Laminate stacks

Figure 7-57 Effect of Changing Laminate Stacking Sequence...

That is, the fundamental laminate design problem can be expressed as given the loading N, Ny, and N, find the laminate stacking sequence in Figure 7-51. That is, what are the laminae orientations 01, 02 03- nnany of each orientation are needed, i.e., what... 

Momentum control gyroscopes and precision guidance instruments are used to control and detect movement in satellites, space probes and platforms, airplanes and missiles. They are, composed of a number of extremely complex electromechanical systems with circuit card assemblies, wire windings, lamination stacks, ball, roller, and gas bearings, and potted components which contain small voids and crevices. Tolerances on these assemblies can be in the microinch range. These instruments can contain lubricants and the previously discussed damping fluids. 

Analysis of Films. After heating, the films in the laminate stack were separated for analysis by the methods described below. To ensure that excess surface impurities (e.g., salt) were removed, the film surfaces were usually washed repeatedly with concentrated HC1 followed by actone and water rinses. Prior to RBS analysis the films were coated with several hundred angstroms of carbon. 

Calculated concentrations are based on the diffusion equation for a semi-infinite medium (see text) and are given immediately under the experimental values. Diffusion coefficients are calculated from the total copper absorbed by the laminate stack. 

A number of laminate stacks in which non-preoxidized and preoxidized films were loaded with N,N -diphenyloxamide, at concentrations of 3.8 X 10 3, 3.8 X 10 4, and 3.8 X 10 5 mol/kg (0.1-0.001 wt % ), were run at 90°C for a variety of times and analyzed by RBS. Within the reproducibility of the experiments the general pattern of results is essentially the same as for non-loaded samples. An occasional run was observed to give significantly slower diffusion with the oxanilide loaded films than with unloaded films, but this effect was not reproducible. Furthermore, no corresponding differences of significance in the surface concentration patterns were seen with these samples. These results agree with the selected diffusion experiments reported in Table I. 

Adhesion is a more difficult problem. There are many chemically different interfaces in a laminant stack glass-EVA, EVA-solar cell surface (oxidized silicon or some anti reflection (AR) coating), cell back surface metallization-EVA, EVA-back sheet, and EVA-bus bars (copper or tinned copper). Each of these interfaces is important, because mechanically good adhesive bonds will often fail by delamination after exposure to humidity in the field. Water vapor will permeate through polymers and, if there is a non-chemically bonded surface, water may collect and cause failure by displacement. Tables I, II, and III provide details of some of the research efforts in adhesion. 

In the preparation of certain laminates (e.g., polyimide) dielectric monitoring is used to determine the stage in the processes at which laminating pressure can be increased so as not to extrude excessive resin out of the laminating stack and yet not have voids and poor interlaminar adhesion because the resin is too far advanced when pressure is finally applied. Dielectric monitoring in this manner is also called dielectrometry or dielectric spectroscopy. 

BACKUP material a material placed on the bottom of a laminate stack in which the drill terminates its drilling stroke. 

ENTRY material A material placed on top of a laminate stack. 

If shear or off-axis stresses are not negligible then the property levels need to be checked by an appropriate method. The design may need to be altered to reduce the stress levels or change the fibre orientation or alter the laminate stacking sequence. 

Laminated stacks are fired in belt or box furnaces to bum out organic binders and den-sify the ceramic and metallic constituents. Burnout and firing can be accomplished in one continuous operation so that the part does not experience thermal gradients from end to end as temperature is changed. Finished parts may be metallized with either a screen-printed thick film or sputtered and etched thin-film conductor. 

In construction, a transducer is similar to a small transformer. Two coils of wire are wound onto a nickel lamination stack. The work horn is screwed to one end of a stub, the other end of which has been bonded to the nickel stack. The assembly, together with a cooling fan, is mounted into a small press head which allows vertical pressure, normally under lOkgf/cm, to be applied by the applicator or work horn to the work. The applicator can be changed for undertaking different applications such as spot, ring or bar welds or more complex shapes. 

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