Laminates performance

We want to study the effect of the number of layers on laminate performance. The fair comparison is to keep the total laminate thickness constant to consider only equal-weight laminates. Then, we vary the number of layers by dividing the laminate into more and more iayers. That is, we construct the sequence of antisymmetric cross-ply laminates with an increasing number of layers but of constant thickness as in Figure 5-12. 

To study the effect of number of layers on laminate performance, we construct a sequence of equal-weight (constant thickness) angle-ply laminates with an increasing number of layers as in Figure 5-15. 

Cydohexanedimethanol, 1,4- dim ethyl o1 cycl oh exa n e, or 1,4-bis (hydroxymethyl) cyclohexane (8), is a white, waxy soHd. The commercial product consists of a mixture of cis and trans isomers (6). This diol is used in the manufacture of polyester fibers (qv) (64), high performance coatings, and unsaturated polyester molding and laminating resins (5). 

In addition to their role in composites, high performance fibers are also found in coated and laminated textile products, three-dimensional fabric stmctures, multifunctional property improvement, and intelligent or self-adaptive materials. 

Glass—PVB laminates become mote rigid with a decrease in temperature, and below —7° C approach the performance of soHd glass. At temperatures above 38°C these laminates ate less rigid and provide improved penetration resistance. Some appHcations utili2e he at-strengthened or tempered glass for... 

Most laminated glass appHcations are concerned with impact strength, and minimum performance levels are required by specification. The impact strength of two pHes of laminated, aimealed glass and various PVB thicknesses are available (4). Aircraft laminates may utilise electrical resistance heating as deicing for vision enhancement. 

Automotive and architectural laminates of PVB develop maximum impact strength near 20°C, as shown in Figure 2. This balance is obtained by the plasticizer-to-resin ratio and the molecular weight of the resins. It has been adjusted to this optimum temperature based on environmental conditions and automobile population at various ambient temperatures. The frequency and severity of vehicle occupant injuries vs temperature ranges at the accident location have been studied (5), and the results confirm the selection of the maximum performance temperature and decreasing penetration resistance at temperature extremes. 

The above-mentioned codes contain requirements for accelerated durabiUty tests. In addition, interlayer manufacturers and laminators expose test samples for several years under extreme weather conditions, eg, the Florida coast and Arizona desert. The laminated products weather extremely well, with no change in the plastic interlayer. Occasionally, clouding is noted around the edges when exposed to high humidity for long periods, but this is reversible. Colored areas of PVB laminates may fade while subjected to extensive uv/solar irradiation, which could cause an appearance issue. This has not, however, been shown to alter the laminate s other performance properties. 

The ASA (now ANSI) performance code for Safety Glazing Materials was revised in 1966 to incorporate these improvements in windshield constmction. The addition of test no. 26 requiring support of a 2.3-kg ball dropped from 3.7 m defined this level of improvement. It was based on a correlation estabUshed between 10-kg, instmmented, head-form impacts on windshields, on 0.6 x 0.9-m flat laminates, and the standard 0.3 x 0.3-m laminate with the 2.3-kg ball (28). Crash cases involving the two windshield interlayer types were matched for car impact speeds and were compared (29). The improved design produced fewer, less extensive, and less severe facial lacerations than those produced in the pre-1966 models. 

The constmction of the E-111 windshield shown in Eigure 8 replaced a glass—silicone laminate previously used. The all-plastic windshield has improved impact resistance so that it is birdproof to 250 m/s (33). In this instance, the scratch resistance of glass was waived to obtain the impact performance at the allowed weight. 

High performance composites may be laminates wherein veils of carbon fiber ate treated with an epoxy resin, stacked up to the desired final product thickness, and then laminated together under heat and pressure (see Composite materials Carbon and graphite fibers). Simply mixing together carbon or glass fibers and polymeric resins to form a reinforced plastic leads to a composite material, but this is not a laminate if not constmcted from discrete phes. 

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). 

Some high performance laminates consisting of carbon fiber webs and epoxy resins are cured in autoclaves. An autoclave is a pressure chamber in which the pressure is appHed hydrostatically. 

Table 1. Performance Properties and Values for Decorative Laminates...

Table 2. Performance Properties of 3.2-mm Thick Industrial Laminates ...

Mechanical Properties. The performance of various polyester resin compositions can be distinguished by comparing the mechanical properties of thin castings (3 mm) of the neat resin defined in ASTM testing procedures (15). This technique is used widely to characterize subtle changes in flexural, tensile, and compressive properties that are generally overshadowed in highly filled or reinforced laminates. 

Table 4. Silane Performance in Glass-Cloth-Reinforced Laminates ...

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