Analysis on a plate with a hole using Solidworks

AIM : To perform a static analysis on two models of plate with holes.

OBJECTIVES :

1. To create the model in Solidworks and perform the analysis.
2. To compare the results for stress, strain and displacement.

INTRODUCTION : Plate structure with holes is widely applied in engineering practices. The reason making holes on the plate could vary, some for installing bolts and other connectors, and others for reducing weight without mainly affecting mechanical properties.

STRESS CONCENTRATION - Whenever a machine component changes the shape of its cross-section, the simple stress distribution no longer holds good. This irregularity in the stress distribution caused by abrupt changes of form is called stress concentration. A stress concentration (stress raisers or stress risers) is a location in an object where stress is concentrated. An object is strongest when force is evenly distributed over its area, so a reduction in area, e.g., caused by a crack, results in a localized increase in stress. A material can fail, via a propagating crack, when a concentrated stress exceeds the material's theoretical cohesive strength. The real fracture strength of a material is always lower than the theoretical value because most materials contain small cracks or contaminants that concentrate stress. It occurs for all kinds of stresses in the presence of fillets, notches, holes, keyways, splines, surface roughness or scratches etc.

METHODS TO REDUCE STRESS CONCENTRATION - The presence of stress concentration can not be totally eliminated but it may be reduced to some extent.

1. A device or concept that is useful in assisting a design engineer to visualize the presence of stress concentration and how it may be mitigated is that of stress flow lines.
2. The mitigation of stress concentration means that the stress flow lines shall maintain their spacing as far as possible.
3. Some of the changes adopted in the design in order to reduce the stress concentration are as follows:
4. Avoid abrupt changes in cross section
5. Place additional smaller discontinuities adjacent to discontinuity
6. Improve surface finish

PROCEDURE :

• Geometry Modelling -
• At first, 3D models were created according to the following dimensions,

• The model were sketched and extruded to the given length,

• Case 1. -

• Case 2. -

• Simulation Setup -
• For the finite element analysis, Solidworks Simulation was used and Static analysis was setup. The material selected for both cases were ' Plain Carbon Steel'. The properties of 'Plain Carbon Steel' are -

• A fixture was used to fix the short face of plates as stated in the challenge statement, while a force of `1000N` were applied on the opposite of fixed face to stretch the plate. Then meshing were applied on the part body for analysis. For accurate results global mesh size was set to `2.5mm` for a fine meshing.

• Case 1. - Plate with single hole at the center,

• Mesh properties -

• Case 2. - Plate with single hole at the center and two holes at `90mm` from central hole on both sides,

• Mesh properties -

RESULT :

• Case 1. - Plate with single hole at the center,

Stress Plot based on Von-Mises Study

Displacement Plot

Equivalent Strain Plot

Comparison Plot

• Case 2. - Plate with single hole at the center and two holes at `90mm` from central hole on both sides,

Stress Plot based on Von-Mises Study

Displacement Plot

Equivalent Strain Plot

Comparison Plot

• In addition to these plots, plot for factor of safety were also found out.
• Summary in tabular form -

CONCLUSION :

1. For case 1, the value of stress and strain calculated are higher than that of case 2. It is because stress concentration is much higher in case 1 around the circular hole, whereas for case 2, the stress concentration gets distributed due to abrubt change in dimensions and the sharp bending of force flow line is reduced and it follows a smooth curve.
2. Hence, the factor of safety for case 2 is much higher than case 1. This is one of the suitable method to reduce stress concentration in a plate when it is subjected to loading.