Yasumasa Hamaguchi

Static and Fatigue Strengths of a G40-800/5260 Carbon Fiber/Bismaleimide Composite Material at Room Temperature and 150°C

The objective of this study was to investigate the static and fatigue strengths of a G40-800/5260 carbon fiber/bismaleimide composite material, a type of high temperature CFRP, at room temperature (RT) and 150°C and to evaluate the practicality of this material. The stacking sequence of the material is quasi-isotropic, 32 plies [+45/0/-45/90]4s. Static tensile and compressive tests were performed at RT and high temperatures for non-hole (NH) and open-hole (OH) specimens. In addition, the effectiveness of notched strength criteria was discussed on the basis of test results. Fatigue tests yielded the S-N relationships of OH specimens for three kinds of stress ratio R (=minimum stress/maximum stress), R=0.1 (tension), 10 (compression), and -1 (tension-compression) at RT and 150°C. This study laid emphasis on investigating the static and fatigue strengths at 150°C and the role of compression load repetition in tension-compression fatigue. Major findings are as follows. (1) Static NH and OH compressive strengths, OH compression fatigue strength, and OH tension-compression fatigue strength were temperature-dependent and classified as matrix-dominant properties. These fatigue strengths decreased with increasing load cycles. (2) An open hole greatly reduced static tensile and compressive strengths at both RT and 150°C. (3) The ratio of compression strength to tension strength under static or fatigue loading was fairly low for both NH and OH specimens at RT and 150°C, except for the case of NH static strength at RT. (4) The compression stress range mostly controlled fatigue lives in tension-compression fatigue tests at RT and 150°C. (5) The material tested showed no large static and fatigue strength reduction at 150°C except for NH compressive strength; however, it should be used with care when structures have open holes and encounter compression loading, especially at high temperatures.

Bonding and debonding behavior of FRP sheets under fatigue loading

The purpose of this study is to improve the examining and understanding of the bonding behavior of Fiber Reinforced Polymer (FRP) sheets bonded to concrete blocks and steel plates under fatigue loading. First, a series of experimental investigations is summarized in the paper. The fatigue behavior of bonding surface between FRP sheets and concrete is finally characterized by the conducted P–S–N diagram representing the relationship among the probability of FRP debonding (P), the bond stress amplitudes (S), and the number of cycles (N) at debonding on a semi-logarithmic scale. The different debonding modes for various fracturing surface are also investigated and evaluated.

Impact damage and CAI strength of MR50K/PETI5 carbon/tough-polyimide composite at room and high temperatures

This study determined the compression-after-impact (CAI) behavior and strength of a carbon/tough-polyimide composite material, MR50K/PETI5, whose PETI5 resin has been specially developed for the next generation supersonic transport (SST) at NASA. First, an impact test imposed impact damage on CAI specimens at room temperature, and the load and absorbed energy were measured; in addition, the damage was examined with an ultrasonic C-scanner and a 3D ultrasonic inspection system. Second, CAI strength and failure strain were measured at room temperature and at 180° C. Third, the damage induced by the CAI test was examined with an optical microscope. Test results were compared with those of T800H/PMR-15 carbon/polyimide composite, where PMR-15 is a typical brittle resin, and the characteristic CAI behavior and strength of a carbon fiber/highly-tough resin composite were determined.

Microcracking and Compressive Strength Degradation of Carbon Fiber/Polyimide Resin Composites by Thermal Cycling

The objective of this study was to investigate the effect of thermal cycles, encountered by an Super Sonic Transport (SST) in service, on the cumulative frequency of microcracks and the degradation of compressive strength in carbon fiber/polyimide resin composite materials.One thermal cycle was designated as a sequence from room temperature (RT) to -54°C, and then to +177°C, finally back to RT. Transverse microcracks initiated on the sectional free edge surface of the laminates were observed and counted by using an optical microscope. Approximate 10000 thermal cycles were given for five kinds of carbon fiber/polyimide composite material: IM7/PIRA, IM600/PIXA-M, IM600/PIXA-MT3, IM7/K3B, IM7/R1-16, as well as a Ti/Gr (polyimide CFRP) fiber metal laminate. For IM7/R1-16 thermal cycling tests were conducted up to 40000 cycles.Transverse microcracks were observed not only on the sectional free edge surface but also on the inside cross section of specimens cut after thermal cycling tests for IM7/R1-16. Static open-hole-compressive (OHC) strength was measured at RT before and after thermal cycling tests on the five kinds of material except for IM7/PETI-5. Static nonhole-compressive (NHC) strength was measured at RT on IM600/PIXA-M and IM600/PIXA-MT3. In addition, in order to know the estimates of thermal stress generated by the thermal cycles, the thermal stresses were calculated by the classical lamination theory (CLT) using basic lamina data given in a reference.

Statistical analysis of S-N data of carbon/epoxy composites obtained by axial-load fatigue tests.

Fifteen sets of S-N data of carbon/epoxy composites obtained by axial-load fatigue tests were collected from published papers and statistically analyzed. For simplicity of the analysis, the analyzing range of S-N observations in a set of S-N data was limited and the form of S-N curve and the distribution of fatigue life were assumed realistically. Fatigue life scatter and fatigue strength scatter were derived from the deviations of S-N observations from the S-N curve of which equation was determined by the least-squares method. It was found that the amount of fatigue strength scatter is practically constant regardless of S-N data obtained at different laboratories and the amount of fatigue life scatter is dependent of the slope of the S-N curve.