Nonlinear Effects on Composite Laminate Thermal Expansion.
MATERIALS SCIENCES CORP BLUE BELL PA
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The thermomechanical behavior of unidirectionally fiber reinforced laminae in plane stress has been described by a set of nonlinear thermomechanical stress-strain relations. A general procedure for analysis of in-plane loaded symmetric laminates, composed of such laminae, has been established for simultaneous loading and temperature inputs. A or -45 deg laminate subjected to heating and uniaxial load has been analyzed in detail. Analyses of GraphitePolyimide laminates have shown that the thermomechanical strains cannot be separated into mechanical strain and free thermal expansion strain. Consequently the free thermal expansion coefficient is generally not useful for computation of thermal strains in a loaded nonlinear laminate. Moreover, a laminate such as the or -45 deg which behaves isotropically for free thermal expansion behaves anisotropically when loaded and heated. Elastic properties and thermal expansion coefficients of unidirectional GraphitePolyimide specimens were measured as a function of temperature to provide inputs for the analysis. The or -45 deg symmetric GraphitePolyimide laminates were tested to obtain free thermal expansion coefficients and thermal expansion coefficients under various uniaxial loads. The experimental results demonstrated the effects predicted by the analysis, namely dependence of thermal expansion coefficients on load, and anisotropy of thermal expansion under load. Numerical agreement of analytical and experimental results was fair. The significance of time dependence on thermal expansion was demonstrated by comparison of measured laminate free expansion coefficients with and without 15-day delay at intermediate temperature. MM
- Laminates and Composite Materials