The setup and application of the multi-scale in-situ test system for fatigue damage analysis

This essays aims at introducing the setup for the multi-scale in-situ test system which is applied for the fatigue crack initiation test. The setup of the experiment system is first introduced, including the image capturing system, optical path system, image acquisition and storage system and the three-axis mobile platform. Then the preparation of micro speckle and the corresponding technique for spatial adjustment are improved to realize the DIC measurement in micro scale. Finally three experiments from macro-meso scale to macro scale: fatigue initiation test, the observation of micro crack and the fatigue crack growth rate in macro scale were conducted to verify the application of the system. The test result can indicate the location of crack initiation, the crack growth rate and the evolution of displacement/strain field, etc

The setup and application of the multi-scale in-situ test system for fatigue damage analysis

This essays aims at introducing the setup for the multi-scale in-situ test system which is applied for the fatigue crack initiation test. The setup of the experiment system is first introduced, including the image capturing system, optical path system, image acquisition and storage system and the three-axis mobile platform. Then the preparation of micro speckle and the corresponding technique for spatial adjustment are improved to realize the DIC measurement in micro scale. Finally three experiments from macro-meso scale to macro scale: fatigue initiation test, the observation of micro crack and the fatigue crack growth rate in macro scale were conducted to verify the application of the system. The test result can indicate the location of crack initiation, the crack growth rate and the evolution of displacement/strain field, etc

A collision-free trajectory planning method for redundant manipulator spraying for inner surface of pipe

Obstacle avoidance is an important content in the research of redundant manipulator. To automate spraying for inner surface in a complex curved pipe, its a challenge to plan collision-free trajectory for the manipulator. A hybrid planning algorithm based on genetic algorithm and pseudo-inverse method is presented in this paper. Firstly, the collision problem between the manipulator and curved pipe is simplified to collision detection problem between polyhedron. The manipulator joints are represented by bounding volumes, and the curved pipe is deemed to polyhedron. Secondly, in the hybrid genetic algorithm, the initial population is obtained by using the pseudo-inverse method, by establishing the distance relationship between the vertices of the bounding volume and its cross-sectional plane polygon. The fitness function is constructed to evaluate the collision situation between the manipulator and pipe. Via the continuous evolution of the population, the collision-free trajectory is obtained finally

The study of the relationship between life limiting factor and stress level for FGH96

FGH96 is a Chinese made powder metallurgy nickel based superalloy. This reserach aims to investigate the effect of stress on the microstructure of the worst fatigue life at 600°C. The specimens were first polished by abrasive paper and then electropolished to elimate the effect of surface residual stress. The fatigue tests were conducted at 600°C, and the loading ratio was 0.05 at the frequency of 5Hz. Tests were conducted at 900, 1000, 1100, 1200MPa respectively. The fatigue life under the same condition were compared and the fractography of specimens were examined under SEM to further identify the life-limiting factors of the material. The initiation mode transferred from facet initiated to inclusion initiated from lower stress level to higher stress level. Meanwhile, the initiation position transferred from internal to surface with the increase of stress level. This means at higher stress level, fatigue life is mainly limited by inclusion at surface while at lower stress level the limit is controlled by internal facet

Influence of orientation and temperature on the fatigue crack growth of directionally solidification superalloys DZ125

The influence of orientation and temperature on the fatigue crack growth of a directionally solidification superalloys named DZ125 were investigated in this study. The specimens were designed based on ASTM E647 standard and the compliance method was employed to monitor the crack growth. Tests were conducted at room temperature, 760°C and 850°C respectively. The longitudinal and transverse orientation were both studied in this tests. Results show that the orientation dependence is weak at elevated temperature compared with that at room temperature. However, the temperature influences the fatigue crack growth rate significantly and the largest difference can be an order of magnitude on the da/dN-ΔK graph. But the reduction in higher ΔK area of elevated temperature can still be observed. Potential reasons and hypothesis were explained in this paper. In addition, the crack growth mode appears to transfer from type I with the increase of temperature which also reflects the influence of temperature

The study of the relationship between life limiting factor and stress level for FGH96

FGH96 is a Chinese made powder metallurgy nickel based superalloy. This reserach aims to investigate the effect of stress on the microstructure of the worst fatigue life at 600°C. The specimens were first polished by abrasive paper and then electropolished to elimate the effect of surface residual stress. The fatigue tests were conducted at 600°C, and the loading ratio was 0.05 at the frequency of 5Hz. Tests were conducted at 900, 1000, 1100, 1200MPa respectively. The fatigue life under the same condition were compared and the fractography of specimens were examined under SEM to further identify the life-limiting factors of the material. The initiation mode transferred from facet initiated to inclusion initiated from lower stress level to higher stress level. Meanwhile, the initiation position transferred from internal to surface with the increase of stress level. This means at higher stress level, fatigue life is mainly limited by inclusion at surface while at lower stress level the limit is controlled by internal facet

Influence of orientation and temperature on the fatigue crack growth of directionally solidification superalloys DZ125

The influence of orientation and temperature on the fatigue crack growth of a directionally solidification superalloys named DZ125 were investigated in this study. The specimens were designed based on ASTM E647 standard and the compliance method was employed to monitor the crack growth. Tests were conducted at room temperature, 760°C and 850°C respectively. The longitudinal and transverse orientation were both studied in this tests. Results show that the orientation dependence is weak at elevated temperature compared with that at room temperature. However, the temperature influences the fatigue crack growth rate significantly and the largest difference can be an order of magnitude on the da/dN-ΔK graph. But the reduction in higher ΔK area of elevated temperature can still be observed. Potential reasons and hypothesis were explained in this paper. In addition, the crack growth mode appears to transfer from type I with the increase of temperature which also reflects the influence of temperature

Microstructure-sensitive modeling of competing failure mode between surface and internal nucleation in high cycle fatigue

Competing fatigue failure between the surface and internal nucleation has been widely observed in metals under the high cycle fatigue regime. To characterize different boundary conditions in surface and internal grain aggregates, a hybrid statistical volume element model was developed by binding two identical periodic stochastic polycrystal microstructure cubes together and superimposing them with a new 2.5 directional periodic boundary condition afterwards. Additional isotropic elastic media was attached on the surface of the hybrid statistical volume element model to represent the oxide layer formed at elevated temperature. Microstructure-sensitive modeling with a crystal plasticity model was implemented by computing multiple hybrid statistical volume elements under two stress levels. The results implied that grains in the surface volume of the hybrid statistical volume element generally tended to deform more easily than their counterparts in the internal one, and the oxide layer had a weak effect in suppressing the surface deformation. It was also demonstrated that the combination of the 2.5 directional periodic boundary condition, additional oxide layer and nonlinear constitutive model jointly brought stochastic effect into the two identical microstructural cubes. Significant competition between the surface and internal nucleation was captured under both stress levels. Since the detrimental influence of oxidation in accelerating crack formation was not considered, the lifetimes from both types of nucleation were overlaid on each other. Given the disruption of the oxide layer under high stress levels, the simulation reproduced the experimental discovery that the probability of surface nucleation increases with the ascending stress level. It is also clarified that the oxide layer cannot prevent surface nucleation under low stress levels, rejecting the hypothesis of the impact of the oxide layer on complete internal nucleation

Recent Discovery of Nitrogen Heterocycles from Marine-Derived <i>Aspergillus</i> Species

Nitrogen heterocycles have drawn considerable attention because of their structurally novel and significant biological activities. Marine-derived fungi, especially the Aspergillus species, possess unique metabolic pathways to produce secondary metabolites with novel structures and potent biological activities. This review prioritizes the structural diversity and biological activities of nitrogen heterocycles that are produced by marine-derived Aspergillus species from January 2019 to January 2024, and their relevant biological activities. A total of 306 new nitrogen heterocycles, including seven major categories—indole alkaloids, diketopiperazine alkaloids, quinazoline alkaloids, isoquinoline alkaloids pyrrolidine alkaloids, cyclopeptide alkaloids, and other heterocyclic alkaloids—are presented in this review. Among these nitrogen heterocycles, 52 compounds had novel skeleton structures. Remarkably, 103 compounds showed various biological activities, such as cytotoxic, antimicrobial, anti-inflammatory, antifungal, anti-virus, and enzyme-inhibitory activities, and 21 compounds showed potent activities. This paper will guide further investigations into the structural diversity and biological activities of nitrogen heterocycles derived from the Aspergillus species and their potential contributions to the future development of new natural drug products in the medicinal and agricultural fields