Question 8.CS.2D: FEA Analysis of a Crimping Tool Problem A crimping tool was ...
FEA Analysis of a Crimping Tool
Problem A crimping tool was analyzed for stress and deflection with classical methods and simplified geometry in Case Study 2B (p. 209). Analyze this assembly with FEA and compare the results to the earlier study.
Given The geometry and loading are known from Case Study 2A on p. 84. The thickness of link 1 is 0.313 in, of links 2 and 3 is 0.125 in and of link 4, 0.187 in. All material is AISI 1095 steel.
Assumptions A static analysis is acceptable due to a small number of load cycles.
See Figures 8-34 to 8-35.
1 Figure 8-34 shows the loads and constraints applied to the crimping tool assembly of Case Study 2B. The tool is supported (constrained) by the palm of the hand on the top handle and a force is applied to the bottom handle by the fingers until the required crimp force (F_{c} = 2000 lb) is applied by the jaws of the tool to the part being crimped. The geometry was defined in Case Study 2A.
2 Figure 8-35a shows an FEA mesh of quadrilateral elements applied to the assembly with boundary constraints and loads applied. The links are connected with pins in the model. A set of nodes along the top surface is constrained in y and x to represent the constraint of the palm of the hand. The required finger force F_{h} is applied to the bottom handle.
3 Figure 8-35b shows the stress distribution in the part with the applied boundary conditions and loads of 2000 lb at the crimp. Results of the two methods are compared in Table 8-3. Table 8-4 shows the pin forces calculated by each method.*
4 In Case Study 2B a simplification was made to the geometry at the right end of link 1 to make it compatible with a closed-form solution of a curved beam. We do not have to make any such geometric simplification here as the mesh can fit to the real geometry. The closed form solution gave a maximum stress of 74 kpsi at point P. The FEA study indicates that the largest stress in the part is 81 kpsi at point P. The difference is probably due to the geometric simplification made in the previous solution.
* Note that the pin forces must be calculated in advance of doing a closed-form stress analysis as they are needed in the stress equations. An FEA calculation, on the other hand, needs only the applied loads and boundary conditions to calculate the stresses. The reaction forces can then be back-calculated from the stresses. It is a good idea to check the reaction forces that result from the FEA analysis and compare them to a static force analysis of the system using ΣF=0 and ΣM=0. If they agree, it verifies that your FEA model is reasonable.
| Table 8-3 Closed-Form (CF) vs. FEA Principal Stress Results |
||
| Link | Stress (kpsi) | |
| CF | FEA | |
| 1 | 74.0 | 81.2 |
| 2 | N.A. | 45.5 |
| 3 | –50.0 | –40.0 |
| 4 | 31.0 | 26.9 |
| Table 8-4 Closed-Form (CF) vs. FEA Pin Force Results |
||
| Force | Magnitude (lb) | |
| CF | FEA | |
| F_{12} | 1560 | 1574 |
| F_{14} | 452 | 456 |
| F_{23} | 1548 | 1545 |
| F_{43} | 1548 | 1545 |
