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Clevis Kinematic Assessment with ANSYS
A standard connection, used to allow relative rotational motion between parts, commonly consists of two clevises connected by a pin - regularly referred to as a hinge, as shown in Figure 1, above. Typical use would allow for an easy extraction of the pin to separate the parts; however, after an accident condition, extracting the pin or rotating the parts could prove difficult. A clevis geometry sample was therefore created for the purpose of both physical and analytical testing to determine the expected loads to operate the hinge. The intent of the analytical work was to provide a validated and reliable means of predicting the response of a clevis after an accident event.
The accident event (loading condition) on the hinge consisted of a normal load that tensioned the clevis. The magnitude of the applied load caused the full cross section of the pin to yield and induce plasticity. Afterwards, the connection was unloaded and the following kinematic assessments were evaluated:
- Torque required to rotate the pin 180° (Figure 2a.)
- Force required to completely remove the pin from the assembly (Figure 2b.)
- Torque required to rotate the upper clevis to a position 90° to the lower clevis (Figure 2c.)
Figure 2. Clevis Kinematic Assessments
ANSYS Workbench was used to simulate the loading conditions, incorporate all the necessary details of the problem and obtain the desired kinematic assessments. The ANSYS Workbench environment also enabled the problem to be created parametrically, which allowed for easy changes to be made to the simulation. The parametric approach allowed for a single model to be created and used to assess all the kinematic assessments and include all the following aspects of the analysis:
- Plasticity: The inclusion of this material behavior in the analysis was critical to capture the response of the hinge during and after the accident event. The plasticity left residual deformations in the hinge that greatly affected how much load was required to rotate and extract the pin.
- Pin Clearance: The pin was smaller than both of the clevis lug's pin holes, leaving clearances between the parts; however the interaction between the two clevises and pin was included through the use of contact elements. The contact elements used represented curved surfaces, included effects of friction and large relative displacements. When the torque required to rotate the pin was assessed, a smooth curve was obtained based on these interactions.
- Constraints: Setting up and loading the problem posed many challenges; for instance:
1) After the accident event, a constant and minimal normal clevis load needed to be maintained during the pin rotation (with a bent pin and ovalized holes).
2) After the accident event, the pin was to be fully extracted without over constraints. Additionally, the clevises had to freely separate (after the pin was removed) under the constant normal load applied.
3) After the accident event, the upper clevis had to be rotated but also maintain a constant minimum normal load and allow the pin to freely move without over constraint.
Each of these challenges were uniquely handled with ease in ANSYS Workbench by using its suite of powerful automated constraints.
The kinematic assessment data was obtained for each case in chart, contour and animation form, allowing for easy comparison to test data. Sample results are shown for reference in the Figures 3 & 4 below. With the customer's validation of analysis methodology, ANSYS will be used as a predictive tool in future designs of related hardware under similar loading events.
Figure 3. Clevis contour results shown through
the center of hinge (6x displacement scale)
Figure 4. Pin force and moment data exported from ANSYS to be used in comparison with physical testing.
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