On the evening of May 27th, an accident occurred in the Ferris wheel of a playground in Andhra Pradesh, India, and many people fell in one carriage. A 10-year-old girl was killed and another six were seriously injured, including three children. According to reports, some people found that the Ferris wheel bolts were loose and reminded the administrator beforehand, but the administrator was in a state of drunkenness and was not repaired in time to cause an accident. The administrator was arrested by the police after being beaten by the masses.
The small bolts have such serious consequences. Let's analyze why the bolts loose have such serious consequences.
First of all, for the connection subjected to the static load condition, if the loose bolt causes the uneven force of the bolt, the load of the loose bolt will be reduced, and the force of the loose bolt will increase, which is slightly different according to the specific structure. If there are a large number of bolts at the joint, there is no lethal effect if one bolt is loose. If there are only two bolts at the joint, once one of them is loose, the other bolt will bear most of the load, and the force is also in the form of force. A relatively large change occurs. After the load is large enough, the tight bolt may break first, and then the loose bolt bears all the loads, so that the load cannot be broken, and the consequences are unimaginable.
Figure 2. Average force when both bolts are tightened
Figure 3, when one of the bolts is loose, the loose bolts are subjected to most of the load and there is a risk of breakage.
Figure 4. The loose bolts are broken due to excessive load. The loose bolts will also be broken when subjected to full load.
When the bolt is subjected to fatigue load, if one bolt is loose, the pre-tightening force is greatly reduced. When the alternating load is applied, the pre-tightening force of the bolt varies widely, and the stress amplitude of the bolt itself is higher than other bolts. Early fatigue fracture.
Loose bolts may cause serious consequences. The mechanical equipment must be regularly maintained to check whether the bolts are loose, so as to prevent them from happening and to adhere to safety first.
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