Transient Structural Analysis of Long Piston and Cam Assembly

OBJECTIVE:

To perform a transient analysis on a piston and cam mechanism model.

Run the analysis with Frictionless contact, Frictional with 0.1 and 0.2 as the frictional contact for a total of 3 cases.

Find out the Equivalent Stress, Directional Deformation and Equivalent Elastic Strain and compare them for all the three cases.

Give an inference as to why the results vary between cases.

SOLUTION:

Step 1: Part design

The assembly of the long piston and cam was given. Since the focus of study is to understand the behaviour of the follower, the other two components are defined as rigid in nature. The material for all the bodies in the model was defined as structural steel.

Step 2: Connections

Two contacts were defined for the model, one between the follower and barrel and the second one between the follower and cam. The friction behaviour between the contacts were changed for the three cases, with no friction condition for the 1^st case, 0.1 for 2^nd and 0.2 for the 3^rd.

Further, three joints were defined for the model. The barrel was given a fixed condition, the cam was defined as a revolute joint and a translation joint was established between the barrel and follower.

Step 3: Meshing

In the meshing step, a face sizing mesh was defined on the follower tip and the guideway on the cam with an element size of 2mm. The default mesh size for the entire model was defined as 4mm with the quality of smoothing as low.

Step 4: Analysis settings

The analysis is carried out over 9 steps. For the 1^st step, the intial time step is 0.1s, minimum time step is 0.05s and the maximum time step is 0.2s. The weak springs was set as program controlled, the large deflection was turned on and all the output controls were changed to yes condtion. For step 2-9, the maximum time step was set as 0.3s with all other conditions as same. A rotation setting was given for the cam, ranging from 0 to 270 degree with 30 degree increment.

Step 5: Results

1. Results for frictionless conditions

1. Results for frictional coefficient = 0.1

1. Results for frictional coefficient = 0.2

Step 6: Comparison and Inference

Coefficient of friction	Max equivalent stress (MPa)	Max equivalent strain	Max directional deformation (mm)
frictionless	4398.5	0.022157	11.902
0.1	4563.5	0.022879	11.994
0.2	5104.9	0.025594	12.083

It is observed that the maximum stress, strain and deformation is developed when the frictional coefficient is 0.2. Also, these values show an increasing trend as the frictional coefficient increases. This can be seen as the effect of the friction between the surfaces. As friction increases, higher force is required to perform the task. This develops a higher resisting force in the opposite direction, resulting in higher stresses, strains and deformation.