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· Ferris Wheel, Merry-Go-Round, Pirate Ship, Pendulum, Bumper Car, Rotor and so on.
Stage Decoration Light
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Kids Ride Decoration
· Castles, Robot, Mini Carousels, Car, Train and etc.
From the simulation test, it can be concluded that when a spring is subjected to an axial load PV, additional horizontal forces and moments are introduced at its ends. These extra forces inevitably lead to increased stress at certain points along the spring. This added stress is referred to as "additional stress" or S. Furthermore, the presence of this additional stress becomes more apparent through stress measurement tests. Strain gauges are placed at regular intervals on the inner wall of a specific section of the spring to measure shear stress under the action of PV. Theoretically, the stress values across each segment should be nearly identical. However, in practice, the stress distribution around the circumference is highly uneven. In one particular test, the maximum stress in the active ring (first effective ring) was approximately 30% higher than the average stress within the same circle. Despite this variation, the average stress at all measured points closely matched the theoretically calculated value based on the applied load PV.
It is evident that the primary cause of this uneven stress distribution stems from the additional forces acting on the spring's ends. Compared to the outer large spring, the smaller inner spring in a multi-turn structure has lower bending rigidity and stability. This makes it more susceptible to stress concentration caused by these additional forces, resulting in an unequal stress distribution. Consequently, even though the spring group is designed for equal strength, the inner ring may experience significantly higher local stresses, which reduces the overall fatigue life of the spring. As a result, the inner ring is more prone to failure compared to the outer ring.
To understand how the additional force influences the stress distribution, we analyze it from a mechanical perspective. When the spring is only subjected to an axial load PV without any other forces, the shear stress is given by S = 16PV × r. However, when additional forces are present, the stress state changes. According to literature [2], the point where the additional force has the most significant impact on the stress occurs at the upper and lower end rings of the spring.
Assuming no additional stress, the average working stress at point A is SA, and the dynamic load coefficient is A. The stress cycle characteristic is r1 = (SA - SAA)/(SA + SAA) = (1 - A)/(1 + A). When additional stress is considered, the average working stress becomes SA + ΔSA, with the same dynamic load coefficient A. The new stress cycle characteristic becomes r2 = (SA + ΔSA - SAA)/(SA + ΔSA + SAA). If ΔSA is set to B × SA, then r2 = (1 + BA)/(1 + B + A).
From the fatigue Goodman curve analysis, it is clear that as the average stress increases while the stress amplitude remains constant, the fatigue life of the spring decreases. Without additional stress, the point lies at position "1," whereas with additional stress, it shifts closer to position "2." If the average stress increases further, it may move beyond the curve to position "3," where the number of cycles is less than N. Although both positions "1" and "2" satisfy the N-cycle requirement, position "2" has a much lower safety factor, indicating that the additional stress raises the average stress, thereby reducing the spring’s fatigue life and safety margin.
To address these issues, several improvement measures can be implemented. First, from a manufacturing standpoint, ensuring the verticality and parallelism of the spring helps minimize the occurrence of additional stress. Second, from a design perspective, it is advisable to avoid multi-turn structures whenever possible. If such designs are necessary, the working stress of the inner ring should be reduced by 10%–15% compared to the outer ring to prevent premature failure due to instability. Third, for high-strength small springs in multi-turn structures, advanced manufacturing techniques can be used to enhance their fatigue resistance. Fourth, applying prestressing technology during production introduces residual stresses that offset part of the operational stress, thereby reducing the actual stress experienced by the spring. Finally, when designing axle box springs, it is crucial to account for stress increases caused by horizontal and longitudinal displacements of the frame, especially in high-speed locomotive suspensions.