Laminate behavior fatigue

On the other hand, for aircraft and spacecraft structures, real laminate behavior is pretty typically linear. Laminate behavior is reasonably linear even with some 45° layers which you would expect to contribute their nonlinear shear deformation characteristic to the overall laminate and degrade its relative performance. If you go beyond the behavior of a laminate and look at a large structure, typically the load-response characteristics are linear. Even around a cutout, linear behavior exists. Beyond that apparent linear performance of many laminates, you might not like to operate in some kind of a nonlinear response regime. Certainly not when in a fatigue environment and probably not in a creep environment either would you like to operate in a nonlinear behavior range. 

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

The manner in which the laminate design is approached can be expressed in flow-chart form as in Figure 7-59. There, some initial laminate is arbitrarily selected to start the procedure. Then, the laminate load-deflection behavior is evaluated by use of the laminate strength analysis procedure described in Section 4.5. That evaluation is theoretical in nature. The next step is to evaluate the laminate fatigue life, and that evaluation can only be done experimentally, although progress is... 

Zawada et al.44 showed that the proportional limit, expressed in strain (0.3%) rather than in stress, was identical for unidirectional and cross-ply laminates of SiCf/1723. Moreover, the fatigue limit of the unidirectional composite, expressed in strain, corresponded well with the measured fatigue strain limit of the cross-ply laminates. This indicates that the fatigue limit of a cross-ply laminate is primarily governed by the 0° plies and that the influence of the 90° plies is minimal (this result is expected to hold only for room temperature fatigue—see Chapter 5 for a discussion of how transverse plies influence cyclic creep behavior). The 90° plies develop transverse cracks early... 

It is important to note that the uniaxial loading of an off-axis plate generates a local (inherent) multiaxial stress state. It is therefore worth mentioning the investigations by Kawai and coworkers for the description of the off-axis fatigue behavior of UD and woven reinforced laminates [61,71,72] and their fatigue damage mechanics model [61]. The model is based on the nondimensional effective stress concept, which is the square root of the Tsai—Hill polynomial. 

The trend is similar to that discussed on page 345 for short fiber composites, but at the same time it is opposite to the general behavior of plain samples of both short fiber and continuous fiber composites, where the fatigue strength decreases when the biaxiality ratio A2 increases. However, on the basis of the limited amount of data available, it is impossible to justify the experimental evidence and further research is indeed needed to clarify the mechanisms responsible for this peculiar behavior. Results on [0/ 45]2s, [0/ 45/90]s, and [02/ 45]s graphite/epoxy cruciform laminates reported by Jones et al. [16] are less clear than those just discussed—in some cases increasing the biaxiality ratio Ai decreased the fatigue life, and for others the life was increased. 

Quaresimin M, Susmel L, Taheja R. Fatigue behavior and life assessment of composite laminates under multiaxial loadings. Int J Fatigue 2010 32 2-16. 

Quaresimin M, Susmel L. Multiaxial fatigue behavior of composite laminates. Key Eng Mater 2002 221-222 71-80. 

Susuki 1. Fatigue damage of composite laminate under biaxial loads. In Jono M, Inoue T, editors. Proceedings of mechanical behavior of materials — VI, vol. 2 WS7f3. Kyoto, Japan Pergamon Press 1992. pp. 543—8. July 29-August 2. 

Fujii T, Lin F, Morita Y. Fatigue behavior of plain woven glass-fabric laminates under tension/torsion combined loading (Effect of shear stress and cyclic condition on fatigue failure). Nippon Kikai Gakkai Ronbunshu, A Hen/Trans Jpn Soc Mech Eng Part A 1994 60 650—7 [in Japanese]. 

Fujii T, Lin F. Fatigue behavior of a plain-woven glass fabric laminate under tension/ torsion biaxial loading. J Compos Mater 1995 29(5) 573—90. 

Kawai M, Taniguchi T. Off-axis fatigue behavior of plain weave carbon/epoxy fabric laminates at room and high temperatures and its mechanical modelling. Composites Part A 2006 37 243-56. 

R E Swain III, The role of the fiber/matrix interphase in the static and fatigue behavior of polymeric composite laminates, Dissertation, Department of Engineering Science and Mechanics, Virginia Polytechnic Institute State University, February, 1992. 

Heffernan, P. J. (1997). Fatigue Behavior of Reinforced Concrete Beams Strengthened with CFRP Laminates. PhD thesis. Department of Civil Engineering, Royal Military College of Canada, Kingston, Ontario, Canada, p. 157. 

Figure 2. Fatigue crack propagation behavior of UD laminates )...

Kimpara I, Saito H (2007) Part II Post-impact fatigue behavior of woven and knitted fabric CERP laminates for marine use. Long-term durability and damage tolerance of innovative marine composites (NICOP), Technical Reports and Data Base for Office of Naval Research Project, Feb 2007... 

Reinforced Plastics Congress, British Plastics Federation, London, Paper No. 19, pp 145-151 Russell AJ, Street KN (1985) Moisture and temperature effects on the mixed-mode delamination fracture of unidirectional graphite/epoxy. Delamination and debonding of materials, ASTM 537 STP 876, American Society for Testing and Materials, Philadelphia, pp 349-370 Saito H, Kimpara I (2007) Effect of water absorption on compressive strength after impact and post impact fatigue behavior of woven and knitted CFRP laminates. Key Eng Matra-334-335 517-520... 

Loading Rate and Temperature Dependence on Flexural Fatigue Behavior of a Satin Woven CFRP Laminate. J. of Composite Mat, 28,13 (1994), p. 1250- 1260... 

Diao, X., Ye, L, and Mai, Y.-W. (1997) Fatigue behavior of CF/PEEK composite laminates mode from commingled prepreg. Part I experimental studies. Composites Part A, 28A, 739 747. 

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