Composite laminates properties

The study of the mechanical behaviour of the composite gas cylinder was based on the following theories i) mieromechanics models to predict the composite laminae properties, ii) classical Laminate Theory (CLT) to predict composite laminate properties, iii) Elasto-plastie behaviour of the steel liner, iv) Tsai-Wu failure eriteria in the composite laminate, v) Von-Mises stress in the steel liner and, vi) Soderberg eriterion in the analysis of the steel liner fatigue behavior. 

By comparison, high performance composite laminates ate not only ctossphed like plywood, but actually have laminae stacked at very specific angles to one another to achieve optimal uniform properties in the x—y plane (2). 

Melamine (I,3,5-triamino-2,4,6-triazine) was first prepared by Liebig in 1835. For a hundred years the material remained no more than a laboratory curiosity until Henkel patented the production of resins by condensation with formaldehyde. Today large quantities of melamine-formaldehyde resins are used in the manufacture of moulding compositions, laminates, adhesives, surface coatings and other applications. Although in many respects superior in properties to the urea-based resins they are also significantly more expensive. 

The important point to note from this Example is that in a non-symmetrical laminate the behaviour is very complex. It can be seen that the effect of a simple uniaxial stress, or, is to produce strains and curvatures in all directions. This has relevance in a number of polymer processing situations because unbalanced cooling (for example) can result in layers which have different properties, across a moulding wall thickness. This is effectively a composite laminate structure which is likely to be non-symmetrical and complex behaviour can be expected when loading is applied. 

Two simple invariants, U, and U5, were shown in the previous subsubsection to be the basic indicators of average laminate stiffnesses. For isotropic materials, these invariants reduce to U. =Qi. and U5 = Qqq, the extensional stiffness and shear stiffness. Accordingly, Tsai and Pagano suggested the orthotopic invariants U., and U5 be called the isotropic stiffness and isotropic shear rigidity, respectively [7-16 and 7-17]. They observed that these isotropic properties are a realistic measure of the minimum stiffness capability of composite laminates. These isotropic properties can be compared directly to properties of isotropic materials as well as to properties of other orthotropic laminates. Obviously, the comparison criterion is more complex than for isotropic materials because now we have two measures, and U5, instead of the usual isotropic stiffness or E. Comparison of values of U., alone is not fair because of the degrading influence of the usually low values of U5 for composite materials. 

ASTM D 4255 (1983). Guide for testing in plane shear properties of composite laminates. 

One of the most important properties which control the damage tolerance under impact loading and the CAI is the failure strain of the matrix resin (see Fig. 8.8). The matrix failure strain influences the critical transverse strain level at which transverse cracks initiate in shear mode under impact loading, and the resistance to further delamination in predominantly opening mode under subsequent compressive loading (Hirschbuehler, 1987 Evans and Masters, 1987 Masters, 1987a, b Recker et al., 1990). The CAI of near quasi-isotropic composite laminates which are reinforced with AS-4 carbon fibers of volume fractions in the range of 65-69% has... 

Any on-line process control model used for computer-aided manufacturing of high-performance composite laminates must include a thorough treatment of void stability and growth as well as resin transport. These two key components, along with a heat transfer model and additional chemorheological information on kinetics and material properties, should permit optimized production of void-free, controlled-thickness parts. A number of advances have been made toward this goal. 

Two types of composite physical property tests were conducted to measure properties which are sensitive to the degree of adhesion and failure mode of the fiber-matrix interphase. Short beam shear tests (ASTM D2344-84) were conducted on 18 ply unidirectional laminates. The support span-to-thickness ratio... 

Elmughrabi, A. E., Robinson, M., and Gibson, A. G. Effect of stress on the fire reaction properties of polymer composite laminates, Polym. Degrad. Stabil. 2008, 93, 1877-1883. 

The fabrication of composite laminates having a thermosetting resin matrix is a complex process. It involves simultaneous heal, mass, and momentum transfer along with chemical reaction in a multiphase system with time-dependent material properties and boundary conditions. Two critical problems, which arise during production of thick structural laminates, are the occurrence of severely detrimental voids and gradients in resin concentration. In order to efficiently manufacture quality parts, on-line control and process optimization are necessary, which in turn require a realistic model of the entire process. In this article we review current progress toward developing accurate void and resin flow portions of this overall process model. 

Ling Liu, Bo-Ming Zhang, Dian-Fu Wang, Zhan-Jim Wu, Effects of cure cycles on void content and mechanical properties of composite laminates. Composite Structures 73 (2006), pp. 303-309. 

Interpolation or intercalation (see Intercalation Chemistry) is said to occur when additional species are placed into a host stmcture to change either composition or properties. At one extreme, intercalation can refer to the insertion of gnest molecnles into cage stmctures such as that of the zeolites (see Zeolites), or between the layers of laminated compounds snch as the clays (see Silicon Inorganic Chemistry). At the other extreme, the insertion of small atoms snch as C or N into metal phases to form interstitial alloys (see Alloys Carbides Transition Metal Solid-state Chemistry Nitrides Transition Metal Solid-state Chemistry), is inclnded in the category. A large variety of stmctures can be found in snch materials, and... 

Kashtalyan, M. and C. Soutis. 2000. The effect of delaminations induced by transverse cracking and splitting on stiffness properties of composite laminates . Composites Part A 31(2) 107-119. 

In Table 7, typical key laminate properties for thermoset and thermoplastic composites are given. It is immediately apparent that suitable toughening (discussed previously) can achieve superior compression after impact and comparable edge delamination... 

The resin content in both composites is about 37% by weight. The porosity of the composites was characterized by ultrasonic C-scans. The test specimens of no measurable porosity were used. The resin specimens and the composite laminates were cured in a hydraulic press at 250 F and 75 psl for one hour, and subsequently postcured at the same temperature in the absence of pressure for another two hours. Additional curing for up to 16 hours in the case of HX-205 and F-185 resins showed no measurable changes in dynamic mechanical properties. 

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