Question 5.1: A [0/±60] graphite/epoxy laminate is quasi-isotropic. Find t...
A [0/±60] graphite/epoxy laminate is quasi-isotropic. Find the three stiffness matrices [A], [B], and [D] and show that
1. A_{11} = A_{22}; A_{16} = A_{26} = 0; A_{66} = \frac{ A_{11} – A_{12}} { 2}.
2. [B] ≠ 0, unlike isotropic materials.
3. [D] matrix is unlike isotropic materials.
Use properties of unidirectional graphite/epoxy lamina from Table 2.1. Each lamina has a thickness of 5 mm.
TABLE 2.1
Typical Mechanical Properties of a Unidirectional Lamina (SI System of Units)
Property | Symbol | Units | Glass/ epoxy |
Boron/ epoxy |
Graphite/ epoxy |
Fiber volume fraction | V_f | 0.45 | 0.50 | 0.70 | |
Longitudinal elastic modulus | E_1 | GPa | 38.6 | 204 | 181 |
Transverse elastic modulus | E_2 | GPa | 8.27 | 18.50 | 10.30 |
Major Poisson’s ratio | \nu_{12} | 0.26 | 0.23 | 0.28 | |
Shear modulus | G_{12} | GPa | 4.14 | 5.59 | 7.17 |
Ultimate longitudinal tensile strength | (\sigma_1^T)_{ult} | MPa | 1062 | 1260 | 1500 |
Ultimate longitudinal compressive strength | (\sigma_1^C)_{ult} | MPa | 610 | 2500 | 1500 |
Ultimate transverse tensile strength | (\sigma_2^T)_{ult} | MPa | 31 | 61 | 40 |
Ultimate transverse compressive strength | (\sigma_2^C)_{ult} | MPa | 118 | 202 | 246 |
Ultimate in-plane shear strength | (\tau_{12})_{ult} | MPa | 72 | 67 | 68 |
Longitudinal coefficient of thermal expansion | \alpha_1 | μm/m/°C | 8.6 | 6.1 | 0.02 |
Transverse coefficient of thermal expansion | \alpha_2 | μm/m/°C | 22.1 | 30.3 | 22.5 |
Longitudinal coefficient of moisture expansion | \beta_1 | m/m/kg/kg | 0.00 | 0.00 | 0.00 |
Transverse coefficient of moisture expansion | \beta_2 | m/m/kg/kg | 0.60 | 0.60 | 0.60 |
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