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Advanced Engineering Science

Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-16-10-2021-31
Total View : 2

Abstract :

Inverted planetary roller screw (IPRS) is a kind of linear transmission mechanism which has advantages of high load carrying capability, long fatigue life, high transmission accuracy and low noise. Due to these advantages, it has wide application prospect in the fields of aerospace, weapon equipment, CNC machine tools and petrochemical industry. Up to the present, there is little research about this mechanism. Therefore, a model was derived to calculate load distribution, axial deformation and contact fatigue life. Firstly, surface equation of screw, roller and nut was established. Based on Surface meshing theory, the meshing points of the roller with the screw and nut in a pitch were derived respectively. According to the surface equations and the location of contact points, an accurate method to calculate the elastic deformaion between the meshing surface was derived. Secondly, A model of IPRS's load distribution was obtained based on the geometric relationships between Hertz deformation, thread deformation and axial deformation. Based on its load distribution condition and motion principle, a fatigue life model was deduced using Lundberg-Palmgren equation. Then, a program was compiled in the MATLAB Environmet to calculate load distribution axial deformation and contact fatigue life. By comparing calculationg result with the expriments, the load distribution and axial deformation model was verified. The influence of the key parameters on the performance of IPRS was analyzed and the following results were derived. The load distribution was mainly influenced by the number of teeth, the number of rollers and the helix angle, and increased with the increases of these three factors. The axial stiffness was mainly influenced by the number of teeth, the number of rollers, the helix angle and the outer diameter of the nut, and increased with the increases of the number of rollers and the outer diameter of the nut, increased first and then decreased with the increase of the number of teeth and the helix angle. The contact fatigue life was mainly influenced by the number of teeth, the number of rollers, the contact angle and the radius of thread profile, and increased with the increases of the number of teeth, the number of rollers and the radius of thread profile, decreased with the increase of contact angle.

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Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-16-10-2021-30
Total View : 3

Abstract :

In order to find out the damage evolution rule of the concrete with initial damage caused by early freezing under the coupling of freeze-thaw cycle and sulfate erosion, initial damage to concrete specimens by freezing and thawing them at the 7th and 14th day during the preparation of concrete specimens was carried. Based on this, different initial damage degree on macro performance and internal structure was researched. Then according to the principle of damage mechanics, the dynamic modulus of elasticity and compressive strength were defined as damage variables, by regression fitting analysis of damage process of variable, and the damage evolution equation of different initial damage specimen caused by early freeze-thaw was established in corrosion and freezing environment. The results indicated that two kinds of concrete specimens with different initial damage are affected by early freeze-thaw in the decay process of their mechanical properties and their form are " lead effect", which is closely related to the degree of initial damage. At the same time, the comparison and analysis of the change process of ultrasonic pulse propagation velocity and internal defect zone of concrete inferred that early freeze-thaw accelerates the propagation speed of cavity and crack, and the initial value of macroscopic mechanical properties of concrete and the ability of resisting salt and freezing in later stage are affected. The dynamic modulus of elasticity and the damage evolution equation of compressive strength can be used as a general formula for the attenuation of mechanical properties of concrete with similar damage degree, which can provide a theoretical basis for evaluating the service status and predicting the life of structures in similar environments. At the same time, the damage relationship between dynamic modulus of elasticity and compressive strength can be deduced from each other, which can reduce the limitation of data acquisition due to the shortage of instruments.

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