In order to quantitatively evaluate the reforming effect of the silicate-based surface penetrants on the mortar, silicate-based surface penetrants were applied to the mortar and a Vickers hardness test was carried out. The test factors were the W/C of the mortar, the amount of the silicate-based surface penetrants used, the main component of the silicate-based surface penetrants, the molar ratio of the silicate-based surface penetrants, and the surface water content of the mortar. In the Vickers hardness test, the amount of increase in Vickers hardness and the range of increase in Vickers hardness (reforming depth) were used as evaluation items. From these series of results, the effects of each test factor examined on the increase in Vickers hardness and the reforming depth due to the application of the silicate-based surface penetrants were summarized. The increase in surface moisture content affected both the amount of increase in Vickers hardness and the depth of reformation. The W/C of the mortar affected the increase in Vickers hardness. In addition, the amount of surface penetrants used and the main component of the surface penetrants affected the reforming depth.

This study examines the mechanical properties and heat resistance of polypropylene (PP) /polyamide6 (PA6) composites containing small amounts of cellulose nanofibers (CNFs). Powdered CNFs with a length of 10μm or above, and diameters of 20nm were used. Using twin-screw extruder operating at 150rpm and 200°C, CNF/PP/PA6/MAPP composites were prepared by using melt-kneading. To form good interface between CNFs and PP, maleic acid polypropylene (MAPP) was filled in the matrix of composites. Using the manufactured composites, tensile, bending and Charpy impact tests, and deflection temperature measurements were performed. As a result of these tests, Young’s modulus and Charpy impact strength of 1wt%CNF/PP/PA6/MAPP composites were higher than those of PP/PA6/MAPP composites when PA6 weight fraction was changed from 5 to 20wt%. Moreover, the deflection temperature of 1wt%CNF/PP/PA6/MAPP composites was higher than that of PP/PA6/MAPP composites. The addition of 1wt%CNF improved synergetic effect of PA6 and PP.

To investigate the effect of the direction of fiber orientation of the adherend CFRP on fatigue behavior of adhesively bonded CFRP/aluminum joints, fatigue crack growth tests were conducted on double cantilever beam (DCB) joints with unidirectional and woven CFRP and aluminum alloy adherends using a heat cured filmy type epoxy adhesive. Fatigue crack growth tests showed that fatigue threshold, Δ G_th of the woven CFRP/aluminum joint was slightly larger than that of the unidirectional CFRP/aluminum joint, and the slope of region II of the crack growth rate for the woven CFRP/aluminum joint was smaller than that of the unidirectional CFRP/aluminum joint. Moreover, it was also observed that cracks propagated to the aluminum interface for the unidirectional CFRP/aluminum joints and to the CFRP interface for the woven CFRP/aluminum joints. To investigate the cause of the difference in crack propagation direction between the two types of joints, crack propagation simulation was conducted using the finite element method for two types of joints, crack growth analysis also revealed that cracks of both the unidirectional and woven CFRP/aluminum joints propagated toward the CFRP interface. The direction of crack growth of the woven CFRP/aluminum join was consistent with the simulated result, whereas the direction of the unidirectional CFRP/aluminum joint differed from the simulated results. This cause was assumed to be due to that the maximum value of normal stress on the unidirectional CFRP/aluminum interface was larger than the maximum value on the woven CFRP/aluminum interface.

Advanced lightweight and heat-resistant materials that can be applied to blades in jet engine have been actively developed. Ceramic-matrix composites are addressed as one of the candidates. In contrast, attention has been focused on the microstructural control based on biomimetic knowledge to realize even better heat-resistant materials. In this study, we focused on red abalone consisting mainly of a nacreous layer and investigated its mechanical properties. As a result, it was found that the nacreous layer composed of calcium carbonate exhibits nonlinear deformation behavior, which is attributed to the sliding deformation of the organic layer between the plates. A finite element analysis was also performed based on the brick model, which introduces a nonlinear cohesive model for layer cracking and interlayering. The results showed that the nonlinear deformation behavior and the zigzag propagation of cracks in the microstructure can be simulated adequately. In the future work, we will investigate the block shape in the brick model from rectangular to polygonal and the material constants in the adhesion model on the macroscopic deformation behavior and fracture toughness values.

In this study, experimental investigations were conducted to create fatigue limit diagrams for NSSC180 ferritic stainless steel, which is used for automobile exhaust system parts, subjected to excess deformation, in order to clarify the relationship between the mean stress and the fatigue limit. The fatigue tests were conducted under a fixed maximum stress, which allowed a fatigue design diagram to be obtained. The results indicated that the fatigue limit curve has a region where the effect of increasing the mean stress on the decrease in the fatigue limit is more moderate than that predicted by a modified Goodman line. Furthermore, it was found that a fatigue design based on static crack initiation is more appropriate than the modified Goodman line for higher values of mean stress.

Creep property of abnormal structure formed in long-term used Mod.9Cr-1Mo steel weldments and its effect on creep strength of welded joint are presented. The abnormal structure is defined as a structure in which the hardness is clearly lower than that in the normal region, and the grain is coarsened. Creep strength of the abnormal structure is significantly lower than that of normal weld metal and base metal. The creep remaining life of aged materials in the actual service condition is estimated using standard specimen. The predicted creep lives with abnormal structure are shorter than those without abnormal structure and the data are correlated below 99% confidence lower limit of welded joint of Gr. 91 steel. Full thickness welded joint specimen consisting of more than half abnormal structure in the weld metal ruptured at the weld metal before the HAZ. Time to creep rupture decreased with increasing the abnormal structure ratio in thickness direction. Finally, a simplified prediction method is developed to predict creep life of welded joint with abnormal structure formed in weld metal.

In order to predict the failure of mechanical parts, it is necessary to understand the residual stress and its source, the inherent strain. In this study, the distribution of three-directional residual stress components was measured for a carburized18NiCrMo14-6 cylindrical roller test piece which has 80 mm diameter and 240 mm length using a method combining the contour method and the X-ray diffraction method (the extended contour method). Moreover, the inherent strain distribution was evaluated from measured residual stress by inverse analysis. First, it was shown that the distribution of three-directional residual stress components can be accurately reproduced using the extended contour method by numerical experiments of a carburized cylindrical specimen. Next, it was demonstrated that the distribution of three-directional residual stress components can be measured using general-purpose equipment by actually measuring the same type specimen. Furthermore, the inherent strain distribution was evaluated. Compressive residual stress and corresponding inherent elongation strain were detected in the carburized layer. In contrast, tensile stress and inherent shrinkage strain were determined in the layer just below the case. Finally, the factors that generate each inherent strain have been investigated by thermo-elastic-plastic analysis. Possible explanations are (i)the increase in transformation strain due to the change in carbon content, (ii)the delay in martensite transformation and (iii)the decrease in martensite transformation rate due to the decrease in the cooling rate at the core.