In the present study, tensile tests and creep tests of unidirectional CFRP laminates are performed at off-axis angles (15°, 30°, 45°, 60°,75°) and 90°. The purpose of this study is to model the nonlinear deformation behavior and creep deformation behavior. A CFRP material used is T 700 S/2500 carbon/epoxy system. To discuss the effect of temperature, the tests are performed at both room (25℃) and high (65℃) temperatures. In the creep tests, constant tensile stresses are applied on the specimens for 400 minutes. Both longitudinal and transverse strains are recorded as a function of time. The creep compliance increases rapidly for the specimen with large off-axis angles. To model the creep behavior, an effective creep compliance model is applied. It is found that the strain-time behavior in unidirectional laminate can be described by the effective creep compliance model.

View full abstract

Transverse strength of CFRP is very influenced by the fiber/matrix interfacial tensile strength, which is modified with physical anchor effect in irregular fiber surface. The objective of the present study is to clarify the effect of fiber surface morphology on the transverse strength and transverse cracking behavior in CFRP laminates. Tensile tests were conducted on [9010] and [03/903]s laminates with two types of carbon fiber, TR50S and TR40. TR 50S and TR40 have irregular and smooth fiber surface, respectively. Experimental results show that transverse strength is larger in laminates with TR 50 S. Transverse cracking is also suppressed in the laminates with TR50S. These results proves the high fiber/matrix tensile strength with TR50S.

View full abstract

Finite element analysis is conducted to simulate deformation in a soft organ pressed with the use of a plastic tourniquet. A model liver which consists of soft hepatic tissue covered with stiffener membrane (serosa) and contains one blood vessel is considered for simulation. Deformation and stress distribution of both the liver and plastic tourniquet pressing over it are calculated in terms of a finite element code. Effect of Young's modulus and thickness of the plastic tourniquet and effect of distance between pressing points on the stress distribution and the decrease in cross-sectional area of the blood vessel are discussed. It is found that the rate of decrease in crosssectional area of the blood vessel increases with increasing Young's modulus and thickness of the tourniquet while it decreases with increasing distance between pressing points.

View full abstract

Fracture behavior of C/C composite subjected to bi-axial tensile loading was examined using pipe specimens. The bi-axial tensile load was applied by the combination of inner pressure using water and axial load by a conventional mechanical testing machine. Preliminary experiments showed that this method was appropriate to both C/C and fiber reinforced plastic tubes. The C/C tubes exhibited higher tensile fracture strains under bi-axial tensile loading than that under uni-axial loading. This is suggested to be due to fiber/matrix interfacial fractures appeared only under bi-axial tensile loading.

View full abstract

Effect of heat treatment under magnetic field on creep characteristics of advanced heat resistant ferritic steels for USC power plants has been investigated to explore fundamental guiding principles for improving creep rupture strength of the steel at elevated temperatures over 873 K. A model steel with a composition of Fe-0.08 C-9 Cr-3.3 W -3 Co-0.2 V-0.05 Nb-0.05 N-0.005 B-0.3 Si-0.5 Mn (in mass%) has been prepared by vacuum induction melting and processed by hot-forging and rolling into a 16 mm square bar. Specimens taken from the bar were heated at 1373 K for austenitization and subsequently cooled under the magnetic field up to 3 Tesla for controlling the martensitic transformation. Creep testing were performed at 923 K and the microstructural evolution during creep was examined using FE-SEM observation and chemical analysis of the extracted residue. Creep rupture strength of the steel is found to increase by the heat treatment under magnetic field, during which martensitic transformation occurs. This is attributed to the finely distributed precipitates such as MX and M23C6 in the specimens heat treated under the magnetic field. It is thus suggested that the heat treatment under magnetic field increases the nucleation sites for precipitation during tempering, resulting in increase in the amount of the fine precipitates and retardation of growth of the precipitates.

View full abstract

A GFRP tank used for 20 years at hot water was investigated and observed at the surface and cross section of tank wall. The investigation of so long time used sample is very rare case. We can see the strange phenomenon that corrosion occurred the surface layer than the inner layer of tank wall. In generally, severe corrosion occur in the surface that contact with environmental agents. In this case, high performance matrix resin used in surface layer and something low performance matrix resin used in inner layer. This deference of corrosion performance for matrix resin is cleared for long time use.

View full abstract