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Selection of ply sequence
- Thread starter Mano1689
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There are a number of broad rules about stacking sequence. Firstly, if you get the sequence wrong you may end up with odd coupling effects such as the laminate bends when a axial load is applied, or twists when a bending moment is applied.
To prevent bending under direct loads, use a symmetric lay-up where for every ply of a given material at a given angle to the load direction and at a given position above or below the laminate mid-plane there must be an equivalent ply of the same material at the same angle and the same distance away from the mid-plane. For example an 8 ply laminate +45/-45/0/90 must have the sequence 90/0/-45/+45 on the other side of the mid plane. You can not have +45/-45...-45/+45 or the laminate will bend when a load is applied.
To prevent twisting under an applied bending moment the laminate should be balanced, where by the equivalent plies must be at opposite angles, but such a laminate will bend under direct loads.
You should always aim for a symmetric laminate, because the twisting under bending effect decays with the third power (cubed) of the laminate thickness so for even moderately thick laminates twisting will not be a major issue.
Another aspect of stacking sequence is that of grouping like plies together. The fracture mechanics people will tell you that grouping like plies improves the fracture toughness. However, grouping plies decreases the impact resistance of the laminate. There is a long winded explanation why, which I can give you if you are interested. You are far better to intersperse ply orientations throughout the laminate.
So; symmetric laminates and intersperse ply orientations rather than grouping plies.
Regards
Blakmax
To prevent bending under direct loads, use a symmetric lay-up where for every ply of a given material at a given angle to the load direction and at a given position above or below the laminate mid-plane there must be an equivalent ply of the same material at the same angle and the same distance away from the mid-plane. For example an 8 ply laminate +45/-45/0/90 must have the sequence 90/0/-45/+45 on the other side of the mid plane. You can not have +45/-45...-45/+45 or the laminate will bend when a load is applied.
To prevent twisting under an applied bending moment the laminate should be balanced, where by the equivalent plies must be at opposite angles, but such a laminate will bend under direct loads.
You should always aim for a symmetric laminate, because the twisting under bending effect decays with the third power (cubed) of the laminate thickness so for even moderately thick laminates twisting will not be a major issue.
Another aspect of stacking sequence is that of grouping like plies together. The fracture mechanics people will tell you that grouping like plies improves the fracture toughness. However, grouping plies decreases the impact resistance of the laminate. There is a long winded explanation why, which I can give you if you are interested. You are far better to intersperse ply orientations throughout the laminate.
So; symmetric laminates and intersperse ply orientations rather than grouping plies.
Regards
Blakmax
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