Patent ID: 7660704
Filing Date: 2010-02-09
Classification: G06F

Abstract:
1. A method of designing a tolerance load of a screw-tightening element, composed of a screw component and a tightening object to be fastened in a screw-tightening structure, which is susceptible to a fluctuating cyclic load, the method comprising: representing, using a computer, material characteristics of the screw component with factors including at least one of an elastic limit, a fatigue limit, a true breakdown stress and a tension strength; representing a material characteristic of the tightening object with a factor including an elastic limit; providing a plurality of damage patterns associated with the material characteristics of the screw component and the tightening object; providing a first critical load of a tension force and a second critical load of a compressive force, wherein the first and second critical loads are give by: R=Kb [(F/Kb)+(F/Kf)]=F[1+(Kb/Kf)]=F[1+(1/γ)=F(1+β) and S=Kf [(F/Kb)+(F/Kf)]=F[1+(Kf/Kb)]=F[1+(1/β)=F(1+γ) where R=the first critical load, S=the second critical load, F=a tightening force applied to the screw-tightening element, Kb=a spring constant of the screw component, Kf=a spring constant of the tightening object, β=a ratio of a spring constant Kb to a spring constant Kf, and γ=a ratio of the spring constant Kf to the spring constant Kb; calculating tolerance values of the fluctuating cyclic load acting on the screw-tightening element based on the damage patterns of the screw-tightening element using the elastic limit of the tightening object, wherein the damage patterns include a fatigue fracture of the screw component, a loosening of the screw component due to plastic deformation thereof, a loosening of the screw component due to plastic deformation of the tightening object, an occurrence of a gap formed at a tightened area due to elongation of the screw component within an elastic deformation thereof, and an occurrence of a gap formed at the tightened area due to contraction of the tightening object within an elastic deformation thereof; and comparing the tolerance values of the fluctuating cyclic load for determining a tolerance load available for the screw-tightening element to withstand the fluctuating cyclic load.