By the reason of the additional side force acting on the force transducers affecting the rotation effect of the combinatorial load cell,the paper describes the effect of the spherical plain thrust bearings structure on the additional side force. A three-dimensional finite element model of the late-model high-accuracy combinatorial load cell was established and analyzed. From the results, it shows that the magnitude of the additional side force fluctuation increases with the height of the bearing base increasing. At the same time, the magnitude decreases with the friction coefficient of the inner and outer ring of bearing increasing. The results provide guidance for the design of the combinatorial load cell.
The study of the size effect was one of the most important subjects in the field of micro-forming. To investigate the stress of the thin sheet in the bulging test with the second order size effect, a constitutive equation considering the strain gradient hardening was proposed. Based on the equation, the stress of the thin sheet during the bulging test was calculated by the finite element method. The bulging tests with various thicknesses of brass sheets and radiuses of punching balls were performed to verify the proposed equation. The results showed that the constitutive equation could capture the stress variations, while the simulation using the constitutive equation from the conventional theory of plasticity showed the results with large deviation from those of the experiment. It was found that the stress was sensitive to the thickness of the sheet and the radius of the punching ball in bulging test of thin brass sheet. The bulging of the thin brass sheet with a thickness below ten times of its material intrinsic length would cause the generation of the geometrically necessary dislocations, which induced the strain gradient hardening. Besides that, the decrement of the punching ball radius would also increase the inhomogeneous deformation and enhance the strain gradient hardening during the thin sheet bulging process. The strain gradient hardening during the thin sheet bulging test was related to the strain of the sheet. The hardening effect of the strain gradient was obvious when the strain was small. The strain gradient hardening should be considered in the thin sheet bulging test with the second order size effect.
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