Influences of stress ratio on constant amplitude fatigue behavior of CFRP laminates have been examined and a rational fatigue life prediction method has been developed. First, constant-amplitude ...fatigue tests are performed at room temperature on a quasi-isotropic CFRP laminate 45/90/-45/0 2s for six kinds of stress ratios. The experimental results show that fatigue strength is lower for fatigue loading with larger amplitude. It is observed that the stress amplitude for a given fatigue life becomes largest under a fatigue condition in which stress ratio is equal to the ratio of compressive strength to tensile one. A procedure to construct a nonlinear constant fatigue life (CFL) diagram is developed on the basis of the static strengths in tension and compression and the reference S-N relationship for a critical stress ratio equal to the compression-tension static strength ratio. The fatigue lives predicted on the basis of the nonlinear CFL diagram agree well with the experimental results over the range of fatigue life up to 106 cycles for all the stress ratios tested. It is demonstrated that the proposed fatigue life prediction method can also be successfully applied to the fatigue behavior of different types of CFRP laminates 0/60/-60 2s, and 0/90 3s.
A large part of surreys, pastes and thick emulsions exhibit as a yield stress fluid and they sometimes show a wall-slip that forms a low-viscous shear layer near the wall surface. The occupation of ...the wall-slip makes lower the apparent viscosity and induces misunderstanding about the rheological property of the test sample. The wall-slip appears easier on the lower roughness of the wall. We measure the stress-strain-shear rate relations of a yield stress fluid using the parallel plate flow cells, which have a different roughness, and examine the viscous and elastic contributions on the strain. In order to evaluate the viscous and elastic contribution of the strain, the one-mode Maxwell model fitting is applied to the stress-strain relationship below the yield stress point. The strain induced by the viscosity is strongly affected by the roughness of the plate and the apparent viscosity in the smooth plate decreases below 1/10 to the rough plate's viscosity. To avoid the wall-slip effect to the viscosity without making the plate rough, we propose that a small number of spherical particles disperse the test fluid to block the flow at the vicinity of the wall. The dispersing particles do not change the elasticity, but the viscosity can be improved up to the rough plate's value.
The prefrontal cortex and the basal ganglia form mutually connected networks and are thought to play essential roles together in guiding goal-directed behaviors. Yet, these structures seem to have ...independent pathways to motor outputs as well, suggesting differential contributions to goal-directed behaviors. We hypothesized that the prefrontal cortex guides actions to a direction required by external demands and the basal ganglia guide actions to an internally motivated direction. To test this hypothesis, we used a task in which monkeys were required to make a memory-guided saccade to a direction indicated by a visual cue while only one direction was associated with reward. We observed a functional dissociation between the lateral prefrontal cortex (LPFC), which commonly represented the cue direction, and the caudate nucleus (CD), which commonly represented the reward-associated direction. Furthermore, cue-directed and reward-directed signals were integrated differently in the two areas; when the cue direction and the reward direction were opposite, LPFC neurons maintained tuning to the cue direction, whereas CD neurons lost the tuning. Different types of spatial tuning in the two brain areas may contribute to different types of goal-directed behavior.
A subset of caudate neurons fires before cues that instruct the monkey what he should do. To test the hypothesis that the anticipatory activity of such neurons depends on the context of ...stimulus-reward mapping, we examined their activity while the monkeys performed a memory-guided saccade task in which either the position or the color of a cue indicated presence or absence of reward. Some neurons showed anticipatory activity only when a particular position was associated with reward, while others fired selectively for color-reward associations. The functional segregation suggests that caudate neurons participate in feature-based anticipation of visual information that predicts reward. This neuronal code influences the general activity level in response to visual features without improving the quality of visual discrimination.
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