Thick laminates

In small pieces or as inserts, laminates may be used unsupported because they are quite stiff and strong. The modulus of a high pressure decorative laminate is about 7 GPa (106 psi) at room temperature. Thick laminates range up to 25 mm and are very strong, having flexual strength of 130 MPa (19,000 psi). These products are used unsupported as toilet partitions, laboratory tops, and so forth. 

Cross-linked polyester composites have a relatively low coefficient of thermal conductivity that can provide beneficial property retention in thick laminates at high temperatures as well as remove the need for secondary insulation. The coefficient of thermal expansion of glass-reinforced composites is similar to aluminum but higher than most common metals. 

If the side lengths are zero, i.e., for a very thick laminate, then a saddle shape exists at point S (saddle) w/ith = a and Ky =-b, wfhere a = b. As the side lengths increase, i.e., as the laminate becomes thinner, the saddle shape still exists, but tl curvature decreases in amplitude, i.e., the saddle gets more sh lowf. 

Jamea M. Wl ey, Stress Analysis of Thick Laminated Composite and Sandvrich Plates, Journal of Composite Materials, October 1972, pp. 426-440. 

Low exotherm Void-free thick laminates, low heat generated during cure. Encapsulating electronic components, electrical premix parts—switch-gear. 

Figures 10 and 11 show a manufacturing application in which a resin s flow properties are measured in-sltu at a particular point in a thick laminate during cure in an autoclave. The sensor was inserted on the tool surface and in the center of a thick 192 TGDDM graphite epoxy laminate. Figure 10 shows the noise free raw data taken by the center sensor during cure in the 8x4 foot production size autoclave. Using the procedures described, the ionic mobility was measured at both the tool surface and the center of the thick laminate. In Figure 11, the sensor values of a show a 10 to 20 minute time lag in the point of maximum flow on the surface versus the laminate s center. Measurements of a versus q, as shown in...

In situ frequency dependent electromagnetic-impedence measurements provide a sensitive, convenient, automated technique to monitor the changes in macroscopic cure processing properties and the advancement of the reaction in situ in the fabrication tool. This chapter discusses the instrumentation, theory, and several applications of the techniques, including isothermal cure, complex time—temperature cure, resin film infusion, thick laminates, and smart, automated control of the cure process. 

Figure 4.13 is a plot of the viscosity determined by the sensor at each of the four positions in the thick laminate during cure in the autoclave. The FDEMS sensor data show that the middle ply achieves its first viscosity minimum 20 minutes after the plies on the surface of the... 

Figure 4.13 The viscosity of the thick laminate as determined from the frequency dependence of the FDEMS sensors at the surface, thirty-second, sixty-fourth, and center plies...

The occurrence of voids has been thoroughly documented in thick laminates [2], In almost all cases, they are apparently associated with the prepreg surface. The exact mechanism of void formation depends on the system, but in the most general case it can include mechanical entrapment as well as nucleation of stable voids in the resin phase. 

Heat transfer models of the autoclave process are the most accurate and well understood of all the process models. Much of this understanding is because the models are so easily verified through thermocouple measurements. Thermocouples are the most common part-sensing technique used in production. The challenging aspects are the incorporation of the affects of resin flow, resin kinetics, and autoclave position on heat transfer properties. The importance of incorporating resin kinetic models is to properly predict conditions that may lead to exotherms, especially for thick laminates [17]. 

Probably the first major publication of a process model for the autoclave curing process is one by Springer and Loos [14]. Their model is still the basis, in structure if not in detail, for many autoclave cure models. There is little information about results obtained by the use of this model only instructions on how to use it for trial and error cure cycle development. Lee [16], however, used a very similar model, modified to run on a personal computer, to do a parametric study on variables affecting the autoclave cure. A cure model developed by Pursley was used by Kays in parametric studies for thick graphite epoxy laminates [18]. Quantitative data on the reduction in cure cycle time obtained by Kays was not available, but he did achieve about a 25 percent reduction in cycle time for thick laminates based on historical experience. A model developed by Dave et al. [17] was used to do parametric studies and develop general rules for the prevention of voids in composites. Although the value of this sort of information is difficult to assess, especially without production trials, there is a potential impact on rejection rates. 

Barbara, G. M. and Mitchell, J. G., Formation of 30- to 40-micrometer-thick laminations by highspeed marine bacteria in microbial mats, Appl. Environ. Microbiol., 62, 3985, 1996. 

Using this concept, it has been shown by cone calorimetry that over a 3 min combustion period, 3 and 6 mm thick laminated structures, made with different fire-retardant skin and unfilled core combinations can give similar resistance to ignition and comparable HRR and smoke extinction area (SEA) results to fully fire-retardant compositions (Table 7.4). Mechanical properties, in particular impact strength, were also found to be greatly enhanced by this approach, since less fire-retardant filler is present in the material. Whereas this approach has been demonstrated to be effective with hydrated fillers, it is applicable to all fire-retardant types. 

In dry conditions decorative laminates will shrink, and in damp they will expand unless suitable precautions are taken the associated movements can give rise to stress cracking of laminates and the bowing of composite boards. Since the phenol-formaldehyde resins are more stable in this respect than melamine-formaldehyde, laminates with phenolic kraft cores have dimensional stability better than those with melamine core papers—and thick laminates incorporating many plies of phenolic core paper are more stable than thin laminates with fewer plies. 

A relatively thick laminate (1.2 to 1.5 mm) is required to provide adequate... 

Rigid insulation board (includes wallboard and softboard) 0.15-0.40 9.5-25.0 Heat and sound insulation as sheathing, interior paneling, base for plaster or siding, thick laminated sheets for structural decking, cores for doors and partitions, acoustical ceilings... 

Water B2 9 0.32 DuPont Avimid K lM-61ib.2.3 mm thick Laminate... 

Membrane Fabrication, Lamination and Reinforcement. The thermoplastic copolymer of TFE and PVEX monomer can be extruded or molded into a thin film by conventional methods. Extrusion is most appropriate for continuous production of large membranes because it facilitates control of film thickness. Lamination can be performed with a roll press to obtain multilayer membrane. To improve their mechanical properties, membranes are generally reinforced with an inert material such as fabric made of PTFE (67, 68), fibriled PTFE (69), or wire netting (70). 

The TCEs were measured on samples machined from the 1/8" thick laminates by using two techniques. In a horizontal quartz tube dilatometer, samples 2" long and 1/4" wide were measured in the 2" direction. The measurements were made in accordance with procedures defined in ASTM E-228. Since the dilatometer is horizontal, measurement of shrinkage, if any, requires that the probe be kept in contact with the specimen. This is done by means of a light spring which applies a load of about 3 ozs on the sample at room temperature. Measurement of expansion can also be made without the spring load. 

Typically for thermoplastic composites, is estimated to be about 0.05-0.06 W/m and k about 8 X 10 m/ C. For glass-reinforced PP thermoplastic composites, a 2.5 mm thick laminate has been found to give a temperature variation of about 7 C, sufficient to result in significant differences in both the flow characteristic of the matrix and the degree of crystallinity after cooling. Of course, heating at both sides would help to reduce this difference. 

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