On the effects of environmental conditioning on residual stresses in composite laminates

Harper, Brian; Weitsman, Y.

doi:10.1016/0020-7683(85)90041-1

Cited by 65 publications

(40 citation statements)

References 13 publications

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“…Initial crescent-shaped fiber debonds coalesce on drying and/or cyclic moisture exposure to form discrete continuous cracks [28,29]. This introduces new pathways for moisture to enter the material, altering the moisture uptake and making the diffusion non-Fickian.…”

Section: Degradation and Damage From Moisturementioning

confidence: 99%

Accelerated Tests of Environmental Degradation in Composite Materials

Reynolds

McManus

2001

Composite Structures: Theory and Practice

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High temperature polymer matrix composites are key candidates for the structural components of proposed supersonic transport aircraft. The operational environment of these vehicles exposes the airframe to harsh conditions, including temperature extremes and moisture. These environments have been seen to cause visible damage in polymer matrix composites in timescales much less than the lifetime of the vehicle. Therefore, there is an urgent requirement for accelerated testing of the key components of the environment. A first step to this goal is to identify the components of the environment responsible for the damage. The effects of a realistic moisture and thermal environment on two high temperature polymer matrix composites (PETI-5 and PIXA-M) have been investigated in this work. An extensive test program was developed to test the response of the materials to this baseline environment and its individual components: time at moisture, moisture cycling, time at temperature and thermal cycling. Mechanism-based models were used to design accelerated moisture cycles and acceler ed thermal cycles in an attempt to speed up the response to these environmental factors. These accelerated cycles were also used in the test program. The results showed visible damage in the form of cracking in both r.terials.The PIXA-M material was found to show more damage than the PETI-5. Cracking was confined to a thin layer of material next to the exposed edge. This suggests that the environmental exposure is reducing the effective fracture toughness of the material in this layer more than in the interior. Analysis suggests that this layer is exposed to more of the environmental components and fluctuations than the material in the interior. The individual components of time at moisture and thermal cycling were seen to cause cracking, while time at temperature did not, and moisture cycling did not appear to accelerate moisture damage. The combined environments in the baseline cycle caused more damage than any one component of the cycle on its own. Evidence points to the combined effects of time at moisture and thermal cycling as being the dominant parameters causing damage, while moisture cycling controls the extent of the damaged region. Although the designed accelerated cycles were not successful in accelerating the damage from the baseline cycle, they were instrumental in establishing what were the dominant parameters. It is suggested that a promising way of accelerating the damage observed under the realistic conditions is by combining an isomoisture environment with a cyclical stress environment, which can be achieved either thermally or mechanically.Thesis Supervisor:

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Section: Degradation and Damage From Moisturementioning

confidence: 99%

Accelerated Tests of Environmental Degradation in Composite Materials

Reynolds

McManus

2001

Composite Structures: Theory and Practice

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“…To avoid this issue, prediction of the dimensional changes has been of interest to many investigators who tried to address the issue by developing simple equations [53,54] as well as analytical and numerical models [6,12,25,26,30,32,[55][56][57][58][59][60]. The model that incorporates more phenomena can provide more accurate predictions.…”

Section: Numerical Modelsmentioning

confidence: 99%

Experimental and numerical study of distortion in flat, L‐shaped, and U‐shaped carbon fiber–epoxy composite parts

Roozbehjavan

Tavakol

Ahmed

et al. 2014

J of Applied Polymer Sci

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In this study, flat composite panels were fabricated to find the effect of different manufacturing parameters, including stacking sequence, part thickness, and tooling material, on distortion of carbon fiber‐epoxy composite parts. L‐shaped and U‐shaped panels were also made to investigate the effect of stacking sequence on spring‐in angle and warpage of the curved panels. Results showed that distortion of the flat panels caused by asymmetry in the stacking sequence was an order of magnitude greater than distortion of the panels with an unbalanced stacking sequence; whereas in the curved panels, the panel with an asymmetric stacking sequence showed the least spring‐in angle, and the largest angle was observed in the symmetric panel. MSC Marc was used to predict distortion of the panels, and the simulation results were compared with the experimental results for several stacking sequences of the flat and the L‐shaped panels. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40439.

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“…Based on their optimal cooldown path for AS4/3502 graphite/epoxy, a 10-15% reduction in residual stresses may be obtained, however, it was not seen experimentally. Using double beam method, Harper showed that cure shrinkage may contribute up to 25% of residual stresses in 3502 epoxy [41].…”

Section: -3 Theoretical Studiesmentioning

confidence: 99%

“…The model predicts 10% reduction in residual stresses in epoxy-resin composites if optimum cooldown path is applied although this has not yet been supported by experimental data. Harper and Weitsman conducted an experimental and theoretical investigation on the effect of cure shrinkage, moisture, and cooldown path on residual stresses in polymer composites during cooldown [38][39][40]. The presence of moisture was shown to enhance viscoelastic behavior.…”

Section: -3 Theoretical Studiesmentioning

confidence: 99%

Cure Cycle Optimization in Polymer Composites

Madhukar¹

2000

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On the effects of environmental conditioning on residual stresses in composite laminates

Cited by 65 publications

References 13 publications

Accelerated Tests of Environmental Degradation in Composite Materials

Accelerated Tests of Environmental Degradation in Composite Materials

Experimental and numerical study of distortion in flat, L‐shaped, and U‐shaped carbon fiber–epoxy composite parts

Cure Cycle Optimization in Polymer Composites

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