Laminates Kevlar/epoxy

Figure 2. Thermal expansion of Kevlar-epoxy laminate as a function of temperature measured in a horizontal dilatometer.

Allred R E (1981) The effect of temperature and moisture content on the flexural response of Kevlar/epoxy laminates Part II. [ 45,0/90] filament orientation, J Compos Mater 15 117-132. 

Two types of cloth are used. The first is "S" type fiberglass, superior to "E" type cloth sold to the public. The second is Kevlar 49, the same a ramid fiber fabric used in Second Chance Flexible Body Armor. Both types of cloth are treated or scoured to make the surface compatible with a variety of laminating resins, including vinylester, polyester and epoxy. 

Kevlar, or aramid as it is generically known, is a highly oriented polymer - poly(p-phenylene terephthalamide). Kevlar fiber has the interesting property of having a linear TCE in its axial direction of -2 x 10 6/°C. The E-glass used in normal PWBs has a positive linear TCE of +5 x 10-room temperature TCEs in the X-Y plane of around 4 to 8 x 10 6/ C(3) and solder joint cracking is greatly reduced or eliminated(2). Quartz is another reinforcement, available in fabric form, which can be used to control the planar TCEs of a laminate PWB. Quartz has a TCE of +0.54 x 10-6/°C in the axial direction. 

Laminate properties of Kevlar fabric/epoxy were calculated by using laminate theory.(6) A lamina stacking sequence of 0° and 90° was adopted for the calculations. 

The model and the data show that the tnermal expansion of a fiber reinforced laminate is controlled by the following factors Tg of resin (if it is within range in which thermal expansion is measured), volume fraction of fiber and matrix, moduli of fiber and matrix as a function of temperature, and expansion coefficients of fiber and matrix as a function of temperature. For example, the model predicts that for Kevlar reinforced laminates made with the epoxy formulation discussed here, a 60% by weight resin content laminate would have a TCE of 7.5 x 10 /°C and for a 35% by weight resin content the TCE would be 4.3 x 10- /°C. 

The reinforcing fabrics used were aramid (Kevlar DuPont) and poly(p-pheny-lene-2,6-benzobisoxazole) (PBO) (Zylon Toyobo). The fabrics were first treated with a 1.5% solution of HB PAMAM (AD-102), dried, then interleaved with an epoxy film structural adhesive (epoxy stage B on polyester net), and compression-molded for 90 min at 120 °C. For the aramid-based composite, FM-73 (Cy-tec) was used as the matrix. For the PBO-based composite, AF-191 (3M) was used as the matrix. The laminates were cut into strips and tested for interlaminar shear strength (ASTM D-2344) using a three-point bending instrament. 

The results show that composites made of primed HMW HB PAMAM ara-mid and PBl fibers in epoxy matrices demonstrate much improved interlaminar shear strength (the Kevlar laminate shear strength increased to 160% and that of the Zylon to 140%). 

The behaviour of Kevlar fibre-epoxy laminates under static and fatigue loading—Part 2 modelling. Compos. Sci. Technol, 37 (4), 371-392. 

Britten, a New Zealand motorcycle company, has used a composite subchassis made of carbon fiber/Kevlar Derakane epoxy vinyl ester resin laminate for their Britten VIOOO racing machine.The Aprila 250 uses cfrp wheels molded in two halves from a 2x2 HS twill... 

TABLE 2.22 Thermal Coefficient of Expansion of Epoxy Glass Fabric Laminate and of Kevlar Rber... 

Figure 1. Low velocity impact of glass, Dyneema, Kevlar and carbon/epoxy laminates, specific absorbed energy (related to areal density) as a function of the incident energy.

LMP, the construction and applications of which have been described elsewhere is some detail (1-3). In the present work, LMP treatments have been performed on substrates of aromatic polyamides, notably du Pont "Kevlar". The excellent mechanical properties of Kevlar fibers and of structures based on this fiber have been well documented, as have some of their shortcomings (4, 5). Our concern is with the apparent difficulty of bonding Kevlar with adhesives of the epoxy and triazine type. A comparison study was carried out for bond strengths in laminates based on control Kevlar multifilament cloth and for similar structures using Kevlar subjected to plasma treatments. The results of that study are reported here, along with complementary data on the various effects of plasma treatment. 

Important fiber materials are surface-treated glass, boron, graphite (carbon), and aromatic polyaramides (eg, DuPont s Kevlar). In most composites the reinforcement constitutes ca 65% of the final mass. Orientation of the fibers is important in establishing the properties of the laminate. Unidirectional, bidirectional, and random orientations are possible. The characteristics of the cured resin system are extremely important since it must transmit the applied stresses to each fiber. A critical region in a composite is the resin-fiber interface. The adhesive properties of epoxy resins make them especially suited for composite applications. 

A modified epoxy matrix for Kevlar FRP composites was produced from ep>oxy/polyphenylene oxide (PPO) blends cured with multifunctional cyanate ester resin [94]. The effects of the PPO content on the cme behavior in the cyanate ester-cmed epoxy were investigated with FTIR. The cme reaction in the ep>oxy/PPO blends was faster than that of the neat epoxy system. FTIR analysis revealed that the cyanate fimctional group reactions were accelerated by adding PPO and that several co-reactions had occurred. Thermal mechanical analysis showed that the thermal stability of the epoxy/PPO matrix is improved by adding PPO. In the respective compursites, the ISS values between Kevlar fiber and the epoxy/PPO blends are almost the same as those between Kevlar fiber and neat epoxy. The ILSS in the respective laminates increases with the PPO content, which was attributed to an increase in the composites ductility. 

Structure. Figure 23.21 shows the structure and cross-sections for an ALIVH product. The PCB consists of laser-produced blind vias. The core material is an epoxy-aramid laminate. The man-made aramid filaments are ideal to be cut with a CO2 or UV laser. If the DuPont Kevlar filaments are added, then the resulting material wiU have a very low coefficient of thermal expansion (CTE).This is useful for mounting ceramic packages and for direct attachment of flip-chip integrated circuits. The structure can be as simple as a two-sided PCB or as complex as a many-layered PCB. The vias consist of a copper-epoxy paste that connects the top and bottom copper foil. If used as a prepreg layer without copper, the vias connect the various ALIVH layer pairs into a multilayer structure. This is not a sequential build-up process, but rather a parallel build-up process. 

More substantial delamination zones were observed under monotonically increased loads of quasi-isotropic carbon/epoxy laminate with moisture content m = 0.7% than in the dry case (Ogi et al. 1999) while a comparative drop of 5% was noted in the tensile strength of wet uniaxially reinforced Kevlar-graphite/ epoxy hybrid composites (Haque et al. 1991). Similar conclusions are implied elsewhere (Ogi and Takao 1998). An indirect confirmation of that case is implied in the above article by the observation that when plotted vs. a monotonically increased stress, the Poisson s ratio grows faster in the wet case than its dry counterpart. 

Norwood LS, Marchant A (1981) Recent developments in polyester matrices and reinforcements for marine applications, in particular in polyester/kevlar composites. In Marshall IH (ed) Composite structures. Applied Science Publishers, New York, pp 158-181 O Brien TK, Raju IS, Garber DP (1986) Residual thermal and moisture influences on the strain-energy release rate analysis of edge delamination. J Compos Technol Res 8 37 7 Ogi K, Takao Y (1998) Effect of moisture on stress-strain response and damage evolution in quasi-isotropic laminates. J Jpn Soc Compos Mater 24(l) 20-29 Ogi K, Kim HS, Maruyama T, Takao Y (1999) The influence of hygrothermal conditions on the damage processes in quasi-isotropic carbon/epoxy laminates. Compos Sci Technol 59 (16) 2375-2382... 

Typical Use Construction. PVC, ABS, metals, wood, Epoxy/Kevlar. Typical Use Laminating and bonding of PVC, etc. ... 

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