mat Composite with an Open Hole

The easiest and most reliable joining method is the mechanical joint with a bolt and nut or rivet. However, in the case of composite laminates, mechanical joint properties decrease because of lower interlaminar properties compared to in-plane properties around hole.xa0This study investigated needle punching process with the aim of improving the mechanical properties in the thickness direction of fiber-reinforced plastic composite laminates with an open hole. Needle punching process was applied to glass fiber chopped strand matused as the reinforcement for the composite laminates. Open-hole tensile tests and observations of end cross-sections after the tests were performed. The tensile properties and fracture mechanism of the specimens subjected to needle punching process were investigated. In addition, characteristic distance (a parameter for evaluating resistance to fracture in open-hole tensile test specimens) was also calculated to examine the effects of needle punching process conditions on fracture toughness. Tensile strength was improved by more than 15% by needle punching process. However, when a certain needle punching density was exceeded, the mechanical properties worsened. In addition, characteristic distance increased with increasing needle punching density. Thus, these results suggest that there is an optimal needle punching density with respect to strength and characteristic distance.

Microstructural Modification of AZ91 Magnesium Alloy Using Friction Stir Processing and Carbon Fibers

The microstructure of cast magnesium (Mg) alloy, AZ91, was modified by a friction stir process (FSP) technique. FSP was applied to AZ91 plate with a narrow slit, in which carbon fibers (CFs) were filled. The rotating FSP tool consisting of probe and shoulder could modify the microstructure of the material by sever plastic deformation (SPD) and simultaneously disperse CFs into the matrix. Microstructural observation revealed that sever stirring of material by a tool resulted in the grain refinement due to the dynamic recrystallization and distribution of CFs into the stir zone (SZ). The distribution was not uniform depending on the plastic flow in the SZ, but any worm-hole defects were not formed. Hardness of FSPed AZ91 in the SZ was higher than the as-casted AZ91 because of the grain refinement and distribution of hard CFs.

Investigation of Evaluation Method for Braiding Strings

The purpose of this study is to evaluate the various properties for braiding strings quantitatively. Flexibleness, compression and reconstruction properties in transverse direction was quantified by using universal testing machine, and relationship between quantitative data, feeling of human being, and braiding structure was investigated. From the result, loading and un-loading curves of the braid fabricated by an expert were smoother than that by a beginner. These results meant the braids fabricated by expert should be uniformly braided. Consequently, by understanding the internal structure of the braids and using mechanical testing for the braids, not only the quality of the braids, feature of the braids for suitable usage can be determined.