Modeling physical aging in polymeric composites
Abstract
A conduct of physical aging in polymeric composites was investigated. A carbon/epoxy composite IM7/977-3 was used for this study. Momentary creep test was used to characterize physical aging in elastic and creep compliances, respectively. Experimental data showed that physical aging affects elastic and creep compliances in different ways. The aging effect on elastic compliance can be modeled by an exponential function of aging time. For individual momentary creep, physical aging was negligible. In different aging time, momentary creep compliance decreased as aging time increased. Using aging shift factors, momentary creep compliances in different aging times were shifted and collapsed into a reference curve. Using this reference curve associated with the aging shift, a momentary creep compliance curve for any given aging time can be predicted. An effective time model was developed to characterize physical aging in long-term creep behavior. The real creep time was replaced by the effective time, which counted aging effect on shift factors in power law model. An effective creep compliance model was developed to characterize physical aging in orthotropic composites. By using a one-parameter creep potential function, momentary creep compliances with different fiber orientations were collapsed into a single master curve. By using the aging shift method and effective time model, long-term effective creep compliance for times up to 100 times of the initial aging time was successfully predicted. Moisture and temperature can proportionally relax the elastic compliance throughout the period of aging and creep tests. In a given aging time, the increment of creep compliance due to moisture absorption becomes smaller as moisture content increases and reaches saturation. But, the increment of creep compliance due to temperature becomes larger as ambient temperature increases. For a constant moisture content or ambient temperature, momentary creep compliance in different aging times can be shifted by using aging shift factors to collapse into a reference curve. By choosing a condition of 23°C and 0% moisture content as reference, moisture-temperature equivalences in physical aging of elastic and creep compliances were developed, respectively. Classical laminate theory was adopted to characterize physical aging in elastic compliance of composite laminates by replacing constant elastic properties by aging dependent elastic properties. However, laminate theory is not applicable to characterize physical aging in creep compliance. To this effect, momentary creep tests for laminates were employed. The aging shift factors for relaxation time and shape factor were obtained. Then, effective time model are applicable to predict the long-term creep of composite laminates under physical aging.
Degree
Ph.D.
Advisors
Sun, Purdue University.
Subject Area
Aerospace materials
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