Writer: Eric Bearing Limited
Damage to the outer ring of a bearing is a common form of failure and a relatively high proportion of failures. As the main parts of mechanical equipment, FAG bearings will directly affect work efficiency when they fail. Therefore, many bearing damages are more concerned. However, when the outer ring of the bearing is damaged, many people do not know the degree of damage to the outer ring of the bearing. What measures should be taken to remedy the most appropriate? Next, Eric Bearing Limited will share the comparison of the first ten modes of FAG deep groove ball bearing outer ring damage, hoping to help you when using the bearing.
Let's take a certain type of FAG deep groove ball bearing as an example to see the comparison of the first ten modes of deep groove ball bearing outer ring damage:
The object is: a FAG deep groove ball bearing with an outer diameter D1 of 80mm and an inner diameter of D2 of 35mm. The calculation of the bearing outer ring size shows that the radial thickness of the bearing is 6.7mm at its maximum and 4.25mm at its thinnest point. The finite element model of the bearing outer ring is established according to the actual size. The model uses solid45 elements, the elastic modulus is 2.1 x 10 5MPa, the Poisson's ratio is 0.3, and the density is 7800kg/m³. The sweep method is used to divide the grid, and the grid at the crack is divided densely in order to save computing resources. It is divided into three scales: Zone 1 unit size is 0.5mm x 0.5mm; Zone 2 unit size is 0.5mm x 0.15mm; Zone 3 unit size is 0.5mm x 3mm; Zone 4 unit size is 0.5mm x 4mm. After the complete bearing is divided, there are a total of 63270 elements and the number of nodes is 70110. The width of the crack in this simulation is 0.5mm, and the depth direction is gradually increased at 0.5mm intervals. Finally, 15 calculation steps are used to simulate the entire process of the outer ring from intact to broken.
2. The relationship between frequency change and damage
Through the modal calculation of 15 cases of no damage, crack depth of 0.5 mm ~ 6.5 mm, and disconnection, the first ten modal frequencies of various damage cases are extracted. It can be seen that as the degree of damage increases, the outer ring of the bearing The natural frequency moves to low frequency, and decreases nonlinearly with the increase of the damage. The natural frequency of the same damage decreases to a different degree. This is different from that only when the damage occupies a higher potential energy in a certain order of formation. The theoretical analysis results of greater impact are consistent.
Generally speaking, there is a corresponding relationship between frequency change and damage; when a crack occurs, the natural frequency decreases; for a certain modal frequency, the smaller the crack depth, the smaller the frequency shift, the larger the crack depth, the greater the frequency change. However, the natural frequencies of each mode have different sensitivity to damage. FAG 51230 MP bearings online , pls click here :
3. The relationship between modal stress and damage
When there is a crack, the stress concentration of each mode is obvious, and the stress concentration becomes larger and larger as the damage develops. The same damage has different effects on different orders of deformation and stress concentration. When the damage is located at the mode node, the mode shape is greatly affected by the damage, and the stress concentration is obvious. For example, the damage point has a larger stress concentration at the bend. This shows that when there is a crack, the occurrence of a certain order of resonance can greatly promote the development of the crack at the node of the mode.
4. The relationship between modal displacement, strain and damage
The relationship between modal displacement and modal strain and the degree of cracks in the outer ring is analyzed separately, and the sensitivity of modal displacement and modal strain to crack damage is compared. Because there must be a corresponding strain mode corresponding to each displacement mode, they are two manifestations of the same energy balance state and their proportions are the same. Here, the sensitivity of modal displacement and modal strain to crack damage is compared by comparing the maximum modal displacement and the maximum modal strain. When the crack depth is less than 4.5mm, the displacement mode increases with the degree of damage, but the change is small; the modal displacement begins to decrease; the modal displacements of other orders do not change much with the increase of the crack depth; the modal displacements of each order After the fracture, they all increased significantly. When the structure is damaged, the displacement mode changes greatly when the crack position is at the mode node position.
In the initial stage of the crack, the strain of other orders except the high-order tenth order has a large change. The modal strain of the odd order has a large jump at the initial stage of the crack, which is 0.5mm, which is about 200%. When the crack is 1mm The even-order modal strain of the outer ring has a significant jump of about 700%; with the increase of the crack depth, the modal strain increases almost linearly until the outer ring is broken; when the crack depth is 4.5mm, the eighth-order mode The state strain has a large jump, while the ninth-order mode strain is greatly reduced.
Outer ring damage will change the modal displacement and modal strain, and the overall trend will increase, but there will also be a decrease; the same degree of damage has different contributions to the change of modal displacement and modal strain of different orders, so the modal Strain and modal displacement have the same locating effect on damage; modal strain is much more sensitive to modal displacement, especially in the early stage of damage, the variable of modal strain can reach about 200%, while modal displacement is in the early stage of damage. Not obvious.
Through the modal analysis of the FAG bearing outer ring cracked state, the relationship between the natural frequency and various modal parameters and the degree of damage can be quantitatively identified. Summarized as follows:
(1) It is difficult to reflect the early damage of the structure by relying solely on the frequency value. When the damage develops to a certain extent, the natural frequency drops significantly, but only the presence of damage can be found, and the location and extent of the damage cannot be determined;
(2) The modal displacement is sensitive to crack damage. When the same degree of damage is located at a certain mode node, the displacement mode changes at that point, and the stress is concentrated, otherwise the displacement mode changes less; different degrees of damage make the same mode mode The modal displacement changes are different, which realizes the quantitative identification of damage. Therefore, the comprehensive analysis can realize the quantitative location analysis of the fault.
(3) Modal strain is the most sensitive to structural damage and has the same positioning effect as modal displacement.