Based on Tanaka and Mura’s fatigue model and Griffith theory for fracture,an energy-equilibrium model was proposed to explain the complex stress effect on fatigue behavior.When the summation of the elastic strain ene...Based on Tanaka and Mura’s fatigue model and Griffith theory for fracture,an energy-equilibrium model was proposed to explain the complex stress effect on fatigue behavior.When the summation of the elastic strain energy release and the stored strain energy of accumulated dislocations reach the surface energy of a crack,the fatigue crack will initiate in materials.According to this model,for multiaxial stress condition,the orientation of the crack initiation and the initiation life can be deduced from the energy equilibrium equation.For the uniaxial fatigue loading with mean stress,the relation between the maximum stress or the minimum stress and the stress amplitude is in agreement with an ellipse equation on the constant life diagram.If the ratio of the mean stress to stress amplitude is less than a critical value-0.17,and the stress amplitude keeps constant,the fatigue crack initiation life will decrease with the increase of the compress mean stress.In this model,the mean stress does not cause damage accumulation with the fatigue cycles in crack initiation.For this reason,the loading sequence of different load levels would induce the cumulative damage to deviate from the Palmgren-Miner cumulative damage rule.The procedure of estimating the damage under random loading is also discussed.展开更多
The characteristic of enterprise competitiveness is different between different life cycle stages. In this paper we surveyed the enterprise competitiveness＇s differences in various stages of the life cycle and the ev...The characteristic of enterprise competitiveness is different between different life cycle stages. In this paper we surveyed the enterprise competitiveness＇s differences in various stages of the life cycle and the evolution model of three aspects of enterprise com- petitiveness as resource, capability and dynamic capability by questionnaire survey. The result shows that there are significant differences between different life cycle stages of en- terprise competitiveness in China. The enterprise competitiveness is stronger and stronger during the periods from the enterprise＇s birth to maturity, while in the enterprise＇s recession period the competitiveness becomes much weaker. The competitiveness＇s constitutive features in each stage are as follows： in the enterprise＇s born stage the enterprise is lack of resources and its competition mainly relies on the ability; in the enterprise＇s growth stage the enterprise＇s resources become richer and are as important as enterprise＇s ability in the constitution of enterprise competitiveness; in the maturity stage the enterprise＇s people, money and material resources all become very rich but the role of capability in enterprise competitiveness begins to decrease; in the enterprise＇s recession stage the en- terprise resources begin to exhaust, and the enterprise＇s competitiveness returns to rely on capability, and in this period the enterprise＇s learning ability, innovation ability and dynamic mechanisms perform worst, which will affect the enterprise＇s revival and lead to the ultimate death of enterprise. These conclusions have great value for reference to the enterprise＇s competitive strategy making for different life cycle stages.展开更多
基金supported by the National Basic Research Program of China (Grant No. 2012CB937500)the National Natural Science Foundation of China (Grant Nos. 11072243 and 11202210)
文摘Based on Tanaka and Mura’s fatigue model and Griffith theory for fracture,an energy-equilibrium model was proposed to explain the complex stress effect on fatigue behavior.When the summation of the elastic strain energy release and the stored strain energy of accumulated dislocations reach the surface energy of a crack,the fatigue crack will initiate in materials.According to this model,for multiaxial stress condition,the orientation of the crack initiation and the initiation life can be deduced from the energy equilibrium equation.For the uniaxial fatigue loading with mean stress,the relation between the maximum stress or the minimum stress and the stress amplitude is in agreement with an ellipse equation on the constant life diagram.If the ratio of the mean stress to stress amplitude is less than a critical value-0.17,and the stress amplitude keeps constant,the fatigue crack initiation life will decrease with the increase of the compress mean stress.In this model,the mean stress does not cause damage accumulation with the fatigue cycles in crack initiation.For this reason,the loading sequence of different load levels would induce the cumulative damage to deviate from the Palmgren-Miner cumulative damage rule.The procedure of estimating the damage under random loading is also discussed.
文摘The characteristic of enterprise competitiveness is different between different life cycle stages. In this paper we surveyed the enterprise competitiveness＇s differences in various stages of the life cycle and the evolution model of three aspects of enterprise com- petitiveness as resource, capability and dynamic capability by questionnaire survey. The result shows that there are significant differences between different life cycle stages of en- terprise competitiveness in China. The enterprise competitiveness is stronger and stronger during the periods from the enterprise＇s birth to maturity, while in the enterprise＇s recession period the competitiveness becomes much weaker. The competitiveness＇s constitutive features in each stage are as follows： in the enterprise＇s born stage the enterprise is lack of resources and its competition mainly relies on the ability; in the enterprise＇s growth stage the enterprise＇s resources become richer and are as important as enterprise＇s ability in the constitution of enterprise competitiveness; in the maturity stage the enterprise＇s people, money and material resources all become very rich but the role of capability in enterprise competitiveness begins to decrease; in the enterprise＇s recession stage the en- terprise resources begin to exhaust, and the enterprise＇s competitiveness returns to rely on capability, and in this period the enterprise＇s learning ability, innovation ability and dynamic mechanisms perform worst, which will affect the enterprise＇s revival and lead to the ultimate death of enterprise. These conclusions have great value for reference to the enterprise＇s competitive strategy making for different life cycle stages.
