The present study proposed a method to evaluate the cure shrinkage process using the microbond specimens of an epoxy resin droplet adhered to a single carbon fiber, and discussed the interacted process of fiber-resin adhesion and resin curing in the residual stress development which occurs in the carbon-fiber-reinforced thermoset-epoxy composites. In our experiments, microbond specimens were first prepared and observed with an optical microscope under an isothermal heating condition. Moreover, we utilized the image processing techniques based on Carroll’s theory for the geometrical shape of resin droplets to evaluate the time variation in the characteristic shape parameters during the resin curing process, including droplet volume, diameter, contact angle on the fiber, and fiber embedded length. We compared the results among three different heating conditions for the resin curing and those between non-vacuum and vacuum conditions when the microbond specimen was prepared as well, and discussed the validity of the proposed method by investigating the characteristics of resin curing process. From the results, we confirmed that the volume change during the curing could be appropriately evaluated when the microbond specimen was placed in a vacuum for the degassing before the curing. Moreover, the results revealed that the fiber-resin interaction significantly reduced the cure shrinkage at the fiber/resin interface. It implies that the suppression of the cure shrinkage in the vicinity of the interface may lead to the build-up of the residual stress.
The purpose of our study is to investigate the influence of fiber breakages of recycled carbon fibers at pelletizing on a tensile strength of the composite. The recycled carbon fibers used in this study were obtained by extracting from a wasted prepreg by pyrolysis method in a muffle furnace under air condition at 600℃ for 30, 90 and 180 min, respectively. It was confirmed, at first, the tensile strength was reduced since tiny flaws on the carbon fiber were induced due to oxidization in a recycling process. Recycled carbon fibers were compounded with PP (polypropylene) resin by twin extruder machine where the conditions of the barrel temperature and screw rotation were changed. A specific mechanical energy (SME) for extruding unit mass of compound was introduced by monitoring the rotational torque and the revolutions of the extruder machine, in order to discuss the changes of residual fiber lengths in pellets. Master curve was prepared to show the relation between residual mean fiber length in the pellet and the SME, considering the change of strength of the single recycled carbon fiber. It seemed that the shift factor was related with the fiber stress on the fiber at the extrusion. Residual mean fiber length in the molded specimen was also predicted where a mechanical model proposed was referred considering the master curve for calculating the strengths of composites with chopped recycled carbon fibers. The estimated strengths in this study well agreed with experimental data.
To study the effects of specimen size and tensile-torsional combined stress ratio on fracture strength in compression molded short-glass-fiber-reinforced phenolic resin composites (SGP), tensile-torsional combined tests were carried out using round-bar specimens. Moreover, the finite element method analysis was employed to calculate the effective volume of the specimen. Finite element models were validated by the digital image correlation techniques. The fracture strength followed the Tsai-Hill failure criterion in the tensile-torsional stress plane. The angle of fracture surfaces was approximately perpendicular to the maximum principal stress directions. The greatest value of maximum principal stress was therefore assumed as fracture strength of SGP. The fracture strength was decreased with increasing the effective volume of the specimen regardless of fiber volume fraction and loading mode. Those relationships were well described by the equation of the effective volume theory as the double logarithmic chart based on Weibull statistical theory.
The effects of loading rate on the crack growth behavior of adhesively bonded carbon fiber reinforced plastic (CFRP) joints were investigated. The split Hopkinson pressure bar (SHPB) apparatus and the digital image correlation (DIC) technique were employed to obtain the mode I fracture toughness of adhesively bonded CFRP joints during crack propagation. The fracture toughness of titanium alloy adhesively bonded joints was also obtained for comparison. The effect of bending vibration caused by inertial force was suppressed by controlling the incident wave of the SHPB apparatus in the impact test. In addition, the strain based evaluation formula was used for the fracture toughness tests in order to improve the accuracy of the fracture toughness evaluation. The fracture toughness of the CFRP adhesively bonded joints slightly increased as loading rate increased at the onset of crack growth. However, it slightly decreased during crack propagation with increasing loading rate for the loading rate of less than 1.67 × 10-2m/s and it increased for the loading rate of greater than 1.67 × 10-2m/s. The loading rate dependence of the titanium alloy adhesively bonded joints did not appear both at the onset of crack growth and during crack propagation. The fracture toughness of the CFRP adhesively bonded joints was higher than those of the titanium alloy adhesively bonded joints regardless of loading rate.
The size distributions of ejecta resulting from projectile perforation of CFRP (carbon fiber reinforced plastic) plates were examined. Size of ejecta collected from the test chamber after impact experiments were measured. The effects of projectile diameter and specimen thickness on size distribution of ejecta were examined. Penetration hole area increased with projectile diameter. The projectile diameter increased ejecta size and the number of ejecta on the impact side and rear side of targets. Most of the ejecta showed aspect ratio less than 0.2. The specimen thickness also increased ejecta size and the number of ejecta other than the projectile diameter of 1.6 mm. When the projectile diameter was 1.6 mm and the impact velocity was 3.5 km/s, the specimen thickness did not affect ejecta size and the number of ejecta. When the vertical axis of the ejecta distribution with respect to aspect ratio was divided by the number of ejecta having length over 3 mm, all results of t/d < 1 were roughly on a curve for impact side and rear side respectively. Experimental formulas for the curves were proposed.
The application of Glass Fiber Reinforced Thermoplastics (GFRTP) using continuous fibers is increasing in automotive industry due to their affordable prices with good mechanical properties. Diaphragm molding, which is one of molding methods of GFRTP, has the advantage in the molding cost because this method requires only a single die instead of the matched dies. In diaphragm molding, GFRTP are placed on the single mold and an upper diaphragm material is pressed against the mold by air pressure to mold. As a disadvantage of this method, since it is difficult to apply a blank holding force, wrinkles are easily formed. While in the laying-up test for FRP and the drape test for NCF, it has been reported that the formability was improved by using in-plane tension to the ± 45° direction of blank material, it is also expected in the diaphragm molding. To reduce the cost of trial molds and shorten a trial manufacture period, it is important to analyze the formability of the diaphragm molding. In this study, the diaphragm molding of GFRTP using in-plane tension by springs to ± 45° direction of blank material was conducted to improve the formability, and the FEM analysis of diaphragm molding was carried out and compared with the experimental result. By applying the in-plane tension to the blank material, the diaphragm molding formability was improved because of the larger shear angle of ± 45° direction of blank materials. The shear angle and wrinkle positions in diaphragm molding can be predicted by FEM analysis.
Carbon Fiber Reinforced Thermoplastics (CFRTP), which have high specific strength and specific rigidity, superior productivity and recyclability, have been expected to reduce the weight of cars. Since the thermoplastics resin has higher viscosity than thermosetting resin during molding process, the deformation characteristic of CFRTP in the molten state depends on the material properties of the resin. It is necessary to clarify the mechanical properties of CFRTP under high temperature that is higher than melting point of the matrix resin. While bias-extension test using temperature controlled chamber has been applied for the evaluation of mechanical properties of CFRTP under high temperature, strain measurement is one of the important issues to be overcome. In this study, tensile test of FRTP under high temperature over melting point of the matrix resin by using far infrared ray heaters to heat only the gauge of specimen has been developed. This method allows us to observe the specimen surface and to measure strain of the specimen. Mechanical properties of CF/PA6 have been evaluated under high temperature by this method. The tensile strength and tensile modulus of CF/PA6 decreased as the temperature increased, and even under the high temperature, which is higher than the melting point of the matrix resin, the effect of the viscosity of the matrix resin should be taken into account. Under the relatively higher temperature condition (e. g. 280°C), smaller shear deformation occurred and larger shear locking angle of CF/PA6 was obtained due to lower viscosity of matrix resin. On the other hand, under the relatively lower temperature condition (e. g. 240°C) shear locking angle of CF/PA6 became smaller, i. e. larger shear deformation after the stretching between fiber bundles occurred due to higher viscosity of the matrix resin.
The cementitious material deterioration by biogenic sulfuric acid attack in sewage environments has become a severe problem for sewage related facilities. In general, it has been said that by using blast furnace slag sand to cementitious material is improved the resistance to sulfuric acid attack. In this research, we focused on blast furnace slag sand, and investigated, on resistance to sulfuric acid attack of mortar, the influence each of chemical composition, fineness modulus and sand to cement ratio of mix proportion. As a result, we indicated that the relationship between sulfuric acid attack resistance of mortar by using blast furnace slag sand and chemical composition of CaO, and fineness modulus, and sand to cement ratio of mix proportion, was a linear, respectively. We also indicated that sulfuric acid attack resistance of mortar by using blast furnace slag sand was improved larger chemical composition of CaO, smaller fineness modulus and larger sand to cement ratio, respectively. We found that by a change of 1% in chemical composition of CaO, by a change of 1.00 in fineness modulus and by a change of 1.0 in sand to cement ratio were changed the mortar weight loss of about 5%, about 13% and about 2.6～3.7%, respectively. Moreover, from the result of multiple linear regression analysis, it was clear that fine particle of under 0.3mm of blast furnace slag sand was improved the sulfuric acid attack resistance of the mortar.
Fabrication of high Curie-point (Tc) PTCR materials using BaTiO3 (BT) -(Bi1/2Na1/2)TiO3 (BNT) ceramics was investigated. Fine powders of BaTiO3, which was synthesized by thermal process, were used as starting materials. BaTiO3 powders, Bi2O3, Na2CO3, TiO2 and Gd(NO3)3 (water solution) were mixed with (C2H5O)4Si by wet milling for 24h. After drying, the powders were pressed into disks, which were a diameter at 20mm and thickness of 2mm. These disks were sintered in air at 1340℃ for 2h. Gd-doped 95 mol% BT-5 mol% BNT samples with 1.2 mol% of excess of Na2CO3 have low room-temperature resistivity (ρRT) in the range of Gd concentration from 0.08 to 0.1 mol%. Tc of the samples increased from 170℃ to 180℃ with an increase in the amount of BNT (5 to 8 mol%). As a result, 0.1 mol% Gd and 1.6 mol% of excess Na2CO3 doped 92 mol% BT-8 mol% BNT sample has ρRT of 1500 Ω・cm and PTCR jump of 4.6 orders of magnitude with Tc about 180℃.
Appropriate ceramic materials with strong adhesion to a resin, which is used for thin-film devices, were selected by using a combination of an orthogonal array and a response-surface method. In this technique, at the first step, important factors that significantly influence the adhesion strength were selected from various factors that characterize ceramic materials by using an orthogonal array with molecular simulations. As a result, the short-side and long-side lattice constants a and b were selected from four ceramic-material factors (a, b, the surface energy density, S, and the cohesive energy, C). At the second step, the adhesion strength was described as a function of the selected important factors by using a response-surface method. From this function, the ideally most appropriate values for a and b that made the adhesion strength maximum were obtained. The ideal values for a and b were obtained as 0.245nm and 0.424nm, respectively. At the third step, the most appropriate ceramic material whose lattice constants were the closest to the ideal values (a =0.245nm and b=0.424nm) was selected by use of the simulation results of lattice constants. As a result, a SiO2/Al2O3/TiO2 multilayer whose lattice constants were a =0.243nm and b =0.421nm (the closest to the ideal values) was selected as the most appropriate ceramic material with the strongest adhesion to the resin.