You have been assigned with the design of a composite shell for the wing of PC9 aircraft. Under Design
Limit Load (DLL), the composite laminate is subjected to given ??, ?? and ???. The laminate
configuration based on the aerospace design guidelines is required. Assume that zero and 90-degree
plies do not contribute towards the shear strength of the laminate.
Part A: Determining failure properties
In-plane material failure properties for a single ply of IM7/977-3 unidirectional pre-preg need to be
calculated. Using the 10% rule, determine the following:
A1. Longitudinal tensile strength along 0
A2. Longitudinal compressive strength along 0
A3. Transverse tensile strength along 0
A4. Transverse compression strength
Part B: Preliminary laminate configuration
Using the failure properties from Part A, estimate the minimum number of plies required in the main
directions: ?0, ?45 ??? ?90.
2) Final laminate configuration
For any aerospace composite structure, we need to follow the following design guidelines:
• Use a minimum of 10% of plies in each of the principal directions [0,90, ±45]
• Use balanced/symmetrical laminates to avoid warping
• Use a maximum of four adjacent plies in any one direction
• Place ±45°plies on the outside surfaces of shear panels
• For thicker laminates (>16 plies) adjacent UD plies should be oriented with no more than 60°
C1. Apply these design guidelines and finalise the number of plies in the main direction:
?0, ?45 ??? ?90.
C2. Report the laminate configuration.
Part D: Control
After finalising the laminate configuration, now it is the time to check the load-bearing capacity of the
D1. Use eLaminate spreadsheet and calculate the in-plane properties of the finalised laminate: ??,
??, ???, ??? and ???.
D2. Use the unnotched failure strain for tension and compression (given in Table 1) and applied load
(??, ?? and ???) in eLaminate spreadsheet to calculate the minimum Margin of Safety (M.S.) from
D3. Comment on the safety of the designed laminate.
Part E: Notched strength
Circular holes may be introduced in the designed laminate for bonding to stringers. The stress
concentration factor and notched strength of the laminate should be analysed.
E1. Using the in-plane properties from D1, calculate the stress concentration factor, ??.
E2. The Point Stress Criterion (PSC) is a simple empirical formulation to calculate the notched strength
of composite laminates. Assume that the characteristic length for this laminate is ?? = 0.5 ??.
Determine the largest circular hole radius where the notched strength of the laminate is 40% of
its un-notched strength.
Part F: What-if analysis
During the service time, the composite laminate can be subjected to Design Ultimate Load (DUL),
where ??? = ??? × 1.5. As a final check, calculate the margin of safety for ??, ?? and ???
considering the laminate configuration from C2 when it is subjected to DUL.
State whether each of the following statements is True (T) or False (F):
Q1. Since carbon fibre and epoxy are brittle materials with low fracture toughness values of
1.6 MPa√m and 0.5 MPa√m, respectively, therefore, the carbon/epoxy composite is also
Q2. In sandwich laminates under bending, the core supports shear stress while skin is under
Q3. Material properties in a composite laminate is a function of fibre orientation only.
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