Some statements from "Practical Analysis of Aircraft Composites"
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Section 21.4. At a minimum, three conditions are usually considered:
- CTD (cold temperature, dry) also known as “cold/dry”
- RTD (room temperature, dry), RTA (room temperature, ambient), or RTW (room temperature, wet)
- ETW (elevated temperature, wet) also known as “hot/wet”
The CTW (cold temperature, wet) and ETD (elevated temperature, dry) conditions are typically subcritical compared to the CTD and ETW conditions. Therefore, the CTW and ETD conditions are not tested as often.
Section 21.4.3. ETW. At the ETW condition, the strength and stiffness of a polymer matrix is reduced. This combination (elevated temperature and wet environment) is considered because there is a synergistic detrimental effect.
At the ply level, the ETW condition reduces the compression strength and the shear modulus. At the laminate level, the compression and bearing strengths are reduced (See also Section 21.10.6). This is because the softened matrix has a reduced ability to support the fibers. The laminate properties from Table 21.5 are in agreement with these expectations. Interlaminar properties, which are dominated by the matrix material, are especially sensitive to the ETW condition (See Section 21.13).
For carbon fiber laminates, the reduction of in-plane strength is usually most severe for the compression strengths (OHC and FHC) in the ETW condition (maximum reduction of approximately 25–35%).[R1, R2, R17, R18, R19] This is because the epoxy matrix is sensitive to the ETW environments, and the matrix significantly affects the laminate’s compressive strength. Tensile strengths (OHT and FHT) are less affected and have a maximum strength reduction of approximately 15–25%.
Section 21.4.4 CTD. At the cold temperature and dry condition, the fibers and epoxy become more brittle and stiff. Tension strength may be reduced because of embrittlement,[R16] and there may be a reduced ability to soften the effect of stress concentrations. Compression strength increases because of the added stiffness of the matrix, which stabilizes the fibers.
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[R1] National Center for Advanced Materials Performance (NCAMP), Hexcel 8552 IM7 Unidirectional Prepreg 190 gsm & 35% RC Qualification Material Property Data Report, Test Report Number: CAM-RP-2009-015 Rev A, April 22, 2011.
[R2] National Center for Advanced Materials Performance (NCAMP), Hexcel 8552 IM7 Unidirectional Prepreg 190 gsm & 35% RC Qualification Statistical Analysis Report, Report Number: NCP-RP-2009-028 Rev A, November 16, 2012.
[R16] Baker, A., Dutton, S., and Kelly, D., Composite Materials for Aircraft Structures, Second Edition, AIAA, Reston, Virginia, 2004.
[R17] National Center for Advanced Materials Performance (NCAMP), Hexcel 8552S AS4 Plain Weave Fabric Qualification Statistical Analysis Report, NIAR Document NCP-RP-2010-011 Rev B, November 15, 2012.
[R18] National Center for Advanced Materials Performance (NCAMP), Hexcel 8552 AS4 Unidirectional Prepreg Qualification Statistical Analysis Report, Report Number: NCP-RP-2010-008 Rev D, October 26, 2011.
[R19] National Center for Advanced Materials Performance (NCAMP), Newport NCT4708 MR60H 300gsm 38%RC Unidirectional Material Allowables Statistical Analysis Report, Report Number: NCP-RP-2010-074 Rev N/C, November 22, 2011.
Brian
